vol.2 n.1 - journal of aerospace technology and management

2010

12

Jan/Abr.

Journal of Aerospace Technology and Management V. 2, n. 1, Jan. – Apr. 2010 1

Journal of Aerospace Technology and ManagementJ. Aerosp. Technol. Manag.

Vol 2, Nº. 1, Jan. – Apr. 2010

EDITOR IN CHIEFFrancisco Cristóvão Lourenço de Melo

Institute of Aeronautics and Space (IAE) São José dos Campos, SP, Brazil

[email protected]

ASSOCIATE EDITORSAdriana Medeiros Gama

Ana Cristina AvelarAntonio Pascoal Del’ Arco Junior

Carlos de Moura Neto Cynthia Cristina Martins Junqueira

Elizabeth da Costa Mattos João Luiz Filgueiras Azevedo

Jorge Carlos Narciso Dutra Roberto Roma de Vasconcelos

Vinícius André Rodrigues Henriques Waldemar de Castro Leite

EDITORIAL PRODUCTIONAna Cristina Camargo Sant’Anna

Glauco da SilvaHelena Prado de Amorim Silva

Márcia Maria Ernandes Robles Fracasso

EXECUTIVE EDITORAna Marlene Freitas de Morais

Institute of Aeronautics and Space (IAE) São José dos Campos, SP, Brazil

[email protected]

Journal of Aerospace Technology and ManagementV. 2, n. 1, Jan. – Apr. 20102

EDITORIAL BOARDAcir Mércio Loredo-Souza - Federal University of Rio Grande do Sul - Porto Alegre - Brazil Adam S. Cumming - Defence Science and Technology Laborator - Fort Halstead - UKAdriano Gonçalves - Institute of Aeronautics and Space - São José dos Campos - Brazil Adolfo Gomes Marto - Institute of Aeronautics and Space - São José dos Campos - Brazil Alain Azoulay - Superior School of Eletricity - Paris - France Alberto W. S. Mello Jr. - Institute of Aeronautics and Space - São José dos Campos - Brazil Alexandre Garcia - Institute of Aeronautics and Space - São José dos Campos - Brazil Amilcar Porto Pimenta - Technological Institute of Aeronautics - São José dos Campos - Brazil Anderson Ribeiro Correia - Institute of Aeronautics and Space - São José dos Campos - BrazilÂngelo Passaro - Institute for Advanced Studies - São José dos Campos - BrazilAntonio Eduardo Carrilho da Cunha - Military Institute of Engineering - Rio de Janeiro - BrazilAntonio Henriques de Araujo Junior -State University of Rio de Janeiro - Rio de Janeiro - BrazilAntonio Sérgio Bezerra Sombra - Federal University of Ceará - Fortaleza- Brazil Avandelino Santana Jr. - Institute of Aeronautics and Space - São José dos Campos - Brazil Bert Pluymers - Catolic University of Leuven - Leuven - Belgium Carlos Alberto Alves Cairo - Institute of Aeronautics and Space - São José dos Campos - Brazil Carlos E. S. Cesnik - University of Michigan - Ann Arbor - USACharles Casemiro Cavalcante - Federal University of Ceará - Fortaleza - Brazil Christian Giorgio Roberto Taranti - Institute of Aeronautics and Space - São José dos Campos - Brazil Claudio Jorge Pinto Alves Technological Institute of Aeronautics - São José dos Campos - BrazilClésio Luis Tozzi - State University of Campinas - Campinas - Brazil Cosme Roberto Moreira da Silva - University of Brasília - Brasília - BrazilCristina Moniz Araújo Lopes - Institute of Aeronautics and Space - São José dos Campos - BrazilDonizeti de Andrade - Technological Institute of Aeronautics - São José dos Campos - Brazil Edílson Alexandre Camargo - Institute of Aeronautics and Space - São José dos Campos - Brazil Edson Aparecida de A. Querido Oliveira - University of Taubaté - Taubaté - Brazil Edson Cocchieri Botelho - São Paulo State University - Guaratinguetá - Brazil Edson Luis Zaparoli - Technological Institute of Aeronautics - São José dos Campos - Brazil Eduardo M. Belo - São Carlos School of Engineering - São Carlos - BrazilEdvaldo Simões da Fonseca Jr. - University of São Paulo - São Paulo - Brazil Emerson Sarmento Gonçalves - Institute of Aeronautics and Space - São José dos Campos - Brazil Enda Dimitri Bigarella - Embraer - São José dos Campos - BrazilEvandro Nohara - University of Taubaté - Taubaté - BrazilÉzio Castejon Garcia - Technological Institute of Aeronautics - São José dos Campos - Brazil Fabrice Burel - National Institute of Applied Sciences - Lion - France Fausto Ivan Barbosa - Technological Institute of Aeronautics - São José dos Campos - Brazil Fernando Luiz Bastian - Federal University of Rio de Janeiro - Rio de Janeiro - BrazilFlamínio Levy Neto - Federal University of Brasília - Brasília - BrazilFlávio Araripe D’Oliveira - Institute of Aeronautics and Space - São José dos Campos - Brazil Francisco Carlos P. Bizarria - Institute of Aeronautics and Space - São José dos Campos - Brazil Francisco Dias Rocamora Jr. - Institute for Advanced Studies - São José dos Campos - BrazilFrancisco Piorino Neto - Institute of Aeronautics and Space - São José dos Campos - BrazilFrancisco Souza - University of Uberlândia - Uberlândia - BrazilFrederic Plourde - Superior National School of Mechanics and Aerotechnics - Poitiers - France

Editorial Board


Gerson Marinucci- Institute for Nuclear and Energy Research São Paulo - BrazilGilberto Fisch - Institute of Aeronautics and Space - São José dos Campos - Brazil Gilmar Patrocinio Thim - Technological Institute of Aeronautics - São José dos Campos - Brazil Gilson da Silva - National Industrial Property Institute - Rio de Janeiro - Brazil Hazin Ali Al Quresh - Federal University of Santa Catarina - Florianópolis - BrazilHugo Enrique Hernández Figueroa - State University of Campinas - Campinas - BrazilHugo P. Simao - Princeton University - Princeton - USAInácio Malmonge Martin - University of Taubaté - Taubaté - Brazil João Amato Neto - University of São Paulo - São Paulo - Brazil João Batista P. Falcão Filho - Institute of Aeronautics and Space - São José dos Campos - Brazil João Francisco Galera Monico - São Paulo State University - São Paulo - Brazil João Marcos Travassos Romano - State University of Campinas - Campinas - Brazil João Pedro Escosteguy - Institute of Aeronautics and Space - São José dos Campos - Brazil Joern Sesterhenn - University of Munich - Munich - Germany Johannes Quaas - Max Planck Institute for Meteorology - Hamburg - Germany José Alberto Fernandes Ferreira - University of Taubaté - Taubaté - Brazil José Ângelo Gregolin - Federal University of São Carlos - São Carlos - BrazilJosé Atílio Fritz F. Rocco - Technological Institute of Aeronautics - São José dos Campos - Brazil José Carlos Góis - University of Coimbra - Coimbra - Portugal José H. Sousa Damiani - Technological Institute of Aeronautics - São José dos Campos - BrazilJosé Leandro Andrade Campos - University of Coimbra - Coimbra - Portugal José Maria Fonte Ferreira - University of Aveiro - Aveiro - Portugal Jose Maria Fernandes Marlet - Embraer- São José dos Campos - BrazilJosé Rufino de Oliveira Jr. - National Industrial Property Institute - Rio de Janeiro - BrazilKoshum Iha - Technological Institute of Aeronautics - São José dos Campos - Brazil Leila Peres - State University of Campinas - Campinas - BrazilLigia Maria Souto Vieira - Technological Institute of Aeronautics - São José dos Campos - BrazilLiu Yao Chao - University of Vale do Paraíba - São José dos Campos - BrazilLuciene Dias Villar - Institute of Aeronautics and Space - São José dos Campos - Brazil Luis Augusto T. Machado - National Institute for Space Research - Cachoeira Paulista - Brazil Luis Carlos de Castro Santos - Embraer - São José dos Campos - Brazil Luis Cláudio Rezende - Institute of Aeronautics and Space - São José dos Campos - Brazil Luis E. Loures da Costa - Institute of Aeronautics and Space - São José dos Campos - Brazil Luis Fernando Figueira da Silva - Pontifical Catholic University - Rio de Janeiro - Brazil Luiz Alberto de Andrade - Institute of Aeronautics and Space - São José dos Campos - BrazilLuiz Antonio Pessan - Federal University of São Carlos - São Carlos - BrazilLuiz Carlos Sandoval Goes - Technological Institute of Aeronautics - São José dos Campos - Brazil Luiz Claudio Pardini - Institute of Aeronautics and Space - São José dos Campos - Brazil Márcia Barbosa Henriques Mantelli- University of Santa Catarina-Florianópolis - BrazilMárcio S. Luz - Department of Aerospace Science and Technology (DCTA) - São José dos Campos - Brazil Márcio T. Mendonça - Institute of Aeronautics and Space - São José dos Campos - Brazil Marcos Aurélio Ortega - Technological Institute of Aeronautics - São José dos Campos - Brazil Marcos Daysuke Oyama - Institute of Aeronautics and Space - São José dos Campos - Brazil Maria Filomena F. Ricco - Department of Aerospace Science and Technology (DCTA) - S. J. Campos - Brazil Marisa Roberto - Technological Institute of Aeronautics - São José dos Campos - Brazil

Editorial Board

Maurizio Ferrante - Federal University of São Carlos - São Carlos - Brazil Michael Gaster - University of London - London - UK Michelle Leali Costa - São Paulo State University - Guaratinguetá - BrazilMiguel Beltrame Jr. - University of Vale do Paraíba - São José dos Campos - BrazilMiguel J. R. Barboza - Engeneering Schol of Lorena - Lorena - BrazilMirabel Cerqueira Resende - Institute of Aeronautics and Space - São José dos Campos - Brazil Miriam Kasumi Hwang - Institute of Aeronautics and Space - São José dos Campos - BrazilNicolau A.S. Rodrigues - Institute for Advanced Studies - São José dos Campos - BrazilPaulo Celso Greco - São Carlos School of Engineering - São Carlos - BrazilPaulo Giácomo Milani - National Institute for Space Research - São José dos Campos - BrazilPaulo Gilberto de Paula Toro - Institute for Advanced Studies - São José dos Campos - BrazilPaulo Varoto - São Carlos School of Engineering - São Carlos - Brazil Pedro José de Oliveira Neto - Institute of Aeronautics and Space - São José dos Campos - Brazil Pedro Paglione - Technological Institute of Aeronautics - São José dos Campos - Brazil Renato Felix Nunes - Institute of Aeronautics and Space - São José dos Campos - Brazil Rita de Cássia L. Dutra - Institute of Aeronautics and Space - São José dos Campos - Brazil Roberto Costa Lima - Naval Research Institute - Rio de Janeiro - BrazilRogério Pirk - Institute of Aeronautics and Space - São José dos Campos - Brazil Romis Ribeiro Faissol Attux - State University of Campinas - Campinas - BrazilSamuel Machado Leal da Silva - Army Technological Center - Rio de Janeiro - BrazilSergio Frascino M. Almeida - Technological Institute of Aeronautics - São José dos Campos - Brazil Sérgio Henrique da Silva Carneiro - Brazilian Air Force - Brasília - Brazil Silvana Navarro Cassu - Institute of Aeronautics and Space - São José dos Campos - BrazilTakashi Yoneyama - Technological Institute of Aeronautics - São José dos Campos - Brazil Tessaleno Devezas - University of Beira Interior - Covilha - Portugal Ulrich Teipel - University of Nuremberg - Nuremberg - Germany Vassilis Theofilis - Polytechnic University of Madrid - Madrid - SpainVera Lúcia Lourenço - Institute of Aeronautics and Space - São José dos Campos - BrazilWilson F. N. Santos - National Institute for Space Research - Cachoeira Paulista - BrazilWim P. C. de Klerk - TNO Defence - Rijswijk - The NetherlandsWladimyr Mattos da Costa Dourado - Institute of Aeronautics and Space - São José dos Campos - Brazil

Editorial Board


CONTENTS

EDITORIAL

7 The importance of research for progressVoorwald, H. J. C.

TECHNICAL PAPERS

9 Optimizing the e-beam profile of a single carbon nanotube field emission device for electric propulsion systemsMologni, J. F., Alves, M. A. R., Braumgratz, F., Fonseca, E., Siqueira, C. L. R., Braga, E. S.

17 A new particle-like method for high-speed flows with chemical non-equilibriumGuzzo, F. R., Azevedo, J. L. F.

33 Degradation of carbon-based materials under ablative conditions produced by a high enthalpy plasma jetPetraconi, G., Essiptchouk, A. M., Charakhovski, L. I., Otani, C., Maciel, H. S., Pessoa, R. S., Gregori, M. L., Costa, S. F.

41 Study of the thermal decomposition of 2,2’,4,4’,6,6’-hexanitrostilbeneSilva, G., Iha, K., Cardoso, A. M., Mattos, E. C., Dutra, R. C. L.

47 Evaluation of nanoparticles in the performance of energetic materialsRocco, J. A. F. F., Gonçalves, R. F. B., Iha, K., Silva, G.

53 Studies on compatibility of energetic materials by thermal methods Mazzeu, M. A. C., Mattos, E. C., Iha, K.

59 Complex permeability and permittivity variation of carbonyl iron rubber in the frequency range of 2 to 18 GHzGama, A. M., Rezende, M. C.

63 Microwave absorbing paints and sheets based on carbonyl iron and polyaniline: measurement and simulation of their propertiesFolgueras, L. C., Alves, M. A., Rezende, M. C.

71 Aglomerações industriais no setor aeroespacial e automobilístico no Vale do Paraíba Paulista: uma comparação de trajetórias de formação Automotive and aeronautical clusters in the São Paulo state’s Vale do Paraíba: a comparison of formation trajectoriesLuz, M. S., Minari, G. M., Santos, I. C. D.

Journal of Aerospace Technology and ManagementVol. 02, N. 01, Jan. - Apr. 2010

ISSN 1984-9648ISSN 2175-9146 (online)


83 Gestão sistêmica de projetos em uma instituição pública de pesquisa e desenvolvimentoSystemic management of projects in a public research and development institution Oliveira, L. H., Del’Arco Junior, A. P. , Brandão Neto, N.

105 Comparisons between aerovane and sonic anemometer wind measurements at Alcântara Launch CenterFisch, G.

THESIS ABSTRACTS

111 Study of internal boundary layer downwind of coastal cliffs with application to the Brazilian Launching Center of AlcântaraPires, L. B. M.

111 Barriers and facilitators in the technology transfer to the space sector: case study of partnership programs of the Brazil (AEB) and USA (NASA) space agenciesVasconcellos, R. R.

112 Development of SiC piezoresistive sensors aiming aerospace system applicationsFraga, M. A.

112 Proposed model to simulate faults in the electrical network service used by sounding rocketsSpina, F. D.

113 Operational analysis of the solid propellant mixer system by Petri netsRangel, A. P.

113 Petri nets applied to algorithm analysis for self-test of spatial vehicles integration towerPetterle, R.

114 Development of a pressure sensitive paint technique to measure surface pressure in aerodynamic modelsPedrassi, M.

114 Characterization of the interlaminar fracture toughness of carbon/epoxy compositeFarah, J. C.

115 Investigation of the mechanism of functioning of the Gas Dynamic Igniter (GDI)Nascimento, L. B.


Herman Jacobus C. Voorwald*Provost of UNESP São Paulo – Brasil

[email protected]

EditorialThe importance of research for progress

The importance of research and development (R&D) investment has become more evident every day, among the factors directly related to the good economic performance of the so-called emerging countries around the turn of the 20th to the 21st centuries. Although there could be quite large differences between the economic growth models of these nations, for instance, consider the differences between South Korean and Chinese models, all of such models are based upon substantial investments in the production of knowledge.

International university rankings have indicated, in recent years, an increasing participation, among the best positions, of education institutions from emerging countries, such as Taiwan, Hong Kong, China, South Korea, among others, thus reinforcing the clear connection between significant investments on scientific and technological production and an ever increasing competitiveness of the country’s industrial base.

The realization of this direct correlation with the economy performance has forced European Unity countries to establish, in 2006, the goal of reaching 3% of their gross national product (GNP) in R&D spending until 2010. In that particular year, South Korea spent 2.9% of its GNP and the European average reached only 1.8%.

Brazil has very good news with regard to its scientific production. Our position among the nations, in terms of international level scientific production, has been steadily improving, from 20th place in 2000 to 15th place in 2007, and finally reaching 13th place in 2008, ahead of The Netherlands, in 14th place, and Russia, in 15th place.

Despite the fact that such indicators may have several flaws, one cannot fail to recognize that the growth has been significant. Furthermore, it has been the result of an outstanding dedication from the scientific community, especially if we incorporate the information that, only in recent years, Brazil has reached 1% of GNP investment level in science and technology applications.

In this context, in 2007, the federal government has established the goal of reaching the 1.5% of GNP mark in R&D investment until 2010. There is no complete evidence, at this point, that the initiative has reached its desired goals. Furthermore, it may not be relevant because, regardless of the results, we will still be quite far from the investment levels sought by other nations in terms of a direct impact in the production of knowledge as well as of its consequences in the competitiveness of the country’s economy.

The data from the present decade indicate that the three state universities from the State of São Paulo contribute 40% of the overall Brazilian scientific production. Without prejudice with regard to the state government actions for the past 21 years, it is fair to state that such unrivaled performance is intrinsically related to the fact that such universities are the only ones in Brazil to effectively profit from the university autonomy established in Article 207 of the Federal Constitution in terms of teaching and scientific matters as well as in terms of budgetary, financial, estate and accounting issues.

*Herman Jacobus Cornelis Voorwald graduated in Mechanical Engineering at UNESP (Universidade Estadual Paulista “Júlio de Mesquita Filho”) in 1979, got his Master’s degree in Mechanical Engineering at ITA (Instituto Tecnológico de Aeronáutica) in 1983 and Ph.D. at Mechanical Engineering at UNICAMP (Universidade Estadual de Campinas) in 1988. He has experience in Material and Metallurgical Engineering, focusing on Mechanical Properties of Metals and Leagues. Since 2009 he is provost of UNESP and is also Member of Superior Council of FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) since 2007.


The present global scenario demonstrates that the Brazilian research and higher education institutions cannot avoid their responsibility in the efforts for economic and social development in accordance to the principles of sustainability, continuous improvement in the quality of life, environmental conservation and reduction of social inequalities. Furthermore, such scenario evidences that participation in this process is also a challenge for both public authorities and the industrial sector in the country.


Juliano Fujioka Mologni*Engineering Simulation and Scientific Software

São Paulo – [email protected]

Marco Antonio Robert AlvesState University of Campinas

Campinas – [email protected]

Filipe BraumgratzState University of Campinas


Edson FonsecaState University of Campinas


Cesareo L. R. SiqueiraEngineering Simulation and Scientific Software

São Paulo – [email protected]

Edmundo Silva BragaState University of Campinas


* author for correspondence

Optimizing the e-beam profile of a single carbon nanotube field emission device for electric propulsion systemsAbstract: Preliminary studies on field emission (FE) arrays comprised of carbon nanotubes (CNT) as an electron source for electric propulsion system show remarkably promising results. Design parameters for a carbon nanotube (CNT) field-emission device operating on triode configuration were numerically simulated and optimized in order to enhance the e-beam focusing quality. An additional focus gate (FG) was integrated to the device to control the profile of the emitted e-beam. An axisymmetric finite element model was developed to calculate the electric field distribution on the vacuum region and a modified Fowler-Nordheim (FN) equation was used to evaluate the current density emission and the effective emitter area. Afterward, a FE simulation was employed in order to calculate the trajectory of the emitted electrons and define the electron-optical properties of the e-beam. The integration of the FG was fully investigated via computational intelligence techniques. The best performance device according to our simulations presents a collimated e-beam profile that suits well for field emission displays, magnetic field detection and electron microscopy. The automated computational design tool presented in this study strongly benefits the robust design of integrated electron-optical systems for vacuum field emission applications, including electrodynamic tethering and electric propulsion systems.Keywords: Electric propulsion, Carbon nanotube, Finite element analysis.

INTRODUCTION

Field Emission (FE) cathodes consisted of Carbon Nanotubes (CNT) applied to electric propulsion systems are being developed due to their superiority over thermionic cathodes regarding power, mass and expellant consumption (Oakwa et al., 2007 and Marreses-Reading, 2002). The initial studies demonstrating the outstanding performance of CNT as a cold electron field emitter were firstly reported in 1995 by (Chernozatonskii et al., 1995). The highly stable crystalline structures along with high aspect ratios are the CNT’s main characteristics responsible for high current density emitted and great field enhancement factors (Young, 1958). Regarding field emission phenomenon, CNTs are either arranged in a form of a film with a variety of densities and patterns, or projected as an individual CNT electron source. The first field emission experiment of a single nanotube as an electron source was reported by Rinzler et al. (1995) whereas the emission results followed an approximate Fowler-Nordheim (FN) behavior. Further studies on single CNTs field emitter were conducted on numerous

areas, including theoretical analysis (Seidl et al., 2000 and De Heer et al., 1995), high vacuum experiments (Choi et al., 2004) and numerical simulation (Chen et al., 2007).

Understanding the fundamental CNT emission properties is necessary to design field emission systems with optimal performance. A previous work by Edgecomb and Valdre (2001) reported the electrostatic properties behavior of single CNT system as a function of the emitter aspect ratio. Besides electric field distribution and current density, the e-beam profile is an important characteristic and must be considered especially in applications involving field emission displays and electron microscopy. A highly focus e-beam shape can considerably improve the performance of field emission displays by improving their brightness and avoiding cross-talks between adjacent phosphorous cells. According to Itoh (1998) and Lei (2004), a good focusing also enhances the resolution of critical-dimension scanning electron microscopy (CDSEM) and boosts the performance of electric propulsion systems. This paper reports a numerical investigation of e-beam shape for an individual CNT field emitter operating on a triode configuration system with an integrated FG. The effects of physical design parameters and electrode voltage on the emitted e-beam shape are herein presented. Furthermore,

Received: 08/03/10 Accepted: 25/03/10

Fnac

Text Box

DOI: 10.5028/jatm.2010.02010915


Mologni, J.F. et al

an automated computational tool was developed to numerically simulate several physical models using the finite element method (FEM).

THE FINITE ELEMENT MODEL

The ideal computational model is the one that provides the most accurate results with less complexity. Since we intend to perform simulations on a variety of scenarios, the computational process is critical and must be taken in consideration. Figure 1 shows the configuration of the device detailing the geometric variables considered on our simulations.

the electrical loads used as input variables. To investigate the effects of these variables on emitted e-beam profile is the main objective of this paper.

The positive voltage applied to the extraction gate generates an electric field that accelerates the electrons on the CNT surface toward the vacuum region via quantum tunneling. The electrons are then accelerated in the direction of the anode and their trajectories are influenced by the electric field generated by the FG.

The coaxial FG act as an electrostatic lens and control the e-beam final profile, with little participation on the emitted current density (the FG slightly affects the current emitted; some studies will be presented later on in this paper). For that reason, the aperture of the FG is always larger than the extraction gate.

Considering the nature of the geometries and loads presented in the system, one can use symmetry techniques in order to simplify the model and, therefore, reduce computational effort. It is possible to observe the rotational symmetry around the longitudinal axis of the CNT nanostructure. Mathematical calculations may be applied only on one half of the cross-sectional view and the results may be rotationally expanded. Figure 2 details the finite element model with gates rotationally expanded 180o and the CNT structure along with the cathode rotated 360o.

Figure 1: Cross-sectional schematic plot of the individual CNT FE system with an integrated FG. The inset image details the CNT tip radius.

Some physical parameters such as the CNT tip radius (rn) and height (hn), the extraction gate radius (rg) and height (hg), the FG radius (rf), the gate thickness (tg) and the distance between the cathode and anode (ht) are assumed as constants in this study. Conventionally, the cathode voltage is grounded and is set to zero. The values of the constant parameters are shown on Tab. 1.

Table 1: Constant parameters

Parameter rn hn rg hg rf tg ht Va

Value 5 40 30 50 60 20 4 300

Unit nm nm nm nm nm nm mm V

The FG height (hf) is the only physical parameter considered in this study that influences the e-beam profile. The FG voltage (Vf) and the extraction gate voltage (Vg) are

Figure 2: The axisymmetric finite element model 3D. The SiO2 insulator layers and the vacuum mesh are omitted in this plot for a better visualization of the system. The cathode and CNT nanostructure are represented by white elements. The dark gray elements represent the FG and the light gray, the extraction gate.

NUMERICAL ANALYSIS

Considering the absence of charge-space effects and the symmetry of our model, the potential distribution (Ф) is evaluated using the following 2-D Laplace equation:


Optimizing the e-beam profile of a single carbon nanotube field emission device for electric propulsion systems

∇2Φ =

∂2Φ

∂x2+∂2Φ

∂y2= 0 (1)

The electric field distribution is then calculated by numerically differentiating the potential distribution with respect to x and y Cartesian coordinates. Numerical and graphical results for each step of our mathematical procedure are shown on Figures 3 to 5 using the following parameters: Vf=-10V; Vg=150V; and hf=100nm.

Figure 3 shows the resulting electrical potential and electric field distribution. The maximum electric field value is found at the CNT tip surface and is responsible for the field emission phenomena. As observed in Fig. 4, the electrical potential varies linearly at regions positioned distantly from the CNT structure. As a result, the electrons situated in this region flow linearly toward the anode surface. The developed tracing algorithm considers only two forces acting over the electron trajectories in this area: the electric field generated by the anode voltage and the electron inertial forces previously acquired by the extraction gate and FG electric fields.

CNT surface area. A computer algorithm code was already developed for this purpose and presented by Fransen, Rooy and Kruit (1999).

I

tip= J (E) ds

CNT∫∫ (3)

Figure 5 shows the distribution of current density emission at the CNT surface. It is possible to notice that only a small effective area of the CNT tip is responsible for the emitted current. To predict the emitted electrons trajectories, we need to set the initial coordinates on the CNT surface. All nodes located on the effective emitter surface area with non-zero current density values are selected to be the initial coordinates of the electron trajectories.

Figure 3: (a) Cross-sectional view showing the voltage contour plots on vacuum region; (b) Electric field distribution.

Using the electrostatic analysis results, one can determine the emission current density from the CNT emitter using the following FN equation (Liao et al., 2007 and Niemman et al., 2007), where (J) is the current density emitter ; (A) = 1.54 × 10-6; (B) is -6.83 × 107; (φ) is the work function of the emitter in eV; (E) is the electric field in V/m, (t) can be approximated to 1; v(y) = -0.75y2 – 0.26y + 1.01; and y = 3.79 × 10-4 (E0.5 / φ).

J (E) =

AE2

φt 2 ( y)⎛

⎝⎜

⎞

⎠⎟ exp −

Bφ 3 / 2v( y)E

⎛

⎝⎜

⎞

⎠⎟ (2)

The total emitted current (Itip) is then evaluated via surface integral using the electric fields values over the entire

Figure 4: Spatial electric potential distribution.

Figure 5: Surface plot showing the spatial emission current density on the surface of the CNT emitter. As expect-ed, the maximum current density is found on coordi-nates (x,y)=(0,0).

The projection of the electron trajectory f(t,y) toward the anode via vacuum is calculated according to the motion Eq. 4:


Mologni, J.F. et al

f (t, y) = m a = F = q E + v × B ( ) (4)

Where the mass of electron (m) is 9.109e-31 kg, charge of electron (q) is –1.602e-19 C, E is the electric field vector, B is the magnetic field vector, F is the Lorentz force vector, a is the acceleration vector and v is the velocity vector. The time integration is evaluated using the 4th order Runge-Kutta (RK) numerical method:

y´= f (t, y)0; y(t

0) = y

0 (5)

Where yn+1 is the RK4 approximation of y(tn+1) and:

y

n +1= y

n+α

6k

1+ 2k

2+ 2k

3+ k

4( );tn +1= t

n+α

k

1= f t

n, y

n( );k2= f t

n+α

2, y

n+α

2k

1

⎛

⎝⎜

⎞

⎠⎟ (6)

k

3= f t

n+α

2, y

n+α

2k

2

⎛

⎝⎜

⎞

⎠⎟ ; k

4= f t

n+α , y

n+αk

3( )

where k is the RK function and is α constant.

When located at the vacuum mesh, the electron tracing follows from element to element. The exit point of the current element becomes the entry point of a new element. The exit location and velocity for an element is obtained by integrating the equations of motion using the RK method described above. The particle tracing algorithm exploits the following assumptions:

1. No relativistic effects (electron velocity is much smaller than speed of light and the electron mass is constant).

2. The electric field within an element is constant. These simplifications reduce the computational time of the tracing algorithm.

The effectiveness of focusing is measured by the current-weighted beam radius at the anode surface. It represents the e-beam spot size (rb) and is calculated by:

rb= 2 ×

J (r)r2πr dr0

∞

∫J (r)2πr dr

0

∞

∫ (7)

Where J(r) is the electron current density at the anode as a function of the distance from the azimuthal symmetry axis and r is the tip radius.

A computational batch process algorithm was developed and the mathematical procedures described above were performed several times with multiple input variables. The analysis output the following parameters: e-beam

spot size on the anode, visual e-beam profile, current density and electric field distribution.

RESULTS AND DISCUSSION

The Response Surface Modeling (RSM) technique was used to demonstrate the dependence of each input variable (hf, vf and vg) on the output result (EFmax, rb). The computational automated code presented by Mologni et al. (2006) allows the generation of RSM on the fly, interpolating a matrix of discrete results using polynomial fit functions.

Since the additional FG was integrated to the structure to work as a focus lens only, it’s reasonable to primarily investigate the influence of vf and hf on the current density. Based on the FN Eq. (2), one can conclude that the emitted current density is proportional to the maximum electric field value (EFmax) located at the tip of the emitter structure. A simulation to obtain RSM of the EFmax as a function of Vf and hf was then performed.

A linear relationship between the EFmax and Vf for any given value of hf is observed on Fig. 6. This is expected since all other electrical loads considered in the system are kept constant during this analysis and the space charge effect is disregarded. It is also possible to note an exponential dependence of the EFmax as a function of hf. When the FG is positioned far from the extraction gate (hf >> hg), the influence of Vf on EFmax tends to saturate. This is explained by the high anode voltage and the great distance between the FG and the CNT emitter. If the FG is satisfactorily positioned far from the extraction gate so parallel electric potential lines between the gates can be observed, the saturation effect is achieved. The behavior of the variables presented above are only valid when we assume that Vf is applied for focusing purposes only and is very small compared to the anode and extraction gate voltages.

Figure 6: The dependence of the maximum electric field value on FG height and voltage.



For our study, the e-beam profiles were classified into four broadens categories:

1. No focusing – No bias is applied to the focus gate (Fig. 7a).

2. Under-focused – Vf is highly positive and attracts the electrons on the vacuum region (Fig. 7b).

3. Over-focused – Vf is negative enough to repel the electrons and at least one trajectory cross the central symmetry axis before reaching the anode (Fig. 7c).

4. Focused – The smallest rb possible provided by the best combination of hf and Vf (Fig. 7d).

rb increases. High values of rb are also observed when vf is extremely positive and the e-beam profile tends to be under-focused.

Figure 7: E-beam profile classification.

The values of trajectory, velocity and time are calculated for each emitted electron using the Lorentz Eq. (4). When a bias is applied to the FG, the electric field generated by vf first decreases the electron velocity to adjust the trajectory and, then, accelerates the electron toward the anode. The region near the FG is considered to be a turbulent electric field region due to the variant FG electric potential. The combination of the FG and EG electric fields in this area force the electron to change its trajectory in a significant way. When the electron leaves the turbulent electric field region, the dependence of the electron velocity relies only on the anode electric field. Besides the boost on the performance of field emission displays and CDSEM, the collimation effect combined with high velocity electrons also enhances the accuracy of FE systems when they are applied to detect the presence and the strength of magnetic fields (Fig. 8).

Figure 9 shows the resulting e-beam spot size for a set of FG height and voltage values. The best e-beam weighted radius that can be achieved in this system is 15.43 nm. If necessary, additional focus gates may be integrated to the system to further increase the focusing properties. The narrowest e-beam radius can be obtained for any hf by applying a different vf. At highly negative values of vf, the e-beam becomes over-focused and the value of

Figure 8: Electron velocity. Parameters used for this analysis: vf=-20 V (for the focused electron trajectory case) and hf=90 nm.

Figure 9: Effects of FG height and voltage on e-beam weighted radius on the anode.

The e-beam profile also shows a dependence on the gate electric field strength. In order to understand the e-beam weighted radius behavior for different gates biases, a simulation considering hf constant was assumed and the results are presented in Fig. 10.

Based on Equations 2 and 3, an evaluation of the threshold voltage (when the FE system begins to emit electrons) was performed and a value of vg=95.43 V was obtained. High values of rb are found at low emission levels, when vg is low enough to emit only a small quantity of electrons from the CNT surface. Some of these electrons are strongly repelled by the extreme negative vf strength and present an


Mologni, J.F. et al

Figure 10: 3D surface plot of the e-beam weighted radius as a function of the applied gate voltages. The focus gate height was set to 90 nm for this particular case.

over-focused trajectory. On the other hand, higher values of vf and vg results on large rb, but, in this case, the e-beam is comprised of under-focused electron trajectories. To correct under-focused trajectories, higher values of vf (in magnitude) are required. It is also important to consider the increase in the effective emitter area (Fig. 5) as the vg values raises, resulting on large e-beam profiles.

With the analysis described above, one can always modulate the biasing of the gates in order to achieve the desired e-beam weighted radius. The numerical procedure herein described may be applied to any FE system by changing the initial finite element model and carefully choosing the boundary conditions.

CONCLUSIONS

In summary, we have performed several simulations indicating the optimal FG physical and electrical parameters to achieve the best e-beam profile for a single CNT FE device regarding electric propulsion systems. An automated computational process was developed to assist the numerous simulations of diverse initial conditions. The algorithm and procedure presented in this paper can be used to simulate any geometry having at least one variable parameter. The influence of the integrated FG on the current density was also analyzed. It was shown that the presence of the FG influence the current density on the surface of the CNT emitter, especially when the FG is positioned near the extraction gate. Physical parameters of the system combined with a range of electrical loads produce a variety of e-beam profiles. The resulted profiles were determined for numerous geometric structures and the smallest e-beam spot size for a given system is achieved by using different combinations of biasing.

ACKNOWLEDGEMENT

The authors would like to acknowledge Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for their support.

REFERENCES

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Chernozatonskii, L.A., et al., 1995, “Electron field emission from nanofilament carbon films”, Chem Phys Lett, Vol. 233, pp. 63-68.

Choi, J.E., et al., 2004, “Carbon nanotube field emitter arrays having an electron beam focusing structure”, Appl Phys Lett, Vol. 84, pp. 1022-1025.

De Heer, W.A., Châtelain, A., Ugarte, D., 1995, “A carbon nanotube field-emission electron source”, Science, Vol. 270, pp.1179-1180.

Edgcombe, C.J., Valdre, U., 2001, “Microscopy and computational modeling to elucidate the enhancement factor for field electron emitters”, J Microsc, Vol. 203, pp. 188-194.

Fransen, M.J., Rooy, T.L., Kruit, P., 1999, “Field emission energy distribution from individual carbon nanotube”, Appl Surf Sci, Vol. 146, pp. 312-327.

Itoh, J. Uemara S.K., Kanemaru S., 1998, “Three-dimensional vacuum magnetic sensor with a Si emitter tip”, J Vac Sci Technol B, Vol. 16, pp. 1233-1235.

Lei, W., Yang, G., Xie, M., 2004, “Study of the triode structure in a field emission display element”, J Vac Sci Technol B, Vol. 24, pp. 962-964.

Liao, K.P., Hu, Y., Lin, T.L., 2007, “Simulation studies of self-focusing carbon nanotube field emitter”, J Vac Sci Technol B, Vol. 25, pp. 84-86.

Marreses-Reading, C., et al., 2002, “Field emission array cathode material selection for compatibility with electric propulsion applications”, Nasa JPL Technical Report, No. 8523, 17p.

Mologni, J.F., et al., 2006, “Numerical study on performance of pyramidal and conical isotropic etched single emitters”, Microelectronics Journal, Vol. 37, pp. 152-157.



Niemman, D.L., et al., 2007, “Effects of cathode structure on the field emission properties of individual multi-walled carbon nanotube emitters”, Nanotechnology, Vol. 18. doi: 10.1088/0957-4484/18/48/485702.

Okawa, Y., et al., 2007, “An experimental study on carbon nanotube cathodes for electrodynamic tether propulsion”, Acta Astronautica, Vol. 61, pp. 989-994.

Rinzler, A.G., et al., 1995, “Unraveling nanotubes: field emission from an atomic wire”, Science, Vol. 269, pp.1550-1553.

Seidl, A., et al., 2000, “Geometry effects arising from anodization of field emitters”, J Vac Sci Technol B, Vol. 2, pp. 929-932.


Fábio Rodrigues GuzzoInstituto Tecnológico de Aeronáutica

São José dos Campos – [email protected]

João Luiz F. Azevedo*Instituto de Aeronáutica e Espaço


*author for correspondence

A new particle-like method for high-speed flows with chemical non-equilibriumAbstract: The present work is concerned with the numerical simulation of hypersonic blunt body flows with chemical non-equilibrium. New theoretical and numerical formulations for coupling the chemical reaction to the fluid dynamics are presented and validated. The fluid dynamics is defined for a stationary unstructured mesh and the chemical reaction process is defined for “finite quantities” moving through the stationary mesh. The fluid dynamics is modeled by the Euler equations and the chemical reaction rates by the Arrhenius law. Ideal gases are considered. The thermodynamical data are based on JANNAF tables and Burcat’s database. The algorithm proposed by Liou, known as AUSM+, is implemented in a cell-centered based finite volume method and in an unstructured mesh context. Multidimensional limited MUSCL interpolation method is used to perform property reconstructions and to achieve second-order accuracy in space. The minmod limiter is used. The second order accuracy, five stage, Runge-Kutta time-stepping scheme is employed to perform the time march for the fluid dynamics. The numerical code VODE, which is part of the CHEMKIN-II package, is adopted to perform the time integration for the chemical reaction equations. The freestream reacting fluid is composed of H2 and air at the stoichiometric ratio. The emphasis of the present paper is on the description of the new methodology for handling the coupling of chemical and fluid mechanic processes, and its validation by comparison with the standard time-splitting procedure. The configurations considered are the hypersonic flow over a wedge, in which the oblique detonation wave is induced by an oblique shock wave, and the hypersonic flow over a blunt body. Differences between the solutions obtained with each formulation are presented and discussed, including the effects of grid refinement in each case. The primary objective of such comparisons is the validation of the proposed methodology. Moreover, for the hypersonic flow over a blunt body, solutions obtained for two meshes are shown, compared and analyzed. The numerical solutions are also compared with experimental data.Keywords: Hypersonic flows, Numerical simulations, Chemical non-equilibrium, Supersonic combustion, CFD.

INTRODUCTION

This work is part of a continuing effort that is being carried out at Instituto de Aeronáutica e Espaço of Departamento de Ciência e Tecnologia Aeroespacial (DCTA/IAE) to develop numerical methods to simulate fluid and gasdynamic flows. The objective of this effort is to conceive comprehensive codes and to test and validate them over simple configurations in which experimental, analytical or numerical solutions are available in the literature. The present paper addresses specifically hypersonic flow problems in which chemical non-equilibrium is present. Hence, there are effects arising from the chemical non-equilibrium condition that cannot be neglected.

Hypersonic flow problems including chemical reactions have become important since the end of World War II with the advent of rockets, hypersonic aircrafts and atmospheric reentry vehicles. For reentry vehicles, the gasdynamic problems become all the more challenging since the flight trajectories traverse a wide range of Mach, Knudsen, Reynolds and Damköhler numbers (Sarma, 2000). The full range of molecular physical phenomena of reentry flights encompasses rarefaction, ionization, radiation, relaxation and thermal and compositional nonequilibrium (Sarma, 2000). For hypersonic aircrafts, the combustion in the engine may take place at supersonic speeds, as in Scramjets (Supersonic Combustion Ramjets) and Shramjets (Shock-Induced Combustion Ramjets) (Ahuja, Tiwari and Singh, 1992). DCTA/IAE is developing a recoverable orbital platform for experimentation in Received: 11/09/09

Accepted: 19/12/09

Fnac

Text Box

DOI: 10.5028/jatm.2010.02011732


Guzzo, F.R., Azevedo, J.L.F.

microgravity environment, called SARA (acronym in Portuguese for Satélite de Reentrada Atmosférica).

Development of a solver for reactive hypersonic flow applications started in DCTA/IAE at the end of 1990s. Successful validations of the numerical formulations and the physico-chemical data were carried out over simulations for reactive flows composed of a stoichiometric H2-Air mixture (Azevedo and Figueira da Silva, 1997; Korzenowski, 1998; Figueira da Silva, Azevedo and Korzenowski, 1999; Pimentel, 2000; and Figueira da Silva, Azevedo and Korzenowski, 2000). Hypersonic flows around wedges were considered. In these configurations, the oblique shock wave triggers the combustion that eventually takes the form of an oblique detonation wave. Comparisons between numerical and experimental results showed a good agreement concerning the overall structure of the flow. Nevertheless, the first attempt to simulate a reactive flow composed of the same mixture around a blunt projectile was not successful (Guzzo, 2003). The configuration simulated was Lehr’s experiment with a steady flow around a sphere-cylinder (Lehr, 1972). The experiment shadowgraph showed that normal shock and the reaction front near the stagnation line seem coupled. These two fronts move away from each other downstream, and such detachment becomes more noticeable as the shock wave becomes more oblique. The first simulation obtained was considered unsuccessful since the detachment was not observed in the numerical solution (Guzzo, 2003). The reaction front remained visibly coupled to the shock wave for the overall solution. The differences between the numerical simulations and the experimental data can be attributed either to numerical errors or to improperly modeled chemical kinetics. The physics of these flows are predominantly driven by reaction kinetics and convection phenomena (Wilson and MacCormack, 1990). The uncertainties of diffusion and mixing can be neglected.

Several authors investigated and simulated both Lehr’s steady and unsteady cases (Lee and Deiwert, 1989; Yungster, Eberhardt and Bruckner, 1989; Wilson and MacCormack, 1990; Matsuo and Fujiwara, 1991; Sussman and Wilson, 1991; Ahuja, Tiwari and Singh, 1992; Singh, Ahuja and Carpenter, 1992; Ess and Allen, 2005). Lee and Deiwert (1989) and Yungster, Eberhardt and Bruckner (1989) simulated Lehr’s experimental data for freestream Mach numbers 4.18, 5.11 and 6.46. They used the Euler equations, a 6-species model plus an inert gas, such as argon or nitrogen, and a 8-reaction chemistry model. The flow field for Mach 4.18 and 5.11 was found to be steady in contrast to the experimental evidence that the flow field is, indeed, unsteady. The grids used were not sufficient to resolve the flow field correctly (Ahuja, Tiwari and Singh, 1992). Wilson and MacCormack

(1990) used the Euler equations, and a 13-species and 33-reaction chemistry model. They showed the validity of the reaction model and the importance of adequate grid resolution to properly model the flow physics. The calculations were not time accurate and, hence, the unsteady behavior was not captured (Ahuja, Tiwari and Singh, 1992). Sussman and Wilson (1991) also used the Euler equations, and a 13-species and 33-reaction chemistry model to simulate the flow field for Mach number 4.79. They proposed a new formulation based on logarithmic transformation. Such formulation greatly reduced the number of grid points needed to properly resolve the induction zone. They successfully simulated the unsteady case (Ahuja, Tiwari and Singh, 1992). However, frequency was slightly underpredicted. Ahuja, Tiwari and Singh (1992) used the Navier-Stokes equations, and a 7-species and 7-reaction chemistry model to simulate the flow field for freestream Mach numbers 5.11 and 6.46. They successfully simulated the unsteady case and the frequency oscillation was found to be in a good agreement with the experimentally observed frequency (Ahuja, Tiwari and Singh, 1992). Matsuo, Fujii and Fujiwara (1995) used the Euler equations and a 8-species and 19-reaction chemistry model to simulate the flow field for Mach numbers 4.18 and 4.79. A fine grid distribution, such as 161 x 321 points, was used, and the authors have obtained successful solutions with a good agreement concerning the frequency of the oscillations.

There is a major difference between simulating the steady and the unsteady cases. For the flow field with an unstable reaction front, the critical zone that requires accurate solution is the region near the stagnation line, between the normal shock wave and the projectile leading edge. The unsteady pattern of the overall flow field is due to the convection trigged by the coupled oscillatory reaction front and the convective phenomena in this region of the flow. On the other hand, for the steady case, the numerical solution must be accurate in the region of the induction zone just before the oblique reaction front. In this region, as the shock wave becomes more oblique and the temperature increment diminishes, the detonation wave gradually aligns to the local flow. As long as the chemical kinetics is strongly nonlinear with the species mass fraction, the simulation must be able to properly represent the induction zone in a region of flow that progressively tightens to reacted gases. Ahuja and Tiwari (1994) used the Navier-Stokes equations and a 9-species and 18-reaction chemistry model to simulate Lehr’s experiment for Mach number 6.46, which is a steady flow. The detachment between the shock wave and the reaction front was not clearly noticeable. Ess and Allen (2005) simulated Lehr’s experiments for freestream Mach numbers 4.48 and 6.46. They used the Navier-Stokes equations and a 9-species and 19-reaction


A new particle-like method for high-speed flows with chemical non-equilibrium

chemistry model. They successfully simulated the unsteady flow field for Mach 4.48 and the oscillation frequency compares well with the frequency obtained experimentally (Ess and Allen, 2005). In the steady flow case, for Mach number 6.46, they used two meshes in order to demonstrate the sensitivity of the physical problem to spatial resolution. In the coarse mesh, with half the number of cells in both directions, the shock and the reaction front remained visually attached. In the finer mesh, the detachment is barely observable. Wilson and Sussman (1993) also simulated Lehr’s experiment for Mach number 6.46. They obtained good agreement with the experiment concerning the position of the shock wave and of the reaction front. They used a coarse mesh, such as 52 x 52 grid points. Probably, the topology of the mesh may have contributed to reduce the numerical diffusion of the species mass fractions. In the oblique detonation wave region, the diffusion of the mass fraction is minimized if the faces of the cells, that separate unreacted gases to reacted gases, are aligned to the local flow. The mesh influence in the solution may have been significant in the success of the simulation. Wilson and MacCormark (1992) also successfully simulated Lehr’s experiment for Mach number 6.46 using an adaptative mesh algorithm. The final mesh topology probably contributed in the reduction of the numerical diffusion and in the success of the simulation as well.

With the objective of better simulating the flowfield in the region near the oblique detonation wave that progressively aligns to the local flow, a new formulation is proposed in the present paper to couple the chemical kinetics to the fluid dynamics. It is a simple Eulerian/Lagrangian hybrid methodology. The fluid dynamics is defined for a stationary unstructured mesh and the chemical kinetics is defined for finite quantities, or particles, moving through the stationary mesh. The objective of adopting Lagrangian particles is to avoid that the chemical reaction process considers average species mass fractions. The particles carry the chemical composition information and the reaction is performed over each particle independently. The interface between Eulerian and Lagrangian models is conducted in a such way that the density, speed and the internal energy values of the particles are defined as being equal to the corresponding values of the control volume that contains the particle, whereas the mass fractions of the control volume are defined as being equal to the weighted averaged mass fractions of the chemical composition of the particles contained in the control volume.

The paper, initially, concentrates in the comparisons of the hybrid methodology and the conventional Eulerian methodology. Solutions obtained with the two formulations are presented, compared and investigated. For the Eulerian methodology, besides the continuity,

momentum and energy equations, the species equations are also defined for stationary meshes. The coupling is achieved by Strang’s time-step splitting procedure (Strang, 1968). Lehr’s experiment for Mach number equal to 6.46 (Lehr, 1972) is simulated with the Eulerian methodology. Three meshes, different in topology and refinement, are employed. Although the formulation is for unstructured grids, only structured quadrilateral meshes are used. Guzzo and Azevedo (2006) have shown that the regularity and the smoothness of the computational meshes have a very strong positive effect on the quality of solutions. The present calculations are compared to experimental data. An investigation specifically concerned with the reactive mixture is carried out to clarify the challenges of simulating, with the Eulerian methodology, the oblique reaction front that progressively aligns to the local flow. Afterwards, a reactive hypersonic flow around a wedge is simulated using both formulations. Two meshes, different in topology and refinement, are employed. The solutions are presented, compared and analyzed. Another investigation, specifically targeting the reactive mixture, is carried out in order to clarify the characteristics of the solutions obtained with the Eulerian methodology corresponding to the position of the reaction front. Finally, for the hybrid methodology, the solutions are shown for Lehr’s experiment for Mach number 6.46, performed over two different meshes. Analyses of the solutions obtained and comparisons between the solutions and the experimental data are discussed.

NUMERICAL FORMULATION

The major emphasis of the present paper concerns the discussion of the Eulerian/Lagrangian hybrid methodology. For such methodology, the fluid dynamics is defined for a stationary mesh and the chemical kinetics is calculated for particles that move through the stationary mesh. This section, therefore, initially presents the hybrid methodology, discussing both its Eulerian and Lagrangian components, as well as the coupling of such components. Afterwards, brief comments are presented for the fully Eulerian formulation.

Eulerian method

The fluid dynamics is modeled by the axisymmetric Euler equations applied over stationary unstructured meshes. Four equations are included: continuity, two-component momentum and energy equations. The species equations are not considered. The integral form of the Euler equations are written for the i-th volume as

V

i

∂

∂tQ

i( ) + Erdr + Frdz( )Si

∫ + HiV

i= 0, (1)



where r is the radial coordinate, z is the axial coordinate, and Vi is the volume of the i-th cell. Q is the vector of the conserved variables, E and F are the inviscid flux vector, and H is the axisymmetric source term. The definition of these terms is

Q =

ρ

ρuz

ρur

ρε

⎡

⎣

⎢⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥⎥

,

E =

ρuz

ρuz2 + p

ρuzu

r

uzρε + p( )

⎡

⎣

⎢⎢⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥⎥⎥

,

F =

ρur

ρuzu

r

ρur2 + p

urρε + p( )

⎡

⎣

⎢⎢⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥⎥⎥

,

H=

00

− p / r0

⎡

⎣

⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥

, (2)

where ρ is the density, ur and uz are the velocity components in the radial and axial coordinates, ε is the specific total energy and p is the pressure.

Liou’s upwind, flux vector splitting method (Liou, 1994; Liou, 1996), known as AUSM+, is implemented in a cell centered-based, finite volume code for unstructured meshes. The reinterpretation of the formulation for unstructured meshes follows Azevedo and Korzenowski (1998). The 2nd-order spatial accuracy is obtained using MUSCL reconstruction (van Leer, 1979) and the minmod limiter (Hirsch, 1988), in order to extrapolate primitive variables from the centroid to the faces of the cells. The second-order accuracy, five-stage Runge-Kutta (Mavriplis, 1988; Mavriplis, 1990) scheme is employed to perform the time march. The boundary conditions are implemented with the use of “ghost”, or “slave”, cells. For solid wall boundaries, the velocity component normal to the wall in the ghost volume has the same magnitude and opposite sign of its value in the adjacent interior volume, whereas the velocity component tangent to the wall is equal to its internal cell counterpart. For the other properties, zero normal gradients are assumed at the wall. For the entrance boundary, the flow variables receive the freestream values. For the subsonic exit boundary, three properties are extrapolated from interior information. For a supersonic exit boundary, all properties are extrapolated from interior information. For the initial condition, freestream conditions are specified throughout the flowfield. Further details on the boundary and initial conditions are described by Guzzo (2006).

Lagrangian method

The chemical kinetics is defined for particles that move with the fluid. The chemical composition of the p-th particle is defined as

DYp

Dt= Ω

p, (3)

where Y is the vector of the chemical species mass fractions and Ω is the chemical source vector, which are written as

Y =

ρY1

ρY2

|ρY

M

⎡

⎣

⎢⎢⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥⎥⎥

and

Ω =

w1

w2

|w

M

⎡

⎣

⎢⎢⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥⎥⎥

(4)

Here, Yk is the mass fraction and w.k is the mass production term of the k-th chemical species. The chemical reaction kinetics is modeled by Arrhenius law. The VODE numerical code (Byrne and Dean, 1993) is adopted to perform the time integration for the chemical reactions. The reaction rate for each species is determined with the use of the CHEMKIN-II code (Kee, Rupley and Miller, 1991). The variation of the particle position is defined as

Drp

Dt= u

r( )p and

Dzp

Dt= u

z( )p (5)

A simple first-order accuracy, one-stage method is employed to update the position of the particles from stage n to stage n+1,

zjin +1 = z

jin + u

z( )i

n⋅ Δt n ,

rjin +1 = r

jin + u

r( )i

n⋅ Δt n .

(6)

For the initial condition, one particle is added in each cell and a weight, wp, is attributed to it, defined as

wp

p= r

i⋅ max r

il( ) − min ril( )⎡⎣ ⎤⎦, l = 1, 2, ... ,

N

n( )i, (7)

where ri is the radial coordinate of the i-th cell center, ril is the radial coordinate of its l-th node and (Nn)i is the number of nodes. For the entrance boundary, one particle is created periodically in the center of each cell that shares a face with the boundary. A fixed and unique time value is employed for the overall boundary cells. The weight of the particles created in the entrance boundary is defined as

wp

p= r

i⋅ abs r

i1− r

i 2( )⎡⎣ ⎤⎦ (8)

where ril and ri2 are the radial coordinates of the two nodes of the i-th cell located at the boundary. When a particle crosses the exit boundary, this particle is discarded. When a particle crosses a solid wall or an axisymmetric boundary, this particle is reallocated inside the flow field. The particle is positioned at the boundary surface, at the nearest point of the original outside position.



Eulerian-Lagrangian interface

The chemical composition of the control volume is defined as being equal to the weighted averaged chemical composition of the particles contained in the volume, i.e.,

Yk( )

i=

Yk( )

ji⋅wp

ji⎡⎣

⎤⎦

j =1

N p( )i

∑

wpji

j =1

N p( )i∑

(9)

where (Np)i is the number of particles contained in the i-th control volume, (Yk)ji is the mass fraction of the k-th chemical species of the j-th particle contained in the i-th volume and wpji is the weight attributed to that particle. If a control volume contains no particles, the particles contained in the neighbor cells are considered,

Yk( )

i=

Yk( )

jl⋅wp

jl⎡⎣

⎤⎦

j =1

N p( )l

∑⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

l =1

N v( )i

∑

wpjl

j =1

N p( )l∑

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

l =1

N v( )i

∑

, (10)

where (Nv)i is the number of cells that share one face with the i-th volume and (Np)l is the number of particles contained in the l-th neighbor. If there are no particles in the control volume and in its neighbors, the chemical composition of the control volume is not updated. The density, speed and the specific internal energy of the j-th particle contained in the i-th control volume are defined as being equal to the values of the control volume, i.e.,

ρ

ji= ρ

i , u

z( )ji= u

z( )i,

u

r( )ji= u

r( )i,

e

ji= e

i. (11)

A temperature limiter was employed. In the simulations performed, when the fluid crosses the oblique detonation wave, as the mixture reacts, chemical energy is released and the internal energy of the gas decreases due to the gas expansion. The internal energy is considered to be composed of chemical and thermal energies. If a particle crosses the oblique reaction front without reacting, its temperature drops and it remains unreacted. The temperature limiter is a simple solution used to avoid that particles very close to each other carry very different chemical composition. The interested reader is referred to the work by Guzzo (2006) for further details on the temperature limiter. The temperature of the particle, considering the limiter, is defined as

T

ji= max T

ji

0( ) ,min Ti,T

il( )( ), l = 1, 2, ... ,

Nv( )

i, (12)

where Tji is the temperature of the particle without the limiter, Ti is the temperature of the control volume that contains the particle, and Til is temperature of its l-th neighbor volume.

The time advancement of the solution from the n-th stage to the (n+1)-th stage is achieved by three independent steps: one step for the fluid dynamics, one for the chemical reaction process, and another for the particle positioning. These steps can be written as

Q

in +1 = L Q

in ,Δt n( ),

Y

jin +1 =Q Y

jin ,Δt n( ), (13)

r

jin +1 = f r

jin ,Q

in ,Δt n( ) ,

where L is the operator of the fluid dynamics, Q is the chemistry operator, and f is the particle positioning operator. Here, rji is the position vector of the particles, which is written as

r = z

r⎡

⎣⎢

⎤

⎦⎥ (14)

Δtn is the time step of the n-th stage. A time step for each cell is calculated, Δt i, and a single value, Δtn, is used, where Δtn is the minimum value of the Δt i . The time step for each cell is calculated such that the CFL number is kept approximately constant throughout the field (Figueira da Silva, Azevedo and Korzenowski, 1999).

Constitutive equations

The Balakrishnan and Williams (1993) chemical kinetics mechanism is selected to model the H2 and air reactive mixture. The thermodynamic properties are defined using the polynomial tables of JANNAF (Anon., 1970) and Burcat’s database (Burcat, 1984).

Fully Eulerian formulation

The standard approach for handling flows with chemical reactions for finite difference or finite volume methods consists in also solving the species mass fraction equations using the same Eulerian computational grid developed for the fluid dynamics equations. Hence, in the present case, the Euler equations, including continuity, momentum and energy equations are (loosely) coupled to the species equations. In this context, Strang’s time-step splitting procedure (Strang, 1968) is used for time advancement.



As before, the VODE numerical code (Byrne and Dean, 1993) is adopted to perform the time integration for the chemical reactions. The reaction rate for each species is determined with the use of the CHEMKIN-II code (Kee, Rupley and Miller, 1991). The thermodynamic properties are also defined using polynomial tables of JANNAF (Anon., 1970) and Burcat’s database (Burcat, 1984). The Balakrishnan and Williams (1993) chemical kinetics mechanism is selected to model the H2 and air reactive mixture. The same numerical method previously described is used for the solution of the fluid dynamics portion of the problem. The interested reader is referred to the work by Pimentel (2000) and by Pimentel et al. (2002) for further details on the fully Eulerian formulation.


Blunt body problem

Lehr’s experiment for Mach 6.46 (Lehr, 1972) is simulated with the fully Eulerian formulation. The flow is composed of a stoichiometric H2-air mixture. The geometry is a sphere-cylinder of 15 mm diameter. The free stream conditions are T∞ = 292 K and p∞ = 320 mmHg. Simulations are carried out over three structured quadrilateral meshes. The boundaries of the meshes are presented in Fig. 1. Grid 1 is composed of 20,000 nodes and 19,671 cells, in which the distribution is 80 × 250 grid points in the normal and longitudinal directions, respectively. The nodes are equally spaced in each direction. Grid 2 is composed of 30,000 nodes and 29,631 cells, in which the distribution is 120 × 250 points, respectively, in the wall-normal and longitudinal directions. The nodes are also equally spaced in each direction. Grid 3 is composed of 60,000 nodes and 59,451 cells, in which the distribution is 150 × 400 grid points. Specifically for Grid 3, the nodes are not equally spaced in each direction. The density of nodes is greater in the region of the shock wave and the reaction front. In the direction normal to the body, from the entrance boundary to the wall, the distance between the nodes is linearly reduced, from the first to the 75th node, to 1/5 of the initial distance. From the 75th to the 150th node, the mesh spacing is kept constant. In the longitudinal direction, from the exit to the symmetry boundary, the spacing between the nodes is linearly reduced from the first to the last node to 1/3 of the initial distance. Grids 1 and 2 are similar in refinement, but differ considerably in topology, as one can clearly see in Fig. 1. Grid 3 is much finer and comprises only the flow field around the semi-spherical leading edge. Position coordinates are in centimeters in Fig. 1. An actual view of Grid 3 is shown in Fig. 2. In this figure, only one out of every five points is shown.

Figure 3 shows the density and the H2O mass fraction contours for the solutions obtained with the three meshes.

For the solutions obtained with Grid 1 and Grid 2, the pattern observed in Lehr’s experiment (Lehr, 1972) is not seen. It is not clear that the reaction front separates from the shock wave as the two fronts become more oblique. On the other hand, for Grid 3 results, it is possible to notice the beginning of the detachment of the two fronts. As discussed in the next paragraph, however, such detachment is still quite shy of what is observed in the actual experiments. In any event, with the objective of further characterizing the results for the fully Eulerian formulation, Fig. 4 presents the results obtained with Grid 3 in terms of colored contours of density, temperature and molecular oxygen mass fraction, and it also shows the incipient detachment of shock wave and reaction front.

Figure 2: Visualization of Grid 3, with 150 × 400 points in the normal and longitudinal directions, respectively. Only one out of every five points is shown.

Figure 1: Borders of the meshes used to simulate Lehr’s experiment with the fully Eulerian formulation for Mach 6.46 (Lehr, 1972): Grid 1 (80 × 250), Grid 2 (120 × 250) and Grid 3 (150 × 400).



Figure 3: Property contours for the fully Eulerian formulation: a1) Grid 1 density contours; a2) Grid 1 H2O mass fraction contours; b1) Grid 2 density contours; b2) Grid 2 H2O mass fraction contours; c1) Grid 3 density contours; c2) Grid 3 H2O mass fraction contours.

Figure 5 presents a summary of the positions of the shock waves and the reaction fronts for the numerical solutions and for the experimental data. For the numerical solutions, in order to indicate the position of the fronts, two temperature contours are included. The differences in position of the oblique fronts for Grid 1 and Grid 2 evidence the influence of the mesh topology in the results. For Grid 1, for instance, the direction of the oblique reaction front is the same as the one of the longitudinal faces of the cells. For Grid 3, despite

Figure 4: Flow solution obtained with Grid 3: a) density contours, ρ [kg/m3]; b) temperature contours, T [K]; c) contours for O2 mass fraction; d) position of shock wave and detonation wave.

Figure 5: Position of the shock wave and reaction front. Comparison of the present computations and the experimental data (Lehr 1972).

the fact that the shock wave and the reaction front are slightly dislocated upstream, and the distance between them is underpredicted, the positions of the oblique fronts compare better to the experimenal data. The effect of the mesh refinement is very similar to the one observed by Ess and Allen (2005). These authors have



simulated Lehr’s experiment for Mach 6.46 using two meshes. In the coarse mesh, the shock and the reaction front remained visually attached. In the finer grid, the detachment is barely observable, which is essentially the result here obtained.

Chemical reaction analysis 1

In Lehr’s experiment for Mach number 6.46, as the fluid crosses the normal shock wave, the temperature increment is such that the induction time is reduced in a way that it is not possible to distinguish the induction zone. As the shock wave becomes more oblique and the temperature increment diminishes, the induction time increases and the detonation wave starts to move away from the shock wave. At a certain point, the temperature increment is not sufficient to ignite the mixture and the detonation wave progressively aligns to the local flow. Some control volumes in this region of the flow are inevitably composed of gases with very different chemical compositions. In order to clarify the effect of using average species mass fraction for the condition of these control volumes, simulations of chemical reactions under constant volume mode are carried out. Three initial chemical compositions are considered. For the first test, the initial mixture is solely composed of unreacted gases. For the second one, the mixture is composed of 99% of unreacted gases and 1% of reacted gases. For the third test, the mixture is composed of 95% of unreacted gases and 5% of reacted gases. Figure 6 shows the temperature evolution for the three simulations. The initial conditions are a stoichiometric H2-air mixture, ρ = 0.002 g/cm3 and internal energy such that T = 1200 K for the unreacted mixture. The results demonstrate that even a small variation of the initial chemical composition reduces the induction time considerably. These simulations indicate that the use of average species mass fraction may have anticipated the oblique reaction front for the numerical solutions obtained with the fully Eulerian formulation, as presented in Figs. 3, 4 and 5.

Wedge flow

Hypersonic flow around a wedge is simulated with the Eulerian and with the hybrid Eulerian/Lagrangian formulations. The freestream conditions are a stoichiometric H2-air mixture, pressure equal to 0.266 atm, temperature equal to 300 K and Mach number equal to 7. The wedge semi-angle is equal to 35°. Simulations were carried out over two structured quadrilateral meshes. The meshes differ mainly in refinement. The boundaries of the meshes are presented in the Fig. 7. Grid 1 is composed of 34,200 nodes and 33,787 cells, in which the distribution is 114 × 300 points in the transversal and longitudinal directions, respectively. The nodes are equally spaced in each direction. Grid 2 is composed of 90,000 nodes and 89,251 cells, in which the distribution is 150 × 600 points. The nodes are also equally spaced in each direction. Position coordinates are in centimeters in Fig. 7.

Figure 7: Boundaries of the meshes used to simulate the flow around a wedge: a) Coarse mesh (114 × 300), Grid 1; b) Fine mesh (150 × 600), Grid 2.

Figure 6: Temperature versus time for a chemical reaction under constant volume mode. Effects due to a small quantity of reacted gas in the initial mixture.

Figure 8 shows the density and the H2O mass fraction contours of the solutions obtained. The overall structure of the flow is similar for all simulations. The distance that separates the shock wave from the detonation wave is progressively reduced up to the triple point and, then, the two fronts remain coupled downstream. Moreover, the same structure of the transition region, that exists between the initial oblique shock wave and the resulting oblique detonation wave, is observed for all solutions. The effect of the mesh is more significant for the Eulerian formulation, since the triple point is better defined for the finer mesh. Further comparison of the results can be seen in Fig. 9, which shows density, temperature and molecular oxygen mass fraction contours for the simulations



Figure 9: Density [kg/m3], temperature [K] and O2 mass fraction contours for M∞ = 7, p∞ = 0.266 atm and T∞ = 300 K flow of a stoichiometric H2-air mixture over a wedge. Solutions in (a), (b) and (c) use the standard Eulerian formulation, whereas results in (d), (e) and (f) use the hybrid formulation.

Figure 8: Property contours: Eulerian formulation: a1) Grid 1 density contours; a2) Grid 1 H2O mass fraction contours; b1) Grid 2 density contours; b2) Grid 2 H2O mass fraction contours; Hybrid formulation: c1) Grid 1 density contours; c2) Grid 1 H2O mass fraction contours; d1) Grid 2 density contours; d2) Grid 2 H2O mass fraction contours.



in the fine grid (Grid 2) and with both formulations. These flow visualization figures indicate that, in the fine grid, the calculations with the different formulations yield quite similar results, which then provides validation for the presently proposed formulation. It must be emphasized that the wedge flow calculations, using the fully Eulerian formulation implemented in the present computational code, have been extensively validated in the work of Pimentel (2000) and Pimentel et al. (2002), among other references. Hence, such results provide confidence in the proposed hybrid formulation.

Figure 10 shows the positions of the shock wave and of the reaction front for the various solutions obtained. Two temperature contours are used to indicate the position of the fronts. Figure 10(a) presents the influence of mesh refinement in the position of the two fronts for the Eulerian formulation, whereas Fig. 10(b) does the same for the hybrid formulation. In a similar fashion, Fig. 10(c) shows the influence of the formulation in the simulations performed for Grid 2. The effect of the mesh is more significant for the Eulerian formulation, since the reaction front as well as the triple point position move downstream with the

grid refinement, as shown in Fig. 10(a). Such behavior is not observed for the hybrid formulation, Fig. 10(b). The positions of the shock wave in the solutions obtained with Grid 2 are similar for the two formulations, as shown in Fig. 10(c), but the reaction front and the triple point position are slightly moved upstream for the Eulerian formulation.

Chemical reaction analysis 2

A second investigation of the reactive mixture is carried out in order to clarify the effects regarding the use of average species mass fraction in the induction zone. The previous analysis of the chemical reaction addressed the influence in the oblique reaction front that is approximately aligned to the local flow, in which some volumes may be composed of gases with very different chemical composition. The analysis of the present section addresses the reaction front approximately normal to the local flow. In this condition, the mixture of the control volumes in the induction zone is not composed of gases with very different chemical compositions.

Simple one-dimensional simulations of chemical reactions under constant volume conditions are carried out. The Eulerian mesh used is presented in Fig. 11. The density, energy and velocity are kept constant in space and time. The freestream conditions consider unreacted stoichiometric H2-air mixture, ρ = 0.002 g/cm3 and T = 1200 K. The simulations are performed from the instant t0 = 0 μs to the instant tN = 20 μs. For a number of volumes equal to N, the time that the fluid takes to traverse a volume, Δtvol, may written as

Δt

vol=

tN

N. (15)

For simplicity, two independent steps are considered, the first one for the fluid dynamics and the second one for the chemical reaction, in this order, i.e.,

Yi

n + 12 = Y

in + Y

i−1n − Y

in( ) ⋅ f

Δ t( ),Y

in +1 = C Y

i

n + 12 , f

Δ t⋅ Δt

vol

⎛⎝

⎞⎠

, (16)

where C is the chemistry operator and Y is the vector of the chemical species mass fractions. Y is defined as

Y =

Y1

Y2

|Y

M

⎡

⎣

⎢⎢⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥⎥⎥

(17)

fΔt is the time step divided by the time that the fluid remains within each cell, i.e.,

Figure 10: Position of shock wave and reaction front: a) effect of grid refinement for the Eulerian formulation; b) effect of grid refinement for the hybrid formulation; c) effect of the formulation for Grid 2.



Figure 11: One-dimensional mesh used to simulate the time evolution of a reactive mixture under constant volume conditions.

fΔ t=

ΔtΔt

vol (18)

The numerical code VODE (Byrne and Dean, 1993) is adopted to time integrate the chemical composition from the instant t to the instant t + Δt.

Figure 12: Effects of the use of the average species mass fraction. Comparison to the original time-evolving temperature profile: (a) 20 cells, (b1) and (b2) 100 cells, (c1) and (c2) 1000 cells.

For the initial and the entrance boundary conditions, the freestream properties are defined for all the volumes. Convergence is achieved when the maximum absolute variation of the temperature in a volume from the instant t to t + Δt becomes lower than a certain tolerance. As expected, before combustion starts, the variation of the temperature is insignificant, and convergence is only allowed when the maximum temperature variation starts to decrease. Figure 12 presents the converged solutions for three meshes, the first one containing 20 cells, as shown in Fig. 12(a), the second one containing 100 cells, as shown in Figs. 12(b1) and (b2), and the last one containing 1000 cells, as shown in Figs. 12(c1) and (c2). Figures 12(b2) and 12(c2) are simply enlargements of their corresponding Figs. 12(b1) and 12(c1), respectively. Six different time step values are considered, f

Δt = 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0. The simulation performed with f

Δt equal to 1.0 corresponds to a simulation without considering averaged species mass fraction, since the integral information contained in a cell is passed to the following cell without mixing. The solutions presented in Fig. 12 have evidenced that the induction time is reduced when averaged species mass fraction is considered. This effect is minimized by the mesh refinement and by increasing the time step. These results and observations explain why the reaction front and the triple point moved downstream with the grid refinement for the Eulerian formulation in the simulation of the flow over a wedge, as shown in the Fig. 10(a). Moreover, such results also suggest that, even for the finer mesh, the distance from the detonation wave to the shock wave may have be underpredicted, as shown in the Fig. 10(c).

Blunt body results using the hybrid formulation

As before, a supersonic flow composed of a stoichiometric H2-air mixture over a sphere-cylinder of 15 mm diameter is simulated. The configuration is the same of Lehr’s



experiment for Mach number equal to 6.46 (Lehr, 1972). The freestream conditions are T∞ = 292 K and p∞ = 320 mmHg. Two simulations are carried out over two different structured quadrilateral meshes. The two meshes differ from each other in refinement and topology. The boundaries of the meshes are presented in Fig. 13. The coarse mesh, Grid 1, is composed of 6,000 nodes and 5,831 cells, in which the distribution is 50 × 120 points in the wall-normal and longitudinal directions, respectively. The fine mesh, Grid 2, is composed of 25,000 nodes and 24,651 cells, in which the distribution is 100 × 250 points in the wall-normal and longitudinal directions, respectively. For both meshes, the nodes are equally spaced in each direction. Position coordinates are in centimeters in Fig. 13. It should be pointed out that these grids are considerably coarser than the ones used for the analysis of the blunt body problem using the fully Eulerian formulation. Moreover, Fig. 14 presents a visualization of the fine grid (Grid 2) for the present simulations. Both an overall view of the grid and an enlargement of the mesh near the front symmetry axis are shown in the figure.

observed in the numerical solutions. Near the stagnation line, it is not possible to distinguish the reaction front from the normal shock wave. As the shock wave becomes more oblique downstream, the two fronts separate from each other. One can observe that the contours for the coarse grid, both for density and for water mass fraction, are a bit wavy. This behavior occurs because Grid 1 is really too coarse. The property contours are much better defined in the solution for Grid 2, as one can clearly see in Fig. 15. However, as pointed out, even for the coarse grid results, the shock wave and the detonation front separate from each other as they move downstream.

Figure 14: Visualization of the fine mesh (Grid 2), with 100 × 250 points in the normal and longitudinal directions, respectively: (a) Complete grid; (b) Grid near the frontal stagnation point.

Figure 15: Density and the H2O mass fraction contours: a1) Grid 1 density contours; a2) Grid 1 H2O mass fraction contours; b1) Grid 2 density contours; b2) Grid 2 H2O mass fraction contours.

Figure 13: Boundaries of the meshes: a) coarse mesh (50 × 120 points), Grid 1; b) fine mesh (100 × 250 points), Grid 2.

Figure 15 shows the density and the H2O mass fraction contours of the solutions obtained for the two meshes. The same pattern of Lehr’s experiment (Lehr, 1972) is

Further visualization of the results with the hybrid formulation can be seen in Fig. 16. This figure shows density, temperature and O2 mass fraction contours, and the position of the shock wave and detonation front, for the calculations with the fine grid (Grid 2) and using the hybrid formulation here proposed. These results, again, clearly demonstrate the separation between the shock wave and the detonation front as one moves away from the blunt body frontal stagnation region. The results in Fig. 16 should be compared to those in Fig. 4, in which one can barely distinguish the separation of the two fronts from the contour plots and Fig. 4(d) confirms that such separation is clearly incipient even for that extremely refined grid. It should also



Figure 16: Flow solution obtained with the hybrid formulation for Grid 2: a) density contours, ρ [kg/m3]; b) temperature contours, T [K]; c) contours for O2 mass fraction; d) position of shock wave and detonation wave.

be pointed out that, in the final solution shown in Fig. 16, a total of approximately 218,000 particles are distributed throughout the computational domain. Moreover, the shock wave position is considered as the M = 6 contour and, in the same fashion, the detonation wave position was taken as the contour for which the O2 mass fraction is equal to 0.2.

Figure 17 shows the position of the shock wave and the reaction front for the two solutions, i.e., for the two grids and using the hybrid formulation, and for the experimental data. For the numerical solutions, in order to indicate the position of the fronts in the figure, four temperature contours were included. The effects of the mesh refinement and topology were not significant, since the numerical solutions compare well to each other. Comparisons between the numerical solution and the experiment shadowgraph showed good agreement concerning the shock wave and the reaction front positions, although the last was slightly dislocated. Although not completely coincident with the experiment, the solutions obtained indicated that the numerical errors may have been reduced with the use of the current formulation (for comparison purposes, see, for instance, the results in Guzzo, 2003, or the results in Fig. 5). Differences still remaining between numerical simulations and experimental data can be attributed either to the need of further grid refinement or to improperly modeled chemical kinetics. Both issues will be further addressed in the forthcoming discussion. In any event, and again comparing to the results shown, for instance, in Fig. 5, it is evident that a far better agreement with experiment is achieved with the present hybrid formulation.

Figure 18 shows zooms of two regions of the flow solution using Grid 2, that is, near the axis of symmetry, or normal reaction front, and near the oblique reaction front. This visualization evidences the challenges of the present simulations. Within the same flow field, the regime goes from frozen (Damköhler number « 1) to equilibrium (Damköhler number » 1). The Damköhler number is defined as the flow timescale over the chemical reaction timescale, and it is used to relate chemical reaction timescale to other phenomena occurring in a system. Figure 18(a) shows that, when the chemical reaction timescale is much lower than the convective time scale, the gas reacts nearly instantaneously, whereas Fig. 18(b) shows the opposite behavior away from the stagnation region. The streamtraces show how the reaction front aligns to the local flow as the shock and reaction fronts become more oblique. As long as the chemical kinetics is strongly nonlinear with the chemical composition, the use of average species mass fraction over an arbitrary mesh topology to simulate this region of the flow may require a prohibitively extensive grid refinement.

Figure 17: Position of the shock wave and reaction front. Comparison to experimental data (Lehr, 1972).

Figure 18: Zoom over Grid 2 solution with streamtraces: a) normal reaction front; b) oblique reaction front.



The results presented in the paper have attempted to convey the idea that the use of average species mass fraction in the calculation of the chemical reaction processes introduces additional error, which the hybrid formulation here proposed has helped reduce considerably. However, there are still several other sources of errors, which are present and which must be adequately treated for a successful simulation. In order to avoid any confusion, it is important to stress, first of all, that the paper has not addressed any modeling errors. Modeling errors are associated with the ability of the governing equations to adequately represent the phenomena present in the flowfield or, for instance, the ability of the chemical kinetics mechanism (Balakrishnan and Williams, 1993) adopted to correctly model the H2 and air reactive mixture behavior. The paper has focused on numerical errors. Nevertheless, it is clear that numerical errors can also have very diverse sources. The paper has addressed effects that come about due to mesh refinement and mesh topology, and the influence of the different treatment of the chemical reaction equations, i.e., Lagrangian versus Eulerian approach. Other aspects of numerical errors have not been addressed. For instance, the effect of the spatial discretization scheme, for the convective terms, is a very important aspect which has not been discussed at all in the present paper. A detailed discussion of numerical errors associated with the spatial discretization schemes can be seen in Azevedo, Figueira da Silva and Strauss (2010).

CONCLUDING REMARKS

A simple Eulerian/Lagrangian hybrid methodology is proposed and its formulation is presented. This methodology couples an Eulerian description of the gasdynamic equations with a particle formulation to represent the chemical kinetics. The objective of adopting a Lagrangian particle formulation for the chemical kinetics is to avoid the use of averaged species mass fractions in the chemical reaction process, which would necessarily occur if the standard, fully Eulerian formulation were used. In this latter approach, the coupling between fluid dynamics and chemical kinetics is achieved by Strang’s time-step splitting procedure, in which fractional time steps are taken, alternatively, in the fluid dynamic equations and in the chemical equations, but using a single Eulerian grid for both sets of equations. The authors further emphasize that the present paper has not specifically addressed aspects related to computational costs. The reason for such approach rests on the fact that, as implemented, the two formulations here discussed have comparable computational costs and, hence, this is not an issue in the present case. It is clear, though, that a particle method may have additional advantages for numerical performance enhancements at almost no extra effort from the user, particularly in the

multi-core machines that are currently becoming the rule in most computational environments. Such a discussion, however, is beyond the scope of the present work.

Simulations of hypersonic reactive flows over a blunt body and over a wedge are performed using the two different formulations to couple the chemical reaction to the fluid dynamics. For the simulations of hypersonic flows over a blunt body with the Eulerian formulation, the mesh format and refinement significantly influence the final solution. For the simulations of hypersonic flows over a wedge with the Eulerian formulation, the distance from the reaction front to the shock wave is underpredicted. This effect is reduced with the refinement of the mesh. The effects of the mesh topology and refinement are considerably less significant for the hybrid formulation. The paper also discussed two independent investigations of the behavior of the reactive mixture, which have shown that the use of averaged species mass fractions may reduce the induction time and shorten the induction zone. The second of such investigations has also demonstrated that these effects may be minimized by mesh refinement and by increasing the time step. Finally, Lehr’s experiment for freestream Mach number equal to 6.46 is successfully simulated using the presently proposed hybrid formulation using two different meshes. The grids differ in refinement and topology. The solutions compare well with each other, indicating that the numerical errors may have been reduced with the use of the current formulation. The overall structure of the flow shows good agreement with the experimental data. The shock wave position is also in good agreement with the experiment, and the reaction front presented the same inclination but a slight dislocation from the experimental position. The present results seem to indicate that the hybrid formulation is less influenced by grid parameters and, hence, is a more robust approach for the hypersonic problems of interest.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the partial support for this research provided by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), under the Integrated Project Research Grant no. 312064/2006-3. Partial support for the present work was also provided by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), under the Process No. 2004/16064-9.

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Pimentel, C.A.R., Azevedo, J.L.F., Figueira da Silva, L.F., and Deshaies, B., 2002, “Numerical Study of Wedge Supported Oblique Shock Wave-Oblique Detonation Wave Transitions”, Journal of the Brazilian Society of Mechanical Sciences, Vol. 24, No. 3, pp. 149-157.

Sarma, G.S.R., 2000, “Physico-Chemical Modelling in Hypersonic Flow Simulation”, Progress in Aerospace Science, Vol. 36, No. 3, pp. 281-349.

Singh, D.J., Ahuja, J.K., and Carpenter M.H., 1992, “Numerical Simulation of Shock-Induced Combustion/Detonation”, Symposium on High-Performance Computing for Flight Vehicles, Washington, D.C.

Strang, G., 1968, “On the Construction and Comparison of Difference Schemes”, SIAM J. Num. Anal., Vol. 5, pp. 506-517.

Sussman, A.M., and Wilson, G.J., 1991, “Computation of Chemically Reacting Flow Using a Logarithmic Form of the Species Conservation Equations”, Proceedings of the 4th International Conference on Numerical Combustion, Tampa, FL, pp. 224-227.

van Leer, B., 1979, “Towards the Ultimate Conservative Difference Scheme. V. A Second-Order Sequel to Godunov’s Method”, Journal of Computational Physics, Vol. 32, No. 1, pp. 101-136.

Wilson, G.J., and MacCormack, R.W., 1990, “Modeling Supersonic Combustion Using a Fully-Implicit Numerical Method”, AIAA Paper No. 90-2307, 26th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Orlando, FL.

Wilson, G.J., and MacCormack, R.W., 1992, “Modeling Supersonic Combustion Using a Fully-Implicit Numerical Method”, AIAA Journal, Vol. 30, No. 4, pp. 1008-1015.

Wilson, G.J., and Sussman, M.A., 1993, “Computation of Unsteady Shock-Induced Combustion Using Logarithmic Species Conservation Equations”, AIAA Journal, Vol. 31, No. 2, pp. 294-301.

Yungster, S., Eberhardt, S., and Bruckner, A.P., 1989, “Numerical Simulation of Shock-Induced Combustion Generated by High-Speed Projectiles in Detonable Gas Mixtures”, AIAA Paper No. 89-0673, 27th Aerospace Sciences Meeting and Exhibit, Reno, NV.


Gilberto Petraconi*Technological Institute of Aeronautics


Alexei Mikhailovich EssiptchoukLuikov Heat and Mass Transfer Institute

Minsk – [email protected]

Leonid Ivanovich CharakhovskiLuikov Heat and Mass Transfer Institute

Minsk – [email protected]

Choyu OtaniTechnological Institute of Aeronautics


Homero Santiago MacielTechnological Institute of Aeronautics


Rodrigo Sávio PessoaTechnological Institute of Aeronautics

São José dos Campos – [email protected].

Maria Luisa GregoriInstitute of Aeronautics and Space


Sônia Fonseca CostaInstitute of Aeronautics and Space



Degradation of carbon-based materials under ablative conditions produced by a high enthalpy plasma jetAbstract: A stationary experiment was performed to study the degradation of carbon-based materials by immersion in a plasma jet. In the experiment, graphite and C/C composite were chosen as the target materials, and the reactive plasma jet was generated by an air plasma torch. For macroscopic study of the material degradation, the sample’s mass losses were measured as function of the exposure time under various temperatures on the sample surface. A microscopic analysis was then carried out for the study of microscopic aspects of the erosion of material surface. These experiments showed that the mass loss per unit area is approximately proportional to the exposure time and strongly depends on the temperature of the material surface. The mass erosion rate of graphite was appreciably higher than the C/C composite. The ablation rate in the carbon matrix region in C/C composite was also noticeably higher than that in the fiber region. In addition, the latter varied according to the orientation of fibers relatively to the flow direction. These tests indicated an excellent ablation resistance of the C/C composite, thus being a reliable material for rocket nozzles and heat shielding elements of the protection systems of hypersonic apparatuses from aerodynamic heating.Keywords: Graphite, C/C Composite, Ablation, Plasma torch, Calorimetric probe, Enthalpy probe.

INTRODUCTION

To develop and qualify composite materials used as ablative coatings for thermo-structural protection of rocket engines, launch pad and atmospheric reentry vehicles is a constant challenge in the aerospace field. There are several types of materials used in these ablative thermal protection systems, as each material presents certain advantages and disadvantages in terms of its properties (specific mass, mechanical strength, melting temperature, etc.) and environmental conditions that they are subjected to (heat flow, temperature, mechanical stress, etc.). Between these materials, the graphite and carbon-fiber-reinforced composite (usually referred to as C/C composite) are

materials often chosen because of their heat resistance and strength at elevated temperature (Patton et al., 2002). These materials present better ablative resistance and lower erosion rate than resin-based materials even under extremely severe thermal conditions. The ablative performance of C/C composite is significantly influenced by both base materials characteristics and environmental parameters during the ablation process.

For solid rocket nozzle applications, one of the key requirements of the C/C composite is a low thermal conductivity (40 W/m.K) to minimize both the thickness of pyrolized carbon layer and the temperature rise at the reverse side of the composite (Park and Kang, 2002). Also, when a C/C composite is submitted to ablative conditions Received: 17/12/09

Accepted: 04/03/10

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DOI: 10.5028/jatm.2010.02013340


Petraconi, G. et al.

in air at high temperatures, it would be desirable that the reinforcing fibers and matrix remained unchanged, keeping their original structure, properties and shape during all the ablation process (Cho and Yoon, 2001).

In order to test the ablative resistance of carbon based materials, experiments of thermal degradation have been conducted using different techniques such as accelerating atomic oxygen (AO) and high flux plasma jet. As pointed by Fujimoto, Shioya and Satoh (2003), although there are several researches on degradation of monolithic carbon or graphite due to the impact of AO, there is little information on carbon-based materials such as C/C composite, especially when plasma jet ablation apparatus is used.

This paper presents a study of a plasma jet characteristics aimed at ablative resistance essays and, in conjunction with scanning electron microscopy (SEM) analyses, micro structural analysis of tested graphite and C/C composite. The experiments with the material samples were carried out in atmospheric environment, at a certain distance, facing the nozzle of the direct-current (DC) arc system. A linear calorimetric probe was used for the arc jet heat flux measurements at various radial and axial positions (Matsumo and Mieno, 2003). Abel’s inversion matrix method was then used to obtain the radial profile of the heat flux density at various longitudinal positions (Lochte-Holtgreven, 1968). Having these profiles, we could specify the region of the plasma jet where heat conditions (specify magnitude and uniformity) are appropriate to simulate thermal resistance of material samples under hypersonic flight in atmosphere. Moreover, the ablation resistances of graphite and C/C composite samples exposed to the high enthalpy plasma were compared.

EXPERIMENTAL

Plasma torch setup

A linear non-transferred plasma torch with “hot” cathode and stepped anode was used to generate a reactive plasma jet (Fig. 1) to which the material sample, fixed in a sample holder, was exposed. The plasma-forming gas was air at a flow rate of 4.5 x 10-3 kg/s. The DC arc plasma torch was designed for continuous operation at a power up to 50 kW. In this work, the torch parameters were adjusted to the arc current 135 A and arc voltage 300 V. Enthalpy of the produced plasma jet decreases with the distance from the torch nozzle attaining 3 MJ/kg at 80 mm distance, being compared to 5 MJ/kg at 10 mm one. This enthalpy range corresponds to conditions of a reentry flight under Mach numbers 7 to 10 at the altitude of about 40 km (Barros, 2008), being in the field of practical interest.

Linear calorimetric probe technique

An effective utilization of thermal plasma sources requires a thorough understanding of the heat transfer mechanism from the jet flow to the materials under study. The mapping of the heat flux density from plasma jet was carried out by using a water-cooled calorimetric probe (Fig. 2), constituted of a copper tube (outer diameter d = 3 mm, inner diameter 2 mm) equipped with two thermocouples. The probe was assumed to be fully catalytic. Since the radiation loss from the cold surface of the probe is negligible, the measurement corresponds to the total convective and chemical heat flux reaching the surface.

Figure 1: Schematic illustration of an apparatus for ablation test using arc plasma torch.

Figure 2: (a) Linear calorimetric probe in front of the plasma torch arrangement; (b) the approximation to the radial distribution of the heat flux density used in the calculations.

The water mass flow rate m was adjusted for each experiment in order to obtain the maximal response characteristic of the probe. In addition, the maximum temperature of the outlet water was maintained below 60°C in order to avoid the warming of the probe surface. The probe was installed perpendicularly to plasma jet and could be moved in axial and radial directions. The temperature increase of the cooling water was measured


Degradation of carbon-based materials under ablative conditions produced by a high enthalpy plasma jet

using chromel-alumel thermocouples (diameter 0.1 mm) mounted at the inlet and outlet of the probe.

It was assumed that heat flux is symmetrical with respect to the z-axis (plasma jet axis) and at any point is a function of r and z, i.e. the radial and axial distances, respectively, in cylindrical coordinates. Figure 2b show the approximation to the radial distribution of the heat flux density measured by the calorimetric probe used in the computational model.

The transversal plan of jet section was divided in k concentric circles (Fig. 2b). Within each region, limited by circles, the heat flux per unit area is assumed to be constant (qj = const). Hatched parts of the probe on the Figure 2b correspond to the regions with qj = const: a realistic picture of the distribution is shown on the upper half of the probe, while on the bottom half – the distribution used in calculations is displayed. Thus, at position i, the heat flux per unit length that entered to the probe is

Qi = 2 lijq j

j= i

k

∑ , where

lij = j2 − i2 + 2 j −1( ) − j2 − i2 − 2 j −1( )( )ΔR

is the extent of the probe with qj = const. Hence, a column-vector of heat flux density is determined as q1, a column-vector of the heat flux per unit length that enters to the probe as Q and the matrix of extents as L:

L =

l11 l12 ... l1k

0 l22 ... l2k

... ... ... ...0 0 ... lkk

, (1)

We obtain a simple equation:

L ⋅ql = Q . (2)

The experimental values of the total heat flux ( Qitotal )

that enters to the probe at i-th position were calculated as

Q

itot = c

pm(T

out− T

in) , where cp is the specific heat

of water, m is the mass flow rate of the cooling water,

(Tout – Tin) is the temperature increase of the water. Thus, using the method of inverse matrix (Matsumo and Mieno, 2003), we obtain the radial heat flux density distribution.

In equation 2, it was assumed that the heat flux per unit area is constant along the extent ijl (Fig. 2). However, in transversal section (i.e. along the circle of the probe tube), the heat flux distribution is non-uniform. Such

distribution is presented by (Auweter-Kurtz, M. et al, 2000), who gives a computed heat flux distribution around the cylindrical surface exposed to gas at 6000 K moving in transverse direction at velocity M = 0.53. The surface temperature of cylinder of 400 K, used in calculation, corresponds to our conditions of measurements. Figure 3 clearly displays a strong variation of q around the cylinder surface. The probe is most thermally loaded at stagnation point, whereas at the opposite point (i.e., at 180° in the Fig. 3) the heat flux density is four times less. In order to obtain q in stagnation point (that is more important), we assumed a uniform heat flux density distribution with q = qmax = const applied only for a part of circumference of the calorimetric probe. Figure 3 shows that, for this particular case, the arc of the probe circumference must be limited by angle of Θ = 100 degrees. For other flux conditions, this angle is variable within the range of 80 to 110 degrees. Thus, we used Θ = 90° in our calculations.

Figure 3: Heat flux density distribution on the cylinder surface q = f(θ) and equivalent heat flux for q = qmax = const Adapted from Auweter-Kurtz, M. et al, 2000.

A comparison of the heat flux obtained by such method was calculated by commonly used relationship based on Fay and Riddell’s equation, (Equation 3), where the enthalpy enters as parameter (Polezhaev and Shishkov, 1970).

Enthalpy probe technique

The measurements of the plasma flux enthalpy distribution were carried out by the enthalpy probe, described by Dresvin (1972). The procedure was similar to the heat flux probe method presented above, however supplied with the small orifice (~1 mm) directed towards the plasma jet. Gas from the jet was sampled through



this orifice by suction and cooled inside the probe. The enthalpy (h0) was then obtained by measuring the mass flow rate of sampling gas Ggas and the cooling water Gw and the difference between the heat load on the probe cooling circuit under sampling and calibration (i.e. with Ggas = 0) conditions:

h =

Gwcp (ΔTs − ΔTc )

Gair+ h0

, (3)

where ΔTs and ΔTc are the temperature rise if the cooling water is under sampling and calibration flow conditions; h0 enthalpy of the plasma gas at normal conditions.

Closing and opening of the sample channel was alternated in approximately 15 seconds. The measurement of the total pressure on the probe tip allows calculating the plasma velocity “v” as follows.

v =

2( p − p0 )ρ0

(4)

where (p – p0) is the measured dynamic pressure and ρ0 is the local plasma density computed at the local plasma temperature.

The sample of target material was inserted in the graphite holder so that only the transverse area could be exposed to plasma jet. The surface temperature of the target material was controlled by varying the distance from the torch nozzle to the front surface of material sample and was measured by an optical pyrometer (model IR-AH 3SU-Chino). This distance was varied within the range of 0.06 to 0.14 m, in which the samples’ surface temperature (1697 – 1995) K attains a steady-state condition. The erosion rate was calculated as mass loss by area in unit time. For this calculation, the sample dimension and the mass were measured before and after the test. The time of high-temperature exposure of the material sample varied within the range of 40 to 180 s. The average values were taken from the results obtained by repeating the test with four samples under the same operational conditions.

As the target material, a high-density (1.83 x 106 kg/m3) synthetic graphite and C/C composite (GROUP-SNPE, France) with density 1.75 x 106 kg/m3 were used and compared in this work. The specimens were cut into cylindrical geometry, with outer diameter of 0.016 m and thickness of approximately 0.012 m. Thus, the area of the surface exposed to reactive plasma was kept at 2.04 x 10-6 m2.

RESULTS AND DISCUSSIONS

Figure 4 shows the radial distribution of the heat flux density q(r) obtained at distances of 5, 30 and 50 mm from the nozzle of the plasma torch. It is observed that, at small distances from the nozzle, there is a plateau-like profile with approximately constant heat flux density. This plateau (or core of flow) may be observed visually up to 30 mm distance, where the heat flux on the axis q(r = 0) reduces drastically and the distribution profile becomes narrower, as it can be seen at z = 50 mm. The radial distribution of plasma jet velocity at small distances from the torch nozzle also appears practically unchanged at small distances from the nozzle, as shown in Figure 5.

Figure 4: Radial distribution of the heat flux density q measured by calorimetric probe technique.

Figure 5: Radial distribution of the plasma jet velocity v measured by enthalpy probe technique.



The typical surface temperature behavior at Z = 80 mm as a function of the exposure time is shown in Figure 6. The mass losses per unit area are depicted in Figure 7. The curves show that losses vary approximately proportionally to the exposure time. We observe that, for the same exposure time, the specific mass loss for the graphite is considerably higher than for the C/C composite. In this experiment, the steady-state temperature of the material surface was about 1950 K for C/C composite and about 2000 K for graphite, within the range of the experimental data error (Fig. 6). At low heat flux densities, the temperature profiles for both graphite and C/C target are similar: a fast increase during initial stage of heating with subsequent saturation at certain temperature, which depends on the heat flux density.

Figure 8 shows the distribution of the heat flux density q measured by the linear probe at the distance 80 mm from the nozzle and smoothed by fitting. The maximum value of heat flux density is of 2.82 x 106 W/m2 at the axis and of 1.9 x 106 W/m2 at the border of target. The mean value, qmean, is 2.37 x 106 W/m2. This mean value of heat flux is obtained with transverse streamline of the linear probe of 3 mm diameter, thus its applicability has to be validated to represent the effective axial flow on a target material (material sample) of 16 mm diameter.

Figure 8: Heat flux density q distribution as a function of jet radius at distance of 80 mm from the nozzle (hatched shape of 16 mm diameter corresponds to target dimension). Method used: calorimetric probe.

Figure 6: Surface temperature as a function of exposure time for graphite and C/C composite (Z = 80 mm). The error bars was obtained by statistical method.

Figure 7: Specific mass loss as a function of exposure time for graphite and C/C composite. The vertical line stands for the beginning of the surface temperature saturation.

The measured enthalpy and the velocity of gas at the axis of plasma jet as a function of distance from the nozzle are shown in Figures 9a and 9b. At a distance of 80 mm, the measured enthalpy is 2.75 MJ/kg and the velocity is 100 m/s. Applying the well known simplified version of the Fay-Riddell relationship (Auweter-Kurtz, M. et al, 2000) for the heat flux density incident on the target of 16 mm diameter, we obtain:

q = 4.4 *10−4 h

Patm

+ρv2

2R

eff

=4.4 *10−4 * 2.75*106 101325+ 765.53.33*8*10

− 3= 2.368 MW/m2

(5)

Where h is the enthalpy; Reff =0.33R is the effective radius of the front face of target of radius R, according to (Mezines and Masek, 1979); Patm is the atmospheric pressure; ρ is the plasma density; v is the plasma velocity.

This result validated the applicability of the heat flux averaging.

Experimental data with respect to specific mass loss rate for C/C composite and graphite as function of surface temperature are shown in Figures 10a and



10b, respectively. The specific mass loss rate increases approximately linearly with the surface temperature for the C/C composite (Fig. 10a), while similarity to

an exponential growth for the graphite (Fig. 10b) is observed. The linear erosion rates were also somewhat different for these materials. Linear erosion rate for C/C composite was in the range from 13 mm/s to 25 mm/s and for graphite from 15 mm/s to 28 mm/s. This can also be attributed to the difference in the conformation structure between them.

The temperature dependence of the mass loss of carbon material, used as target for the experiments, can be explained by the supposition that carbon atoms at high temperature and in contact with atomic oxygen are more likely detaching the surface by forming CO gas. Kinetics of such reaction is well defined (Hald, 2003). The exponential behavior of the curve of specific mass losses showed for graphite in Figure 10b can be explained as a consequence of an increasing of the whole particulate filler (petroleum coke) loss rate, which is enhanced by loosening bonds produced by erosion of binder carbon formed by graphitized pitches (Marsh, Forrest and Pacheco, 1981). These assumptions will be clearly understood by SEM analysis of the C/C composite and graphite surfaces exposed to reactive plasma.

The SEM micrographs (Fig. 11) show the eroded cross section and surface of graphite. They reveal a texture similar to those obtained by chromic acid attack, a special surface preparation, used for SEM analysis of carbon materials (Marsh, Forrest and Pacheco, 1981). This means that the ionized atoms of plasma act in a similar way of the ionic components of the chromic acid solution, removing preferentially the edge carbons of anisotropic portion from the bulky graphite surface. The remaining structures are, almost all, well oriented graphite flake-like portions, well exemplified in the micrograph of Figure 11b. The morphology of this plasma ion-attacked surface shows that the sets of mosaic structure carbon skeleton are the basis of this synthetic graphite fillers structure (Marsh, Forrest and Pacheco, 1981).

Figure 9: (a) The enthalpy and (b) the velocity of the plasma at the axis of jet as a function of distance from the nozzle.

Figure 10: Specific mass loss rates of carbon based materials: (a) C/C composite; (b) graphite.

Figure 11: SEM of graphite at surface temperature of 1994 K; (a) Eroded cross section and (b) Eroded surface.



The action of plasma on the edge carbons of graphitized materials can also be observed on C/C composites. The SEM micrographs in Figures 12 and 13 show the eroded surface of the C/C sample and also, for comparison, the non-eroded surface of the same sample. The comparative analysis indicates that the strong damaging effect was produced on the sample surface by reactive air plasma. The surfaces are now strongly roughened forming troughs and almost free carbon fibers bundles, whereas the non-eroded specimen shows a smooth surface. These micrographs also show that the matrix region of C/C composite presents earlier erosion in relation to the fiber region, resulting in the exposure of loosely bonded fibers at the surface. More detailed analysis of the surface of this plasma attacked surface (Fig. 13) shows that, as observed in the surface of graphite specimen, ionic attack of C/C composite produces a preferred withdrawal of edge carbon of graphitized matrix, revealing an anisotropic lamellar structure of carbon as the last remaining part of the binder of fiber. For both types of samples, the more rapid reaction promoted over the anisotropic carbon reveals the texture of a carbon skeleton formed by lamellar structure carbon.

fibers bundle axis, as illustrated by Figure 12b, due to the conditions that all carbon positioned at top of fibers present almost the same characteristics, namely edge carbon of basal plane, the erosion rate of them is almost the same, while the binder carbon is transformed in gas. This is the reason to form relatively homogeneous and planar surface profile fibers, or even slightly depressing at the core fibers of each bundle. Moreover, if the plasma jet is directed to shine the fibers longitudinal surface, as shown in Figure 12d, the corrosion occurs always from the fiber localized at surface toward one localized at the middle of the bundle. It is also observed that the corrosion occurs from outermost to inner shell of fiber, probably starting at some structure defects where the higher concentrations of edge carbon are present, and this mechanism leads to the formation of very well sharpen arrow-type fibers or even the formation of fiber island bonded to the bundle by shadowed non-corroded binders. These results show that the fibers directed in parallel to the axis of oncoming flow of oxidative plasma and perpendicularly to the material surface are more corrosion-resistant than fibers positioned along the surface, mainly due to the more homogeneous effects of corrosion along the direction perpendicular to the surface .

It is important to notice that the SEM analyses were performed over the samples which already presented almost half of its original thickness (in direction against the plasma jet direction). This means that the microscopically analyzed surface is not one produced only by fresh plasma contact. It has to be pointed out that the high temperature thermal effect over the bulk of sample is also an important factor on the total erosion produced on the samples.

CONCLUSIONS

This paper presented a stationary experiment performed to study the degradation of carbon-based materials by its immersion in reactive air plasma jet generated by a DC plasma torch with gas enthalpies comparable to those

Figure 12: SEM of C/C composite: (a) Non-eroded surface of fibers bundles region (transversal view); (b) eroded surface of fibers bundle region (transversal view) at 2009 K; (c) Non-eroded surface of fibers bundle region (longitudinal view), and (d) eroded surface of fibers bundle region (longitudinal view) at 2009 K.

Another important fact observed by SEM analysis is the anisotropic corrosion effects produced on carbon fibers as function of plasma jet direction related to fiber axis. If the incident plasma beam is directed parallel to the

Figure 13: (a) SEM of C/C composite: General view of eroded surface of fibers bundle region at 2009 K. (b) SEM of C/C composite: eroded surface of fibers bundle region at 2009 K (interface region).



encountered during motion in earth’s atmosphere at Mach numbers from 7 to 10. For a distance of 80 mm between the specimen surface and the torch tip, the steady-state temperature of the C/C composite target surface was of 1994 K and the heat flux was about 2.4 MW/m2. The degradation of the material, as consequence of oxidative corrosion processes, was studied and useful information was obtained for global mass loss as well as for microscopic damages. The experiments show that the mass loss per unit area is approximately proportional to the exposure time and depends strongly on the temperature of the material surface. The mass erosion rate for graphite is appreciably higher than for C/C composite, probably due to their granular structure, which allows, at certain test time, losses of big amount of particles of filler as a consequence of weakening of bonds by erosion of graphitized binders. This effect leads to exponential dependence of mass loss of graphite as a function of test temperature in comparison to the linear growth of erosion for C/C composite. It was possible to show that the matrix region of C/C composite is eroded at rate noticeably higher than the fiber region, and also that this erosion of matrix is preferentially performed over edge atoms of anisotropic carbon structure, as a consequence of ionic attack of the carbon surface. The plasma torch testing indicated that the tested C/C composite has ablation resistance that allows its consideration as perspective candidate for the heat shielding and rocket nozzle design.

ACKNOWLEDGEMENTS

The authors thank to the Brazilian Space Agency, to Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and to Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for financial support, and to Instituto de Aeronáutica e Espaço for the provision of C/C composite and graphite samples.

REFERENCES

Auweter-Kurtz, M. et al, 2000, “Measurement Techniques for High Enthalpy and Plasma Flows” Available at: http://www.rta.nato.int/Pubs/RDP.asp?RDP=RTO-EN-008.

Barros, E.A., 2008, “Plasma térmico para ablação de materiais utilizados como escudo de proteção térmica em sistemas aeroespaciais”, PhD Thesis, Instituto Tecnológico de Aeronáutica.

Cho, D., Yoon, B., 2001, “Microstructural interpretation of the effect of various matrices on the ablation properties of carbon-fiber-reinforced composites”, Composites Sci. and Technol, Vol. 61, No. 2, pp. 271-280.

Dresvin, S.V., 1972, “Physics and techniques of low temperature plasma”, Moscow: Atomizdat (in Russian).

Fujimoto, K., Shioya, T., Satoh, K., 2003, “Degradation of carbon-based materials due to impact of high-energyatomic oxygen”, International Journal of Impact Engineering, No. 28, pp. 1-11.

Hald, H., 2003, “Operational limits for reusable space transportation systems due to physical boundaries of C/SiC materials”, Aerospace Sci. and Technol, Vol. 7, No. 7, pp. 551-559.

Lochte-Holtgreven, W., 1968, “Plasma diagnostics”. Amsterdam: North-Holland Publishing Company, Amsterdam.

Marsh, H., Forrest, M., Pacheco, L.A., 1981, “Structure in metallurgical cokes and carbons as studied by etching with atomic oxygen and chromic acid”, Fuel, Vol. 60, No. 5, pp. 423-428.

Matsumo, N., Mieno, T., 2003, “Characteristics of heat flux of JxB gas-arc discharge for the production of fullerenes”, Vacuum, Vol. 69, No. 4, pp. 557-562.

Mezines, S.A., Masek, R.V., 1979, “Heat shield material tests in a simulated Jovian entry heating environment”, AIAA, Paper No. 79-0037, presented at 17th Aerospace Sciences Meeting, New Orlean.

Park, J.K., Kang, T.J., 2002, “Thermal and ablative properties of low temperature carbon fiber-phenol formaldehyde resin composites”, Carbon, Vol. 40, No. 12, pp. 2125-2134.

Patton, R.D. et al., 2002, “Ablation, mechanical and thermal conductivity properties of vapor grown carbon fiber/phenolic matrix composites”, Applied Sci. and Manufacturing, Vol. 33, No. 2, pp. 243-251.

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Gilson da Silva* National Industrial Property Institute

Rio de Janeiro – [email protected]

Koshum IhaTechnological Institute of Aeronautics


Andreza M. CardosoInstitute of Aeronautics and Space


Elizabeth C. MattosInstitute of Aeronautics and Space


Rita de Cássia L.DutraInstitute of Aeronautics and Space



Study of the thermal decomposition of 2,2’,4,4’,6,6’- hexanitrostilbeneAbstract: 2,2’, 4,4’, 6,6’- hexanitrostilbene (HNS) is an energetic material, a nitroaromatic compound, with thermal and chemical stabilities, which is employed in the aerospace industry. In this work, the Arrhenius parameters (activation energy and pre-exponential factor) of thermal decomposition reaction were studied and the results were compared with the values reported in the literature. The Kissinger method, applied to DSC’s non-isothermal data of the decomposition temperature was chosen for this study. The activation energy determined for the thermal decomposition of HNS revealed values from 428 kJ.mol-1 to 477 kJ.mol-1, under the experimental conditions employed. Keywords: Explosives, HNS, DSC, FT-IR.


LIST OF SYMBOLS

T Absolute temperatureEa Activation energyda Among variation of the samplem Angular coefficient f Heating ratek Kinetic constantf(a) Kinetic function of the thermal decompositionA Pre-exponential factordt Time’s variationR Universal constant of gases

INTRODUCTION

2,2’, 4,4’, 6,6’- hexanitrostilbene (HNS) is a nitroaromatic compound which has high chemical stability, melting point at 318°C and friction and impact sensitivity, 5 Nm and 240 N respectively, (Silva and Iha, 2004). These are the determinant factors for its use in the manufacture of blasting caps, detonation cords and boosters (Harris and Klassen, 2003; Rogers, 1996).

Among the main methods to obtain HNS, we can assert that the process starting from 2,4,6-trinitrotoluene (TNT), by different routes, is the most widely used on laboratory-

scale (Silva, 2007 ) and industrial too, such as the Shipp’s process (Shipp and Spring, 1970).

The identification of HNS obtained from a process using TNT can be easily performed using infrared spectroscopy by means of the analytical band near 957 cm-1, deformation by vibration (wedding) of wCH=CHtrans. Other small displacements of bands and changes in the intensity of the bands can also be observed when comparing the HNS and TNT spectra. However, the band near 957 cm-1 is even sufficiently resolved to permit quantitative studies of HNS in the presence of TNT, as described by Silva et al. (2008).

Different thermal analysis techniques such as Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TG) have been widely used in the study of thermal decomposition of energetic materials. In recent work, Silva, Nakamura and Iha (2008) used DSC to study the kinetics of thermal decomposition of pentaerythritol tetranitrate (PETN), the a polymorph of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) (Silva et al., 2003) and to study the kinetics of transition a→dHMX (Silva and Iha, 2004). Andrade et al. (2007) used DSC and TG in the study of thermal decomposition of composite solid smokeless propellant. Rocco (2004) studied, also using DSC and TG, the aging of formulations of composite solid propellant based on polyurethane binders used in rockets.

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DOI: 10.5028/jatm.2010.02014146


Silva, G. et al.

Thermogravimetric analysis can also be applied in quantitative determination of different energetic compounds in explosive compositions, as reported by Silva et al. (2008) in a work that compares results of the quantitative determination of TNT and HNS by TG and Fourier Transform Infrared Spectroscopy (FT-IR). The use of thermal analysis techniques is therefore widespread in the study of energetic materials for both aerospace propulsion systems and as suitable material for the manufacture of military warheads. The knowledge of the thermal behavior of an energetic material is essential to guarantee safety during its production, storage and handling.

In general, the kinetic models developed to study the kinetics of solid materials thermal decomposition are in principle based on consideration of the variation in the mass amount of the material in a time function, or the conversion rate of the sample (da/dt), as it is also called, in a process of decomposition due to a thermal stimulation, which can be expressed by Equation 1:

dαdt

= kf (α ) (1)

where:

da: among variation of the sample;dt: time variation;k: kinetic constant;f(a): kinetic function of the thermal decomposition.

The kinetic parameters can be obtained by substituting Arrhenius’s equation, Equation 2, in Equation 1, as shown in Equation 3:

k = − Ea RTAe (2)

dαdt

=− Ea RTAe f (α ) (3)

A: pre-exponential factor;Ea: activation energy;R: universal constant of gases; T: absolute temperature.

Equation 3 can be written in its integral form as Equation 4:

dαf (α )

=− Ea RTAe

0

T

∫0

α

∫ (4)

Replacing the integral of da/f(a) for g(a) and, for a non-isothermic process, considering the temporal variation, f = dT/dt, we have Equation 5:

g(α ) = Aϕ

− Ea RTe0

T

∫ dT (5)

The Equation 5 was the basis for the development of many models used in the study of thermal kinetic decomposition in solid materials (e.g. Kissinger, Ozawa, Friedman, among others). Since the treatment given to them by Kissinger and Ozawa in the development of their methods was similar, calculating the activation energy by these methods leads to numerical results of the same magnitude.

Kissinger’s method was chosen for use in the present study. It consists basically of Equation 6 (Lee, Hsu and Chang, 2002).

lnϕ

p

2

T

ln

AR

pT

− aE

pRT (6)

where:

f is the heating rate (K.s-1);Tp is the Absolute Temperature of the peak in each heating rate (K);A is the pre-exponential factor of Arrhenius (s-1); R is the gas constant (8,3145 J.mol-1 .K-1);Ea is the activation energy of the reaction (J.mol-1).

The activation energy may be obtained by means of Differential Scanning Calorimetry data using different heating rates, where displacements occur at the peak of the reaction temperature.

The association of Kissinger’s equation with the line’s equation (y = mx + b), i.e.: y = ln (f / TP

2), m =-Ea / R, x = 1/Tp, b = ln (AR/Tp) enables the determination of Ea’s value, graphically, as a function of ln (f/TP

2) versus 1/Tp, resulting in a straight line, the slope of which is -Ea/R, and the linear coefficient ln(AR/Tp).

Due to the importance of understanding the thermal behavior of explosives handled, this study aimed to determine the Arrhenius parameters (activation energy and pre-exponential factor) for the thermal decomposition reaction of a synthesized HNS sample against another commercial sample, comparing the results with each other and with the values found in literature.


Study of the thermal decomposition of 2,2’,4,4’,6,6’- hexanitrostilbene

EXPERIMENTAL

The study was conducted with two samples of HNS: a commercial sample, identified as HNS1, and a sample produced at the Chemical Laboratory of the Systems of Defense Division (ASD) of the Institute of Aeronautics and Space (IAE) identified as HNS2. The HNS2 sample was produced by a procedure based on Shipp’s process (Shipp and Spring, 1970). Both samples were previously analyzed by High Performance Liquid Chromatography (HPLC) and showed a close to 100% purity level.

Spectrometric characterization was performed on a FT-IR spectrometer Spectrum 2000 PerkinElmer, region from 4000 to 400 cm-1, resolution of the 4 cm-1, gain 1 and 40 scans. The samples were analyzed according to the transmission technique, KBr pellets in the proportion 0.8:400 mg.

The DSC analyses were obtained using PERKINELMER (Model DSC-8) equipment. The equipment was calibrated on the heating rates used (f), i.e., 5, 7, 10, 12 and 15ºC/min, with zinc and indium. The mass of the samples was approximately 1.0 mg. The analyses were performed in a temperature between 50 and 400ºC. The tests were performed under flow of nitrogen gas (40 mL/min) and in atmospheric pressure, i.e., the lids of the DSC pans were perforated in order not to confine the explosive.


Analysis by FT-IR

Figure 1 shows the FT-IR spectra of both samples studied in this work. There is, in the HNS2 spectrum, the indication of the characteristic band of 957 cm-1 which, as mentioned earlier, is one of the main analytical bands of this compound, wCH=CHtrans. It can be seen in Figure 1 that the spectra are very similar, indicating that it is the same organic compound.

Analysis by DSC

Figures 2 and 3 present the DSC curves of samples HNS1 and HNS2, respectively.

The profile of the thermal curves HNS was similar in both samples. Importantly, with all heating rates used in the experiment, both samples started the decomposition process from the molten state, or possibly in a coexistent state of solid and liquid phases for the same material, since in all DSC curves, we observed an endothermic peak around 318ºC, or immediately prior to the decomposition peak of the material. According to the

4000 3000 2000 1500 1000 400

%T

HNS2

HNS1

wave number (cm-1)

Figure 1: FT-IR spectra of HNS samples obtained by trans-mission technique in KBr pellets, in the proportion of sample 0.8 mg to 400 mg KBr

150 200 250 300 350 4000

5

10

15

20

25

30

35

40

45

50

55

60

65

endo

15oC/min

12oC/min

10oC/min

7oC/min

5oC/min

Hea

t Flo

w (m

W)

Temperature (ºC )

Figure 2: DSC curves of thermal decomposition of HNS1 in an atmosphere of N2

expected behavior for both samples, the DSC data showed that the maximum of the decomposition temperature (Tp) of the material was altered together with the increase in heating rate (f). The data obtained from the DSC curves are presented in Table 1.

The data regarding the DSC curves presented in Table 1 was analyzed by the Kissinger method, Equation 6, in accordance with the methodology shown in the introduction. Figures 4 and 5 show the graphs used to determine the Arrhenius parameters of the thermal decomposition of HNS1 and HNS2, respectively.


Silva, G. et al.

Lee, Hsu and Chang (2002) studied the decomposition of HNS by DSC technique and heating rates ranging between 5 and 20ºC/min. The peaks of thermal decomposition reported by them ranged between 325 and 343ºC, according to the heating rate used. The activation energy was also determined based on the Kissinger method, and the reported value was 197 kJ.mol-1.

Comparison between the values reported by Lee, Hsu and Chang (2002) and the data presented in this work shows that the peaks of the decomposition temperature were between 10 and 18ºC higher for the commercial sample (HNS1), and between 16 and 22ºC higher for the synthesized sample (HNS2). In line with such variations, the activation energy was also substantially different, in the order of 231 kJ.mol-1, HNS1, and 280 kJ.mol-1, HNS2. However, the variation of activation energy between the HNS1 and HNS2 was approximately 50 kJ.mol-1.

In previous studies (Silva, 2004), the activation energy for another energetic material, HMX, was calculated at low

f(ºC/min)

HNS1 HNS2

Temp. decomp. peak (ºC)

Decomp enthalpy

(J.g-1)

Temp. of decomp. peak (ºC)

Decomp. enthalpy

(J.g-1)

5 335.7±1.8 4424±59 341.8±1.1 4021±258

7 338.0±2.9 4316±425 347.6±1.0 4016±112

10 349.4±0.4 4409±193 351.9±0.3 4284±249

12 347.4±3.4 4109±267 355.4±0.5 4471±408

15 351.5±2.5 3893±247 359.2±0.2 4029±286

Table 1: Data obtained from the DSC curves of thermal decomposition of HNS

Arrhenius parameters calculation using the Kissinger method

m* R2 Ea (kJ.mol-1) A (s-1)

HNS1 -0.0515 0.8759 428 1.12 . 1036

HNS2 -0.0574 0.9938 477 1.12 . 1040

Table 2: Kinetic parameters of thermal decomposition of HNS

*Angular coefficient

Figure 3: DSC curves of thermal decomposition of HNS2 in an atmosphere of N2

150 200 250 300 350 4000

5

10

15

20

25

30

35

40

45

50

55

60

65

15 ºC/min

12 ºC/min

10 ºC/min

7 ºC/min

5 ºC/min

endo

Hea

t Flo

w (m

W)

Temperature (ºC)

3,00E-06

3,50E-06

4,00E-06

4,50E-06

5,00E-06

5,50E-06

6,00E-06

6,50E-06

7,00E-06

7,50E-06

1,59E-03 1,60E-03 1,61E-03 1,62E-03 1,63E-03 1,64E-03 1,65E-03

1/Tp

ln( φ

)/Tp2

Figure 4: Kissinger method graph for the determination of activation energy by the thermal decomposition of HNS1

Figure 5: Kissinger method graph for the determination of activation energy by the thermal decomposition of HNS2

3,00E-06

3,50E-06

4,00E-06

4,50E-06

5,00E-06

5,50E-06

6,00E-06

6,50E-06

7,00E-06

7,50E-06

1,57E-03 1,58E-03 1,59E-03 1,60E-03 1,61E-03 1,62E-03 1,63E-03

1/Tp

ln( φ

)/Tp

2

Table 2 shows the values of angular coefficients obtained by linear regression of the points (Figures 4 and 5), the correlation coefficient (R2) for each linear regression, as well as the activation energies values and the pre-exponential factors calculated.


Study of the thermal decomposition of 2,2’,4,4’,6,6’- hexanitrostilbene

heating rates (1, 2, 5, 7, 10ºC/min) and high heating rates (10, 12, 15, 17 and 20 ºC/min). Thus, it was observed that for the same energetic material, with the same particle size, granulometric distribution and crystalline structure (a), it is possible to get a variation of 58 kJ.mol-1 due solely to the heating rates adopted in the experiment. This fact may be justified by a change in the reaction’s mechanism of thermal decomposition. Also in that study (Silva, 2004), it was found that for the same energetic material, a same organic compound - HMX, in different crystalline forms, a and b, the activation energy can show a variation of 133 kJ.mol-1, even under the same analytical conditions.

Silva, Nakamura and Iha (2008), in another study conducted with PETN, observed that under different crystalline forms or due to the acidity occluded in the crystals of the same energetic material, the activation energy may change at about 12 kJ.mol-1 through the thermal decomposition of the material.

Since the particle size, granulometric distribution or cluster formation can change the heat conduction inside the capsule carrier and in the sample itself (Silva, 2007), the values of activation energy for samples of HNS1 and HNS2, when compared to each other, were satisfactory, because the samples clearly have different characteristics. HNS1 presents a fuzzy physical structure while HNS2 is a crystalline material with irregular granulometric distribution.

The variation of the activation energy in relation to that described in the literature (Lee, Hsu and Chang, 2002) may be linked to many factors discussed above (particle size, granulometric distribution, cluster formation, changes in the heating rates used, acidity occluded in crystals, among others).

CONCLUSION

The activation energy determined for the thermal decomposition of HNS following the Kissinger method was, in the experimental conditions used, 428 kJ.mol-1 for HNS1 and 477 kJ.mol-1 for HNS2. It can alter, depending on the physical (particle size, granulometric distribution or clusters formation) or chemical characteristics (acidity occluded in the crystals) in the sample, and depending on the analytical conditions employed, particularly in relation to heating rate used.

Although the values determined are significantly higher than those reported in the literature (Lee, Hsu and Chang 2002), they were considered satisfactory, since the study was conducted using materials with high levels of purity, the spectrometric characteristics of which were confirmed

as HNS and, especially, since the same analytical conditions were used.

ACKNOWLEDGMENTS

To Systems of Defense Division (ASD), Chemistry Division (AQI) and Materials Division (AMR) of the Institute of Aeronautics and Space (IAE) of the General Command of Aerospace Technology (CTA).

REFERENCES

Andrade, J., Iha, K., Rocco, J.A.F.F., Bezerra, E M., Iha, M.E.V.S., Pinheiro, G.F.M.P., 2007, “Análise térmica aplicada ao estudo de materiais energéticos”, Química Nova, Vol. 30, No. 4, pp. 952-956.

Harris, S.M., Klassen, S.E., 2003, “Development of an Ultrafine HNS for Use in Modern Slapper Detonators”, AIAA 2003 00240, Proceedings of 41st Aerospace Sciences Meeting and Exhibit”, Reno, USA.

Lee, J.S., Hsu, C.K., Chang, C.L., 2002, “A Study on the Thermal Decomposition Behaviors of PETN, RDX, HNS and HMX”, Thermochimica Acta, Vol. 392-393, pp. 173-176.

Rocco, J.A.F.F., 2004, “Estudo Sobre o Envelhecimento de Formulações de Propelente Sólido Compósito Baseadas em Binders Poliuretânicos Empregados em Motores-Foguete”, Ph.D. Thesis, Instituto Tecnológico de Aeronáutica, São José dos Campos, S.P., 190f.

Rogers, T.E., Orpington, K., 1996, “Flexible Detonating Cord”, European Patent Office EP 712822.

Shipp, K.G., Spring, S., 1970, “Hexanitrostilbene”, U.S. Patents 3,505,413.

Silva, G. et al., 2003, “Estudo cinético da decomposição térmica do alfa HMX por calorimetria exploratória diferencial”, Anais da Associação Brasileira de Química, Vol. 52, No. 2, pp. 81-83, 2003.

Silva, G. et al., 2004, “Aplicação da Calorimetria Exploratória Diferencial no Estudo da Cinética de Transição Alfa - Delta HMX”, Química Nova, Vol. 27, No. 6, pp. 889-891. doi: 10.1590/S0100-40422004000600009.

Silva, G., 2004, “Avaliação da Energia de Ativação e Sensibilidade de Materiais Altamente Energéticos”, Thesis, Instituto Tecnológico de Aeronáutica, São José dos Campos, S.P., Brazil, 96f.


Silva, G. et al.

Silva, G., Iha, K., 2004, “Caracterização de Material Altamente Energético (HNS) Via Análises Instrumentais”, Proceedings of 6th Simpósio de Guerra Eletrônica, São José dos Campos, S.P., Brazil.

Silva, G., 2007, “Síntese, Caracterização e Quantificação de 2,2’,4,4’,6,6’-Hexanitroestilbeno”, Ph.D. Thesis, Instituto Tecnológico de Aeronáutica, São José dos Campos, S.P., Brazil. 118f.

Silva G. et al, 2008, “Determinação Quantitativa de TNT e HNS por TG e FT-IR”, Química Nova, Vol. 31, No. 6, pp. 1431-1436. doi: 10.1590/S0100-40422008000600029.

Silva, G., Nakamura, N.M., Iha, K., 2008, “Estudo Cinético da Decomposição Térmica do Pentaeretritol-Tetranitrado (PETN)”, Química Nova, Vol. 31, No. 8, pp. 2060-2064. doi: 10.1590/S0100-40422008000800028.


José Atílio Fritz Fidel Rocco*Instituto Tecnológico de Aeronáutica


Rene Francisco Boschi GonçalvesInstituto Tecnológico de Aeronáutica


Koshun IhaInstituto Tecnológico de Aeronáutica


Gilson da SilvaInstituto Nacional da Propriedade Industrial

Rio de Janeiro – [email protected]

* Author for correspondence

Evaluation of nanoparticles in the performance of energetic materialsAbstract: The addition of nanosized metal particles in propulsion systems such as solid and liquid propellants, hybrid propellant and ramjet motors has recently became a major focus of research. Significant increases in the burning velocity and in the specific impulse are some of the advantages of using nano-scale energetic materials in many different types of propulsion systems. Aluminum has been largely employed as a metallic additive in energetic materials, also in a recently new propulsion system (aluminum/ice propulsion, “Alice”), and some studies show that the advantages of using nanosized aluminum instead of microsized aluminum are facilitating the ignition of the systems and allowing better incorporation of the components in the formulations and improving its homogeneity. Some of the combustion processes that require high pressures and even higher temperatures can occur in moderate conditions due to the increase of the surface area of the reactants, in this case, the metallic additive.Keywords: Nanoparticles, Aluminum, Energetic materials.

Avaliação das nanopartículas no desempenho de materiais energéticosResumo: A adição de partículas metálicas nanométricas em sistemas de propulsão, tais como propelentes sólido, líquido, híbrido e de motores aspirados, “ramjet”, tem sido recentemente mais pesquisada. Significante aumento na velocidade de queima e no impulso específico são algumas das vantagens do uso de nanopartículas de materiais energéticos em diferentes tipos de sistemas de propulsão. O alumínio tem sido largamente empregado como aditivo metálico em materiais energéticos, e recentemente em um novo sistema de propulsão (aluminum/ice propulsion, Alice). Estudos mostram que a vantagem do uso de nanopartículas de alumínio em substituição das partículas micrométricas facilita a ignição de sistemas e permite melhor incorporação dos componentes nas formulações, melhorando sua homogeneidade. Alguns dos processos de combustão que requerem altas pressões e temperaturas podem ocorrer em condições moderadas devido ao aumento da área superficial dos reagentes, nesse caso, de aditivo metálico.Palavras-chave: Nanoparticulas, Alumínio, Materiais energéticos.

INTRODUÇÃO

Materiais energéticos combinados sob a forma de propelentes sólidos, explosivos e pirotécnicos resultam em compósitos com características de comportamento mecânico e de queima bem definidas (Wilson e Kim, 2003). Por exemplo, considerando o propelente sólido, sua constituição pode ser compreendida como uma matriz polimérica de origem orgânica denominada binder, altamente carregada principalmente com sais inorgânicos, que representam uma espécie química oxidante, além de

outras como aditivos modificadores de velocidade de queima, agentes de ligação e aditivos metálicos (partículas metálicas finamente divididas) que têm a função de aumentar o impulso específico e reduzir fenômenos de instabilidade de queima (Meda et al., 2005). O impulso específico é o principal parâmetro balístico do propelente. De forma geral, o diâmetro médio destas partículas metálicas incorporadas ao compósito está situado entre 10 e 20 µm e têm o alumínio como principal aditivo balístico (Dokhan et al., 2001), sendo que outros metais como o boro e o magnésio também podem ser empregados para este fim.

Nas condições acima descritas, as partículas de alumínio, quando incorporadas à matriz polimérica, são aprisionadas


Fnac

Text Box

DOI: 10.5028/jatm.2010.02014752


Rocco, J.A.F.F. et al.

no espaço compreendido entre os cristais do sal inorgânico, normalmente o perclorato de amônio (oxidante), em um processo conhecido como empacotamento das cargas, que resulta no compósito denominado grão propelente sólido. Normalmente, o diâmetro médio dos cristais da espécie química oxidante varia entre 200 e 400 µm em uma distribuição do perfil (granulométrico) bem definido e controlado em termos de processo de obtenção (fabricação) do compósito. Desta forma, durante o processo de queima do compósito, quando uma partícula submersa de alumínio metálico é exposta à frente de chama, tende a se posicionar na fase líquida do binder (matriz polimérica) que está em processo de pirólise. Observou-se (Dokhan et al., 2001) que o óxido de alumínio (Al2O3), produto da combustão do alumínio, tende a se manter por um longo período de tempo nestas condições (fase sólida), já que sua temperatura de fusão, da ordem de 2194K, é muito superior à do binder e do sal oxidante. Este fenômeno induz a concentração e aglomeração destas partículas de alumínio na região da frente de chama do compósito em processo de queima. O alumínio metálico é extremamente reativo, mas seu óxido, a alumina (Al2O3), é muito refratário, o que dificulta o seu processo de oxidação.

O processo de combustão de formulações de propelente sólido compósito resulta na formação de produtos condensados que desempenham importante papel na performance do motor-foguete onde este grão propelente está instalado. O conhecimento detalhado das características de dispersão destas partículas no meio reativo, do mecanismo de aglomeração, da distribuição de tamanhos residuais e tempo de queima é essencial em termos de design e performance do motor-foguete que contém este propelente. Estas partículas e aglomerados formados a partir destes condensados (residuais) têm um diâmetro médio da ordem de 1 µm e englobam de 80 a 90% dos óxidos formados a partir do processo de combustão do propelente sólido. Participam efetivamente na eliminação de altas frequências de oscilação intrínsecas ao processo de combustão do grão propelente sólido instalado na câmara de combustão e que pode comprometer o desempenho do motor-foguete.

A diminuição do tamanho médio das partículas metálicas incorporadas à formulação do propelente sólido (compósito), da escala micrométrica para a nanométrica, pode resultar em grandes alterações no comportamento de queima do material como, por exemplo, um aumento em sua velocidade de queima além do aumento da energia nominal liberada. Por exemplo, Armstrong et al. (2003) verificaram em seus experimentos que, para um sistema constituído de partículas de perclorato de amônio (oxidante) e partículas de alumínio metálico com diâmetro médio variando entre 100 e 100.000 nm ensaiados em uma câmara de combustão do tipo strand burner e também

pressões operacionais variando desde a atmosférica até 200 MPa, a velocidade de queima esteve inversamente relacionada ao tamanho da partícula de alumínio.

A correlação da pressão “P” com a velocidade de queima “r” de uma dada formulação de propelente sólido pode ser descrita pela lei de Vielle, que é expressa algebricamente da seguinte forma (Equação 1):

r = ß Pα (1)

onde ß e α são constantes determinadas experimentalmente.

A Equação 1, apresentada em sua forma algébrica, tem uma interpretação teórica. Deve ser ressaltado que, para formulações que apresentam altos valores do expoente de pressão (α), estas tendem a apresentar instabilidades de queima a altas pressões operacionais na câmara de combustão do motor-foguete.

Por fim, deve-se denotar que, atualmente, há uma tendência de se incorporarem nanopartículas metálicas ou de materiais energéticos, explosivos, nas formulações de propelentes sólidos e composições explosivas, tendo em vista que o que se busca é exatamente aumentar o valor da energia liberada destes materiais durante seu processo de queima. Isto pode representar um aumento no rendimento das máquinas térmicas (motores-foguete, sistemas explosivos) que os contêm. Porém, as pesquisas realizadas até este momento não deixaram claro o aumento do valor da energia causado pelo uso destas nonopartículas. Deve-se, portanto, desenvolver metodologias neste sentido, porque as pesquisas correntes são promissoras.

CARACTERIZAÇÃO DE MATERIAIS ENERGÉTICOS

Em termos laboratoriais, para avaliar as alterações de queima provocadas pela adição das nanopartículas em composições de propelentes e explosivos independentemente do estado físico, são comparadas as curvas obtidas pelas técnicas de análise térmica: termogravimetria (TG) e calorimetria exploratória diferencial (DSC). Especialmente pelo emprego da técnica DSC é possível quantificar a energia liberada da fase exotérmica da queima do material pela integração direta da área que compreende a respectiva fase na curva DSC. Dessa forma, podem se contrapor de forma direta as energias liberadas pelas composições contendo partículas e escalas nano e micrométricas. Estas considerações são válidas quando todos os outros parâmetros envolvidos na análise da curva DSC são mantidos constantes. Parâmetros tais como: razão de aquecimento, massa inicial da amostra, vazão de gás inerte, gás inerte, tipo de panela empregada no ensaio, condições da panela empregada (aberta/fechada).


Evaluation of nanoparticles in the performance of energetic materials

PRINCIPAIS CONTRIBUIÇÕES DO EMPREGO DE MATERIAIS ENERGÉTICOS NANOPARTICULADOS

“ALEX”: Nanosized aluminum

Sob o nome comercial de “ALEX” (Argonide Corporation, USA), as partículas esféricas ultrafinas obtidas por eletroexplosão com diâmetro médio variando entre 100 e 200 nm de alumínio provocaram mudanças significativas de performance balística sob determinadas condições em compósitos energéticos (Cliff, Tepper e Lisetsky, 2001). Por exemplo, em formulações de propelente sólido compósito, houve um aumento da velocidade de queima em comparação à mesma participação em massa do alumínio na escala micrométrica (Cliff, Tepper e Lisetsky, 2001). O “ALEX” queima na superfície da frente de chama, ao contrário do alumínio particulado na escala micrométrica, que se oxidará apenas na corrente formada acima desta mesma superfície, causando perda em termos de energia química potencial e problemas de aglomeração na região da tubeira do motor-foguete (Cliff, Tepper e Lisetsky, 2001).

Quando se trata de compósitos explosivos, significativas alterações de desempenho ocorrem pela adição do “ALEX” às suas formulações (Cliff, Tepper e Lisetsky, 2001). Sua incorporação ao ADN (Dinitramida de Amônia) resultou em um aumento na velocidade de detonação de 4380 m/s (97:3 ADN/Viton) para 5070 m/s (73:24:3 ADN/ALEX/Viton) (Cliff, Tepper e Lisetsky, 2001). Além disto, sua compatibilidade com binders baseados no PBLH (polibutadieno líquido hidroxilado) é total, permitindo sua integração de forma idêntica ao alumínio na escala micrométrica. Naturalmente, devido à sua maior área específica, algumas alterações se fazem necessárias neste processo de incorporação ao binder.

Comparadas às formulações convencionais que empregam alumínio metálico de partículas com diâmetro médio na escala micrométrica (18 a 30 µm), o uso de nanopartículas de alumínio oferece a possibilidade de aumentar a velocidade da energia liberada, melhorar o processo de combustão e o controle sobre a performance de conversão da energia química (ligações) em cinética (propulsão) de composições explosivas e de propelentes (Park et al., 2005). Por exemplo, sabe-se que pode ocorrer um aumento na velocidade de queima de combustíveis e propelentes numa razão de 5 a 10 vezes quando se empregam nanopartículas de Alumínio (Al). Todavia, não há estudos que indiquem esses valores precisamente (Prakash, McCormick e Zachariah, 2004). Além disto, Park et al. (2005) mostraram que a energia de ativação envolvida na oxidação pelo ar de nanopartículas de alumínio com diâmetro médio da ordem de 24 a 65 nm foi muito menor do que para as mesmas partículas

na escala micrométrica (15 a 30 µm). Exemplos de partículas consideradas oxidantes incluem o Fe2O3, MoO3 e o CuO. Os parâmetros termodinâmicos que envolvem a combustão de partículas de alumínio oxidadas pelas três espécies químicas anteriormente citadas indicam que a temperatura de chama adiabática pode ser calculada com base no programa de equilíbrio químico denominado CEA (NASA-GLENN, Chemical Equilibrium Program) (Prakash, McCormick e Zachariah, 2004).

Diferentes processos de obtenção de nanopartículas têm sido desenvolvidos, em especial o “Electric Explosion of Wire” (Kotov, 2003), que gera partículas com formato esférico.

Combustível líquido

Em se tratando de combustíveis líquidos, como o querosene empregado na propulsão de engenhos por motores aspirados, a adição de partículas de alumínio metálico em escala nanométrica pode significar uma otimização de seu processo de ignição e combustão pela diminuição do tempo de retardo e aumento da densidade de energia em termos volumétricos. Dessa forma, combustíveis baseados em hidrocarbonetos, como é o caso do querosene, e que podem ser estocados para utilização posterior, passam a ser viáveis em termos de emprego em motores aspirados do tipo Scramjet (“Supersonic Combustion Ramjet”), que têm sido projetados empregando-se originalmente o hidrogênio como combustível (Neely et al., 2003).

Propelente líquido

Para o caso de motores-foguete à propulsão líquida, há estudos (Mordosky et al., 2001) que testaram a combustão sob a forma de gotas (“spray’) de oxigênio gasoso e querosene gelificado por nanopartículas de alumínio (“ALEX”) atomizadas por injetores convencionais empregados na propulsão líquida. A adição das nanopartículas de alumínio ao querosene, conhecido como RP-1, possuem a característica de aumentar significativamente o calor de reação em relação ao querosene não-aditivado. Neste estudo (Mordosky et al., 2001), o diâmetro médio das partículas de alumínio empregadas na gelificação do hidrocarboneto foi da ordem de 100 nm e, teoricamente, isto permitiu deslocar a reação de combustão na direção dos produtos, resultando em um ganho de performance envolvendo parâmetros como: maior temperatura de chama, aumento do impulso específico, da velocidade característica (C*) e da eficiência de combustão. As condições de operação do motor-foguete simuladas nos ensaios foram: pressão operacional na câmara de combustão variando entre 1 e 2,8 MPa (150



a 400 psia); vazão de alimentação na câmara do propelente gelificado variando entre 8 a 40 g/s; vazão de oxigênio no estado gasoso injetado na câmara variando entre 14 a 60 g/L; relação O/F (oxidante/combustível) variando entre 0,5 a 5. A porcentagem em massa de “ALEX” adicionada ao querosene foi fixada em 5% para todos os experimentos conduzidos de acordo com os parâmetros acima descritos.

Propelentes gelatinosos reúnem as vantagens dos propelentes sólidos e líquidos: alto impulso específico, baixa sensibilidade e baixa vulnerabilidade aliada à possibilidade de modulação do empuxo podem ser obtidos com a incorporação de nanopartículas metálicas de alumínio a espécies químicas energéticas no estado líquido e até mesmo à água, como será verificado na sequência. Como exemplo, pode-se citar a mono-metil-hidrazina assimétrica gelificada pela adição de metil-celulose contendo, ainda, alumínio metálico em sua formulação. As propriedades reológicas do propelente afetam de forma significativa grande número de parâmetros operacionais e exigências em termos de produção do propelente gelatinoso, incluindo aspectos de moldagem e combustão do grão no tubo motor-foguete. Outra formulação de propelente gelatinoso pode ser obtida pela adição de nanopartículas de dióxido de silício ao nitrometano, pois têm características de fluidez do tipo não-Newtoniana. Entre outros, Teipel e Förter-Barth (2005) empregaram partículas de dióxido de silício com diâmetro médio da ordem de 7 nm, sendo que a concentração em volume do agente gelatificante variou entre 4 e 8%.

Alice

A adição de alumínio nanoparticulado à água para aplicações em propulsão por motores-foguete ganhou novo impulso com o desenvolvimento do propelente ALICE, anacronismo de Aluminum/Ice.

A combustão entre o alumínio e a água vem sendo pesquisada desde a década de 1960 como um propelente viável em sistemas propulsivos por motores-foguete devido ao fato de esta reação liberar grandes quantidades de energia tendo como produtos da combustão espécies químicas que não agridem o meio ambiente. Atualmente, os propelentes empregados para atingir a órbita da terra e manter-se nela são muito caros. Sendo assim, busca-se uma nova geração de propelentes que possam ser usados tanto na fase booster como sustainer em motores para as aplicações citadas, podendo ainda ser estocados para aplicações em órbita baixa da terra (LEO – Low Earth Orbit). Para propelentes estocáveis aplicados em LEO, existem também exigências de longos períodos de armazenamento, o que impõe grandes problemas, por exemplo, quando se emprega hidrogênio criogênico entre

outros combustíveis. A ideia de se empregar este tipo de propelente no espaço profundo também vem sendo pesquisada. Propelentes baseados no ALICE são baratos e abrem uma série de possibilidades, como a sua fabricação em missões lunares e, até mesmo, em Marte com a recente confirmação de que há água no planeta vermelho.

Aliado a estas vantagens de custo e produtos da combustão ambientalmente corretos, há um fato que merece destaque; a questão da segurança, uma vez que, por se tratar de água no estado congelado, dificilmente há riscos de ignição acidental do propelente baseado no ALICE.

É importante destacar que este propelente se tornou viável recentemente pela redução da escala do tamanho de partícula do alumínio metálico. Vindo da escala de micrômetros para nanômetros, o aditivo metálico tornou-se mais facilmente oxidável, liberando maior quantidade de calor e, como consequência, aumentando o empuxo, ou impulso específico, do propelente.

Subsidiada pela National Aeronautics and Space Administration (NASA), agência espacial norte-americana, recentes testes realizados na Pennsylvania State University nove protótipos de motores-foguete usando o ALICE realizaram vôos atingindo 1.300 pés de altitude.

Água

O emprego de propelentes baseados na reação entre o alumínio e a água para sistemas avançados de propulsão de veículos subaquáticos tem sido proposto por diversos pesquisadores. Neste caso, a água do mar desempenha o mesmo papel que o ar nos sistemas propulsivos aspirados. Devido ao fato de a reação entre o alumínio metálico e a água ser exotérmica, e a combinação Al-H2O apresentar uma alta densidade em termos de impulso específico, torna-se interessante o emprego desta reação em termos de propulsão de microsatélites. De encontro a esta possibilidade, a disponibilização para o mercado de nanopartículas de alumínio e as notícias de sucesso obtido pelo seu emprego em combustíveis líquidos à base de hidrocarbonetos (querosene) em sistemas aspirados têm motivado seu estudo de forma mais ampla. A área específica destas nanopartículas é maior do que quando considerada em escala micrométrica, assegurando em princípio uma rápida cinética de superfície, ou rápida vaporização, quando a película de alumina (se presente) é rompida. Em condições normais, o alumínio metálico não reage com a água, a não ser que se forneça calor para isso, algo em torno de 2300 K para a reação ocorrer em fase vapor. No entanto, quando o “ALEX” (nano) é utilizado, esta mesma reação com a água ocorre de forma completa


Evaluation of nanoparticles in the performance of energetic materials

em um espaço de tempo da ordem de alguns segundos a aproximadamente 70 a 80ºC. Quando o “ALEX” é convertido à forma de gel em meio aquoso e aquecido para produzir uma espuma contendo agora hidrogênio, esta entra em ignição prontamente. Géis, assim obtidos, queimam de forma uniforme em intervalo de pressões variando entre 1 e 70 atmosferas.

Propelente híbrido

Em sistemas de propulsão híbrida que empregam combustíveis sólidos e oxidantes líquidos, destacam-se algumas vantagens sobre sistemas propulsivos convencionais (sólidos e líquidos), tais como: segurança operacional; baixo custo de desenvolvimento; diminuição do impacto ambiental devido às características dos gases produto da combustão; capacidade operacional em termos on-off; e uma alta capacidade de controle do motor-foguete (modulação de empuxo). Nestes sistemas (híbridos) de propulsão, o processo de combustão do grão combustível sólido pode ser controlado pela vazão do oxidante líquido que é injetado na câmara de combustão. A condição limitante do processo de combustão de sistemas híbridos reside no fenômeno de mistura e reação do grão combustível sólido com o oxidante fluindo através da porção central deste mesmo grão, instalado na câmara de combustão do motor-foguete.

O grão combustível sólido pode ter características de comportamento mecânico muito mais dúcteis do que para o caso do grão propelente sólido, o que significa que o primeiro está menos sujeito aos danos estruturais em comparação ao grão propelente sólido, diminuindo assim o risco de falhas durante a operação do motor híbrido. A maior desvantagem do grão combustível sólido reside no fato de que, novamente comparado ao grão propelente sólido, há uma significativa redução da velocidade de queima que impõe um aumento da frente de chama para se manter o mesmo nível de empuxo do motor. Entretanto, esta deficiência pode ser corrigida pela adição de nanopartículas de alumínio à formulação do combustível sólido.

Ainda tratando da propulsão híbrida, Risha et al. (2001) incorporaram na formulação de um combustível sólido, baseado no PBLH, partículas nanométricas de alumínio (“ALEX”), além de boro metálico, mostrando por meio de uma série de experimentos que houve um aumento da velocidade de queima do grão combustível sólido. Em geral, o objetivo da pesquisa de Risha et al. (2001) foi caracterizar combustíveis sólidos altamente energéticos que possuíssem um grande potencial de aplicação prática em sistemas híbridos com alta performance. Para isto, Risha et al. (2001) consideraram condições de contorno,

tais como: a) formulações e processamento de grãos combustíveis sólidos para os testes de combustão; b) demonstração da efetividade dos aditivos metálicos envolvendo o alumínio particulado em escala nanométrica, compostos de boro e motores-teste em escala piloto; c) desenvolvimento de uma sistemática de aquisição de dados instantâneos com o objetivo de verificar parâmetros balísticos, como a velocidade de queima do grão e sua relação por meio da fórmula empírica conhecida como regressão linear; d) avaliação do processo de combustão do boro em condições características encontradas na câmara de combustão do motor híbrido. Em relação ao alumínio (“ALEX”), na formulação do grão combustível sólido, com fator de forma esférico e diâmetro médio fixado em 150 nm, estima-se que a camada de óxido que envolve a partícula seja da ordem de 3,68 nm e o conteúdo de alumínio metálico da ordem de 79,1% em massa.

As condições operacionais do motor-teste híbrido considerado no estudo de Risha et al. (2001) envolveram uma vazão de oxigênio puro máxima de 0,36 kg/s (0,8 lbm/s) e pressão máxima na câmara de combustão acima de 12 MPa (1.750 psig). Os grãos combustíveis sólidos foram moldados em tubos-motores fenólicos com dimensões de 1,5 polegadas de diâmetro e comprimento de 16 polegadas. Foi empregada uma célula de carga de 1000 lbf para verificar o empuxo desenvolvido pelo motor híbrido. O tempo de queima variou de 5 a 7 segundos.

O processamento das formulações de combustíveis sólidos empregados no trabalho de Risha et al. (2001) se apresentou como um dos aspectos críticos do estudo, tendo em vista a grande dificuldade de incorporação das nanopartículas de alumínio ao “binder” exigindo o desenvolvimento de um método específico para, além da incorporação das cargas, a moldagem da massa no estado líquido no tubo-motor híbrido. Para evitar a oxidação do alumínio durante o manuseio (processamento), Risha et al. (2001) empregaram também nanopartículas que foram fornecidas imersas em um solvente específico designadas como WARP-1. No caso, o tolueno que tornou sua incorporação ao “binder” um tanto mais complexa, uma vez que não se sabia se o solvente poderia interferir na reação entre o poliol (PBLH) e o di-isocianato (MDI). No entanto, esta interferência não foi evidenciada, sendo que apenas houve uma correção quanto à participação mássica do alumínio devido à presença do tolueno.

MOTORES

Ramjet

Em formulações de combustíveis sólidos aplicados a motores do ciclo “Ramjet”, é comum a incorporação de partículas metálicas, como o alumínio, o magnésio e



o boro, com diâmetro médio na escala de micrômetros. Estudos sobre o comportamento de queima de formulações de combustíveis sólidos aditivados com partículas de boro em escala micrométrica apontaram algumas dificuldades operacionais, tais como: processos de ignição e combustão altamente complexos (Natan e Gany, 1989). Basicamente, estes estudos indicaram que, para uma combustão autossustentada do grão combustível sólido nas condições de escoamento encontradas no motor “Ramjet”, seria necessário prever um “after-burner” (extensão da câmara de combustão) para oxidar por completo as partículas de boro metálico que emergiam da massa de combustível sólido. Nestes casos, a redução do diâmetro médio destas partículas de alumínio metálico pode representar o mesmo ganho de performance verificado para as formulações de propelentes, explosivos e materiais pirotécnicos.

REFERÊNCIAS

Armstrong, R.W., et al., 2003, “Enhanced propellant combustion with nanoparticles”, Nano Letters, Vol. 3, No. 2, pp. 253-255.

Cliff, M., Tepper, F, Lisetsky, V., 2001, “Ageing characteristics of Alex* nanosized aluminum”, Proceeding of 37th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Salt Lake City, USA.

Dokhan, A., et al., 2001, “The effects of Al particle size on the burning rate and residual oxide in aluminized propellants”, Proceeding of 37th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Salt Lake City, USA.

Kotov, Y.A., 2003, “Electric explosion of wires as a method for preparation of nanopowders”, Journal of Nanoparticle Research, No. 5, pp. 539-550.

Meda, L., et al., 2005, “Nano-composites for solid propellants”, Composites Science and Technology, No. 65, pp. 769-773.

Mordosky, J.W., et al., 2001, “Spray combustion of gelled RP-1 propellants containing nano-sized aluminum particles in rocket engine conditions”, Proceeding of 37th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Salt Lake City, USA.

Natan, B., Gany, A., 1989, “Effects of bypass air on the combustion of boron particles in a solid fuel Ramjet”, Proceeding of 25th AIAA, ASME, SAE, and ASEE, Joint Propulsion Conference, Monterey, CA.

Neely, A.J., et al., 2003, “Hidrocarbon and hydrogen-fuelled scramjet cavity flameholder performance at high flight mach numbers”, Proceeding of 12th AIAA International Space Planes and Hypersonic Systems and Technologies, Norfolk, USA.

Park, K., et al., 2005, “Size-resolved kinetic measurements of aluminum nanoparticle oxidation with single particle mass spectrometry”, J Phys Chem B, Vol. 109, No. 15, pp. 7290-7299.

Prakash, A., McCormick, A., Zachariah, M.R., 2004, “Aero-sol-gel synthesis of nanoporous iron-oxide particles: a potential oxidizer for nanoenergetic materials”, Chem Mater, No. 16, pp. 1466-1471.

Risha, G.A., et al., 2001, “Combustion of HTPB-based solid fuels containing nano-sized energetic powder in a hybrid rocket motor”, Proceeding of 37th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Salt Lake City, USA.

Teipel, U., Förter-Barth, U., 2005, “Rheological behavior of nitromethane gelled with nanoparticles”, AIAA, Journal of Propulsion and Power, Vol. 21, No. 1, pp. 40-43.

Wilson, D.E., Kim, K., 2003, “A simplified model for the combustion of Al/MoO3 nanocomposite thermites”, Proceeding of 39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Huntsville, USA.


Maria Alice Carvalho Mazzeu*Instituto de Aeronáutica e Espaço


Elizabeth da Costa Mattos Instituto de Aeronáutica e Espaço


Koshun Iha Instituto Tecnológico de Aeronáutica


* Author for correspondence

Studies on compatibility of energetic materials by thermal methods Abstract: The chemical compatibility of explosives, pyrotechnics and propellants with those materials is studied to evaluate potential hazards when in contact with other materials during production, storage and handling. Compatibility can be studied by several thermal methods as DSC (differential scanning calorimetry), TG (Thermogravimetry), VST (Vacuum stability test) and others. The test methods and well defined criteria are the most important elements when a compatibility study is being accomplished. In this paper, the compatibility of two very important high explosives used in ammunition, RDX (Cyclo-1,3,5-trimethylene-2,4,6-trinitramine) and HMX (Cyclotetramethylene tetranitramine) was studied with the materials: fluoroelastomer (Viton) and powdered aluminum (Al), using DSC and VST methods. The criteria to judge the compatibility between materials is based on a standardization agreement (STANAG 4147, 2001), and the final conclusion is that explosives and this materials are compatible, but in DSC it was observed that the peak of decomposition temperature of the admixture of RDX with Al decreased in 3º C and another peak appeared after the decomposition peak. Keywords: Compatibility, Energetic materials, Differential scanning calorimetry, Vacuum stability test.

INTRODUCTION

Energetic materials such as propellants, pyrotechnics and explosives have been studied for several years. The purpose of these studies is the development of new products and new utilities to these materials for military and non-military application.

Important information about behavior of energetic materials is acquired by thermal methods. This information is essential to a safe production, storage, handling and disposal. Thermal methods can be used to predict life time, to choose an adequate storage condition or to determine compatibility between materials.

As energetic materials are usually components of a system such as an armament or a rocket, and they are rarely used pure, the incompatibility reaction between the energetic material and the other components may accelerate the aging and alter the thermal stability of the energetic material itself, impairing the safety and functionality of the entire system. This could generate unexpected explosions due to decomposition reactions. Therefore, stability and compatibility of an explosive, as well as pyrotechnics and propellants, should be investigated carefully before they are manufactured and used with safety in technical applications (Vogelsanger, 2004).

Klerk, Meer and Eerlingh (1995) defined the ideal of compatibility as the situation in which the materials do not react with each other even after long storage periods, in varied conditions. For practical reasons, materials are considered compatible if during and after a specific storage period the functionality and the safety of the components are still acceptable. An accomplished analysis in that way would consume a great period of time. For that reason, in practice, it is expected that reliable results for a compatibility investigation be obtained in a short period of time. The solution is the use of some tests based on accelerated aging at higher temperatures such as the measurement of gas liberated after heating under vacuum using the VST technique (vaccum stability test), the study of continuous effects of heating using the DSC technique (differential scanning calorimetry), the study of the mass loss with heating using the TGA technique (thermogravimetric analysis) and others. Among the mentioned methods, the vacuum stability is perhaps the most frequently used. It is considered a basic method used for high explosives, propellants and gunpowder, being complemented by a repeated examination after accelerated storage, and DSC is routinely used to detect cases of gross incompatibility (May, 1978). Vacuum stability test can be accomplished with different pieces of equipment, where the pressure generated by the gasses is measured using mercury manometer or other pressure meters (Chovancová and Zeman, 2007).


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Text Box

DOI: 10.5028/jatm.2010.02015358


Mazzeu, M. A. C., Mattos, E.C., Iha, K.

According to Silva (2003), the thermal analysis methods are the mostly used for the characterization and study of the decomposition and compatibility of explosives. Recently, Sorensen, Konott and Bell (2008) affirmed that it is necessary to pay attention to safe shelf life of energetic materials, and using thermal methods to compatibility studies of materials over extended periods has been readily accepted.

The main advantages of the thermal analysis techniques aiming at compatibility tests in energetic materials are the use of small amounts of material and quicker measurements (Klerk, Schrader and Steen, 1999). In spite of the advantage presented in the use of thermal analysis, STANAG 4147 suggests the use of more than one test method for evidence compatibility, as found in the studies on the explosive TNAD (trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin), in which besides the technique of DSC, other methods as DTA / TG or VST were employed for confirmation when obtaining incompatible results of that explosive with inert or energy materials (Yan et al., 2008).

When using DSC as a technique to determine the compatibility, the results obtained for the pure product in the parameters of decomposition temperature and the format of the peak are compared to the results obtained for the mixtures. If the peak regarding mixture moves for temperatures lower than the peak regarding the energetic material or the material in test, it is an indication incompatibility. The incompatibility degree is measured by the difference of temperature among the peaks. In the vacuum stability test, the volume of liberated gas, when the mixture of parts is similar to an explosive and the materials in test are heated at 100oC for 40 hours, is compared to the volume of gas liberated by the energetic material and the material in test when heated separately, in identical conditions. The compatibility is evaluated through the volume of additional gas produced due to the contact between the two components of the mixture (STANAG 4147, 2001).

The energetic materials RDX and HMX are two important explosives used in armaments and as energy components of propellants composites. They are usually incorporate to curable plastic materials, forming the plastic explosives. The powdered aluminum is frequently incorporate to the explosives to increase their efficiency with considerable earnings in explosion heat and obtainment of higher temperatures for the formed gases (Meyer, Köhler and Homburg, 2002).

The military use of explosives demands a high destruction power, but it has to be safe and easy to handle as well as stock-piled for long periods of time, even in adverse climatic conditions. These explosives should be hard to

detonate, except in conditions of programmed detonation. Another important characteristic is that military explosives have to be loaded into armaments as shells, bombs, missiles and others without difficulties (Mathieu and Stucki, 2004).

To check if RDX and HMX accomplish the requirements, studies of compatibility between these explosives with other materials are necessary. This paper describes the compatibility studies of RDX and HMX relating to a fluoroelastomer (Viton) and to powdered aluminum (Al) using DSC and Vacuum stability tests in order to verify alterations in the thermal stability and the temperature of decomposition of the explosive, as well as alteration in the volume of gas liberated due to presence of inert material or aluminum.

The results obtained for the pure product and for the mixtures (RDX+ Viton, RDX + Al, HMX + Viton, HMX + Al) are herein reported. The methods employed were compared in relation to the reliability of the results.

MATERIALS AND METHODS

Material

RDX (80-120 #) was commercially obtained from IMBEL Company, and HMX (CL 1) was commercially obtained from SNPE Materiaux Energetics. Viton is the trade name of the series of fluoroelastomers manufactured by DuPont Dow Elastomeros Ltda. The aluminum PO 123 (Al) was obtained from Alcoa Company. All the materials were used as supply and were dried previously in a greenhouse at 60oC, in order to eliminate humidity.

Methods

For DSC test, the equipment used was the thermal analyzer DSC PerkinElmer-7 Series Thermal Analysis System, previously calibrated in the reason of heating of 2oC/min, with Indium. Individual sample masses of 1 mg were used, weighed directly in closed crucibles made from aluminium with a pinhole in the cap. For the mixture, 1 mg of the explosive and 1 mg of the material to be tested were directly weighed in the crucibles, so that the two materials were in contact. The heating reason was of 2oC/min, with strip of room temperature at 320oC for the samples with HMX and 270oC for the samples with RDX. The tests were carried out under inert atmosphere, with nitrogen in the flow of 50 mL/min. The results represent an average of three results.

The vacuum stability test is presented in the literature under the acronym VST and it can be accomplished with


Studies on compatibility of energetic materials by thermal methods

450,000

500,000

550,000

600,000

120 160 200 240

Hea

t flo

w (m

W)

RDX+Viton

RDXViton

Endo

Temperature (oC)

Figure 1: DSC curves of RDX, Viton and mixed RDX + Viton at a 2oC min-1 heating rate.

several kinds of meters. For this study the vacuum stability test was accomplished according to the method used at the Chemical Laboratory of Divisão de Sistemas de Defesa (ASD) of Instituto de Aeronáutica e Espaço (IAE). In that test, denominated Chemical Vacuum Stability, the equipment employed consisted of thermostatic block of aluminum with cylindrical lodgings capable of maintaining the temperature in the limits of 100ºC + 0.5º, vacuum bomb with capacity up to 5 mmHg, glass group composed of capillary heating tube where there are the mercury columns and measurement support, with scale in millimeters. We weighed 2.5 g of each sample for the tests with the individual product. For the admixture, 2.5 g of the explosive and 2.5 g of the material whose compatibility is being evaluated were weighed. The equipment was prepared to previously reduce to zero the mercury column, and the samples were warmed under vacuum at 100ºC for 40 hours. The results show the amount of gas liberated, representing an average of three results.

The calculation of the gas volume released by the mixture and by the explosive material when heated individually was done using the formula presented in STANAG 4147, shown by Equation 1.

VR = M - (E + S) (1)

Where:

VR = volume of gas produced as result of the reaction between the components of the test mixture.M = volume of gas liberated from 2.5 g of explosive mixed with 2.5 g of the test material (mL, at STP).E = volume of gas liberated from 2.5 g of explosive (mL, at STP).S = volume of gas liberated from 2.5 g of test material (mL, at STP).


The compatibility study consists of observing alterations when an explosive and inert material such as Viton or a material that increases the supply of energy such as aluminum are put together in thermal conditions that can alter chemical stability. If no alterations are observed, it indicates that the materials are compatible in the conditions of the test that tries to simulate the aging of the explosive aiming at guaranteeing the safety in its handling, storage and use.

In the study of compatibility of RDX with Viton, the DSC curves for pure RDX, pure Viton and RDX mixed with Viton are presented in Fig. 1. In the pure RDX DSC curve appears a sharp endothermic peak temperature of 205oC and, immediately after, a wide exothermic peak temperature of 225oC is observed. The first peak

(endothermic) corresponds to the melting process and the second peak (exothermic) corresponds to the decomposition process (Pinheiro, 2003).

The Viton DSC curve does not show any peak in the decomposition area of RDX. For the mixture between RDX with Viton, the DSC curve did not show alteration in the corresponding melting temperature and the corresponding decomposition temperature, indicating compatibility between the materials. The compatibility indication is confirmed because there is no alteration in the peak format or new peaks, and the decomposition peak begins at the same temperature with and without Viton.

For the compatibility study of the mixture of RDX with Al, the DSC curves are presented for pure RDX, pure Al and RDX with mixed Al. The endothermic peak temperature regarding the melting process is of 205oC, the exothermic peak temperature regarding the decomposition process of RDX is of 225oC and the exothermic peak temperature regarding the decomposition temperature of the mixture of RDX with Al is of 222oC, as it can be observed in the Fig. 2. The aluminum does not present any peak in the decomposition area of RDX.

According to criteria established by STANAG 4147, temperature variation of 4oC or more would be indicative of incompatibility; therefore, RDX and the aluminum would be considered compatible. However, it is observed that beyond the small displacement in the decomposition temperature, a new peak appears, in the temperature of 233oC, which is a significant alteration, demanding further investigation before using that mixture. As that peak appears after the decomposition temperature, it can be an indicative of secondary reactions happening between products of the decomposition of RDX and Al (Antic



and Dzingalasevic, 2006;Keicher, Happ and Kretschmer, 1999). To obtain more data on Al possible interference in RDX, the compatibility study may be carried out using other methods such as TG before affirming that RDX and the aluminum are totally compatible.

In the studies with HMX, the DSC curves present small endothermic peaks in the strip from 170 to 190oC, which correspond to the crystalline transition of the β-HMX for the form crystalline δ-HMX (Pinheiro, 2003). The exothermic peak temperature of 274oC indicates the decomposition of HMX with the presence of a small peak before the main peak. The presence of Viton do not show any interference in the peaks of crystalline transition, as it can be observed in the Fig. 3, in which the curves DSC of HMX with Viton, pure HMX and pure Viton are presented.

In the same way, the mixture with aluminum do not present variation in the results, and it can be observed in the DSC curves of HMX with Al, pure HMX and pure Al, as illustrated by Fig. 4.

Table 1: Decomposition temperatures obtained by DSC and alterations observed on peaks of the explosives.

T decomposition (oC)

Format alterations on peaks

RDX 225.3 ± 0.6 --

RDX + Viton 225.1 ± 1.0 None

RDX + Al 222.0 ± 1.0 New peak, after decomposition peak

HMX 274.0 ± 0.4 --

HMX + Viton 275.8 ± 0.3 None

HMX + Al 274.7 ± 0.4 None

450,000

500,000

550,000

600,000

120 160 200 240

Hea

t flo

w (m

W)

RDX RDX+Al

Al

Endo

Temperature (o C)

Figure 2: DSC curves of RDX, Al and mixed RDX + Al at a 2oC min-1 heating rate.

450,000

500,000

550,000

110 170 230 290

Hea

t flo

w (m

W)

Endo

Viton

HMX+Viton

HMX

Temperature ( o C)

Figure 3: DSC curves of HMX, Viton and mixed HMX + Viton at a 2oC min-1 heating rate.

The presence of Viton or aluminum did not bring significant alterations for decomposition temperature, being in 275oC, in the mixture with the aluminum and in 276oC in the mixture with Viton. In the mixture with Viton, a small displacement of the peak appears, albeit no change in the format was observed. The existent peak of HMX decomposition before the exothermic peak also did not present alteration when the pure product and the mixtures were compared. Therefore, HMX presents indication of compatibility with Viton as well as with aluminum.

Table 1 displays the DSC values obtained for decomposition temperature of the pure explosives and of the mixture, as well as the observations about peaks alterations.

Figure 4: DSC curves of HMX, Al and mixed HMX + Al at a 2oC min-1 heating rate.

450,000

500,000

550,000

110 170 230 290

Hea

t flo

w (m

W)

Al

HMX +Al

HM

Endo

Temperature (oC)


Studies on compatibility of energetic materials by thermal methods

Table 2: Volume of gas liberated obtained by the vacuum stability test.

Volume of gas liberated (mL)

Value of volume of gas liberated by the

mixture (mL)

RDX 0.07 ± 0.02 ---

HMX 0.33 ± 0.00 --

Al 0.10 ± 0.01 ---

Viton 0.05 ± 0.04 ---

RDX + Al 0.92 ± 0.02 0.75 ± 0.02

RDX + Viton 0.60 ± 0.02 0.48 ± 0.04

HMX + Al 0.96 ± 0.03 0.53 ± 0.03

HMX + Viton 0.48 ± 0.01 0.10 ± 0.04

Table 3: Summary of results obtained for the compatibility study using DSC and vacuum stability test.

DSC Vacuum stability test

Viton Al Viton Al

RDX C C* C C

HMX C C C C*A new peak appears after RDX decomposition peak.C: Compatible.

The greatest advantage of vacuum stability test in relation to DSC is the sample quantity. While in DSC amounts of samples are around 1 mg of each material to be studied, the vacuum stability test was accomplished with 2.5 g of each material, which increases the possibility of physical contact between them. However, the vacuum stability presents some disadvantages, mainly due to the use of mercury, a highly poisonous product, and to the consuming of a great amount of time in the handling and preparation of the test, completion of the column and cleaning of the mercury, all procedures that should be done very carefully.

A summary of the results obtained for the compatibility study are presented in Table 3.

CONCLUSION

To initiate a compatibility study, normally the DSC technique is used because it is faster and provides enough information to define the need of deeper studies; however, ideally, one should use two or more techniques for confirmation of compatibility among materials. As the results can vary using different equipment and different laboratories, the criteria, established in STANAG 4147, cannot be considered to be absolute. The careful analysis of the obtained results and the knowledge of the behavior of the materials provide more reliable criteria to evaluate the compatibility of systems.

The compatibility of the systems RDX with Viton, RDX with aluminum, HMX with Viton, HMX with aluminum was studied using the thermal methods: DSC and vacuum stability test. All systems were found to be compatible according to STANAG 4147. However, the mixture RDX and HMX Al may be considered relatively less compatible than the other mixtures, and this must be taken into account when ammunition is being developed and new applications are being studied.

REFERENCES

Antic, G., Dzingalasevic, V., 2006, “Characteristics of cast PBX with aluminum”, Scientific Technical Review, Vol. 56, No 3-4, pp. 52-58.

Chovancová, M., Zeman, S., 2007, “Study of initiation reactivity of some plastic explosives by vacuum stability test and non-isothermal differential thermal analysis”, Thermochimica Acta, Vol. 460, pp. 67-76.

Keicher, T., Happ, A., Kretschmer, A., 1999, “Influence of aluminium/ammonium perchlorate on the performance of underwater explosives”, Propellants, Explosives, Pyrotechnics, Vol. 24, p. 140-143.

Klerk, W.P.C., Schrader, M.A., Steen, A.C., 1999, “Compatibility testing of energetic materials, which technique?”, Journal of Thermal Analysis and Calorimetry, Vol. 56, pp. 1123-1131.

Vacuum stability

The results of vacuum stability test provide the volume of liberated gas at 100ºC for 40 hours by HMX, RDX, Viton e Al and mixtures RDX + Al, RDX+Viton, HMX + Al and HMX + Al, as well as the difference between the pure products and the nixture.

Table 2 presents the volume of gas liberated, calculated through Eq. 1. The mixture of RDX with Al presents the largest increase in volume of gas liberated (0.75 mL), indicating that the aluminum alters the amount of liberated gas, but it cannot be considered to be indicative of incompatibility. The STANAG 4147 defines as a criterion for compatibility a maximum variation of 5 mL in the standard temperature and pressure conditions (STP) when materials are mixed and tested with the vacuum stability test; the difference is calculated between mixture and pure products. The values found for the mixtures are lower than 1 mL (STP), indicating compatibility of RDX with Viton, RDX with Al, HMX with Viton and HMX with Al.



Klerk, W., Meer, N. V., Eerlingh, R., 1995, “Microcalorimetric study applied to the comparison of compatibility tests (VST and IST) of polymers and propellants”, Thermochimica Acta, Vol. 269-270, pp. 231-243.

Mathieu, J., Stucki, H., 2004, “Military high explosives”, Chimia, Vol. 58, pp. 383-389.

May, F.G.J., 1978, “Australian test procedures for determination of compatibility and stability of military explosives”, Journal of Hazardous Materials, Vol. 2, pp. 127-135.

Meyer, R., Köhler, J., Homburg, A., 2002, “Explosives”, 5th ed (Verlag GmbH, Weinheim), Alemanha, Wiley-Vch.

Pinheiro, G.F.M., 2003, “Decomposição térmica de explosivos”, Tese de doutorado, Instituto Tecnológico de Aeronáutica, São José dos Campos, SP, Brasil, 178p.

Silva, G. et al., 2003, “Estudo cinético da decomposição térmica do α HMX por calorimetria exploratória diferencial”, Anais da Associação Brasileira de Química, Vol. 1, No 2, pp. 10-12.

Sorensen, D.N., Knott, D.L., Bell, R.F., 2008, “Two-gram DTA as a thermal compatibility tool”, Journal of Thermal Analysis and Calorimetry, Vol. 91, pp. 305-309.

STANAG 4147 (Ed. 2), 2001, “Chemical compatibility of ammunition components with explosives (non-nuclear applications)”.

Vogelsanger, B., 2004, “Chemical stability, compatibility and shelf life of explosives”, Chimia, Vol. 58, pp. 401-408.

Yan, Q-L. et al., 2008, “Compatibility study of trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin (TNAD) with some energetic components and inert materials”, Journal of Hazardous Materials, Vol. 160, pp. 529-534.


Adriana Medeiros Gama*Institute of Aeronautics and Space


Mirabel Cerqueira RezendeInstitute of Aeronautics and Space


*Author for correspondence

Complex permeability and permittivity variation of carbonyl iron rubber in the frequency range of 2 to 18 GHzAbstract: The complex dielectric permittivity (e) and magnetic permeability (m) of Radar Absorbing Materials (RAM) based on metallic magnetic particles (carbonyl iron particles) embedded in a dielectric matrix (silicon rubber) have been studied in the frequency range of 2 to 18 GHz. The relative permeability and permittivity of carbonyl iron-silicon composites for various mass fractions are measured by the transmission/reflection method using a vector network analyzer. The concentration dependence of permittivity and permeability on the frequency is analyzed. In a general way, the results show that e´ parameter shows a more significant variation among the evaluated parameters (e”, m”, m’). The comparison of dielectric and magnetic loss tangents (e”/e” and m”/m’, respectively) shows more clearly the variation of both parameters (e and m) according to the frequency. It is also observed that higher carbonyl iron content fractions favor both dielectric and magnetic loss tangents. Keywords: Carbonyl iron, Silicon, Permeability, Permittivity, Radar Absorbing Materials (RAM).

INTRODUCTION

Magnetic granular composites consisting of metallic magnetic particles embedded in a dielectric matrix have been widely used in electromagnetic applications such as electromagnetic wave absorber (also named Radar Absorbing Material, RAM) and electromagnetic shielding materials (Park, Choi and Kim, 2000). With the fast advancement of wireless communication and defense industry, radar absorbing materials are becoming more and more important in both civil and military applications, respectively (Liu et al., 2003; Feng, Qiu and Shen, 2007; Yusoff et al., 2002).

In general, RAM can be divided into two types: dielectric and magnetic ones. For single-layer microwave absorbers that have mainly magnetic losses in comparison to those that have mainly dielectric losses, broader bandwidth and higher absorption at smaller layer thickness can be achieved (Giannakopouou, Kontogeorgakos and Kordas, 2003). In this way, it can be cited carbonyl iron as a typical magnetic particle used in the magnetic RAM processing, attending the microwave frequency range. This magnetic filler type presents as main characteristics high Curie temperature (~1000K), good thermal stability, that allows its application at higher temperatures and high specific saturation magnetization intensity (4pMs) (Deng et al.,

1999). Thus, this magnetic particle has been widely used in the electromagnetic shielding and in RAM processing (Liu et al., 2003; Yong, Afsat and Grignon, 2003).

This paper shows a study involving the evaluation complex magnetic permeability (m = m’ - jm’’) and dielectric permittivity (e = e’ - je’’) behaviors of an elastomeric RAM processed with different carbonyl iron contents, in the frequency range of 2 to 18 GHz.

EXPERIMENTAL

Carbonyl iron powder was chosen as absorbing filler and silicon rubber was used as polymeric matrix. Both components are commercially available. The densities of the employed carbonyl iron and silicon matrix are 7.8 and 1.28 g/cm3, respectively. The carbonyl iron contents into the processed elastomeric RAM were 30, 35, 40, 45, 50, 55, 60, 65 and 70% in mass concentration. The elastomeric RAM were prepared by conventional mechanical mixture of the two raw materials. The homogeneous mixtures were molded in a coaxial die with inner diameter of 3 mm and outer diameter of 7 mm. The polymer curing was performed at room temperature for about 24 hours. At the end, flexible cylindrical composite specimens were produced.

The S parameters (scattering parameters) were measured and used to calculate the complex magnetic permeability


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Gama, A.M., Rezende, M.C.

and dielectric permittivity of all the prepared RAM samples. The measurements were performed according to the transmission/reflection method using an HP 8510C vector network analyzer, adapted with an APC7 coaxial transmission line, in the frequency range of 2 to 18 GHz. Figure 1 shows a schematic representation of the measurement system utilized.

Figure 1: Representation of the transmission/reflection line Source: Bartley (2006).

The Nicolson-Ross modeling was applied in m and e calculations (Bartley and Begley, 2006).


The real (storage) and imaginary (loss) permeability (m’ and m’’) and dielectric permittivity (e´ and e´´) behaviors are shown in Figures 2 and 3, respectively. Figure 4 shows the dielectric (tan de = e’’/e’) and magnetic (tan dm = m’’/m’) loss tangents.

Figures 2 and 3 show that m’ and e’ components for the pure silicon rubber (0% mass concentration) present the lowest values. With the increase of the frequency, m’ values approach to 1.0 and e´ varies around 2.6. The imaginary components (m” and e”) also present the lowest values for these parameters (from 0.0 to –1.2 and from 0.0 to 0.7, respectively). In the same way, the loss tangents present the lowest values. These behaviors mean that the pure silicon matrix presents low magnetic and dielectric losses.

´

2 4 6 8 10 12 14 16 180

2

4

6

8

ε

Frequency (GHz)

0% 30% 35% 40% 45% 50% 55% 60% 65%70%

2 4 6 8 10 12 14 16 180,0

0,3

0,6

0,9

1,2

1,5

ε ´´

Frequency (GHz)

0% 30% 35% 40% 45% 50% 55% 60% 65% 70%

Figure 2: (a) Real and (b) imaginary dielectric permittivity of RAM (30 to 70% mass concentration) studied.

A

B

2 4 6 8 10 12 14 16 180

1

2

3

μ´

Frequency (GHz)

0% 30% 35% 40% 45% 50% 55% 60% 65% 70%

2 4 6 8 10 12 14 16 180,0

0,2

0,4

0,6

0,8

1,0

μ´´

Frequency (GHz)

0% 30% 35% 40% 45% 50% 55% 60% 65% 70%

A

B

Figure 3: (a) Real and (b) imaginary magnetic permeability of the RAM (30 to 70% mass concentration) studied.


Complex permeability and permittivity variation of carbonyl iron rubber in the frequency range of 2 to 18 GHz

Figure 3a shows that the real permeability (m’) values present a slight increase with the magnetic filler concentration increase into the RAM sample. For example, at 2 GHz, m’ is equal to 1.2 and 2.2 for the samples with 30 and 70% of carbonyl iron, respectively. On the other hand, this magnetic parameter decreases gradually until nearly 1.0, as the frequency increases. This observation is expected considering the typical behavior of magnetic materials with the frequency increase. It is known that this property decreases with the frequency increase due to the decreasing of both effects domain-wall motion and relaxation effects (Gama, 2009). Similar behavior is reported in the literature (Feng et al., 2006).

In general, the imaginary permeability (m’’) (Fig. 3b) presents a behavior similar to that observed for m’ (Fig. 3a). In this case, the increase of the imaginary parameter with the increase of magnetic filler concentration is also verified. However, considering the frequency increase, this parameter presents a behavior distinct from that observed for m’. In this case, m’’ generally shows a slight increase until 14 GHz and, afterwards, this property decreases.

Comparing Figures 2 and 3, it is observed that the real permittivity (e’) presents a more accentuated increase with the carbonyl iron concentration increase in relation

to that observed for m’. Moreover, for a same mass fraction, the e’ parameter keeps almost constant with the frequency variation. The e’ variation with the carbonyl iron mass fraction is attributed to the polarization of the dielectric dipoles of the filler in the RAM. In this case, it is considered that the dipoles are in-phase with the oscillation of the electrical field vector of the electromagnetic wave. On the other hand, the dielectric losses (e”) show an increase with both filler concentration and frequency. This behavior is more accentuated for the mass fractions above 55% and suggests that the loss processes during the dipole oscillation, under the electromagnetic wave influence, is more significant for higher frequencies, in accordance with Feng et al. (2006).

The magnetic loss tangent (m’’/m’) plots (Fig. 4b) show a slight increase concomitant to the frequency increase that is attributed to spin inversion losses (Feng et al., 2006).

The dielectric loss tangent (e’’/e’) curves (Fig. 4a) present a conclusive behavior only for the more concentrated samples (65 and 70%) that show an increase of this parameter concomitant to the frequency increase. Less concentrated samples present, in a general way, values in the range of 0.00 and 0.05.

Nelson (2005) reported that the dielectric losses present different loss mechanisms with the increase of frequency. When the frequency is relatively low (below GHz), the losses are determined mainly by the conductance and are independent of the frequency. Conversely, in frequencies in the microwave range, the losses involve two loss mechanisms: polarization relaxation and electrical conductance (Gama, 2009; Nelson, 2005). Thus, the two dielectric loss peaks at about 10.0 and 15.0 GHz (Fig. 4a) can be attributed to these two loss mechanisms.

CONCLUSIONS

The results of this study involving the electromagnetic properties of radar absorbing materials based on carbonyl iron/rubber show the dependence of both complex magnetic permeability (m) and dielectric permittivity (e) parameters on the frequency, in the range of 2 to 18 GHz. Firstly, the complexity involving the behavior of these parameters in the microwave frequency range is observed . It is also observed that e’ parameter shows the most significant variation among the evaluated parameters (e”, m”, m’), with the carbonyl iron concentration. The comparison of dielectric and magnetic loss tangents (e”/e’ and m”/m’, respectively) shows more clearly the variation of both parameters (e and m) with the frequency. It is also observed that higher carbonyl iron content fractions favor both dielectric and magnetic loss tangents. Finally, based on the literature data, it is possible to suggest that the dielectric

Figure 4: (a) Dielectric and (b) magnetic loss tangents of the RAM (30 to 70% mass concentration) studied.

2 4 6 8 10 12 14 16 180,00

0,05

0,10

0,15

0,20

0,25

0,30

μ´/μ

Frequency (GHz)

0% 30% 35% 40% 45% 50% 55% 60% 65% 70%

2 4 6 8 10 12 14 16 180,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

μ´´/μ

´

Frequency (GHz)

0% 30% 35% 40% 45% 50% 55% 60% 65% 70%

A

B


Gama, A.M., Rezende, M.C.

loss mechanisms for the RAM, in the microwave range, involve polarization relaxation, electrical conductance and spin inversion for magnetic losses.

ACKNOWLEDGEMENTS

The authors acknowledge the financial assistance of Financiadora de Estudos e Projetos (FINEP) (Process number 1757-6) and the National Council for Research and Development (CNPq) (Process number 305478/09-5).

REFERENCES

Bartley, P.; Begley, S., 2006, “Materials measurement”, Available at: <http://www.die.uniroma1.it/personale/frezza/biblioteca/dispense/MisureMateriali.pdf>.

Deng, L.J., et al., 1999, “The development and application of magnetic materials in the field of RAM”, J Funct Mater, Vol. 30, No. 2, pp. 118-121.

Feng, Y.B., et al., 2006, “Electromagnetic and absorption properties of carbonyl iron/rubber radar absorbing materials”, IEEE Transactions on Magnetics, Vol. 42, No.3, pp. 363-368.

Feng, Y.B.; Qiu, T.; Shen, C.Y., 2007, “Absorbing properties and structural design of microwave absorbers based on carbonyl iron and barium ferrite”, Journal of Magnetism and Magnetic Materials, Vol. 318, No. 1-2, pp. 8-13.

Gama, A.M., 2009, “Comportamento da permissividade e permeabilidade complexas, de 2 a 18 GHz, de absorvedores de micro-ondas à base de ferro carbonila e ferrita de MnZn”, Tese de doutorado, ITA.

Giannakopouou, T.; Kontogeorgakos, A.; Kordas, G., 2003, “Single-layer Microwave absorbers: influence of dielectric and magnetic losses on the layer thickness”, J Magn Mater, Vol. 263, pp. 173.

Liu, A.X., et al., 2003, “Preparation and microwave absorbing property of nanosize PSZFe magnetic particles”, Acta Poly Sin. No. 5, pp. 757-760.

Nelson, S.O., 2005, “Density-permittivity relationships for powdered and granular materials”, IEEE Trans Instrum Meas., Vol. 54, No. 5, pp. 2033-2040.

Park, M.J.; Choi, J.; Kim, S.S., 2000, “Wide bandwidth pyramidal absorbers of granular ferrite and carbonyl iron powders”. IEEE Transactions on Magnetics, Vol. 36, No. 5, pp. 3272-3274.

Yong, W.; Afsat, M.N.; Grignon, R., 2003, “Complex permittivity and permeability of carbonyl iron powders at microwave frequencies”, IEEE Antennas and Propagation Society Int Symp, Vol. 4, pp. 619-622.

Yusoff, A.N., et al., 2002, “Electromagnetic and absorption properties of some microwave absorbers”, Journal of Applied Physics, Vol. 92, No. 2, pp. 876-882.


Luiza de C. Folgueras*Instituto de Aeronáutica e Espaço,


Mauro A. AlvesInstituto de Aeronáutica e Espaço,


Mirabel C. RezendeInstituto de Aeronáutica e Espaço,



Microwave absorbing paints and sheets based on carbonyl iron and polyaniline: measurement and simulation of their propertiesAbstract: This paper presents the processing and characterization of electromagnetic radiation absorbing paints and sheets based on magnetic and dielectric materials dispersed in polymeric matrices. Two different paint formulations containing carbonyl iron and/or polyaniline, using polyurethane as matrix, were prepared. Silicone sheets were also produced with polyaniline conducting polymer as filler. Measurements of the electric permittivity and magnetic permeability of the materials were also carried out. Simulations for the silicone sheets were performed in order to correlate the electromagnetic parameters with the material thickness. The paints absorbed 60 to 80% of the incident electromagnetic radiation and the silicone sheets absorbed 90%, indicating the material’s radar absorbing potential. Keywords: Absorbing media, Radar absorbing material, Conducting polymer, Dielectric materials, Magnetic materials.

INTRODUCTION

Electromagnetic radiation absorbing materials or Radar Absorbing Materials (RAMs) have been the focus of much research due to increasing government regulation to control the levels of electromagnetic radiation emitted by electronic equipment, and also to new norms and standards issued regarding compatibility and electromagnetic interference produced by this type of equipment. RAMs are also important tools in electronic warfare, since they can be used to camouflage potential targets from radar detection. Furthermore, microwave absorbers have been widely used to prevent or minimize electromagnetic reflections from large structures such as aircraft, ships, and tanks and to cover the walls of anechoic chambers (Stepanov, 1968; Emerson, 1973; Lawrence, 2000; Hemming, 2002). RAMs can be produced in different forms such as paints, sheets, and thin films (Lee, 1991; Olmedo, Hourquebie, Jousse, 1997; Skotheim, Elsenbaumer, Reynolds, 1998; Chandrasekhar, 1999; Folgueras, Rezende, 2008). Usually, these materials are obtained by the dispersion of one or more types of absorbing fillers in a polymeric matrix, which is then applied onto a substrate. Understanding the methods to produce RAMs by combining components, additives and polymeric matrices is decisive on the final application of the resulting material. Depending on the electromagnetic properties, the material can be either used as an absorber or a reflector of electromagnetic radiation (Afsar et al. 1986; Knott, Shaffer, Tuley, 2004). The need for RAMs

as paints has increased as a result of the new civilian and military applications found for these materials. The use of materials with specific characteristics and new processes enable developing RAMs with special physical properties, resulting in paints that respond differently to electromagnetic radiation. Materials used as RAMs have dielectric and magnetic losses, and the dependence of these losses on frequency is responsible for their performance, resulting in the absorption and/or scattering of electromagnetic waves. An ideal absorber might comprise a layer of material with numerically equal values of complex permeability and permittivity and high loss tangents over a wide range of frequencies. The former ensures a perfect impedance match with air, thus enabling incident signals to enter the material without front-face reflection, and the latter promotes rapid attenuation afterwards. In ferrites, the complex permeability is frequency-dependent; the dispersion is caused by the high-frequency magnetization reversal processes: the rotation of the magnetization vector and movement of domain boundaries. In dielectric materials, such as polyaniline, the complex permittivity of a material is related to its dielectric conductive properties (Naito, Suetake, 1971; Lee, 1991; McCurrie, 1994; Olmedo, Hourquebie, Jousse, 1997).

Electric permittivity (ε) and magnetic permeability (µ) are parameters related to a material’s dielectric and magnetic properties; they are among the most important characteristics of absorbing materials, and are directly associated with their absorbing properties (Hippel, 1954; Balanis, 1989; Clark et al. 1995; Chen et al., 2004). The


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Folgueras, L.C., Alves, M.A., Rezende, M.C.

relative permittivity and permeability are represented by Equations 1 and 2, respectively; the values of these parameters are obtained from the experimental values of the transmission and reflection coefficients of the material.

εr = ε’ - iε’’ (1)

µr = µ’ - iµ’’ (2)

When the material is lossy, some of the incident electromagnetic energy is dissipated, its permittivity and permeability are complex: Equations 1 and 2 (Sucher, Fox, 1963; Kovetz, 2000; Daniels, 2007; Orfanidis, 2009) show the real (ε’, µ’) and imaginary components (ε”, µ”). In the case of a magnetic material, losses are produced by changes in the alignment and rotation of the magnetization spin (Jarem, Johnson, Scott, 1995; Thostenson, Chou, 1999; Johnson, 2004).

The determination of m and ε of a material is usually based on measurements of complex electromagnetic parameters (S parameters), the reflection and transmission coefficients (S11 / S22 and S12 / S21, respectively), using a vector network analyzer. To analyze a material based on the value of these parameters, it is necessary to take into account other variables such as frequency band, intrinsic electrical properties of the material and its thickness (Fig. 1).

Materials with high conductivity and limited ability to store energy, such as metals, have high dielectric losses. In this case, the penetration depth approaches zero and the material has reflector-like characteristics. In materials with low dielectric losses, the penetration depth is larger and, as a result, little energy is absorbed by the medium, rendering the material transparent to electromagnetic radiation. In the case of absorbing materials, most of the electromagnetic energy is attenuated. The attenuation results from the interplay of several factors such as electric conductivity, dielectric loss and electromagnetic penetration depth, which need to be less than the thickness of the material (Thostenson, Chou, 1999; Oh et al., 2004; Rmili et al, 2005).

Organic polymers that conduct electricity are a class of polymers often referred to as “synthetic metals” due to their ability to combine the chemical and mechanical properties of polymers with the electrical properties of metals and semiconductors (Anand, Palaniappan, Sathyanarayana, 1998; Falcou et al., 2005).

Absorbing materials can be grouped into two categories: narrowband (or resonant) and wideband absorbers. Resonant materials are more common, while the wideband ones are produced by the combination of different materials (Ruck et al., 1970). The main application of both materials is essentially the same, i.e., the absorption of electromagnetic radiation. Thin sheet absorbers are prepared by dispersing a lossy material over a matrix. The absorption obtained depends on the thickness and the absorption mechanisms are independent of each other. By choosing a thickness that is a match to complex permittivity and permeability, the absorption bandwidth can be considerably increased, both at normal and oblique incidence of the electromagnetic wave (Naito, 1970; Naito, Suetake, 1970; Nicolson, Ross, 1970; Miller, 1986; Musal, Hahn, 1989).

The absorption of electromagnetic energy of a single-layer RAM as a function of frequency can be calculated analytically using Equations 3 and 4 (Balanis, 1989; Chen et al., 2004).

R(dB) = 20log

10

iA tan(kd) −1iA tan(kd) +1

⎛

⎝⎜

⎞

⎠⎟ (3)

where

A =μ

ε,

k =

2π fc

με , and i = −1 (4)

In (3) and (4), m and ε are, respectively, the complex permeability and permittivity of the absorbing material,

d = material thickness δ = skin depth E = electric field H = magnetic field

Electromagnetic radiation

δ

d

Z

Y

X

E

H

εµ

Figure 1: Diagram of a RAM showing the influence of thickness and other parameters.

The amplitude of an electromagnetic wave that propagates through a conducting medium is attenuated as the wave advances into the medium (Fig. 1) (Balanis, 1989; Lima, 2005). The electromagnetic penetration depth (called skin depth) and electric field attenuation at the surface of the material are important parameters in the production of RAMs (Quéffélec, Le Floc´h, Gelin, 1998; Guru, Hiziroglu, 2004).


Microwave absorbing paints and sheets based on carbonyl iron and polyaniline: measurement and simulation of their properties

k is the wave number, f is the frequency of the incident wave, c is the speed of light in vacuum, and d is the thickness of the absorbing layer. Both the permeability and permittivity vary along with the frequency.

In this context, the main objective of this work was to describe how we produce RAMs in the form of paints and sheets to absorb electromagnetic radiation in the frequency range of 8-12 GHz (X-band).

EXPERIMENTAL

A. Production of the paints

Two different absorbing centers were used to produce the absorbing paints: conducting polyaniline, which behaves as a dielectric; and commercial-grade carbonyl iron powder, a magnetic material. Polyaniline was synthesized at laboratory scale in the Materials Division of IAE. Briefly, the process consisted of the oxidization of aniline by ammonium persulfate in an acidic medium (dodecylbenzenesulfonic acid). The resulting polyaniline was obtained as a conducting powder (MacDiarmid et al., 1984; Skotheim, Elsenbaumer, Reynolds, 1998; Rannou et al., 1999; Mattoso, MacDiarmid, Epstein, 1994; Folgueras, Rezende, 2008).

Two paint formulations were prepared: one consisting of carbonyl iron powder (90% w/w) dispersed in the polyurethane matrix, and the other of carbonyl iron powder and polyaniline (15% w/w) dispersed in the same polymeric matrix. The absorbing fillers were mixed with the matrix material by mechanical agitation for 30 minutes. Next, the resulting material was applied to flat aluminum plates (20 x 20 cm) with a brush. The thickness of the paint layer containing only carbonyl iron was 1.10 mm, the paint layer containing carbonyl iron and polyaniline had a thickness of 1.85 mm. In order to evaluate some of the properties of these paints, they were also applied to a polymeric substrate, which facilitated their removal for further analyses. All paints were cured at room temperature.

B. Production of the silicone sheets

The doped polyaniline powder (17% w/w) was added to a matrix composed of two types of silicone rubber, L9000 and RTV630 (GE Silicones). The mixture was homogenized by mechanical agitation, and the processed materials were poured into (30 x 30 cm) molds and dried at 70°C. After this, two types of sheet forms were obtained, each corresponding to the different types of silicone rubber used. The sheet produced with L9000 silicone

rubber had a thickness of 2.80 mm, and the one produced with RTV630 silicone rubber was 4.40 mm thick.

C. Electromagnetic measurements

For the electromagnetic characterization of the paints, reflection/absorption measurements in the frequency range of 8-12 GHz were carried out using the Naval Research Laboratory (NRL) arch method (Skolnik, 1970; Knott, Shaffer, Tuley, 2004). The NRL arch (Fig. 2) consists of a wooden structure in the shape of a semicircular arch, enabling the proper positioning for emitting and receiving antennas (horn type). The samples are placed at the center of the arch curvature; first, the antennas are positioned at the highest position in the arch, and then each antenna is moved 10° to each side of this position. The antennas always pointed to the center of the sample. The setup also included a spectrum analyzer (Anritsu, model MS 2668C) and a frequency generator (Agilent Technologies, model 83752A). A flat aluminum plate was used as a reference for the reflection/absorption measurements; its reflectivity and absorptivity were considered to be 100% and 0%, respectively. The main advantage of the NRL method with respect to the others such as the waveguide method is that it allows measuring the properties of relatively large samples in free space conditions.

Antennas

Sample position

Figure 2: NRL arch used to measure the properties of the processed materials.

The transmission line technique (with a waveguide) was used to measure the complex electric permittivity and magnetic permeability of the processed paints in the microwave frequency range of 8-12 GHz (X-band). A closed waveguide (rectangular cross section) was coupled to a network vector analyzer (Agilent Technologies, model 8510C), an S-parameter tester (Hewlett Packard, model 8510A) and a synthesized frequency generator, both operating in the frequency range of 45 MHz – 26 GHz. This setup measured the S-parameters of the material;



the transmission and reflection coefficients S12 / S21 and S11 / S22, respectively. Commercial software (Agilent Technologies – 85071E) was used to calculate the values of the complex permittivity and magnetic permeability as functions of the frequency. Figure 3 shows the setup used in the measurements.

Figures 5 and 6 show the measurements of the attenuation of electromagnetic radiation and the complex electric permittivity, ε, and magnetic permeability, m, of the paints produced. Figures 5(a) and 6(a) show that both paints acted as RAMs in the frequency range used in this study. The paint containing only carbonyl iron (Fig. 5a) attenuated the incident wave by about 7 dB, which corresponds to an absorption of 80% of the electromagnetic energy. The paint containing both polyaniline and carbonyl iron (Fig. 6a) attenuated the wave by about 4 dB, corresponding to about 60% of absorption of the electromagnetic energy.

Figure 5b shows the measured values of the electric permittivity of the carbonyl iron paint, about 16.0 and 10.0 for the real and imaginary parts, respectively. The permeability values for this paint were 4.0 and approximately zero for the real and imaginary parts, respectively. It is known that the larger the value of the imaginary component of permittivity (ε”), the larger the losses of the material. Thus, a material with low dielectric loss can store energy, but will not dissipate much of the stored energy. On the other hand, a material with high electric losses does not store energy efficiently; a certain amount of energy will be transformed into heat within the material. In general, the smaller the magnetic permeability, the larger the resonance frequency, in which the material exhibits good absorption properties; but for frequencies higher than 2 GHz, the permeability is related to the energy anisotropy in the material (Bady, 1969; Vinoy, Jha, 1996; Jiu et al., 2004).

Sample position

)b( )a(

Figure 3: The transmission line technique setup: (a) vector network analyzer, (b) closed system rectangular waveguide and the position of the sample within the waveguide.


Figure 4 shows the appearance of the processed paints applied to a polymeric substrate. The polymeric substrate was used to enable removing the layer of paint undamaged for further analyses. It was observed that the paint containing polyaniline and carbonyl iron reflected more light and was darker than the paint produced with only carbonyl iron. After their removal from the substrates, the paint samples were weighed,, being verified that the polyaniline paint had a mass smaller than the one containing carbonyl iron. This was expected since the specific mass of carbonyl iron (7.8 g/cm3) is larger than that of polyaniline (~1.2 g/cm3).

Peeled o paint

(b) (a)

(c) (d)

Figure 4: Paints on a plastic substrate. Formulations containing (a) carbonyl iron and polyaniline, (b) thickness of the paint layer, (c) carbonyl iron only and (d) paint peeled off the metal plate for measurements.

Figure 5: Electromagnetic characteristics of the paint produced with carbonyl iron. (a) Attenuation of the incident radiation, and (b) relative electric permittivity, ε, and magnetic permeability, m. The prime and double primes refer to real and imaginary values, respectively.



Figure 6b shows the relative values of permittivity and permeability of the paint produced with polyaniline and carbonyl iron. The measured values of the real and imaginary parts of the electric permittivity were 5.5 and 1.5, respectively; and the measured values of the real and imaginary parts of the magnetic permeability were 1.2 and 0.3, respectively. This paint can be considered a hybrid absorbing material since it has dielectric and magnetic characteristics (Lee, 1991; Knott, Shaffer, Tuley, 2004). For this paint, the permittivity values are smaller than those measured for the carbonyl iron paint. This is due to a superposition of effects from the magnetic phenomena associated with the presence of the carbonyl iron and the electronic polarization of the polyaniline molecules, which act on the incident electromagnetic wave.

of the incident energy. When this material was evaluated using the back metal plate, it absorbed 88% of the incident energy; thus, 64% of the incident energy was attenuated due to physical processes occurring within the material, and 29% of the attenuation was caused by the intrinsic properties of the absorbing material. Similarly, Figure 9 (material with 4.40 mm) shows that the reflected and transmitted energy values were 42% and 35%, respectively. When this material was applied to a metal plate, 71% of the energy was absorbed; in this case 23% of the energy was absorbed intrinsically.

Figure 7 shows the aspect of the processed silicon sheets absorbers. Both types of different substrates (L9000 and RTV 630) used for processing the absorbing material demonstrated similar aspects.

Figure 8 depicts the results derived from the S-parameters measurements (reflected, transmitted and absorbed energy) for the two silicone sheets produced in this study. By this coefficient, its possible energy value was absorbed intrinsically by the material. It can be observed (material with 2.80 mm) that the reflected and transmitted energy were, on average, equal to 45% and 26%, respectively,

8 9 10 11 120

10

20

30

40

50

60

702.80 mm

Ener

gy c

oeffi

cien

ts (%

)

Frequency (GHz)

Er Et Ea

Figure 8: Curves of absorbed (Ea), transmitted (Et) and reflected (Er) energies for silicone type L9000.

8 9 10 11 120

10

20

30

40

50

60

70

4.40 mm

Ener

gy c

oeffi

cien

ts (%

)

Frequency (GHz)

Er Et Ea

Figure 9: Curves of absorbed (Ea), transmitted (Et) and reflected (Er) energies for silicone type RTV630.

Figure 6: Electromagnetic characteristics of the paint produced with polyaniline and carbonyl iron. (a) Attenuation of the incident radiation, (b) relative electric permittivity, ε, and magnetic permeability, m. The prime and double primes refer to real and imaginary values, respectively.

Figure 7: Silicone sheets (a) metallic mold and processed sheet, (b) thickness of the material, (c) sheet bond on metallic plate with adhesive.

(a) (b)

(c)



The dielectric properties of the absorbing silicone sheets are shown in Figures 10 and 11. It is obvious that these materials have distinct electromagnetic properties. These differences can be used to develop RAMs with different characteristics. The average real and imaginary values of the relative permittivity are close to 6.0 and 2.0, respectively, for the material produced with the silicone rubber L9000 (Fig. 9). For the material produced with the silicone rubber RTV630 (Fig. 10), the average real and imaginary permittivity values are 3.5 and 5.0, respectively.

CONCLUSIONS

Based on the results obtained in this study, we conclude that the paints produced have the potential to be used as RAMs, since they attenuated 60 to 85% of the incident electromagnetic radiation. The attenuation measured for the paint containing conducting polyaniline can be explained by the fact that when this polymer is surrounded by a matrix, conduction paths are formed in the material, allowing the dissipation of energy due to electrical losses. The carbonyl iron in the paints also contributed to the dissipation of electromagnetic energy due to magnetic anisotropy effects, a characteristic of this material for frequencies larger than 2 GHz.

The sheets produced with a silicone matrix attenuated the incident radiation to approximately 90%, demonstrating that these materials can be used as absorbers of electromagnetic radiation. Also, the analytical calculations demonstrated the importance of optimization tools to produce absorbing materials with the required properties.

The attenuation behavior of the paints suggests that their electric conductivity is related to the type of absorbing center and insulating material (matrix) used in the paint formulation, which modify the impedance of the RAM and the ability to attenuate the incident radiation.

An important characteristic of the materials produced is their low density (no larger than 1 g/cm3) compared to conventional absorbers based on ferrites (absorption 10 dB), with densities ranging from 4 to 5 g/cm3.

ACKNOWLEDGMENTS

The authors wish to thank the Departamento de Ciência e Tecnologia Aeroespacial (DCTA) / Instituto de Aeronáutica e Espaço for the technical and financial support and also the Brazilian government funding agencies CNPq (Projects numbers: 559246/2008-0, 151803/2008-0 and 150048/2010-6) and FINEP (Project number: 1757/03) for the financial support.

8 9 10 11 1201234567

2.80 mm

µ''

µ'ε''

ε'

Perm

ittiv

ity a

nd P

erm

eabi

lity

Frequency (GHz)

Figure 10: Complex permeability (m) and permittivity (ε) of the absorbing sheet with silicone type L9000.

8 9 10 11 12

0

1

2

3

4

4.40 mm

µ''

µ'ε''

ε'

Perm

ittiv

ity a

nd P

erm

eabi

lity

Frequency (GHz)

Figure 11: Complex permeability (m) and permittivity (ε) of the absorbing sheet with silicone type RTV630.

Based on the experimental data, it is possible to optimize the thickness of the materials with respect to the energy absorption. Figures 12 and 13 show how changes in the thickness affect the energy absorption. These results were obtained analytically using Equation 3. It can be observed that the resonant absorption peak is displaced with respect to frequency, but its amplitude does not vary significantly.

8 9 10 11 12 13-12

-10

-8

-6

-4

-2

0

Atte

nuat

ion

(%)

94

90

84

68

60

37

02.80 mm real resultAnalytical Results

Atte

nuat

ion

(dB

)

Frequency (GHz)

2.8 mm 3.0 mm 3.2 mm 2.6 mm

Figure 12: Energy absorption of single-layer RAMs as a function of frequency and different layer thicknesses for silicone rubber type L9000.

Figure 13: Energy absorption of single-layer RAMs as a function of frequency and different layer thicknesses for silicone rubber type RTV630.

8 9 10 11 12 13-5

-4

-3

-2

-1

0

Atte

nuat

ion

(%)

75

60

50

37

20

04.40 mm real resultAnalytical Results

Atte

nuat

ion

(dB

)

Frequency (GHz)

3.5 mm 4.0 mm 4.40 mm 5.0 mm



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Márcio da Silveira Luz*Comando-Geral de Tecnologia Aeroespacial


Gustavo Matheus MinariUniversidade de Taubaté

Taubaté – [email protected]

Isabel Cristina dos SantosUniversidade de Taubaté

Taubaté – [email protected]

*Author for correspondence

Aglomerações industriais no setor aeroespacial e automobilístico no Vale do Paraíba Paulista: uma comparação de trajetórias de formação Resumo: Este artigo apresenta uma comparação das características relevantes observadas nos clusters aeroespacial e automobilístico do Vale do Paraíba Paulista e analisa o adensamento das cadeias produtivas e tecnológicas. Para tanto, os procedimentos metodológicos adotados eram de natureza qualitativa, empregados por meio de pesquisa documental. Os resultados indicam que o governo estabeleceu, em meados de 1945, o atual Departamento de Ciência e Tecnologia Aeroespacial (DCTA), como centro de Pesquisa e Desenvolvimento (P&D) e, em 1979, a Embraer, como indústria estatal de construção aeronáutica. Procurou-se também gerar condições para que empresas nacionais surgissem ao seu redor e substituíssem a dependência do fornecedor internacional para fornecimento de sistemas e subsistemas aeroespaciais, desenvolvendo capacidade tecnológica própria. Por seu lado, o cluster automobilístico em estudo iniciou-se no Vale do Paraíba Paulista (VPP) pela regionalização de empresas multinacionais de construção automobilística migradas da região do grande ABC Paulista à procura de espaço físico para o seu crescimento, contando também com incentivos fiscais favoráveis. Os resultados da pesquisa indicam que, a despeito de diferenças fundamentais em relação ao adensamento de suas cadeias produtivas, mostraram resultados adversos semelhantes.Palavras-chave: Clustering, Cluster aeroespacial, Cluster automobilístico, Trajetórias de formação.

Automotive and aeronautical clusters in the São Paulo state’s Vale do Paraíba: a comparison of formation trajectoriesAbstract: This paper presents a comparison of the relevant characteristics of São Paulo State’s Vale do Paraíba automotive and aerospace clusters observed and analyzes the technological and productive chains strengthening. In order to accomplish it, the adopted methodological procedures are of qualitative nature, by means of documentary research. The results pointed out that the government established, in the mid-1945, the currently named Departamento de Ciência e Tecnologia Aeroespacial (DCTA), as a research and development (R&D) center and, by 1979, Embraer, a state-owned aeronautical construction industry. It was also sought to generate conditions so that domestic companies could emerge around and replace the dependency on aerospace systems and subsystems international suppliers by developing indigenous technological capacities. The automotive cluster under study started in the São Paulo State’s Vale do Paraíba (PPV) by means of the regionalization of multinational automotive construction firms migrated from ABC Paulista region looking for physical space for their growth, also relying on tax benefits. The survey results indicate that, in spite of fundamental differences with regard to their productive chains strenghtening processes, they showed similar adverse results.Keywords: Clustering, Aerospace cluster, Automotive cluster, Formation trajectories.


Fnac

Text Box

DOI: 10.5028/jatm.2010.02017182


Luz, M.S., Minari, G.M., Santos, I.C.D.

INTRODUÇÃO

Este trabalho visa a comparar o resultado de duas estratégias aparentemente opostas de industrialização empregadas no Brasil: a primeira foi a do setor automobilístico, empregada no governo de Juscelino Kubitschek e sucessores que, com a existência de uma base industrial instalada no país, atraiu empresas integradoras e montadoras automobilísticas estrangeiras para produzirem autopeças nacionais, gerando um sistema setorial de produção; a segunda foi a do setor aeronáutico, construída em torno de uma companhia integradora, produtora de aviões, nacional (primeiramente estatal) na esperança de que, ao seu redor, também se constituísse um competente sistema setorial de produção. A região do Vale do Paraíba Paulista (VPP) congrega as principais atividades industriais e de pesquisa do setor aeroespacial brasileiro, sobretudo aeronáutico, bem como algumas das mais importantes unidades da indústria automobilística. Por essa razão, esta região foi escolhida para a análise.

Materiais e procedimentos metodológicos

Foram pesquisadas as motivações e objetivos mais fortemente relacionados à comparação das características substantivas entre duas diferentes estratégias empreendidas pelo governo para desenvolvimento dos clusters aeroespacial e automobilístico do Vale do Paraíba Paulista. Para tanto, foi realizada uma pesquisa bibliográfica pautada na busca de informações e publicações atuais sobre os tópicos relacionados à teoria de cluster, por Porter et al., buscando conhecimentos progressivos para conclusões a respeito de como esses setores seriam descritos com tais características e de suas principais diferenças e semelhanças relacionadas à questão de adensamento das cadeias produtivas e tecnológicas.

Os dados obtidos foram submetidos à análise descritiva de conteúdo. Os resultados desta análise foram cotejados com as principais contribuições teóricas dos autores examinados na pesquisa bibliográfica.

Contextualização histórica da pesquisa

O cluster aeroespacial do Vale do Paraíba Paulista tem sua formação planejada pelo governo, por volta de 1947, por meio do estabelecimento do núcleo do que viria a ser o Centro Técnico de Aeronáutica, atual CTA como Centro de Pesquisa e Desenvolvimento (P&D). Com relação à indústria aeroespacial, em 1961 foi criada a empresa privada Avibrás Indústria Aeroespacial S/A, especializada na área de Defesa e em 1969, a Embraer, empresa Estatal como fabricante de aeronaves cujas operações industriais iniciaram-se em 1970.

O cluster automobilístico do Vale do Paraíba Paulista foi formado a partir do final da década de 1950, com a instalação de três indústrias montadoras transnacionais originalmente no ABC Paulista que se regionalizaram para atender à necessidade de um espaço físico que comportasse sua nova fase de crescimento, fuga da pressão sindical e contratações de mão de obra com salários mais baixos.

A estratégia de formação de cluster adotada pelo governo para o setor aeroespacial foi criar um centro de Pesquisa e Desenvolvimento (P&D) com o CTA e com empresas de integração de sistemas – a Avibrás e a Embraer – com o objetivo de desenvolver fornecedoras nacionais de sistemas e subsistemas aeroespaciais. Com o tempo, foram atraídas apenas as empresas internacionais, uma vez que o Brasil ainda não tinha essa capacidade desenvolvida.

O cluster automobilístico, em uma estratégia diferente, deu-se pela atração de empresas multinacionais de integração de sistemas para incentivar o desenvolvimento da capacidade nacional e regional de fornecimento de autopeças, uma vez que o país já possuía empresas desse tipo, porém com a possibilidade de maior desenvolvimento.

Outra questão de alta relevância para o processo de aglomeração industrial nos setores pesquisados na região do Vale do Paraíba Paulista foi a inauguração da Rodovia Presidente Dutra, em 1951, que permitiu estabelecer uma ligação viável com os principais centros econômicos do país: São Paulo, Rio de Janeiro e, por proximidade, o sul de Minas Gerais, como apresentado na Figura 1.

Figura 1: Formação dos aglomerados aeroespacial e automobilístico.

Fonte: Adaptado de Santos e Amato Neto (2005), Campos e Krom (2006).

O contexto histórico da industrialização do Vale do Paraíba Paulista se localiza, temporalmente, no espírito de construção do chamado “Brasil Grande”, caracterizado pela criação de uma infraestrutura industrial, formação da mão de obra qualificada para a indústria e respectivas agências reguladoras, pautando a política industrial


Aglomerações industriais no setor aeroespacial e automobilístico no Vale do Paraíba Paulista: uma comparação de trajetórias de formação

brasileira a partir da década de 1940. Importantes etapas e decisões tomadas pelo governo com relação à implantação das indústrias de base tecnológica, a partir da década de 1950, foram articuladas visando a dois grandes objetivos: a gradual nacionalização tecnológica e, mais tarde, a substituição das importações por produção nacional.

REVISÃO TEÓRICA

Clusters industriais

Para Bergman e Feser (1999), os clusters industriais são definidos como grupos de empresas e organizações que, em sociedade, valorizam a produção e o aumento de competitividade do conjunto. São os elos de uma cadeia produtiva inteira que compartilham os efeitos até mesmo do seu processo decisório. Gestores públicos e privados, empreendedores, cidadãos em geral que identificam oportunidades e ameaças impactantes nos negócios das organizações. A interdependência produtiva é uma das características do cluster (Porter, 2002b).

Para Porter (2002a), a influência do governo na formação e desenvolvimento do cluster é inquestionável. Cabe aos governos identificar as potencialidades das diferentes regiões, suas vantagens locais de produção, sejam na oferta de recursos – matérias-primas – ou menores custos e controlar a instalação dos fatores de produção. Em termos de políticas governamentais de estímulo à formação de cluster, cabe ressaltar: o poder de compra, subsídios diretos e indiretos à pesquisa, concessão de incentivos fiscais, infraestrutura técnico-científica, regulamentação de patentes e financiamentos públicos de longo prazo.

Cluster, na verdade, depende de uma institucionalização por parte do governo, com a eleição de um estatuto, tendo os nomes das empresas nele inseridas, reconhecidas pelo nome do conjunto (Porter, 2002a). A relação institucional estabelecida no cluster se dá entre as empresas, os clientes, fornecedores, ambientes de trabalho e canais de distribuição, objetivando aumentar o lucro e gerar crescimento econômico. As organizações tidas como não produtivas podem ser as associações, universidades, escolas técnicas, programas governamentais de financiamentos.

O aumento da competitividade, para as empresas, ocorre em sinergia pela multiplicação das competências individuais. Recursos, quando compartilhados, geram impulsão para patamares de desenvolvimento mais elevados do que individualmente (Bergman e Feser, 1999).

Duas estratégias estão associadas à formação de cluster. A primeira se baseia nos suprimentos produtivos às empresas

de grande porte por parte de pequenas e médias empresas situadas em proximidade geográfica. Nessa formação, o mercado consumidor das pequenas e médias empresas é praticamente garantido, pois atende à necessidade da empresa de grande porte. Outros benefícios são: aumento de capital de risco pela coletividade e vantagens para financiamentos de longo prazo. A segunda estratégia ocorre pela união das pequenas e médias empresas em consórcio, com o objetivo de obter maior competitividade por meio da associação de capacidades produtivas, recursos e conhecimentos (Hoffmann, Gregolin e Faria, 2006).

O governo está inserido em ambas as estratégias como facilitador estrutural (Porter, 2002a). Contudo, a primeira estratégia é mais utilizada em setores automobilísticos: práticas iniciadas no Japão e depois difundidas ao restante do mundo, principalmente para o ocidente (Tachinardi, 2000). A segunda tem foco no desenvolvimento empresarial italiano por meio do movimento conhecido como Nova Itália de 1999 (Arcangelis, Ferri e Padoan, 2004).

As empresas em cluster estão alinhadas e integradas segundo objetivos produtivos e inovadores comuns, viabilizando a transferência e incentivo ao fomento e a disseminação do conhecimento entre os participantes. Por isso, observa-se a inclusão dos membros em redes de comunicação integradas, de maneira que todos têm acesso e participação não só em decisões, mas também em capacitações produtivas.

O conhecimento pode ser pulverizado em duas maneiras: “spill over” vertical, quando, por exemplo, no arranjo, uma empresa de grande porte exige que suas fornecedoras utilizem um mesmo sistema integrado ou mesmo sistemas e certificações de qualidade comuns, o conhecimento induzido; e “spill over” horizontal, quando o conhecimento é pulverizado por meio de prestações de serviços comuns, em que os membros do arranjo produtivo têm relações integradas e disseminam informações técnicas em razão das integrações produtivas.

Sistemas de produção e de inovação

Diferentemente de clusters, o tratamento por meio de Sistemas de Produção e de Inovação privilegia o estudo das partes constituintes e de suas inter-relações. Os Sistemas de Inovação podem ser analisados em seus aspectos nacionais, setoriais e regionais. Assim, os Sistemas de Produção e Inovação são formados por empresas, organizações de P&D e instituições de apoio à coordenação e controle de redes de relacionamentos (Malerba, 1999). A integração ocorre pela produção, criação e comercialização do produto.



List (1909) foi o pioneiro no trato de sistemas de produção. O autor citou o papel do governo na oferta de condições favoráveis ao fortalecimento da cadeia produtiva nacional. Tratando dos sistemas nacionais de produção, List discutiu a dificuldade de desenvolvimento de empresas nacionais com o mercado ocupado por empresas estrangeiras, provenientes de países mais fortes economicamente. As empresas nacionais, segundo ele, sofreriam um processo chamado de esmagamento. Assim, em médio prazo, as ações protecionistas do governo seriam instrumentos políticos sistemáticos para fortalecimento e consolidação econômica nacional.

Lundvall (2001) afirmou que os sistemas nacionais de inovação seriam favorecidos por políticas de inovação que contribuiriam para a capacitação de empresas e das instituições do conhecimento. Essas políticas criariam e difundiriam o conhecimento mediante aprendizagem compartilhada, priorizando a profissionalização que, aliada às novas formas de organização empresarial pela formação de redes e promoção de empresas de serviços e universidades orientadas à inovação, geraria as competências produtivas.

Em um contexto regional, a capacidade de inovação, segundo Dosi, Nelson e Winter (2000), está ligada não só aos investimentos em P&D, mas também à habilidade empresarial de integrar-se em um ambiente propício à inovação, reconfigurando as competências externas com ênfase na coordenação de recursos e atividades, direcionando-as sistematicamente à produção.

CLUSTER AEROESPACIAL DO VALE DO PARAÍBA PAULISTA

Bernardes (2000) avalia que a estabilização econômica e a revisão do modelo de desenvolvimento nacional durante a década de 1990 induziram a indústria aeroespacial brasileira à sua reestruturação produtiva e empresarial, marcada pela privatização da Embraer. A nova dinâmica repercutiu positivamente na economia da região de São José dos Campos, no Estado de São Paulo, geando empregos e renda pela atração de novas plantas empresariais de fornecedores de partes e peças aeronáuticas para a Embraer. Atividades inovativas e produtivas foram estabelecidas em torno da Embraer, que centralizava e organizava os projetos e montagens industriais com um grupo de empresas de base tecnológica atuando em prestação de serviços e fornecimentos produtivos especializados.

Caracterização do setor aeroespacial

O cluster aeroespacial formado no VPP é formado pela Embraer, uma das maiores exportadoras do Brasil, e o

consórcio empresarial High Technology Aeronautics (HTA), que reúne empresas e suas tecnologias de serviços, e venda de peças aeronáuticas. Na área de Defesa, há a Avibrás, responsável pela produção e venda de sistemas de foguetes e caminhões plataformas, e a Mectron Engenharia Indústria e Comércio Ltda (Santos et al., 2003).

Há, ainda, outras empresas nacionais que contribuem com o setor aeroespacial vendendo insumos e serviços, tratamentos térmicos, serviços de engenharia e projetos, softwares, entre outros, às empresas de grande porte, principalmente à Embraer. As relações apresentam níveis diferenciados de integração e propriedades, fluxos de transações comerciais e tecnológicas.

Origem e formação do cluster aeroespacial

Gomes et al. (2005) descreveram que a indústria aeroespacial brasileira foi criada em meados de 1945, quando foi concebida a estratégia de criação do Centro Tecnológico da Aeronáutica (CTA), atual Comando-Geral de Tecnologia Aeroespacial, vinculada ao Ministério da Aeronáutica. O Plano de Instalação do CTA contemplava o planejamento e a construção da estrutura produtiva aeroespacial, juntamente com o Instituto Tecnológico de Aeronáutica (ITA), que seria destinado à formação de engenheiros nas áreas fundamentais da indústria aeronáutica: projeto de aeronaves, de eletrônica específica, materiais, motores e testes de vôo, computação, softwares e outras.

A criação do CTA, do ITA e dos demais institutos foi determinante no surgimento e sucesso da Embraer, que contou com o conhecimento tecnológico acumulado neste centro de tecnologia, e onde foi concebida a aeronave que daria origem à Embraer: o avião Bandeirante. Após esse bem-sucedido “spill over”, a instituição estaria dedicada à pesquisa, desenvolvimento e qualificação de fornecedores para as atividades aeroespaciais.

Na década de 1990, com as privatizações, a Embraer foi vendida a um consórcio empresarial internacional, passando a um novo ciclo de investimentos em projetos e produções, os quais resultaram em alto crescimento econômico (Santos et al., 2003).

Até 1994, a produção aeroespacial era caracterizada pela existência de grandes projetos sem a adequada estrutura nacional de financiamentos e pela falta de instituições financeiras privadas ou públicas para crédito de longo prazo. Além disso, até aquele ano, o desenvolvimento de projetos ocorria sem prévia investigação das condições do mercado e das reais necessidades dos clientes, ausência de gestão empresarial e visão ampla quanto a custos e,



por isso, perda de competitividade frente aos mercados externos (Gomes et al., 2005).

Segundo Gomes et al. (2005), posteriormente à sua privatização, a administração da Embraer passou a se concentrar em reengenharia financeira, patrimonial, organizacional e produtiva; reestruturação das relações com clientes e fornecedores; planos de ação identificados com a missão da empresa e priorização do programa de jatos de 45 lugares, uma estratégia de recuperação de negócios.

O autor ainda cita que a consequência imediata da introdução da nova forma de gestão privada foi a hierarquização da cadeia de produção em três categorias: os denominados parceiros de risco, ou “prime-contractors”, os quais participam das responsabilidades técnicas e financeiras em projetos específicos; os fornecedores de itens críticos aos “prime-contractors”, selecionados sob critérios de qualidade e capacidade tecnológica; finalmente, empresas subcontratadas para prestar serviços e realizar atividades de menor conteúdo tecnológico foram o quarto nível da cadeia produtiva.

Principais instituições atuantes no setor aeroespacial

O CTA e o Instituto Nacional de Pesquisas Espaciais (INPE) são tidos na formação de cluster como importantes centros P&D (Bernardes, 2000). Além do ITA, Bernardes destaca o Instituto de Aeronáutica e Espaço (IAE), o Instituto de Estudos Avançados (IEAv) e o Instituto de Fomento e Coordenação Industrial (IFI). Neles, são realizados projetos de sistemas aeronáuticos, espaciais e bélicos nas áreas de Materiais, Ciências Atmosféricas, Física, Química, Eletrônica e Computação, além de outras atividades, como: homologação de aeronaves, normatização, qualidade, confiabilidade e gerenciamento tecnológico. As atividades são complementadas por simulações computacionais de vôos, ensaios em túneis de vento e integração no solo.

O INPE foi criado em 1961 como uma instituição federal subordinada ao Ministério da Ciência e Tecnologia (MCT). Seus objetivos eram: a realização de P&D nas áreas de Ciências Espaciais e Atmosféricas, com concentração em desenvolvimento de satélites, incluindo testes, rastreamento e controle das aplicações espaciais. O INPE possui cursos de pós-graduação em Meteorologia, Sensoriamento Remoto, engenharia e tecnologia Espacial, Computação Aplicada, Geofísica Espacial e Astrofísica (Bernardes, 2000).

Outras instituições de ensino superior e técnico estão voltadas às atividades aeroespaciais, como a Universidade

de São Paulo (USP), Universidade Federal de São Carlos (USP-UFSCar), Universidade Federal de Minas Gerais (UFMG) e Universidade Federal de Santa Catarina (UFSC), as quais igualmente contribuem para a formação de conhecimento nacional na área Aeronáutica. A Universidade de Taubaté (UNITAU), Universidade do Vale do Paraíba (UNIVAP) e Universidade Paulista (UNIP) também têm a sua contribuição na formação de profissionais qualificados no campo das Ciências Aeroespaciais.

Dentre os participantes que influenciam as atividades de coordenação do setor aeroespacial do Vale do Paraíba Paulista (Bernardes, 2000), estão:

• A Empresa de Aeronáutica Brasileira S/A (Embraer): atuando como indústria nacional de Aeronáutica e coordenadora das atividades produtivas em cadeia de suprimentos. Nela está concentrada a capacidade nacional de montagem de aeronaves, etapa do processo produtivo de maior valor agregado (Furtado, 2006).

• Centro das Indústrias do Estado de São Paulo (CIESP): com a promoção de desenvolvimento local associado à Federação das Indústrias do Estado de São Paulo (FIESP), com projetos para a realização de consórcio entre empresas voltadas ao adensamento da cadeia produtiva e exportação.

• CTA, Fundação Casimiro Montenegro Filho (FCMF) e FUNCATE: de atuação na organização e fomento de P&D de tecnologias aeronáuticas avançadas.

• CECOMPI: o Centro para Competitividade e Inovação do Cone Leste Paulista (Cecompi) responsável pela organização e implantação de parque tecnológico orientado às atividades de P&D do setor aeroespacial e ao fomento de empreendedorismo, arranjos produtivos locais e inovação. O projeto reúne associações, centros de pesquisa, universidades e empresas para o desenvolvimento do setor aeroespacial por meio de programas de financiamento públicos, obtenção de benefícios tributários. As parcerias para financiamentos de projetos se dão principalmente por meio dos programas FINEP e FAPESP (Simões, 2006).

• Secretaria de Desenvolvimento Econômico (SDE): Órgão da Prefeitura de São José dos Campos criado em 1997 para apoiar o desenvolvimento local com ênfase na expansão da atividade econômica dos setores tecnológicos. Com a Embraer, tem desenvolvido planos para institucionalização do APL aeroespacial,



adensando a cadeia de produção mediante incentivos fiscais para atração de novos empreendimentos.

Há ainda outros desenvolvimentos, como o chamado consórcio empresarial da empresa High Technology Aeronautics (HTA), composto por pequenas e médias empresas fornecedoras de partes e peças aeroespaciais que prestam serviços como usinagem, estamparia, submontagem e tratamentos térmicos de materiais.

• Associação das Indústrias Aeroespaciais Brasileiras (AIAB): atua na representação dos interesses de classe do segmento aeroespacial. Tem atuação estratégica, defendendo uma política competitiva e tecnológica para o setor, e pleiteando, junto ao governo Federal, melhores condições para as atividades. Fundada em 1993, congrega empresas do setor por meio de filiações na promoção de programas de desenvolvimento científico visando a oportunidades de negócios para exploração de novos mercados, enfatizando as parcerias entre universidades e empresas.

Bartels (2007) afirma que o setor aeroespacial vive agora uma excelente fase para crescimento econômico. Para ele, o aumento dos volumes de produção de aeronaves para uso comercial, juntamente com o estreitamento das relações de negócio entre a EMBRAER e os seus fornecedores, em 2006 projetou internacionalmente o setor aeroespacial brasileiro, com especial destaque ao aspecto da qualidade dos produtos e dos serviços oferecidos.

Relacionamentos e níveis de cooperações produtivas

Furtado (2006) afirmou que a cooperação da cadeia aeroespacial se dá, internacionalmente, em três níveis. O autor dispõe as seguintes condições:

• No primeiro nível estão as indústrias de integração de sistemas, montagens aeronáuticas e vendas. A Embraer ocupa o primeiro nível da cadeia produtiva na cadeia produtiva aeroespacial nacional, formada na região do Vale do Paraíba Paulista.

• No segundo nível estão os parceiros de riscos, formado por grandes empresas multinacionais, as quais compartilham o projeto, a produção e os riscos financeiros inerentes. À exceção da ELEB, não houve investimentos nacionais para a tecnologia.

• No terceiro nível estão os fornecedores de itens críticos aos parceiros de riscos. Não há empresas nacionais nesse nível, sendo os fornecimentos realizados por empresas multinacionais ligadas à cadeia produtiva aeroespacial internacional.

• O quarto nível é formado por empresas nacionais participantes da cadeia produtiva que prestam serviços de menor intensidade tecnológica, tais como: engenharia, usinagem, tratamentos térmicos para peças aeronáuticas e revestimentos. (Gomes et al., 2005).

CLUSTER AUTOMOBILÍSTICO DO VALE DO PARAÍBA PAULISTA

O primeiro automóvel chegou ao país em 1893. Era um automóvel Peugeot, comprado em Paris pelo brasileiro Henrique Dumont, milionário produtor de café da região de Ribeirão Preto, pai do jovem Alberto que, 13 anos mais tarde, em 1906, faria em Paris o primeiro vôo documentado e se tornaria o pai da aviação.

A caracterização do setor automobilístico

A indústria automobilística brasileira tem início com a instalação da linha de montagem Ford na cidade de São Paulo, em 1919. Suas atividades estavam voltadas para a montagem do veículo conhecido como Modelo T, cujas peças eram importadas. Em 1930, foi instalada na cidade de São Caetano do Sul, SP, a General Motors do Brasil (ANFAVEA, 2007a).

Décadas mais tarde, em razão das dificuldades de importação de peças de automóveis provocadas pela 2ª Guerra Mundial, a indústria automobilística brasileira foi forçada a estimular as pequenas e médias empresas nacionais a produzirem, naquele período, uma série de componentes, como sistemas de molas, baterias, pistões, anéis, dentre outros, procurando suprir a demanda produtiva local (ANFAVEA, 2007a).

A criação do Sindicato Nacional da Indústria de Componentes para veículos Automotores (SINDIPEÇAS), em 1953, foi decisivo para o setor. A instituição organizou naquele ano a Primeira Mostra da Indústria Nacional automobilística, inaugurada por Getúlio Vargas, na cidade do Rio de Janeiro. Esse evento buscava conscientizar as empresas brasileiras fabricantes de autopeças sobre a oportunidade de crescimento de negócios de autopeças, setor que até então se apresentava com baixa produção e em volumes insuficientes. Essa nova perspectiva de crescimento sofreria grande impacto com o suicídio de Vargas em 1954, sendo retomada em sua proporção inicial no governo de Kubitschek.

Em 16 de agosto de 1956, Kubitschek criou o Grupo Executivo da Indústria Automobilística (GEIA), visando a estimular a fabricação local. Antes disso, no mesmo ano, em 15 de maio, foi criada a Associação de



Veículos Automotores (ANFAVEA), responsável pela consolidação da indústria automobilística brasileira (ANFAVEA, 2007a). A necessidade de abastecimento do mercado de reposição de autopeças no Brasil gerou as especializações produtivas e os novos campos de estudos, como a engenharia automobilística, ganharam investimentos.

Em 1970, a Volkswagen do Brasil ampliou seus projetos, privilegiando os produtos de engenharia brasileira. A empresa General Motors contribuiu para a engenharia automobilística ao inaugurar o campo de teste em Indaiatuba, em 1974 (ANFAVEA, 2007a).

Em 1980, houve redução de investimentos no setor devido à crise financeira nacional e aos desequilíbrios econômicos, levando à redução da produção. Em 1990, com a abertura econômica no governo Collor e a elevada pressão sobre a competitividade nacional frente aos produtos importados, a indústria interna foi forçada a se aprimorar e se adaptar às novas condições de mercado. Novas estratégias foram adotadas para o setor (ANFAVEA, 2007a).

Em 2006, o setor automobilístico nacional era formado por: 25 montadoras diferentes, abastecidas por mais de 500 empresas de autopeças; capacidade industrial para produção de cerca de 3,5 milhões de veículos e 98 mil máquinas agrícolas por ano, comercializados por uma rede de 3,6 mil concessionárias distribuídas pelo país como resultado das adaptações e reestruturações produtivas em processos contínuos de desenvolvimento (ANFAVEA, 2007a).

Nos últimos 50 anos, com a instalação de montadoras e suas fornecedoras, o país recebeu recursos para produzir carros e máquinas agrícolas, novos sistemas de produção e de administração, e rígidos sistemas de controle de qualidade resultantes das exigências de certificação e de respeito ao meio ambiente (ANFAVEA, 2007b). O país possui, além do potencial do mercado consumidor doméstico, o parque produtor, a mão de obra qualificada, adequada rede de concessionárias e sistema financeiro de apoio a vendas, fatores considerados diferenciais em relação aos demais países emergentes (ANFAVEA, 2007a).

A regionalização da indústria automobilística

A primeira localidade que acolheu a indústria automobilística brasileira foi o ABC Paulista, no Estado de São Paulo, compreendendo a cidade de São Paulo e vizinhanças. O Quadro 1 expõe a cronologia das principais instalações fabris automobilísticas no Brasil.

Após 1959, ocorreu a regionalização da indústria automobilística, com a instalação de fábricas em outras regiões nacionais (ANFAVEA, 2007a), citados os seguintes motivos:

• As automobilísticas produziram efeitos que ultrapassaram seus espaços físicos que as suportassem, necessitando de novas plantas, procurando, com isso, novas localidades.

• Fuga da pressão sindical que, com o crescimento do setor, ganhava força. As relações de trabalho resultaram em movimentos organizados por parte dos mesmos.

• Busca de contratações com salários mais baixos: em Camaçari (BA), por exemplo, onde a Ford se instalou em meados de 2003, os empregos foram preenchidos por mão de obra do próprio município; 90% dessa mão de obra ganha salários correspondentes a um terço dos valores empregados na região do grande ABC Paulista.

• As indústrias de autopeças ligadas a processos de desenvolvimento de competências e projetos acompanharam-nas sob a oportunidade de ampliação de seus empreendimentos, em parcerias, buscando qualificações e fornecimentos. A região do Vale do Paraíba Paulista, Estado de São Paulo, foi uma das opções.

Ano Empresa Cidade – UF1930 General Motors São Caetano do Sul – SP1953 Ford do Brasil São Paulo – SP1953 Volkswagen São Paulo – SP1956 DaimlerChrysler São Bernardo do Campo – SP1958 Willys Overland do Brasil Taubaté – SP1959 General Motors do Brasil São José dos Campos – SP1959 Toyota São Paulo – SP1967 Ford Motor Co/ Willys Taubaté – SP1973 Volkswagen do Brasil Taubaté – SP1976 Fiat Betim – MG1992 Kia Motors do Brasil Itu – SP1996 Volkswagen do Brasil Resende – RJ, ainda no Vale do

Paraíba1997 Honda Sumaré – SP1999 Renault São José dos Pinhais – PR2001 Peugeot-Citröen Porto Real – RJ2002 Nissan São José dos Pinhais – PR2002 PSA Peugeot Citröen Resende – RJ, ainda no Vale do

Paraíba

Quadro 1: Cronologia das principais instalações automobilísticas no Brasil.

Fonte: ANFAVEA (2007a, p. 14); Santos e Amato Neto (2005), Campos e Krom (2006).



Em 1959, houve a instalação da empresa General Motors do Brasil, na cidade de São José dos Campos, seguida das instalações da Ford do Brasil e da Volkswagen em Taubaté, nos anos de 1967 e 1973, respectivamente.

A instalação das indústrias automobilísticas no Vale do Paraíba Paulista

Campos e Krom (2006) afirmaram que o VPP sofreu grandes mudanças em seu perfil econômico depois da instalação das indústrias automobilísticas. Para eles, a chegada das grandes montadoras proporcionou crescimento em várias outras áreas da economia, como setores de comércio, serviços, hotelaria, redes de ensino, cursos profissionalizantes e outros.

A desconcentração das indústrias automobilísticas da região metropolitana de São Paulo em direção ao VPP deu-se em razão da localização regional estratégica, com a Rodovia Presidente Dutra ligando São Paulo ao Rio de Janeiro, da intervenção dos governos municipais da região com políticas expansionistas para desenvolvimento regional, dentre elas, os incentivos fiscais e doação de terras para instalações industriais, e da disponibilidade de mão de obra não organizada por sindicatos (Campos e Krom, 2006).

Houve investimentos regionais para atração de empresas de alta tecnologia: a criação do Centro de P&D do CTA; a implantação da Refinaria da Petrobras, em 1953; a instalação do INPE, em 1961 e, em 1969, da Embraer. Assim, a vocação econômica no setor primário – plantio de café e cana-de-açúcar – mudou para o setor tecnológico (Lessa, 2004).

Na avaliação de Campos e Krom (2006), apesar da introdução de políticas expansionistas regionais, nesse primeiro momento as indústrias de insumos e fornecimentos de autopeças não acompanharam as multinacionais montadoras para o VPP. Para esses autores, o motivo do estabelecimento das fornecedoras na região foram as parcerias produtivas junto às montadoras, as quais garantiam o retorno do capital por meio das demandas previstas. Outro motivo teria sido a introdução das novas tecnologias de gestão da produção e sistemas de qualidade internacionais, o que exigiu maior proximidade entre montadoras e fornecedores para os seguintes resultados: redução de custos logísticos e tempos de produção, transferência de capital de estoque para investimentos tecnológicos dos processos produtivos, juntamente com a possibilidade de realização de investimentos financeiros com o capital disponível.

A General Motors buscou na cidade de São José dos Campos uma localidade estratégica, próxima à ferrovia

que ligava as cidades de São Paulo e Rio de Janeiro. Sua intenção era instalar uma fábrica de motores de caminhão. Em 1959, a empresa construiu na cidade uma fundição de peças de motores, e o primeiro modelo fabricado foi o de 261 polegadas cúbicas, de 6 cilindros, em linha. Na época, a capacidade produtiva era de 25 mil motores por ano.

Para capacitar a mão de obra, a indústria automobilista criou programas internos de treinamentos, baseando-se na experiência operacional de trabalhadores de São Caetano do Sul (SP). Alguns funcionários foram encaminhados aos Estados Unidos para obtenção de conhecimentos específicos dos processos de produção (CHEVROLET, 2008).

Um dos fatos que influenciou a decisão de instalação da General Motors na cidade de São José dos Campos foi a existência da Escola Técnica Professor Everardo Passos (ETEP), fundada em 1956. Esse é um indício de que havia, naquela época, formação local de mão de obra qualificada (CHEVROLET, 2008).

Segundo Campos e Krom (2006), o primeiro contato de Taubaté com a indústria automobilística se deu com a instalação da multinacional Willys Overland do Brasil que, mais tarde, em 1975, seria adquirida pela Ford. A instalação da montadora se deu pela busca estratégica de localização, atraída pela presença de infraestrutura logística, a Rodovia Presidente Dutra, ligando São Paulo ao Rio de Janeiro, e demais rodovias com acesso ao litoral e ao sul do Estado de Minas Gerais.

A instalação da Volkswagen em Taubaté, em 1970, foi motivada pelos incentivos fiscais e pela doação de terreno como parte das políticas expansionistas ligadas ao Grupo de Expansão Industrial (GEIN) órgão subordinado ao Departamento de Desenvolvimento Econômico Municipal. A indústria iniciou suas atividades produtivas a partir de 1973.

Principais instituições atuantes no setor automobilístico brasileiro

A ANFAVEA foi criada em 1956, na cidade de São Paulo, com a finalidade de representar os interesses do setor automobilístico junto às diferentes esferas da política nacional. Além do papel político, a instituição desenvolve estudos econômicos sobre o mercado automobilístico brasileiro e o desempenho do setor, fornecendo essas informações às empresas montadoras ou fornecedoras de autopeças a ela associadas (ANFAVEA, 2007a).

O Grupo Executivo da Indústria Automobilística (GEIA), agora denominado Novo Grupo Técnico, participa



das negociações de redução nas taxas de impostos de nacionalização, obtenção de licenças de importação de equipamentos e matérias-primas não fornecidas nacionalmente, e das definições de políticas industriais junto ao Governo Federal. E, juntamente com o SINDIPEÇAS, participa das negociações por melhores condições comerciais internas que visam a ampliar a capacidade de consumo de famílias de baixa renda com oferta de financiamentos de longo prazo (ANFAVEA, 2007a).

Consoni (2004) afirmou que as atividades mais complexas de P&D relacionadas ao setor automobilístico estão centralizadas no exterior, sendo realizadas pelas matrizes das montadoras multinacionais, em seus países de origem. Assim, os países subsidiários são empregados em serviços relativos a atividades de engenharia e voltados à adaptação do produto às condições locais e adequações em termos de estradas, materiais, dentre outros, em respostas às demandas particulares de cada mercado consumidor (ANFAVEA, 2007a).

Para Consoni (2004), o processo de desconcentração das atividades em P&D tem ocorrido de maneira lenta, mantendo-se rígida a questão do controle e coordenação no exterior, principalmente sobre a fabricação de itens críticos, sistemas ou subsistemas, os quais foram transferidos a empresas definidas como parceiras globais de fornecimentos. A introdução do sistema global de fornecimentos buscou facilitar a gestão global dos recursos por parte das montadoras em prol da qualidade (Carmo e Hamacher, 1998). Para a formação de mão de obra especializada, o país conta com instituições de níveis técnicos e superiores bem estruturadas, as quais têm grande competência engenharia do produto (Consoni, 2004).

CONSIDERAÇÕES FINAIS

Uma diferença na trajetória dos clusters analisados está na participação estatal no desenvolvimento de cadeia produtiva aeroespacial. O cluster aeroespacial originou-se em torno do avião “Bandeirante” desenvolvido no CTA. Deste projeto, nasceu a Embraer, uma empresa voltada à construção aeronáutica e, posteriormente, à integração da tecnologia aeronáutica. A integração corresponde ao nível mais alto da sua cadeia tecnológica, a “Integração de Sistemas”. Apenas quatro empresas integram jatos comerciais no mundo: Airbus, na Comunidade Europeia, Boeing, nos EUA, Bombardier, no Canadá e Embraer, no Brasil. Todas elas são firmas internacionais, assim como o seu mercado.

No caso da Embraer, as empresas internacionais de grande porte que se organizam como parceiras de risco

nos negócios estão no segundo nível e são chamadas de “prime-contractors”. O terceiro nível é formado por empresas fornecedoras de itens críticos às empresas do segundo e são estrangeiras. As demais empresas, dentre elas as nacionais, atuam no fornecimento de produtos, processos e serviços de menor intensidade tecnológica à Embraer ou suas parceiras, compondo o quarto nível da cadeia produtiva (Furtado, 2006).

Segundo Gomes et al. (2005), os relacionamentos entre empresas e centros de pesquisas e desenvolvimento (P&D) para esse setor poderiam ser mais intensos, uma vez que o processo estaria compreendido em um centro de pesquisas específico já estabelecido: o Comando-Geral de Tecnologia Aeroespacial (CTA) juntamente com sua escola de engenharia, o Instituto Tecnológico de Aeronáutica (ITA). Conforme observou Bartels (2007), as atividades de pesquisa e desenvolvimento relacionadas ao setor aeroespacial brasileiro enfraqueceram-se com o passar dos anos, em decorrência da falta de investimentos por parte do governo nas áreas de tecnologia. Esses investimentos foram sendo retomados gradualmente em dias atuais, porém em proporções menores e junto a instituições privadas, como o CECOMPI, FCMF e FUNCATE, em busca da aproximação de empresas, centros de P&D e universidades. O CTA, realiza, além de pesquisas, a homologação de aeronaves, certificações de qualidade e de mão de obra especializada.

O setor aeroespacial conta regionalmente com excelentes condições de infraestrutura, principalmente com relação à presença regional da Rodovia Presidente Dutra, ligando dois importantes polos econômicos nacionais: as cidades de São Paulo e Rio de Janeiro. Também estão presentes regionalmente escolas técnicas e universidades capacitadas, relacionadas ao desenvolvimento de mão de obra e inovação. Há, além dessas, atividades por parte de sua associação representante de classe (AIAB) em fomento de adensamento da cadeia produtiva e instituição de arranjo produtivo local (APL) para obtenção de maior capacidade produtiva e participações junto a mercados internacionais. Outras entidades também estão envolvidas na questão, como CECOMPI e FCMF (Bartels, 2007).

O setor automobilístico, com 80 anos de existência, vem se adaptando às condições instáveis da economia brasileira. Com foco na competitividade, constantemente foi afetada de forma negativa pelos períodos de crises nacionais, e ainda assim vem obtendo ótimos resultados, pois têm apresentado atualmente nível elevado de exportações e tendências de crescimento.



As grandes montadoras, primariamente estabelecidas na região do grande ABC Paulista, estado de São Paulo, deslocaram-se para outras regiões em busca de espaços físicos que suportassem a continuidade de seu crescimento e desenvolvimento de novas instalações. Dentre outros motivos, a fuga da pressão sindical e procura por mão de obra com salários mais baixos. Uma das localidades escolhidas foi o Vale do Paraíba Paulista.

A formação de cluster na região do Vale do Paraíba Paulista decorreu da instalação das indústrias General Motors, Volkswagen e Ford do Brasil, montadoras transnacionais automobilísticas de grande porte, nas cidades de São José dos Campos e de Taubaté. Juntamente com essas empresas, a instalação de outras empresas relacionadas à cadeia produtiva automobilística para fornecimentos de partes, peças e serviços logrou êxito na regionalização do cluster automobilístico do Vale do Paraíba Paulista, o qual se estenderia até o Vale do Paraíba Médio, região de Resende, Rio de Janeiro, às margens da Rodovia Presidente Dutra.

O governo procurava, com o estabelecimento das grandes montadoras multinacionais, o desenvolvimento da indústria nacional de autopeças voltada para os suprimentos produtivos.

Ao longo dos anos, a capacidade da indústria nacional de autopeças foi transferida às empresas estrangeiras em razão das parcerias globais de fornecimento de autopeças, centralizando a gestão, de maneira global, em suas matrizes. Desta forma, com a globalização de suas fornecedoras, as atividades nacionais ficaram limitadas à prestação de serviços operacionais, de manutenção e revenda de peças originais (ANFAVEA, 2007a).

Quanto às atividades de P&D, a ANFAVEA (2007a) citou o programa Pró-álcool, iniciado nos laboratórios do CTA em 1975, como um dos únicos a atingirem o reconhecimento mundial, o que deu origem ao desenvolvimento de motores movidos a álcool e bicombustíveis (“Flex”). Contudo, o conhecimento tecnologicamente mais sofisticado do produto automobilístico permanece no exterior, nos países originários das grandes montadoras (Consoni, 2004).

Alguns aspectos oferecem riscos ao setor automobilístico, principalmente à manutenção de sua competitividade, tais como: custos financeiros e tributários elevados, falta de pesquisa relacionada ao setor e deficiência de investimentos por parte do governo em infraestrutura rodoviária e portuária para

melhor e mais barato escoamento de produtos rumo ao exterior.

O conceito “cluster regional” para ambos os setores produtivos do Vale do Paraíba Paulista, aeroespacial e automobilístico, apesar da presença dos componentes descritos por Porter (2002b), é feita relativamente. No caso, as empresas de segundo e terceiro nível das cadeias produtivas estudadas possuem tão grande porte quanto as próprias montadoras de primeiro nível, formando também por complementaridades produtivas outros clusters em suas órbitas.

Apesar das distinções verificadas em ambos os clusters em termos de história e estratégia de adensamento da cadeia produtiva e inovativa, a despeito de terem conceitos de criação opostos, em ambos os casos não há nenhuma empresa brasileira fornecedora de sistemas ou subsistemas principais ou itens críticos. Na cadeia automobilística, com a produção de modelos mundiais, surgiram as fornecedoras e parceiras globais, o que implicou “rarefação” ao invés do adensamento da cadeia tecnológica do setor. No caso aeronáutico, ainda que se faça uma exceção à Eleb-Liebherr (50% do capital Embraer e 50% Liebherr), o sistema produtivo e o sistema de inovação aeronáutico brasileiro não se inseriram devidamente nos respectivos oligopólios mundiais produtivos e inovativos: motores e sistemas acessórios, aviônicos, sistemas específicos: APU (Auxiliary Power Unit), ar condicionado e materiais estruturais.

Dessa forma, duas abordagens aparentemente antípodas: a primeira delas caracterizada pelo início com indústrias nacionais desenvolvendo-se ao redor de montadoras (integradoras) estrangeiras, e outra com fornecedores estrangeiros agrupados ao redor de uma integradora nacional, produziram o mesmo resultado, ou seja, proporcionaram um sistema setorial produtivo e inovador tecnologicamente rarefeito, por exemplo, no qual o Conhecimento e o Capital Intelectual fiquem em mãos das respectivas matrizes. Essa concentração de domínio tecnológico não passou despercebida só ao povo comum, mas, também, aos membros distintos da “intelligentsia” nacional, fazendo com que esta desconsiderasse, mesmo sem compreender, a necessidade do “catch-up” tecnológico, ao confundir o “produzir” artefatos tecnológicos, contemplando todo o ciclo de vida de um produto, com a ação restrita de somente “fabricar”.

REFERÊNCIAS

ANFAVEA, 2007a, “Indústria Automobilística Brasileira 50 Anos”, Edição Comemorativa, Associação



Nacional dos Fabricantes de Veículos Automotores, São Paulo, Autodata.

ANFAVEA, 2007b, “Indústria Automobilística Brasileira 50.000.000 de Veículos Produzidos”, Edição Comemorativa, Associação Nacional dos Fabricantes de Veículos Automotores, São Paulo, Autodata.

Arcangelis, G., Ferri, G., Padoan, P. C., 2002, “Firms Clustering and SEE Export Performance. Lessons from the Italian Experience”, Departament of Economics, Rome, University of Rome La Sapienza, 26p, Available in: http://www.wiiw.ac.at/balkan/files/DeArcangelis+Ferri+Padoan.pdf. Access on Apr 9, 2010.

Bartels, W., 2007, “Workshop Feira de Le Bourget”, São José dos Campos, São Paulo, Associação das Indústrias Aeroespaciais do Brasil.

Bergman, E. M., Feser, E. J., 1999, “Industrial and Regional Clusters: Concepts and Comparative Applications”, West Virginia University, Morgantown, Regional Research Institute, 113p, Available in: http://www.rri.wvu.edu/WebBook/Bergman-Feser/contents.htm. Access on Apr 9, 2010.

Bernardes, R., 2000, “O arranjo Produtivo da EMBRAER na região de São José dos Campos”, Seminário Internacional: Arranjos Produtivos Locais e as novas políticas de desenvolvimento industrial e tecnológico, Rio de Janeiro, Instituto de Economia da Universidade Federal do Rio de Janeiro.

Campos, J. C., Krom, V., 2006, “A implantação da indústria automobilística em Taubaté e seus reflexos na cadeia produtiva industrial”, X Encontro Latino Americano de Iniciação Científica e VI Encontro Latino Americano de Pós-Graduação, Universidade do Vale do Paraíba, São José dos Campos, SP.

Carmo, L. F. R. S., Hamacher, S., 1998, “A evolução da cadeia de suprimentos da indústria automobilística no Brasil”, Departamento de Engenharia Industrial, Pontifícia Universidade Católica.

CHEVROLET. “Reportagem: GM atualmente é uma das principais empresas da Região do Vale do Paraíba”, Available in: http://www.clubedochevrolet.com.br/noticia/default.asp?id=167, Access on June 30, 2008.

Consoni, F. L., 2004, “Da tropicalização ao projeto de veículos: um estudo das competências em desenvolvimento de produtos nas montadoras de automóveis no Brasil”, 267f, Tese (Doutorado),

Universidade Estadual de Campinas, Instituto de Geociências, Pós-Graduação em Política Científica e Tecnológica, Campinas, SP.

Dosi, G., Nelson, R. R., Winter, S. G., 2000, “The nature and dynamics of organizational capabilities”, Oxford, Oxford University Press, ISBN: 0198296800.

Furtado, A. T., 2006, “Estudo da cadeia produtiva aeronáutica brasileira: relatório final”, Campinas, IG/DPCT/UNICAMP, 648 p.

Gomes, S. B. V. et al., 2005, “O desafio de apoio ao capital nacional na cadeia de produção de aviões no Brasil”, Revista do BNDES, Rio de Janeiro, Vol.12, No. 23, Jun., p. 119-134.

Hoffmann, W. A. M., Gregolin, J. A. R., Faria, L. I. L., 2006, “Desafios para o desenvolvimento regional: arranjo produtivo local de couro e calçados”, Revista Brasileira de Desenvolvimento Regional, Taubaté, Vol. 2, No. 3, p. 32-53, set-dez.

Lessa, S. N., 2001, “São José dos Campos: o planejamento e a construção do pólo regional do Vale do Paraíba”, Tese (Doutorado), Departamento de História do Instituto de Filosofia e Ciências Humanas da Universidade Estadual de Campinas, Available in: http://www.anpuhsp.org.br/downloads/CD%20XVII/ST%20II/Simone%20Narciso%20Lessa.pdf. Access on Apr 9, 2010.

List, F., 1909 [1841], “The National System of Political Economy”, London, Longmans, Green, and Co., Traduzido por Sampson S. Lloyd, Ed. J. Shield Nicholson, Library of Economics and Liberty, Available in: http://www.econlib.org/library/YPDBooks/List/lstNPE0.html. Access on Apr 9, 2010.

Lundvall, B. A., 2001, “Políticas de inovação na economia do aprendizado. Projeto produtividade local por amostragem setorial e sistemas de inovação no Brasil: novas políticas industriais e tecnológicas”, Revista Parcerias Estratégicas, Brasília, p. 200-218, Available in: http://ftp.unb.br/pub/unb/ipr/rel/parcerias/2001/2615.pdf. Access on Apr 9, 2010.

Malerba, F., 2002, “Sectorial systems of innovation and production”, Research Policy 31, Milan-Itally, CESPRI, Bocconi University, p. 247-264.

Porter, M., 2002a, “What is a cluster?”, Tucson, University of Arizona, 14 p.



Porter, M., 2002b, “Clusters of Innovation Initiative”, Wichita, Monitor Group.

Santos, I. C., Amato Neto, J., 2005, “Estratégias para criação da indústria aeroespacial brasileira”, Revista Brasileira de Gestão e Desenvolvimento Regional, Vol. 1, No. 2, mai./ago., p. 16-40.

Santos, R. F. et al., 2003, “Desempenho econômico recente do cluster aeronáutico da região de São José dos Campos”, Curso de Pós-Graduação em Engenharia Aeronáutica e Mecânica. Instituto Tecnológico de Aeronáutica, ITA, São José dos Campos.

Simões, J., 2006, “Sistema Paulista de Parques Tecnológicos”, Boletim eletrônico dedicado à inovação tecnológica [da] UNICAMP, Campinas, 2006, Available in: http://www.inovacao.unicamp.br/report/news-parquestecnologicos.shtml. Access on Apr 9, 2010.

Tachinardi, M. H., 2000, “Vantagens e defeitos do regime automotivo”, Gazeta Mercantil, Resenha Econômica N° 97, Relatório Especial nº 044/2000, Available in: http://www2.mre.gov.br/unir/webunir/RESENHAS/Rel00/ru0442000.html. Access on Apr 9, 2010.


Lúcia Helena de Oliveira*Department of Aerospace Science and

TechnologySão José dos Campos – Brazil

[email protected]

Antonio P. Del’Arco JuniorInstitute of Aeronautics and Space


Nestor Brandão NetoTechnological Innovation Center of

Department of Aerospace Science and Technology



Gestão sistêmica de projetos em uma instituição pública de pesquisa e desenvolvimentoResumo: O presente estudo descreve o processo de gestão de projetos de pesquisa e desenvolvimento (P&D) de uma instituição pública de pesquisa do setor aeroespacial, integrante do parque tecnológico e industrial do Vale do Paraíba Paulista, o Comando-Geral de Tecnologia Aeroespacial - CTA. A pesquisa exploratória conduzida visa identificar a aplicação de financiamento empregada pelo governo federal e FINEP, como também os instrumentos e as ferramentas disponíveis na instituição incorporando os planos, leis, diretrizes, normas e relatórios que permeiam o processo de gestão de projetos de P&D. Este estudo examinou as atividades de planejamento, acompanhamento e controle de casos reais de projetos. A partir das informações qualitativas e quantitativas coletadas, foram apresentadas as considerações e recomendações, de modo a melhorar a eficácia e a eficiência da gestão desses projetos.Palavras-chave: Gestão de projetos tecnológicos, Instituição pública de pesquisa, Planejamento, acompanhamento e controle de projetos.

Systemic management of projects in a public research and development institution Abstract: The present study describes the research and development (R & D) project management process in an aerospace sector public research institution, belonging to the São Paulo State Paraiba River Valley technological and industrial park, the General Command for Aerospace Technology (Comando - Geral de Tecnologia Aeroespacial – CTA). The exploratory research undertaken aimed to identify the application of federal government and FINEP funding, as well as the instruments and tools available to the institution, including its planning, its regulations, guidelines, standards and reports which pervade the R & D project management process. This study examined the planning, follow-up and monitoring activities associated with real case studies. From the qualitative and quantitative information collected, observations and recommendations were made in order to improve the efficient management of these activities.Keywords: Project management technology, Public research institution, Project planning, monitoring and control.

INTRODUÇÃO

Muito se discute sobre o papel das Instituições Públicas de Pesquisa (IPP) na sociedade brasileira. As IPP têm vivido momentos intensos de remodelagem dos seus processos organizacionais, advindos da grande necessidade de se adaptarem ao desenvolvimento tecnológico e às cobranças da sociedade, procurando atingir patamares superiores de eficiência, competitividade e inovação.

As atualizações da estrutura organizacional e de seus processos auxiliam a responder efetivamente aos desafios que a sociedade moderna as impõe. Além disso, as instituições necessitam do estabelecimento de políticas e estratégias que compatibilizam a condição atual com

suas visões estratégicas, visando à implementação de um elevado nível de sustentabilidade organizacional.

A melhoria do desempenho organizacional deve ser constantemente buscada nas instituições, pois é a essência do gerenciamento, considerada assim, elemento estratégico. Neste sentido, é fundamental a implementação de instrumentos gerenciais que auxiliem e promovam as competências organizacionais.

Os recursos financeiros aplicados na instituição são provenientes do orçamento público, de empresas de iniciativa privada e de agências de fomento, tais como as Fundações Estaduais de Amparo à Pesquisa (FAP) e a Financiadora de Estudos e Projetos (FINEP). Existe, também, o Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) e a Coordenação de


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DOI: 10.5028/jatm.2010.020183104


Oliveira, L.H., Del’Arco Junior, A.P., Brandão Neto, N.

É importante enfatizar também que o desenvolvimento socioeconômico da região do Vale do Paraíba e mesmo do país, é cada vez mais dependente da ciência e tecnologia, da habilidade de produzir conhecimentos e gerar resultados que possam ser utilizados pela sociedade, contribuindo efetivamente para o seu crescimento.

FUNDAMENTAÇÃO TEÓRICA

Conjuntura da Política de Ciência e Tecnologia

A política de Ciência e Tecnologia tem se tornado fator crítico para o futuro das instituições do setor, e em particular para a sociedade em geral. As mudanças requisitadas pela sociedade obrigam as organizações a criarem mecanismos para que suas respostas sejam aquelas que contribuam para a melhoria da qualidade de vida, buscando o desenvolvimento de produtos de alto valor agregado para a nação, em atendimento à missão para qual foram criadas.

De acordo com Weisz (2006), projetos de P&D são investimentos que se caracterizam pelo risco e pela longa maturação. O risco é inerente a qualquer atividade de pesquisa e desenvolvimento, pois não há certeza, a priori, quanto ao grau de sucesso do projeto. Sua outra particularidade é a longa maturação, pois somente após a conclusão, com sucesso, é que se decidirá pelo investimento industrial propriamente, com novos riscos de qualquer projeto: comerciais, políticos e econômicos, entre outros.

Denota-se de Mello (2000), que os investimentos em ciência e tecnologia cada vez mais necessitam de redefinições nos critérios de alocação de recursos financeiros e de financiamento de pesquisa, os quais têm impacto no modo de se fazer ciência e tecnologia.

Segundo Salles Filho (2005), atualmente uma instituição de pesquisa não é mais palco exclusivo dos cientistas e pesquisadores, existe um cenário mais amplo e competitivo, com incremento na participação de organizações privadas. Nos últimos 10 anos, o setor público vem promovendo políticas mais agressivas e consistentes, criando novas e diversificadas fontes de financiamento de P&D.

Gestão de Projetos Tecnológicos

A capacitação e correta aplicação dos recursos financeiros dependem de um gerenciamento de projetos eficaz e eficiente.

Segundo Keelling (2006), a administração de projetos tornou-se um poderoso instrumento de transformação

Aperfeiçoamento de Pessoal Civil de Nível Superior (CAPES), que têm por objetivo, entre outros, aplicar os recursos em bolsas de estudo e auxílio aos pesquisadores.

Neste trabalho são examinados os recursos provenientes do orçamento público federal e da agência de fomento FINEP, que subsidiam os projetos de P&D do Comando-Geral de Tecnologia Aeroespacial-CTA.

O objetivo do estudo é analisar a gestão sistêmica de projetos de P&D em uma instituição pública de pesquisa e desenvolvimento do setor aeroespacial, por meio de instrumentos e ferramentas gerenciais, tendo como base uma pesquisa exploratória feita no acervo de documentação técnica de projeto, visando contribuir para a melhoria da eficiência da gestão de projetos.

A pesquisa foi desenvolvida em três etapas:

• revisão teórica, realizada a partir de artigos impressos e eletrônicos, livros e revistas técnico-científicas, planos, diretrizes, normas e relatórios internos e externos à instituição que servem de subsídios para a gestão de projetos de P&D de alta tecnologia;

• análise do conteúdo dos relatórios de acompanhamento dos projetos e das ferramentas disponíveis para o planejamento, acompanhamento e controle de projetos de P&D, e

• estudo de caso documental de quatro projetos de P&D, que permitiu um exame detalhado do ambiente, visando responder ao objetivo da pesquisa e proporcionar ao trabalho uma abordagem principalmente qualitativa.

O presente estudo é relevante por demonstrar que o entendimento do processo de gestão de projetos de P&D na instituição, por meio da análise da sistemática que permeia o planejamento, acompanhamento e controle da gestão de projetos, permitiu realizar a verificação entre os preceitos da gestão de projetos tecnológicos e a realidade operacional e gerencial da Instituição.

Com a análise desses instrumentos e ferramentas pôde-se recomendar melhorias na eficiência, não só na alocação dos recursos financeiros destinados aos projetos de P&D, bem como na eficiência da gestão desses projetos.

É notória a integração da instituição pública de pesquisa com as universidades e o Parque Industrial de São José dos Campos. O aprimoramento na gestão dos projetos de elevado valor agregado trará reflexos positivos não só para a instituição, como também para as organizações que utilizam a tecnologia advinda dos projetos desenvolvidos na instituição.


Gestão sistêmica de projetos em uma instituição pública de pesquisa e desenvolvimento

e desenvolvimento dentro das organizações. Entre as características da gestão de projetos destacam-se a simplicidade e clareza de propósito e escopo, controle independente, facilidade de medição, flexibilidade de emprego, motivação e moral da equipe, sensibilidade ao estilo de administração e liderança, utilidade ao desenvolvimento individual, discrição, segurança e mobilidade.

Para um melhor gerenciamento de projetos numa instituição de pesquisa é necessária uma análise sistêmica relacionada com o ciclo de vida dos projetos, Fig. 1.

O PMBOK® (op. cit.) cita, também, que o gerenciamento de projetos é um empreendimento integrador, o que requer uma conexão entre as fases dos processos de Planejamento, Execução, Verificação e Ação.

O ciclo PDCA de Deming (1990) (Fig. 2) é uma ferramenta gerencial simples e poderosa e está no centro da filosofia de melhoria contínua. É um método que visa controlar e conseguir resultados eficazes e confiáveis nas atividades de gerenciamento de projetos.

Verificar

Agir

Planejar

Executar

Fonte: Adaptada pela autora baseada em Deming (1990)

Figura 2: Ciclo PDCA

Campos (1999) cita que o processo das fases do ciclo de vida de um projeto, sua inicialização, planejamento, execução, controle e encerramento, garante que a instituição não se engesse, dá autonomia e estimula o empreendedorismo.

Nessa mesma linha, Maximiano (2002) informa que o ciclo de vida é a sequência de fases, que vai do começo ao fim de um projeto, e que o entendimento desse ciclo permite a visão sistêmica do projeto, desde o início até a sua conclusão, facilitando o estudo e aplicação das técnicas de administração de projetos.

Gestão Sistêmica de Projetos

É essencial às atividades de projetos a capacitação em gerenciamento de projetos, com a aplicação de conhecimentos específicos, habilidades, ferramentas e técnicas.

De acordo com o PMBOK® (op. cit.), todas as fases do ciclo de vida de qualquer projeto estão associadas a nove áreas de conhecimento, em relação às quais é necessário estabelecer planos de gestão para maximizar as chances de o projeto ser concluído com sucesso. Trata-se do gerenciamento de integração, escopo, tempo, custos, qualidade, recursos humanos, comunicação, riscos e aquisições do projeto.

Além do entendimento dos ciclos de vida de projeto e do PDCA, é necessário que toda a equipe envolvida em projetos compreenda e utilize os conhecimentos e as habilidades técnicas requeridas, para que se possa gerenciá-los de maneira eficaz de pelo menos cinco áreas de especialização:

• conjunto de conhecimentos em gerenciamento de projetos: refere-se aos conhecimentos específicos em gestão de projetos;

• conhecimento, normas e regulamentos da área de aplicação: dizem respeito ao conjunto de procedimentos e práticas aceitas pela instituição;

• entendimento do ambiente do projeto: os gerentes devem considerar a conjuntura e os contextos cultural, social, político e organizacional;

• conhecimentos e habilidades de gerenciamento geral: incluem as atividades de apoio à administração, tais como: planejamento, gestão financeira, compras, contratos e tecnologia da informação, e

• habilidades interpessoais: referem-se às atividades de comunicação, liderança, negociação e gerenciamento de conflitos e resolução de problemas.

As áreas de especialização necessárias são apresentadas na Fig. 3.

Fonte: Adaptada pela autora baseada no PMBOK®, 2004

Figura 1: Ciclo de vida de projetos

Recursos

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Pro

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Tempo



Importância de Medidores de Desempenho para o Acompanhamento e Controle dos Projetos de P&D

Medição de desempenho pode ser compreendida como a técnica usada para quantificar a eficiência e a eficácia das atividades de negócio (NEELY ET AL.,1995, p. 80). A eficiência é demonstrada pela relação entre a utilização correta dos recursos sobre um determinado nível de satisfação. Por sua vez, a eficácia avalia o resultado de um processo onde a expectativa dos clientes, seja interna ou externa, são ou não atendidas.

Um sistema de medição de desempenho tem por objetivo a condução da organização à melhoria de suas atividades, pelo fornecimento de medidas alinhadas com o ambiente atual e com os objetivos estratégicos, no sentido de permitir o monitoramento do progresso de obtenção das metas traçadas.

O sistema de medição de desempenho requer a elaboração de diversos indicadores, que são dados numéricos, para medir e acompanhar a evolução das metas estabelecidas e que são trazidos, periodicamente, à atenção dos tomadores de decisão da organização.

De acordo com o Planejamento do Sistema de Medição do Desempenho da Fundação Nacional da Qualidade - FNQ (2002), o sistema de medição do desempenho é composto de três níveis, cada um com características próprias, o Estratégico, o Gerencial e o Operacional.

A Figura 4 apresenta a hierarquia do sistema de medição.

No nível estratégico, os indicadores são utilizados para avaliar os principais efeitos da estratégia nas partes interessadas e nas causas desses efeitos, refletindo os

objetivos e as ações que pertencem à organização como um todo, e não a um setor específico.

No nível gerencial, os indicadores são utilizados para verificar a contribuição dos setores e/ou dos macro-processos organizacionais em relação à estratégia e para avaliar se esses setores e/ou macro-processos buscam a melhoria contínua de forma equilibrada.

Já no nível operacional, os indicadores servem para avaliar se os processos ou rotinas individuais estão sujeitos à melhoria contínua e à busca da excelência.

Cabe ressaltar que, os indicadores estratégicos e gerenciais são resultantes de análises técnicas, sendo, portanto, fonte de informações efetivas para a tomada de decisão. Existem outras formas de classificação dos indicadores utilizadas pelas organizações (indicadores financeiros, de produtividade, de qualidade, e outras, dependendo do objetivo do negócio ou atividade), sendo que essa classificação é aplicada em geral nos níveis estratégico e gerencial.

Na metodologia do Balanced Scorecard (KAPLAN e NORTON: 1997) é recomendado identificar as principais ações ou fatores críticos de sucesso necessários para alcançar o objetivo. Desse grupo, é indispensável determinar quais são as ações mais relevantes, e estabelecer indicadores que vão servir como direcionador para o objetivo final.

Para a identificação das principais ações ou fatores críticos de sucesso é imprescindível a visualização da organização como um sistema, ou seja, um conjunto de atividades inter-relacionadas, que consomem recursos e produzem resultados que têm um valor para a organização e/ou para um grupo específico de interessados.

A atividade de monitoramento e a conseqüente avaliação de desempenho necessitam de instrumentos de coleta de

Conjunto de conhecimentos em gerenciamento de

projetos

Habilidadesinterpessoais

Conhecimentos ehabilidades degerenciamento

geral

Entendimento doambiente do

projeto

Conhecimento,normas e

regulamentos daárea de aplicação

Fonte: Adaptada pela autora baseada no PMBOK® ,2004

Figura 3: Áreas de especialização necessárias à equipe de projeto

Fonte: FNQ: Planejamento do Sistema de Medição do Desempenho, 2002

Figura 4: A hierarquia do sistema de medição

Sistema de Medição do Desempenho

Estratégico

Gerencial

Operacional

Variáveis de controleDados em geral

Alinhamento

Sistemas de Informações



informação e de cálculo de medidores que permitam a comparação entre valores efetivos e valores planejados, a avaliação dos desvios e o diagnóstico de pontos de melhoria.

Investimentos em Ciência e Tecnologia em Órgãos Governamentais

As Instituições de P&D requerem muito investimento, principalmente aquelas que envolvem alta tecnologia, como é o caso do setor aeroespacial. O principal órgão financiador desses centros no Brasil é o governo.

O governo federal aloca recursos financeiros às IPP tanto diretamente, por meio de rubricas específicas do orçamento público, quanto por meio de outros órgãos voltados ao fomento da ciência e tecnologia (FINEP, CNPq, CAPES), criadas para apoiar o desenvolvimento científico e tecnológico do país.

Dessa maneira, uma forma de ampliar os recursos financeiros disponíveis às atividades de ciência e tecnologia é a participação nos processos de investimentos dessas agências de fomento.

De acordo com Morais (2007), dada a instabilidade das fontes de recursos, a política dos “Fundos Setoriais” buscou ampliar as fontes de financiamento não-reembolsáveis para as atividades de Ciência, Tecnologia (C&T) por meio de vinculações de recursos no orçamento da União. O primeiro fundo setorial foi criado em 1997, mas implementado somente em 1999, e ganhou impulso em 2000/2001 com a aprovação pelo Congresso Nacional de 14 novos fundos.

As fontes de financiamento são essenciais para apoiar o desenvolvimento de projetos. Porém, para um gerenciamento eficaz, existe a necessidade de se adotar as ferramentas gerenciais apropriadas.

METODOLOGIA APLICADA

A abordagem metodológica utilizada é a pesquisa exploratória, pois, conforme descrito por Marconi e Lakatos (2007), Yin (2005) e Vergara (2000), esse tipo de pesquisa busca um entendimento geral, visando proporcionar maior familiaridade com o ambiente, fato ou fenômeno para a realização de um estudo.

O trabalho analisa e evidencia os aspectos gerenciais do planejamento, acompanhamento e controle de projetos de P&D do CTA, onde se busca estudar as ferramentas, disponibilizadas pelo Governo Federal, para executar o fluxo de recursos orçamentários que chegam à organização, bem como as ferramentas de planejamento e controle utilizadas dentro da instituição pública de pesquisa.

A pesquisa pode ser caracterizada como estudo de caso múltiplo aplicado no Comando-Geral de Tecnologia Aeroespacial – CTA, subordinado ao Comando da Aeronáutica e situado em São José dos Campos, São Paulo.

A opção por estudo de caso deve-se ao fato de que, segundo autores de metodologia científica, tais como Marconi e Lakatos (2004), Yin (op. cit.), Minayo (2007) e Vergara (op. cit.), essa metodologia caracteriza-se como um tipo de pesquisa, cujo objeto é uma unidade que se analisa profundamente. Visa o exame detalhado de um ambiente, de um simples sujeito ou de uma situação particular, proporcionando ao trabalho uma abordagem qualitativa.

A fundamentação teórica apresentada possibilita o entendimento necessário ao desenvolvimento do estudo e fornece o suporte adequado à análise dos instrumentos e ferramentas gerenciais dos projetos do CTA.

Foi realizada uma pesquisa no acervo de documentos de planejamento, acompanhamento e controle dos projetos de P&D existentes nos arquivos da Subdiretoria de Empreendimentos – SDE, analisando-se os diversos registros e documentos históricos que formalizaram a gestão dos projetos.

Fixou-se para a pesquisa documental o período de 1991 a 2007. A evolução do processo de gestão de projetos no CTA evidencia-se de 1991 a 2004. Foram considerados projetos da Instituição para a análise do presente estudo, correspondentes ao período de 2000 a 2007, com origem de recursos provenientes do orçamento público e da Financiadora de Estudos e Projetos (FINEP), agência subordinada ao Ministério da Ciência e Tecnologia.

A pesquisa deu subsídios necessários ao estudo proposto e embasou as análises e considerações apresentadas. Cabe ressaltar que houve a preocupação com o sigilo das informações dos projetos, e foram selecionados somente os que não comprometiam qualquer aspecto de proteção ao conhecimento institucional. A consulta à documentação foi autorizada pela instituição.

Foram escolhidos quatro projetos da instituição, o Perseu, o Apus, o Orion e o Fênix, para que houvesse a verificação do uso das ferramentas e instrumentos disponíveis na instituição para a gestão de projetos. Dentre os instrumentos de acompanhamento e controle de projetos disponíveis foram utilizados o Planejamento Preliminar de Projeto (PPP), o Programa de Trabalho Anual – PTA e a Ficha Informativa de Projeto – FIP, para proceder à análise dos projetos selecionados.

Foram tratados e analisados neste trabalho os indicadores de desempenho quanto ao prazo, meta e custo existentes



nos instrumentos e ferramentas de acompanhamento e controle dos projetos da instituição

Histórico da Instituição Estudada

O Comando-Geral de Tecnologia Aeroespacial tem como atribuição o gerenciamento e a consecução dos objetivos da Política Aeronáutica Nacional para os setores da Ciência, da Tecnologia e da Indústria e a contribuição na formulação e condução da Política Nacional de Desenvolvimento das Atividades Espaciais.

Ele tem como missão ampliar o conhecimento e desenvolver soluções científico-tecnológicas para fortalecer o Poder Aeroespacial, contribuindo para a soberania Nacional e para o progresso da sociedade brasileira por meio do ensino, pesquisa, desenvolvimento, inovação e serviços técnicos especializados, no Campo Aeroespacial.

O Processo de Gestão Orçamentária de Projetos no CTA

O financiamento das pesquisas no âmbito do Governo Federal é efetuado por meio do orçamento público da União, utilizando-se dos instrumentos legais do Plano Plurianual (PPA), da Lei de Diretrizes Orçamentárias (LDO) e da Lei Orçamentária Anual (LOA).

O PPA é o instrumento de planejamento do governo federal que apresenta as orientações básicas das ações do governo. Estende-se do início do segundo ano de um mandato presidencial ao final do primeiro exercício financeiro do mandato seguinte e define as principais metas econômicas, sociais e orçamentárias para as despesas de capital. Define, também, outras despesas decorrentes e as relativas aos programas de duração continuada. Esse instrumento estrutura-se sob a forma de Programas e Ações, que podem ser do tipo Projeto ou Atividade (BRASIL, 2007).

A LDO estabelece as metas e as prioridades do governo para o exercício financeiro subsequente, orienta a elaboração do orçamento federal, dispõe sobre alterações na legislação tributária e estabelece a política de aplicação orçamentária das agências financeiras de fomento. Após a aprovação da LDO, pelo Congresso Nacional, a Secretaria de Orçamento elabora a proposta orçamentária para o ano seguinte (BRASIL, 2007, op. cit.).

A LOA define as prioridades contidas no PPA e as metas que deverão ser atingidas no ano. Essa lei disciplina o orçamento para todas as ações do Governo Federal, estima as receitas e autoriza as despesas de acordo com a previsão de arrecadação (BRASIL, 2007, op. cit.).

No âmbito do Ministério da Defesa utiliza-se a Proposta Orçamentária (PO), documento de apresentação das necessidades orçamentárias de cada organização militar; a Proposta de Lei Orçamentária Anual (PLOA), documento que indica os recursos previstos nas diversas Ações e Programas de cada organização, e o Plano de Ação (PA), que tem por finalidade apresentar a distribuição dos créditos contemplados no Orçamento Geral da União, consolidando as ações programadas (Projetos, Atividades) para um determinado exercício.

A Figura 5 apresenta o esquema do processo de execução orçamentária do Ministério da Defesa e do Governo Federal.

Governo Federal

PPA

LDO

LOA

Ministério da Defesa

Comando da Aeronáutica

PO

PLOA PA

Figura 5: Processo de execução orçamentária governamental do Ministério da Defesa

Processos de Acompanhamento e ControleS Financeiro e Orçamentário dos Projetos de P&D do CTA

Na esfera da instituição de pesquisa analisada, o processo de planejamento, acompanhamento e controle dos projetos é realizado por meio de diversos planos: o Plano Estratégico de Pesquisa e Desenvolvimento (PEPD), o Plano Básico de Pesquisa e Desenvolvimento (PBPD) e o Programa de Trabalho Anual (PTA), além das ferramentas de acompanhamento e controle (relatórios), conforme esquematizado na Fig. 6.

Comando-Geral

PEPD PBPD

InformaçõesGerenciais

Físico-financeirade Projetos

de P&D

Relatórios

Organizações MilitaresSubordinadas

Informaçãofísico-financeira deProjetos de P&D

EX

EC

UÇ

ÃO

AC

OM

PAN

HA

ME

NTO

E C

ON

TRO

LE

Figura 6: Processos de execução física e financeira no CTA

O Plano Estratégico de Pesquisa e Desenvolvimento é um instrumento baseado em diretrizes superiores, preconizado



pelas metodologias de planejamento institucional. Sua finalidade é estabelecer a orientação estratégica do Comando-Geral de Tecnologia Aeroespacial para um horizonte temporal.

O Plano Básico de Pesquisa e Desenvolvimento (PBPD) é outro instrumento de planejamento, em nível gerencial, que contempla as orientações definidas pelo PEPD. Esse Plano apresenta os projetos e as atividades de interesse da Aeronáutica.

O Programa de Trabalho Anual (PTA) é um documento voltado para os aspectos físicos e financeiros essenciais do projeto. É a base para a gestão da carteira de projetos do CTA.

A gestão desses projetos é baseada em normas do CTA, que têm por finalidade estabelecer procedimentos para o processo de acompanhamento e controle dos projetos desenvolvidos na Instituição.

Com base nas orientações estabelecidas nas NCTA são coletadas informações gerenciais, analisadas e tratadas com a finalidade de acompanhar a execução do portfólio de projetos de P&D.

O ponto de partida do projeto é o Planejamento Preliminar de Projeto (PPP), documento que contém os aspectos essenciais para subsidiar a análise e a decisão para a sua execução, com vistas à aprovação.

Após a aprovação e a previsão de recursos financeiros serem asseguradas no PPA, ou em agências de fomento, esse projeto passa a fazer parte do portfólio de projetos e inserido no Programa de Trabalho Anual da organização executora.

O acompanhamento e controle do projeto são realizados por meio da Ficha Informativa de Projeto (FIP), que é um relatório gerencial de acompanhamento físico-financeiro de projetos, elaborado pelo gerente de cada projeto, com a finalidade de prestar informações relevantes, que serão utilizadas para a tomada de decisões. As informações apresentadas nessa ficha, acerca dos desempenhos físico e financeiro do projeto são tratadas e analisadas, gerando indicadores de produtividade e qualidade que auxiliarão a compreensão da evolução do projeto e permitirão possíveis ações corretivas que se fizerem necessárias.

O Guia do PMBOK® (2004) analisa os principais conceitos e técnicas utilizados na administração de um projeto, e conceitua que o seu ciclo de vida define as fases que conectam o início ao final do projeto.

Todo o sistema de planejamento, acompanhamento e controle de projetos de P&D está inter-relacionado, e é desenvolvido de acordo com o ciclo de vida do projeto.

Conforme descrito na fundamentação teórica, o gerenciamento de projetos requer uma conexão entre as fases de planejamento, execução, verificação e ação (ciclo PDCA). Observa-se que na instituição, os processos de execução física e financeira, bem como as NCTA, incorporam o entendimento proposto no PMBOK® (op. cit.), e, possibilitam um correto encadeamento do ciclo de vida de projeto.

O PMBOK® (op. cit.) enfatiza também a necessidade da equipe envolvida no projeto conhecer as normas e as diretrizes das instituição. As NCTA de projetos sintetizam os preceitos, os procedimentos e as práticas adotadas no CTA.

A Figura 7 apresenta a correspondência entre as fases do ciclo de vida, os processos e normas do CTA.

Rec

urso

s

Abe

rtura

Par

alis

ação

Enc

erra

men

to

Desenvolvimento(Execução)

TempoPROCESSOS

NORMAS

Inicialização, Planejamento, Execução, Controle e Encerramento (Ciclo PDCA)

NCTA 0003, NCTA 0005, NCTA 0007, NCTA 0008

Con

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ão(R

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jeto

)

Des

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(Tes

tes)

Pro

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o

Impl

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Fonte: Programa de Trabalho Anual do CTA - ICA 19-45/2007

Figura 7: Correspondência entre as fases do ciclo de vida de projeto, diretriz, normas e processos.

ESTUDO DE CASO

Análise dos Projetos Selecionados

Os projetos selecionados foram analisados de acordo com o descrito no processo de planejamento, acompanhamento e controle de projetos de P&D do CTA.

A análise foi embasada em informações contidas nos documentos selecionados para o estudo, o PPP, o PTA e a FIP do referido projeto. O Plano Básico de Pesquisa e Desenvolvimento, como documento de direção, somente foi considerado como uma ferramenta de consulta, não sofrendo nenhuma análise de conteúdo.

Os recursos financeiros que suportaram a execução dos projetos foram provenientes do orçamento público e da FINEP, agência subordinada ao Ministério da Ciência e Tecnologia.

Em virtude da classificação de sigilo dos projetos, estes puderam ser analisados, porém seus dados não podem ser divulgados na sua totalidade.



Análise do Projeto PERSEU

Trata-se de um projeto enquadrado como de “Desenvolvimento – Especial”, iniciado em fevereiro de 2000. Sua documentação foi elaborada de acordo com o preconizado nas normas técnicas em vigor, e o seu Termo de Abertura foi datado de julho de 2001.

O projeto estava previsto no PBPD triênio 2001 – 2003, tendo como origem de recursos financeiros o orçamento público federal. Foi apresentado o Relatório de Encerramento de Projeto de acordo com o previsto nas normas em vigor.

A seguir é apresentado um resumo da análise documental desse projeto, relativo ao seu objetivo inicial.

Prazo de Duração do Projeto

Em 1999, constava no Planejamento Preliminar um cronograma de execução do projeto de vinte e sete meses. Ao ser iniciado, em 2000, esse prazo foi ampliado em três meses. Durante o desenvolvimento do projeto houve um acréscimo de vinte e cinco meses no cronograma previsto inicialmente.

A Figura 8 mostra o prazo de duração do projeto.

• Os bolsistas e colaboradores externos necessitavam de treinamento específico, comprometendo ainda mais o cronograma de execução.

Recursos Financeiros:

• a alocação dos recursos ocorreu sempre com atraso, tornando inviável a manutenção do cronograma previsto.

Equipamentos e Componentes:

• a alocação tardia dos recursos financeiros impossibilitou ou atrasou a aquisição de equipamentos e componentes nacionais e importados, inviabilizando o cumprimento das metas previstas, postergando a data de término do projeto.

Meta do Projeto

Na análise da execução do projeto observou-se a variação do percentual de atingimento das metas realizadas em relação as previstas, conforme Fig. 9.

20041ª Versão FIP Término Projeto

1999Planejado

27 meses

30 meses

52 meses

Previsão de Duração do Projeto PERSEU

2000

Figura 8: Prazo de duração do projeto PERSEU

As principais razões da dilatação do prazo do cronograma de execução identificadas nas Fichas Informativas foram:

Recursos Humanos:

• problema verificado desde o início do projeto, parcialmente resolvido com a vinculação de bolsistas do programa Rhae – CNPQ. Era prevista a inclusão de técnicos e pesquisadores ao projeto, porém, isso não se concretizou.

Depreende-se desta análise que, apesar dos fatores adversos que afetaram o cronograma inicial de execução física do projeto, o indicador de produtividade medido pela Equação 1, onde P1 mostra o desempenho de execução, é adequado.

Metas realizadas no períodoMetas previstas para o exercício

P1 = (1)

Para se ter uma correta avaliação do desempenho da execução do projeto é preciso levar em consideração, também, o indicador de produtividade P2, medido pela Equação 2:

Figura 9: Relação entre o percentual de meta prevista e reali-zada do projeto PERSEU

2000 2001

2002 2003

2004

32 65 80 100 100

28

62 79 88 100

Relação entre o percentual de meta prevista e realizada do Projeto PERSEU

Meta Prevista Meta Realizada



Prazo previsto inicialmentePrazo reprogramado

P2 = (2)

Analisando-se conjuntamente as Equações 1 e 2, obtêm-se os parâmetros apropriados para a tomada de decisão em relação à viabilidade de continuidade do projeto.

Em 2002, o gerente do projeto verificou a necessidade de ampliar o prazo inicial de trinta para quarenta e dois meses. No ano de 2003 este prazo foi novamente postergado passando para quarenta e seis meses. Finalmente, em junho de 2004 o projeto foi considerado concluído perfazendo cinquenta e dois meses de duração.

As principais razões para a expansão do prazo foram a falta de recursos humanos especializados ao projeto, o atraso na aquisição de equipamentos e componentes nacionais e importados advindos da demora da alocação de recursos financeiros.

A Figura 10 e a Figura 11 demonstram a evolução dos indicadores P1 e P2.

Custo Previsto e Crédito Alocado

O custo total previsto do projeto, conforme indicado no Termo de Abertura, era de R$ 1.082.540,00. Ao se analisar o Programa de Trabalho Anual observou-se que a alocação prevista para os três exercícios financeiros foi realizada, conforme atestam as informações das Fichas Informativas de Projeto de 2000 a 2003, com um valor adicional de R$ 56.984,00, não previsto quando do Planejamento Preliminar do projeto.

Durante a execução, os recursos alocados em termos percentuais foram próximos aos previstos. Em 2000, a alocação de recursos financeiros foi 11% menor que a prevista, porém nos anos subseqüentes superou a previsão de 100%, conforme observado em 2002 e 2003.

A Tabela 1 mostra os créditos previstos no PTA e alocados na FIP, bem como o percentual de alocação de recursos financeiros.

2000 2001

2002 2003

2004

32 %

65 % 80 % 100 %

100 %

28 %

62 % 79 % 88 % 100 %

Evolução do Indicador P1 do Projeto PERSEU

Meta Prevista Meta Realizada

Figura 10: Evolução do indicador P1 - meta prevista x meta realizada do projeto PERSEU

2000 2001

2002 2003

2004

30 meses 30

meses 30 meses 30

meses 30 meses

30 meses 30

meses

42 meses

46 meses

52 meses

Evolução do Indicador P2 do Projeto PERSEU

Prazo Previsto Prazo Projetado

Figura 11: Evolução do indicador P2 – prazo previsto x prazo projetado do projeto PERSEU

A Figura 12 apresenta a relação entre o crédito previsto no PTA e os créditos alocados na FIP.

2000 2001

2002 2003

2004

391.240 431.300 260.000

48.600 0

348.128 426.033

270.091

56.984

0

Relação entre o crédito previsto e o crédito alocadodo Projeto PERSEU

Crédito Previsto PTA (R$) Crédito Alocado FIP (R$)

Figura 12: Relação entre o crédito previsto (PTA) e crédito alocado (FIP) do projeto PERSEU

Tabela 1: Créditos previstos no PTA e alocados na FIP

Ano Crédito Previsto PTA (R$)

Crédito Alocado FIP (R$) %

2000 391.240 348.128 89

2001 431.300 426.033 99

2002 260.000 270.091 104

2003 48.600 56.948 117

2004 0 0 0

Total 1.131.140 1.101.236 98



Verifica-se que apesar da prorrogação do prazo de conclusão, não houve a necessidade de créditos adicionais ao projeto. Apenas em 2003 a alocação de R$ 56.984,00, que representou um recurso extra, da ordem de 5,26%.

Embora, os recursos alocados estejam de acordo com os previstos no Programa de Trabalho, deve-se enfatizar que os projetos tinham alocação de recursos normalmente com atrasos de três meses.

Foi verificado que em 2000, quando do início do projeto, estes recursos foram alocados somente no terceiro trimestre, em 2002, no mês de maio. No exercício de 2003, a alocação de 39% dos recursos ocorreu nos meses de julho e agosto e somente em setembro o restante dos 61% previstos foram alocados ao projeto.

Crédito Alocado e Recurso Aplicado

A análise das Fichas Informativas evidencia a alocação e a aplicação dos recursos financeiros ao longo da duração do projeto, bem como os índices de aplicação desses recursos, conforme apresentados na Tabela 2.

A seguir, a Fig. 13 mostra a relação entre o crédito alocado e o recurso aplicado no projeto.

Analisando-se os valores da Tabela 2 verifica-se, pelos percentuais apresentados, que houve uma efetiva aplicação dos recursos.

No serviço público, a Lei de Licitação nº 8.666, de 21 de junho de 1993, impõe regras específicas para a aquisição de bens e serviços. Esse aspecto normalmente provoca atrasos ou anulações das aquisições de itens necessários ao desenvolvimento do projeto.

Vale ressaltar que o exercício fiscal brasileiro encerra-se obrigatoriamente em trinta e um de dezembro e que todos os processos de aquisição de bens e serviços devem ser finalizados dentro do próprio exercício.

2000 2001

2002 2003

2004

348.128 426.033

270.091 56.984

0

348.127 378.057

270.064

56.984 0

Relação entre o Crédito Alocado e o Recurso Aplicadodo Projeto PERSEU

Crédito Alocado Recurso Aplicado

Figura 13: Relação entre o crédito alocado e o recurso aplicado do projeto PERSEU

Resultados Advindos do Desenvolvimento do projeto PERSEU

Esse projeto teve como fator motivador de desenvolvimento a necessidade estratégica brasileira de produzir equipamentos para uso militar, que tem o seu acesso restrito por políticas de defesa de países desenvolvidos.

Durante sua execução, entre outras competências, pôde ser criada uma estrutura laboratorial que incorporou tecnologias avançadas na área de eletrônica, de fotônica e de usinagem fina. Também possibilitou a capacitação profissional em diversas áreas de pesquisa, desenvolvimento e aplicação da tecnologia obtida, tais como ensaios de prototipação e eletrônica, entre outros.

O projeto serviu de base para a capacitação de três alunos de graduação, quatro de mestrado e um de doutorado.

Análise do Projeto APUS

Iniciado em fevereiro de 2001, o projeto APUS foi enquadrado em Adequação da Infraestrutura – Instalação de P&D. Sua documentação foi elaborada de acordo com o preconizado nas normas técnicas em vigor, tendo recursos financeiros assegurados para os dois exercícios previstos para a sua conclusão. Estava previsto no PBPD triênio 2001 – 2003, com origem de recursos financeiros do orçamento público federal.

Seu objetivo era o de implantar uma infraestrutura e meios para o estudo e desenvolvimento de aplicações tecnológicas, na forma de um laboratório para multiusuários, compreendendo as instalações e equipamentos, a equipe de operação e manutenção e a equipe de apoio científico aos grupos de usuários, dependendo diretamente da conclusão

Tabela 2: Crédito alocado e recurso aplicado na FIP do projeto PERSEU

Ano Custo Alocado FIP

Recurso Aplicado FIP %

2000 348.128 348.127 1002001 426.033 378.057 892002 270.091 270.064 1002003 56.984 56.984 1002004 0 0 0Total 1.101.236 1.053.232 96



de outro projeto, denominado projeto CYGNUS, para que seu objetivo fosse alcançado.

Sem alterar a essência do objetivo inicial, posteriormente foram incorporadas outras aplicações ao projeto, ampliando as suas potencialidades e fazendo com que deixasse, dessa forma, de depender única e exclusivamente da conclusão do projeto CYGNUS, o que comprometeria integralmente a finalização do projeto APUS.

Apresenta-se, a seguir, um resumo da análise documental desse projeto.


O projeto sofreu vários replanejamentos da sua programação inicial. Em dezembro de 2000 constava no Planejamento Preliminar um cronograma de execução de vinte e quatro meses.

Em 2002, houve o primeiro replanejamento, prorrogando o prazo de término em vinte meses. Esse fato ocorreu por que o projeto APUS dependia da conclusão do projeto CYGNUS.

Nesse mesmo ano foi novamente alterada, em mais doze meses, a data de término prevista, a fim de compatibilizar com a nova previsão de conclusão do CYGNUS. Esse prazo provocou não só um novo cronograma de execução, mas, também, adicionou recursos ao projeto APUS.

O novo cronograma alterou a data de término por mais doze meses, para dezembro de 2006. Essa data, com a paralisação do projeto CYGNUS, gerou uma revisão crítica no projeto APUS, acarretando, em 2007, uma alteração por mais doze meses. Finalmente, em 2008, foram necessários mais onze meses para ser concluído, perfazendo assim noventa e um meses de execução.

A Figura 14 mostra o prazo de duração do projeto do projeto APUS.

Após a análise das Fichas Informativas do Projeto APUS, em relação ao motivo da dilatação do prazo do cronograma de execução, verificou-se que as principais razões foram as elencadas a seguir:

• dependência da conclusão de outro projeto: problema verificado de 2002 até 2005, quando o projeto CYGNUS foi paralisado;

• constantes adequações do cronograma do projeto estudado: em 2002 foi necessário compatibilizar o cronograma desse projeto com o do CYGNUS. Nova programação e definição de metas ocorreram em 2004, ainda por falta de conclusão do projeto. Em 2005 houve a última revisão crítica do projeto, resultante da necessidade de adequá-lo à paralisação do projeto do qual dependia;

• recursos financeiros: a alocação dos recursos ocorreu em sua totalidade nos anos de 2001, 2002, 2004 e 2005, porém sempre tardiamente ou em elemento de despesa que impossibilitava a aquisição de equipamentos e componentes. Em 2003 não houve alocação de recursos ao projeto; nos anos 2006 e 2007 o projeto recebeu, respectivamente, 78% e 80% dos recursos financeiros solicitados;

• equipamentos e componentes: a alocação tardia dos recursos financeiros atrasou a aquisição de equipamentos e componentes nacionais e importados. Esse fato foi observado ao longo dos anos de execução do projeto, inviabilizando o cumprimento das metas previstas e postergando a data de término, e

• outras funções assumidas além de gerente de projeto: novas funções assumidas pelo gerente, além da gerência do projeto, atrapalharam o andamento do cronograma previsto.

Meta do Projeto

Analisando-se a execução do projeto, a variação do percentual de atingimento das metas realizadas em relação às previstas pode ser salientada conforme Fig. 15.

Apesar dos fatores que afetaram o cronograma inicial de execução física do projeto, o indicador de produtividade P1, medido pela Equação 1, mostra um desempenho de execução próximo de 85%, nos períodos de 2003 a 2005. Nos demais anos esse percentual aproximou-se de 100%.

A Figura 16 mostra a evolução do indicador P1.

24 meses

24 meses

91 meses

Previsão de Duração do Projeto APUS

2000Planejado

20011ª Versão FIP

2008Término Projeto

Figura 14: Prazo de duração do projeto APUS



Considerando-se o indicador de produtividade P2, o Projeto APUS apresentou a seguinte evolução (Fig. 17):

Analisando-se conjuntamente as Equações 1 e 2, observa-se que as metas foram realizadas conforme o planejado. Entretanto, o índice P2 mostra que para o atingimento dessas metas houve uma continuada alteração do prazo projetado.

As principais razões que fizeram o prazo de término do projeto ser expandido foram a sua dependência em relação à conclusão do projeto CYGNUS, revisões no cronograma do projeto, atraso na aquisição de equipamentos e componentes nacionais e importados e a demora da alocação de recursos financeiros.


O Termo de Abertura do projeto indicava que seu custo total previsto era de R$ 396.000,00 (US$ 158,400.00), conforme o planejamento preliminar do projeto. A análise das Fichas Informativas de Projeto mostrou que a alocação prevista para os exercícios financeiros de 2001 e 2002 foi realizada conforme o Programa de Trabalho Anual.

A FIP indica que em 2002 houve um incremento de 25% no custo previsto, pelo fato de o projeto do qual era dependente não ter sido concluído. Em 2005, uma nova proposição de alteração do seu escopo, culminada com a paralisação do projeto do qual dependia, acrescentou novas metas e custos adicionais de R$ 860.000,00.

A Tabela 3 exibe a previsão de créditos no PTA e os créditos alocados, bem como o percentual de alocação de recursos financeiros:

2001 2002

2003 2004

2005 2006

2007 2008

35 70

88 88 88 88 100 100

30

70 74 75 76 88 98 100

Relação entre o percentual de meta prevista e realizada do Projeto APUS

% Meta Prevista % Meta Realizada

Figura 15: Relação entre o percentual de meta prevista e reali-zada do projeto APUS

2001 2002 2003 2004 2005 2006 2007 2008

35

70

88 88 88 88

100 100

30

70 74 75 76 88

98 100

Evolução do Indicador P1 do Projeto APUS


Figura 16: Evolução do indicador P1 - meta prevista x meta realizada do projeto APUS

2001 2002 2003 2005 2004 2006 2007 2008

24 24 24 24 24 24 24 24 24

44

56 68 68 68

80

91

Evolução do Indicador P2 do Projeto APUS

Prazo Previsto em meses Prazo Projetado em meses

Figura 17: Evolução do indicador P2 – prazo previsto x prazo projetado do projeto APUS

A análise da Fig. 17 mostra o crescimento acentuado do indicador P2, em comparação ao cronograma inicial.

Tabela 3: Crédito previsto no PTA e alocado na FIP do projeto APUS



2001 162.000 162.000 100

2002 234.000 234.000 100

2003 0 0 0

2004 180.000 180.000 100

2005 140.000 140.000 100

2006 475.200 372.654 78

2007 395.200 317.427 80

2008 0 0 0

Total 1.586.400 1.406.081 89



Analisando-se os valores da Tabela 4, por meio dos percentuais apresentados, verifica-se que houve uma efetiva aplicação dos recursos.


2001 2002

2003 2004

2005 2006

2007 2008

162.000 234.000

0 180.000 140.000

475.200 395.200

0

162.000 234.000

0

180.000 140.000

372.654

317.427

0

Relação entre o crédito previsto e o crédito alocadodo Projeto APUS


Figura 18: Relação entre o crédito previsto (PTA) e o crédito alocado (FIP) do projeto APUS

2001 2002 2003 2004 2005

2006 2007

2008

162.000 234.000

0 180.000 140.000

372.654 317.427

0

143.818 234.000

0

180.000 138.780

370.053 299.288

0

Relação entre o Crédito Alocado e o Recurso Aplicadodo Projeto APUS

Crédito Alocado Recurso Aplicado

Figura 19: Relação entre o crédito alocado e o recurso aplicado do projeto APUS

A Figura 18 apresenta a relação entre o previsto no PTA e o alocado na FIP do projeto.

O aumento do prazo de conclusão de 71 meses a mais, do que a previsão inicial, representou um crescimento de, aproximadamente, 301% no custo do projeto.

Documentos apontam que em termos percentuais, os recursos foram alocados em sua totalidade, porém com atraso de três meses. Foi verificado que em 2003 não houve alocação de recursos, e também que em 2006 e 2007 houve uma redução de 22% e 20%, respectivamente, em relação à data prevista.


A Tabela 4 apresenta o índice de aplicação dos recursos financeiros, determinado a partir dos valores alocados e aplicados, evidenciados nas Fichas Informativas de Projeto.

Resultados Advindos do Desenvolvimento do projeto APUS

A ampliação e a manutenção da infraestrutura são vitais para a continuidade da pesquisa e desenvolvimento em um centro de pesquisa. Esse projeto propiciou a capacitação para a pesquisa básica e aplicada em novas aplicações tecnológicas de interesse do setor aeroespacial, além da possibilidade de prestação de serviços à comunidade científica e de suprir demandas de indústrias e outras instituições do país.

Como resultado indireto, esse laboratório passa a ser um importante centro de treinamento, formação e especialização de profissionais para o setor aeroespacial, de defesa, eletrônica, engenharia de materiais, química, bioquímica, física nuclear aplicada e tecnologia nuclear em geral. Durante a sua execução foi desenvolvida, nesse laboratório, uma pesquisa ao nível de mestrado.

Análise do Projeto ORION

Projeto enquadrado como Capacitação – Pesquisa, teve o seu início em março de 2004, constante do PBPD 2005-2008. A documentação desse projeto foi elaborada de acordo com o estabelecido nas normas técnicas em vigor, com exceção de não possuir o Termo de Abertura, previsto na NCTA 0005:1997. Entretanto, apresentou o Relatório de Encerramento de Projeto de acordo com o previsto.

O projeto ORION foi dividido em duas fases, a primeira finalizada em junho de 2004 e a segunda fase iniciando-se no terceiro trimestre de 2005. Teve como origem de

Tabela 4: Crédito alocado e recurso aplicado na FIP do projeto APUS

Ano Crédito Alocado (R$)

Recurso Aplicado (R$) %

2001 162.000 143.818 892002 234.000 234.000 1002003 0 0 02004 180.000 180.000 1002005 140.000 138.780 992006 372.654 370.053 992007 317.427 299.288 942008 0 0 0Total 1.406.081 1.365.939 97



recursos financeiros o orçamento público federal.Um resumo da análise documental desse projeto é apresentado a seguir.


O cronograma inicial previa um horizonte de execução de quarenta e oito meses para alcançar seu objetivo. Foi iniciado em março de 2004, entretanto, no início de 2005 houve a necessidade de dividi-lo em duas fases. No segundo trimestre de 2005 foi concluída a primeira fase, iniciando-se, em seguida, a segunda. Essas fases fizeram com que houvesse um replanejamento, alterando o prazo de término do projeto ORION para trinta e três meses (Fig.20).

Analisando-se o indicador P2 observa-se que o prazo projetado possibilitou que a execução do projeto fosse realizada em um prazo menor, do que o previsto inicialmente, de quatro anos.

Figura 20: Prazo de duração do projeto ORION

2004 2004 2006

48 meses

48 meses

33 meses

Previsão de duração do Projeto ORION

Planejado 1ª Versão FIP Término Projeto

Foi observado, nos documentos do projeto, que a necessidade de decompô-lo em fases não fez o seu prazo de duração ser dilatado, ao contrário, o que ocorreu foi um decréscimo em quinze meses em relação ao cronograma inicial.

Apesar do decréscimo do prazo de conclusão do projeto foi identificado, em suas Fichas Informativas, que o processo de aquisição de materiais e serviços também foi um fator causador de dificuldades, ocasionando atrasos e cancelamentos de alguns desses itens. Entretanto, pode-se verificar que o gerente soube contornar os problemas a contento, de modo a adequar o cronograma sem dilatar o prazo inicialmente previsto.

Meta do Projeto

A análise do desempenho físico do projeto ORION mostra variação, em termos percentuais, no atingimento das metas previstas, em relação às realizadas, mostradas na Fig. 21.

Na Figura 21 observa-se que somente em 2004 houve uma diminuição em 5% das metas pretendidas, nos demais anos esse percentual foi de 100%. A Figura 22 mostra a evolução do indicador P1

2004

2005

2006

30 % 60 % 100 %

25 % 60 % 100 %

Relação entre o percentual de meta prevista e realizadado Projeto ORION


Figura 21: Relação entre o percentual de meta prevista e reali-zada do projeto ORION

2004

2005

2006

30 % 60 %

100 %

25 % 60 %

100 %

Evolução do Indicador P1 do Projeto ORION


Figura 22: Evolução do indicador P1 – meta prevista x meta realizada do projeto ORION

2004

2005

2006

48 meses

48 meses

48 meses

48 meses

33 meses 32

meses

Evolução do Indicador P2 do Projeto ORION

Prazo Previsto Prazo Projetado

Figura 23: Evolução do indicador P2 – prazo previsto x prazo projetado do projeto ORION

Considerando-se o indicador de produtividade P2, o Projeto ORION apresentou a evolução mostrada na Fig. 23.




Ao se analisar o Programa de Trabalho Anual do projeto ORION verificou-se que a necessidade de recursos financeiros prevista para os três exercícios financeiros, era de R$ 570.000,00. Na Ficha Informativa do projeto é indicado um valor alocado de, aproximadamente, 5% a menos em relação ao previsto no PTA. Denota-se, também, que em 2006 esse percentual foi 52% inferior ao previsto.

A Tabela 5 mostra a distribuição dos créditos previstos no PTA e alocados na FIP nos anos de 2004 a 2006.

2004 2005

2006

305.000

155.000 110.000

305.000

146.240

63.215

Relação entre o crédito previsto e o crédito alocadodo Projeto ORION


Figura 24: Relação entre o crédito previsto (PTA) e crédito alocado (FIP) do projeto ORION

A Figura 24 apresenta a relação entre os créditos previstos no PTA e os créditos alocados na FIP.

2004 2005

2006

305.000

146.240

63.215

305.000

145.000

54.072

Relação entre o Crédito Alocado e o Recurso Aplicadodo Projeto ORION

Crédito Alocado (R$) Recurso Aplicado (R$)

Figura 25: Relação entre o crédito alocado e o recurso aplicado no projeto ORION



Ficou evidente, na análise das Fichas Informativas do projeto, que a alocação e a aplicação dos recursos financeiros ao longo da sua execução foram compatíveis, exceto em 2006, quando teve uma aplicação de recursos 15% menor em relação ao valor alocado. Esses fatos são evidenciados na Tabela 6.

Resultados Advindos do Desenvolvimento do projeto ORION

A tecnologia desenvolvida por esse projeto tem alto nível de aplicação civil e militar e, por conseguinte, gerou interesse de empresas nacionais em utilizá-la em novos produtos para uma variada aplicação, além de ampliar os conhecimentos técnicos, favorecendo futuros spin off e o registro de patentes. Apesar de não ser o objetivo do projeto, foi recuperada toda a infra-estrutura laboratorial para desenvolvimento de novos materiais no CTA.

Estudos e capacitação de pessoal foram possíveis durante a execução desse projeto, que teve, inclusive, o reconhecimento em congressos internacionais. Um trabalho de graduação e duas dissertações de mestrado para os cursos do ITA foram feitos durante o projeto. Seis trabalhos foram apresentados em simpósios e congressos internacionais e quatro artigos em congressos nacionais.

Tabela 5: Crédito previsto no PTA e alocado na FIP do projeto ORION



2004 305.000 305.000 100

2005 155.000 146.240 94

2006 110.000 63.215 57

Total 570.000 514.455 90

Tabela 6: Crédito alocado e recurso aplicado na FIP do projeto ORION

Ano Crédito Alocado (R$)

Recurso Aplicado (R$) %

2004 305.000 305.000 100

2005 146.240 145.000 99

2006 63.215 54.072 86

Total 514.455 504.072 98



Análise do Projeto FÊNIX

Na pesquisa documental verificou-se que o projeto FÊNIX iniciou-se em 2002, como uma linha de pesquisa, com a utilização de recursos do orçamento público federal. O seu início oficial no CTA como projeto, ocorreu em 2004, enquadrado como Capacitação – Pesquisa e previsto no PBPD quadriênio 2005 – 2008. A partir de 2004, o projeto recebeu também recursos financeiros da FINEP.

A sua documentação foi elaborada de acordo com o estabelecido nas normas técnicas em vigor, com exceção de não possuir o Termo de Abertura, previsto na NCTA 0005:1997.

Uma análise documental resumida desse projeto é apresentada a seguir.


O cronograma inicial do projeto FÊNIX tem uma duração prevista de noventa e seis meses, conforme descrito no seu PPP. Esse projeto encontra-se em execução, com prazo de término proposto para 2009.

Observa-se na Fig. 26, que seu prazo de duração é o mesmo desde o planejamento inicial. As Fichas Informativas mostram que apesar de existirem obstáculos ao atendimento do objetivo proposto, não houve necessidade de um replanejamento.

Meta do Projeto

A análise do desempenho físico do projeto FÊNIX aponta uma pequena variação em termos percentuais do atingimento das metas previstas em relação às realizadas, conforme mostra a Fig. 27, indicando o esforço gerencial para a realização das metas conforme o cronograma inicial.

2002 2004 2009

96 meses

96 meses

96 meses

Previsão de duração do Projeto FÊNIX

Planejado 1ª Versão FIP Término Projeto

Figura 26: Prazo de duração do projeto FÊNIX

Foi identificado, nas Fichas Informativas, que apesar de não haver alteração do prazo de conclusão, o processo de aquisição de materiais e serviços prejudicou o bom andamento do projeto. Também foi observado que a liberação de 53% dos recursos solicitados em 2006 não prejudicou o seu cronograma, devido aos recursos originados da FINEP. Dessa forma, o gerente soube contornar os problemas satisfatoriamente.

2004 2005

2006 2007

2008 2009

30 % 40 % 55 % 75 % 90 % 100 %

28 % 38 % 50 % 72 % 85 %

Relação entre o percentual de meta prevista e realizadado Projeto FÊNIX


Figura 27: Relação entre o percentual de meta prevista e reali-zada do projeto FÊNIX

Os percentuais de metas previstas e realizadas em 2008 foram obtidos por informações do gerente do projeto, devido ao fato de ainda não ter se encerrado o exercício.

Outro aspecto relevante no projeto FÊNIX é o alinhamento das metas com os prazos previstos, medidos pelos indicadores de produtividade P1 e P2. Como não houve replanejamento do projeto em relação ao prazo previsto, o indicador de produtividade P2 manteve-se em noventa e seis meses.


De acordo com o Planejamento Preliminar desse projeto, o custo previsto foi estimado em R$ 6.525.000,00. Como citado anteriormente, o projeto FÊNIX iniciou em 2002 como uma linha de pesquisa. Assim, não havia alocação de recursos diretamente ao projeto no PTA dos anos de 2002 e 2003, e foram utilizados recursos de outras atividades da divisão, conforme informado em suas respectivas FIP.

Nos anos 2004 e 2005 o projeto recebeu recursos 31% e 12%, respectivamente, acima do previsto no PTA. Em 2006 e 2007, diferentemente do ocorrido, houve uma diminuição de 47% e 19%, respectivamente, dos valores previstos.

Por iniciativa do gerente do projeto, firmando convênio com a FINEP, o projeto teve suporte considerável de recursos, da ordem de R$2.379.000,00, o que impediu



atrasos significativos no cronograma previsto. Esse valor representa percentualmente 6% a mais do que o total alocado pelo orçamento público federal.

A Tabela 7 mostra a distribuição dos créditos previstos no PTA e alocados na FIP, e os recursos previstos pelo convênio FINEP.

aplicados em sua totalidade, exceto em 2008, pois como se encontra em execução não é possível ainda a verificação real da aplicação dos recursos.

2002 2003 2004 2005 2006 2007 2008 2009

0,00 0,00 135.000 437.000 660.000

543.200 506.700 0

140.000 140.000 176.807 491.576 350.576

441.034 506.700 0

0,00 0,00

1.475.320

502.660 0,00 112.660 289.030

0,00

Relação entre o crédito previsto e o crédito alocadodo Projeto FÊNIX

Previsto PTA (R$) Alocado FIP (R$) Alocado pelo Convênio FINEP (R$)

Figura 28: Relação entre o crédito previsto (PTA) e crédito alocado (FIP) do projeto FÊNIX

2002 2003

2004 2005

2006 2007

2008 2009

140.000 140.000

176.807 491.576

350.576 441.034

506.700 0,00

140.000 140.000

176.807 491.576 350.576

441.034 142.682

0,00

0,00 0,00

1.475.320

502.660

0,00 112.660 289.030

0,00

Relação entre o Crédito Alocado e o Recurso Aplicadodo Projeto FÊNIX

Custo Alocado FIP (R$) Recurso Aplicado FIP (R$)

Figura 29: Relação entre o crédito alocado e o recurso aplicado no projeto FÊNIX

A Figura 28 apresenta a relação entre os créditos previstos no PTA e os créditos alocados na FIP.



Conforme demonstrado na Tabela 4, todos os recursos alocados durante os anos de execução do projeto foram

Resultados Advindos do Desenvolvimento do Projeto FÊNIX

A tecnologia obtida com o desenvolvimento do projeto é altamente estratégica para o Comando da Aeronáutica, em função de sua ampla utilização operacional. O projeto permite, além do aumento da capacidade laboratorial, o desenvolvimento de novas tecnologias.

Além disso, em função da constante atualização tecnológica exigida pelo setor aeroespacial, o domínio desses conhecimentos auxiliará na criação de novos produtos, que poderão ser transferidos para a indústria aeroespacial brasileira.

Tabela 7: Crédito previsto no PTA e alocado na FIP do projeto FÊNIX

AnoOrçamento Público Federal FINEP

Previsto PTA (R$)

Alocado FIP (R$) % Previsto no

Convênio

2002 0 140.000 # 0

2003 0 140.000 # 0

2004 135.000 176.807 131 1.475.320

2005 437.000 491.576 112 502.660

2006 660.000 350.576 53 0

2007 543.200 441.034 81 112.660

2008 506.700 506.700 100 289.030

2009 # # # #

Total 2.281.900 2.246.693 98 2.379.670

AnoOrçamentário FINEP

Crédito Alocado FIP

Recurso Aplicado FIP % Previsto no

Convênio(R$)2002 140.000 140.000 100 02003 140.000 140.000 100 02004 176.807 176.807 100 1.475.3202005 491.576 491.576 100 502.6602006 350.576 350.576 100 02007 441.034 441.034 100 112.6602008 506.700 142.682 28 289.0302009 - - - -Total 2.246.693 1.882.675 83 2.379.670

Tabela 8: Crédito alocado e recurso aplicado na FIP do projeto FÊNIX



Houve, nesse projeto, a preocupação com a preservação da propriedade intelectual do Centro, o que resultou no pedido de concessão de dez patentes de produtos e processos passíveis de transferência tecnológica.

Sob o aspecto de resultados intangíveis, muitos estudos e capacitação de pessoal estão sendo possíveis, durante a execução do projeto. Até o momento pode-se contabilizar trinta e sete trabalhos publicados em revistas, cento e trinta e seis em congressos nacionais e internacionais, oito teses de doutorado, estando quatro em andamento, cinco dissertações de mestrado, além de estudos de quatro pós-doutorados.

Síntese da análise do estudo de caso

Com o estudo de caso dos projetos analisados, pôde-se compreender o processo de gestão de projetos de P&D e constatar o quanto é importante o emprego das ferramentas e instrumentos específicos desse processo.

A execução dos projetos foi acompanhada por meio do Planejamento Preliminar de Projeto, do Programa de Trabalho Anual, da Ficha Informativa de Projetos e de relatórios emitidos segundo procedimentos próprios, com periodicidade estabelecida pelo CTA.

O estudo dos quatro projetos, no período de 2000 a 2007, permitiu observar como foi a dinâmica de gerenciamento adotada. A evolução, os problemas ocorridos, os desvios e as medidas corretivas geraram informações que possibilitaram a análise de indicadores de desempenho, tornando possível um acompanhamento e controle mais próximo da realidade gerencial, o que serve também para constatar a realidade institucional, onde se inserem os projetos de P&D do CTA.

Alguns indicadores que permitiram a medição da evolução dos prazos, das metas e dos custos, desses projetos são aqui referenciados.

Indicador de Prazo de duração

Foi verificado que os prazos inicialmente previstos para execução de cada projeto servem de referência para os planejamentos físicos e financeiros. Porém, estão intrinsecamente relacionados com vários fatores críticos que podem interferir no alcance do objetivo proposto. Dentre esses fatores foram relatados como entraves ao bom andamento nos quatro projetos analisados:

• recursos financeiros sempre alocados tardiamente, em função da legislação orçamentária em vigor, e

• atrasos na aquisição de equipamentos e componentes, devido ao processo licitatório federal, que revela-se moroso, devido à logística adotada.

Considerando-se que projeto, segundo o PMBOKÒ (op. cit.), é “um esforço temporário empreendido para criar um produto, serviço ou resultado exclusivo”, e levando-se em conta que o cliente espera receber o que foi combinado no tempo definido, é evidente a necessidade de acompanhamento e controle efetivos em relação ao prazo, para que sejam tomadas as medidas corretivas necessárias, tanto para o realinhamento do projeto, quanto para as atividades que dele dependem.

Além disso, esse indicador é importante, pois a instituição poderá aplicar o resultado advindo do projeto em outras pesquisas ou realocará os profissionais envolvidos em outras atividades ou novos projetos.

Indicador de Meta

Esse indicador auxilia na avaliação periódica do projeto, para o caso de tomada de decisão sobre a sua interrupção ou paralisação, considerando os objetivos estratégicos do CTA, o esforço institucional aplicado (recursos financeiros, de pessoal e infraestrutura) e a aplicabilidade do resultado.

Os indicadores da meta alcançada devem ser sempre analisados em conjunto com o indicador de prazo de conclusão, pois isso facilitará a análise quanto à real evolução dos objetivos propostos, do reconhecimento da complexidade tecnológica em função das competências organizacionais existentes no CTA, e do risco assumido pelo gerente na execução do projeto.

No estudo dos projetos foi verificado que os fatores que afetaram positiva ou negativamente o alcance das metas propostas estavam diretamente relacionados aos fatores relatados como entraves ao bom andamento do projeto, tais como:

• alocação tardia de recursos financeiros, que atrapalhou o bom andamento das metas, e

• atrasos na aquisição de componentes e equipamentos nacionais e importados, impossibilitando ou atrasando a realização das metas no tempo previsto.

Indicador de Custo do projeto

Os instrumentos utilizados pelo CTA, para o planejamento orçamentário oriundo do governo federal, são vinculados



à legislação federal e fundamentados em diretrizes em vigor no Comando da Aeronáutica, executadas conforme orientações que constam no Plano Plurianual e no Sistema Integrado de Planejamento e Gestão.

Os recursos financeiros provenientes das agências de fomento para os projetos são executados por meio das Fundações, obedecendo a regras estabelecidas em lei específica.

A necessidade crescente de recursos financeiros para o desenvolvimento das pesquisas e atividades do Centro, bem como para sua manutenção, é evidente, mas devem ser levados em consideração cenários que possam influenciar a aplicabilidade da tecnologia, em que os indicadores de custo são determinantes na tomada de decisão em relação à continuidade do projeto.

Assim, é fundamental um planejamento orçamentário realista, que leve em consideração a conjuntura política e econômica brasileira e as diretrizes dos órgãos superiores na esfera do CTA, no sentido de se obter um razoável plano de ação para a alocação dos recursos financeiros aos projetos de P&D.

A utilização de recursos financeiros oriundos de agências de fomento deve ser sempre incentivada, por representar um importante incremento ao suporte das atividades de pesquisa na instituição.

Além desse aspecto, existe um fator estratégico que extrapola a execução do projeto. Trata-se da política das agências de fomento quanto à contrapartida da instituição, para a geração de produtos e serviços inovativos que propiciem às indústrias brasileiras o aumento da inovação tecnológica.

Considerações e Recomendações

O gerenciamento de projetos é um empreendimento integrador, havendo a necessidade de uma conexão entre as fases de ciclo de vida de projeto, os planos e os processos de planejamento, acompanhamento e controle para um efetivo gerenciamento, adequação e direcionamento, como citado no PMBOKÒ (op. cit.).

Com base na pesquisa realizada, verificou-se que os instrumentos e ferramentas gerenciais foram, na época, concebidos de acordo com os princípios do que havia de mais moderno no gerenciamento de projetos, de modo a possibilitar um eficiente sistema de planejamento, acompanhamento e controle de projetos de P&D, possibilitando uma visão sistêmica da execução física e financeira dos projetos.

Os indicadores de prazo, meta e custo servem para estabelecer o acompanhamento e controle dos projetos,

evidenciando a sua eficiência e eficácia. Os resultados advindos são informações altamente importantes, mostrando o atendimento ao objetivo proposto, a capacitação e a infraestrutura adquiridas, bem como a possibilidade de novos conhecimentos que podem ser utilizados tanto em outros projetos em execução, como em projetos futuros.

Fatores como a complexidade da tecnologia envolvida no projeto, a necessidade de capacitação de pessoal, de infraestrutura, de recursos humanos e, principalmente, a alocação tardia dos recursos financeiros e os atrasos na aquisição de equipamentos e componentes são relatados nas FIP, como fator condicionante para o sucesso dos projetos.

Um dos principais problemas observados na análise dos projetos deve-se ao fato de que o governo federal disponibiliza recursos financeiros tardiamente, em desacordo com a operacionalização do projeto. Essa condição independe da vontade institucional, que pouco pode atuar para mudar a realidade. Desse modo, essa condição deve ser assumida pela instituição como parte do cotidiano de suas atividades.

Como alternativa a essa situação, pesquisadores têm buscado recursos financeiros adicionais junto à FINEP. O aporte de recursos que a agência injeta na instituição é expressivo, porém, observa-se que isso ocorre por iniciativa do pesquisador.

Pela relevância que assumem esses recursos para a pesquisa e desenvolvimento no CTA, a instituição, identificando as competências existentes, deverá interagir fortemente com as agências de fomento, apoiando os pesquisadores, de modo que não caiba somente aos mesmos esta iniciativa.

Esse fato, além de colocar a instituição como co-responsável por conseguir os recursos extras e necessários aos projetos, faz também com que sejam investidos em áreas e linhas de pesquisa que sejam de interesse direto do Comando da Aeronáutica.

Quanto ao relato dos atrasos na aquisição de equipamentos e componentes, algumas considerações podem ser feitas. Muito se discute em relação à aplicabilidade da Lei de Licitação Pública, nº 8.666/93, para o uso em projetos tecnológicos de P&D. Há mais de cinco anos existe uma proposta de alteração dessa Lei, porém até o momento não foi efetivada.

Como proposta de melhoria, enquanto não se altera a legislação, é importante que o CTA desenvolva mecanismos que possam melhorar o processo licitatório



atual de aquisição de produtos e serviços, definindo processos específicos entre os executores destes e as OM.

Também se pode utilizar a rede de comunicação de dados para agilizar o trâmite interno de aquisição de produtos e serviços, com a certificação de assinaturas digitais. Somente no final do processo, em função das exigências legais, seriam oficialmente assinados os documentos.

Outro instrumento facilitador desse processo é a utilização do Sistema de Registro de Preços, que promove a aquisição de itens de fornecimento contínuo e de natureza comum entre órgãos da esfera federal.

Em relação à aquisição de itens importados, deve-se enfatizar que um processo de aquisição normal no exterior pode demorar cerca de duzentos e noventa e seis dias, conforme descrito em documentação interna do CTA. Essa observação é importante e deve ser considerada pelos gerentes, quando da previsão de conclusão de metas, que demandem a utilização de equipamentos importados.

Para a implantação dessas propostas de melhoria, seria oportuno que o CTA criasse programas de esclarecimento do processo licitatório com o objetivo de melhorar a eficiência da atividade de aquisição de bens e serviços, promovendo, dessa forma, uma maior interação entre o órgão responsável, as OM e os gerentes.

Considerações Finais

Com o estudo de caso dos projetos analisados, pôde-se compreender o processo de gestão de projetos de P&D e constatar o quanto é importante o emprego das ferramentas e instrumentos específicos desse processo.

A execução dos projetos foi acompanhada por meio do Planejamento Preliminar de Projeto, do Programa de Trabalho Anual, da Ficha Informativa de Projetos e de relatórios emitidos segundo procedimentos próprios, com periodicidade estabelecida pelo CTA.

O estudo dos projetos permitiu observar como foi a dinâmica de gerenciamento adotada. A evolução, os problemas ocorridos, os desvios e as medidas corretivas geraram informações, que possibilitaram a análise de indicadores de desempenho, tornando possível um acompanhamento e controle mais próximo da realidade gerencial. Este procedimento serve, também, para constatar a realidade institucional onde se inserem os projetos de P&D do CTA.

Os indicadores de desempenho de custo, meta e prazo proporcionaram uma estrutura de dados coerente e consistente, à luz do preconizado nas abordagens

metodológicas apresentadas neste estudo, contribuindo efetivamente como fonte de informações para a tomada de decisão.

A contribuição do presente estudo é a análise sistêmica da gestão de projetos de P&D no CTA, a identificação de possíveis deficiências existentes no processo de planejamento, acompanhamento e controle dos projetos, e a sugestão de possíveis melhorias, visando contribuir para o aprimoramento da eficiência da gestão de projetos da Instituição.

No CTA, a gestão de projetos de P&D foi paulatinamente sendo modificada e adaptada com a adoção de processos e mecanismos que possibilitassem um aprimoramento contínuo, auxiliando apropriadamente a tomada de decisão em cada nível hierárquico organizacional.

A complexidade da atividade de pesquisa e desenvolvimento aliada às peculiaridades do CTA exigem que toda a equipe envolvida em projetos compreenda e utilize os conhecimentos e as habilidades técnicas, melhorando, dessa forma, o desempenho gerencial.

Do estudo realizado se pôde depreender alguns aspectos que impactam a gestão de projetos de P&D na instituição e que podem ser aperfeiçoados melhorando o desempenho gerencial, tais como:

• necessidade de medição de desempenho para o acompanhamento e controle dos projetos de P&D: a instituição deve reavaliar periodicamente o conjunto de indicadores, com o objetivo de melhorar continuamente as informações que auxiliem na avaliação de resultados e no fornecimento de parâmetros para a tomada de decisão, ampliando os já existentes;

• treinamento: existe a necessidade de toda a equipe envolvida em projetos de P&D utilizar os conhecimentos e habilidades técnicas para um bom gerenciamento. O CTA deve dar continuidade à capacitação em gestão de projetos, utilizando como experiência o curso de gerência de projetos realizado em 1996;

• infraestrutura de apoio aos gerentes: na estrutura organizacional do CTA devem existir setores que apóiem diretamente os gerentes na condução administrativa dos projetos. Um dos fatores de entrave ao bom andamento dos projetos é o atraso na aquisição de bens e serviços, devido ao processo licitatório. Dentre outras funções, esse setor teria a incumbência de auxiliar os gerentes a otimizar o tempo e os recursos alocados aos projetos, e



• incentivo à propriedade intelectual: a instituição pode fazer uso da legislação brasileira referente à propriedade intelectual para garantir direitos sobre a pesquisa como fator estratégico. Como observação, atualmente no CTA existe cerca de cinquenta processos de patentes oriundos de pesquisa interna. Considerando o nível e a quantidade de pesquisa existente na instituição, esse número é relativamente baixo, o que se deve, em parte, à falta de divulgação sobre os procedimentos de obtenção de patentes. O CTA, com a implementação de programas de esclarecimento, deve incentivar o aumento de pedidos de patentes.

Foram identificados os planos, as diretrizes, as normas e os relatórios internos e externos à instituição que afetaram o processo de gestão de projetos de P&D; identificados e analisados os recursos financeiros disponibilizados pelo governo federal e FINEP, e como foram efetuados o planejamento, acompanhamento e controle de projetos, mostrando a dinâmica do gerenciamento, os principais entraves e as sugestões de melhoria para o processo de gestão de projetos de P&D.

Considerando as peculiaridades e a estrutura organizacional da instituição, pode-se afirmar que a gestão de projetos de P&D apresenta desafios a serem transpostos no CTA. A sistemática de planejamento, acompanhamento e controle de projetos deve ser continuamente aperfeiçoada, pois dela depende o sucesso destes na instituição.

Resgatando-se a importância que o presente estudo assume, acredita-se ter sido atingido os objetivos propostos, e ainda ter colaborado para que a instituição tenha um melhor entendimento do processo de gestão de projetos de P&D e dos aspectos que possam inferir no gerenciamento desses projetos.

Espera-se que o estudo possa contribuir para o aperfeiçoamento dos processos gerenciais no CTA, gerando patamares superiores de eficiência e eficácia institucionais, desempenhando assim o seu papel no país e na sociedade.

Agradecimentos

Ao Ten Brig Ar Carlos Alberto Pires Rolla pela confiança e apoio para que este trabalho pudesse ser concretizado.

À Drª Mirabel Cerqueira Rezende, ao Maj Int Élbio de Souza e ao Dr. Odair Lelis Gonçalez pela importante colaboração e valiosas sugestões que muito acrescentaram ao trabalho.

Ao CTA, que permitiu o acesso ao acervo de documentação técnica de projetos, como fonte de estudo de casos para a composição do presente trabalho.

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Minayo M. C., 2007, “O Desafio do Conhecimento: Pesquisa Qualitativa em Saúde”, Abrasco, Rio de Janeiro, R.J. Brasil.

Morais, J. M. de., 2007, “Políticas de Apoio Financeiro à Inovação Tecnológica: Avaliação dos Programas MCT/FINEP para Empresas de Pequeno Porte”, Brasília, Brasil.

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Projeto”, 3. ed. Newton Square, Four Campus Boulevard. Disponível em: <http://www.profissionaisdetecnologia.com.br/downloads/PMBOK__Portugues.pdf.> Acesso em: 01 ago. 2007.

Salles-Filho, S.; Bonacelli, M. B., 2005, “Trajetórias e Agendas para os Institutos e Centros de Pesquisa no Brasil”, Seminários Temáticos para a 3ª Conferência Nacional de C, T&I.

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Gilberto FischInstituto de Aeronáutica e Espaço (IAE)

São José dos Campos – Brazil [email protected]

Comparisons between aerovane and sonic anemometer wind measurements at Alcântara Launch CenterAbstract: This paper aimed to compare the wind measurements in two different types of anemometer: classical aerovane and modern sonic anemometer. The two sensors were installed at Alcântara Launch Center during a dry period of 2008 at 10 m height. The analysis compared the average and maximum wind speed for one- and ten-minute time intervals for each anemometer. The results showed that, considering the range of the measurements (from 3.0 up to 6.5 m/s), the average and maximum wind speed are different by roughly 0.5 and 1.0 m/s, respectively. There is no significant difference between the results from one- and ten-minute time intervals. The substitution of the sensors at the Anemometric Tower at Alcântara Launch Center will lead to an increase of the average and maximum wind speed. Keywords: Masts, Wind speed, Maximum wind.

INTRODUCTION

The Alcântara Launch Center (ALC) is the place from where the Brazilian space vehicles (sounding rockets and the Satellite Launcher Vehicle) are launched. The knowledge of the vertical profile of the wind (in terms of direction and wind speed) and its association with the meteorological systems are very important, especially for the improvement of safety in the activities related to the preparation, integration and launching of rockets (Johnson, 2008). According to Altino and Barbré (2009), the mostly requested information about the environment in the US Space Facility is related with the winds.

The winds can be split in upper air (from 200 m up to 30 km and usually made with radiosondes) and surface winds (from the surface up to 200 m). This latter layer is known as the Atmospheric Surface Layer (ASL) and it is the region at the bottom of the atmosphere where turbulent fluxes are almost constant (varies less than 10% of their magnitude). The turbulence is continuously being generated and/or dissipated, and this layer also suffers the diurnal cycle of solar heating (Fisch, 2009).

Recently, Gisler (2009) carried out a detailed statistical study about the wind characteristics at ASC using the aerovane wind sensors. These sensors have been mounted in a wind tower named Anemometric Tower (70 m height), and it is collecting data at Alcântara

Launch Center since 1995. These measurements have been used to determine the wind climatology (Pereira, 2002; Gisler, 2009), the wind profile and turbulence characteristics (Fisch, 1999; Roballo and Fisch, 2008), as well as to determine the rocket trajectory during launching missions (Leão, 2009). However, with the technology development of the sensors, the ASC authorities are concerned with substituting the old technology from the aerovanes for modern instruments that use the sonic technique. The Space Kennedy Center (KSC) is also suffering a modernization process of these sensors (Short and Wheeler, 2006) as well as others public and private organizations in US (for instance Wastrack et al., 2000). Specifically, the KSC had collected data during 18 days (from 13 up to 30 May 2005) at Cape Canaveral (Florida) at five different towers nearby (their heights ranged from 3 up to 145 m). The one-minute observation from sonic and aerovanes were measured at parallel booms at the same height (see details at Short and Wheeler, 2006). When these instrumentation’s modification would finish, attention should be given to preservation of the time series of the substituted anemometers (compatibility between the old and new time series) as well as to adapting the space launching procedures of using the new sensors (the rules used by Safety Flight Group).

This study aims to compare two different sensors (aerovane and sonic anemometer) by analyzing the difference in average wind speed and maximum wind speed. The data has been collected in a field campaigns held at ALC. This study also aims to contribute to the knowledge of the time series analysis of wind data at Alcântara Launch


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DOI: 10.5028/jatm.2010.0201105110


Fisch, G.

Center in order to preserve the homogeneity of the data for climatology purposes.

DATA, SITE AND METHODS

The climatic pattern at Alcântara shows two distinct rainfall regimes: a dry and a wet season. The Figure 1 shows the rainfall climatic pattern. The dry season is from August to November and it is characterized by strong winds (the average wind is 7.0 m/s) due to the intensification of the thermal contrast between the continent and adjacent ocean (Fisch, 1999). This will trigger a sea breeze circulation which is superimposed to the trade winds producing these strong winds. The wet season is from January to June, being the months of March and April the rainiest ones (Guedes and Oyama, 2004). The data-set used in this work has been collected during an intensive field campaign (named Operação Murici II) held at ASC from 19 to 25 September 2008. The goals of this field campaign were to collect specific data (turbulence data – not shown here) during the dry season. Table 1 presented the diurnal cycle (in three-hour interval) of the wind field at the level 2 (10 m) of the wind tower during the period of the measurements in order to characterize the intensity of the atmospheric flow. The winds were stronger at late morning, reaching values slightly higher than 6.0 m/s. The direction is from NE-E. During the afternoon times, there is a small reduction of wind speed (to a value around 5.0 m/s at late afternoon), and the direction is slightly rotated to the north (NE). During the period of this campaign, no rainfall has been observed at the site or nearby (information extracted from satellite images and radar reflectivity data – not shown).

The sensor used as aerovane is the model 05305 Wind Monitor from R.M. Young (Traverse City, USA). It consists of a body/vane which aligns to the main wind direction. The propeller moves proportionally to the wind speed and its accuracy is estimated as ± 0.3 m/s, with a threshold velocity of 0.5 m/s. The wind speed and direction information is analog measured, and a data processing system determines the one-minute average and maximum winds peed. The sonic sensor is the model WS425 Ultrasonic Wind Sensor from Vaisala (Helsinki, Finlândia) and it has three sonic transdutors equally spaced and mounted in a horizontal plane. The sensor measured the time that the ultrasonic pulses take to go from one transdutor to another (path) in all directions. The transit time increase (decrease) if there is a tail (head) wind, and the difference is proportional to the wind speed along the path. Its accuracy is ± 0.1 m/s or 3% from the average wind speed. A proprietary algorithm is used to quality-control the raw data and produce a one-second wind speed/direction reading. The threshold velocity is almost null (Short and Wheeler, 2006). However, due to the fact that the wind speed at ALC is typically higher than 5.0 m/s, the threshold velocity is an irrelevant parameter for this analysis. The data have been collected at one observation each two seconds (sample rate of 0.5 Hz) and its average and maximum wind speed were storaged for a time interval of 60 seconds (1 min). These values are defined as average and maximum wind speed for one-minute time interval. The Figure 1 shows the sensors at the field (ALC) and their details.

The concept of mean scalar wind speed (the mean is the sum of the all samples divided by the number of samples) was used, as the wind direction was very persistent (Fisch, 1999), and the sensors were installed as orientated to the predominant wind. Initially, the data set has been grouped in average values from 30 values (representing one-minute time interval) and its higher value named as maximum wind speed. With this methodology, the average and maximum wind speed for one-minute time interval have been determined and the data set available consists of approximately 8.400 pairs of values. Later, the same methodology was used to derive the parameters for ten minutes assuming that now the time interval is of ten minutes (300

Table 1: Diurnal cycle of the winds during the field campaign.

Local time (h) 1 3 6 9 12 15 18 21

Wind speed /Standard deviation (m/s) 5.2 5.5 5.7 6.4 6.0 5.1 4.9 5.3

(1.2) (1.1) (1.3) (1.4) (1.2) (1.3) (1.2) (1.1)

Direction (°) 60 63 70 82 76 58 46 51

Figure 1: The instruments used in this comparison: the mast (a), the aerovane (b) and sonic anemometer (c).


Comparisons between aerovane and sonic anemometer wind measurements at Alcântara Launch Center

values for the average wind speed and the maximum was the higher value for this sample). Consequently, the data length was reduced for 842 pairs of values. The ten-minute average is the standard time interval used in engineering studies of the wind (Plate, 1982). The aerovane was calibrated in a wind tunnel from Aerodynamic Division (ALA/IAE) prior and post the field campaign and there was no significant modification at the calibration certificate for the aerovane. Thus, it was decided to maintain the original outputs from the aerovane sampled by the data-logger (from Campbell Scientific Instrument, Logan, UT, US). The differences between the sensors are computed as: measurements by sonic minus measurements by aerovane.


A simple statistics of the average and maximum wind speed between the sensors for both time intervals (1 and 10 minutes) are presented at Table 2. The mean difference for the average wind speed between the sensors was very low, roughly around 0.3 m/s, for the bias and mean square error of the sample for average wind speed were around 0.4 m/s. The highest values for the one-minute average wind speed were 9.5 and 9.8 m/s for the aerovane and sonic, respectively. For the maximum wind speed, the mean difference between sensors increases to 0.8 m/s. The bias and the mean square error were 0.9 and 1.0 m/s, respectively. The extreme values of the wind speed were higher than 12.0 m/s. These values are typical of the stronger winds during the dry season (Fisch, 1999; Gisler, 2009), thus showing the applicability of the results from this intercomparison. The atmospheric turbulence during the field campaign was very strong and its turbulence intensity is around 0.28-0.29 (dimensionless). The ten-minute average is the standard time interval used in engineering studies of the wind (Plate, 1982).

The data set was plotted in dispersion graphics with adjusted linear regression for one and ten-minute time interval (Fig. 2 and 3, respectively). For the one and ten-minute average wind speed (Fig. 2a and 3a), it can be noticed that the values are very consistent with high values of r2 (both are 0.99). In general, the sonic measurements are higher than the actual sensors used to measure the wind speed. The difference between them increases with the velocity, but it is roughly 4% plus an additional constant value (0.2 m/s). This represents 0.3 m/s for typical values of 4.0 m/s (during the wet season) and 0.5 m/s for stronger winds around 10.0 m/s (characteristic of the dry season). The linear regressions adjusted are almost the same for both time intervals. For the maximum wind speed (Fig. 2b and 3b), the same behavior was obtained: the sonic measurements are higher than the aerovane and this difference increases with the wind speed. The differences are almost the double (around 1.0 m/s) from the average wind speed. The differences showed by Short and Wheeler (2006) using the same type of sensors at the Kennedy Space Center are very closed to the results obtained in this study, thus suggesting that both results may be due to the characteristics of the sensors.

Table 2: Statistics between the average and maximum wind speed (m/s) for the sensors Aerovane and Sonic Anemometer for one- minute and ten-minutes time interval.

(m/s)One-minute Ten-minute

Aerovane Sonic Aerovane Sonic

Average Wind speed 4.5 (1.3) 4.8 (1.4) 4.5 (1.2) 4.8 (1.3)

Maximum Wind speed 6.1(1.6) 6.9 (1.7) 7.2 (1.6) 8.2 (1.7)

Bias 0.4 0.9 0.4 0.9

Mean square error 0.4 1.0 0.4 1.1

Extreme values 12.5 13.8 12.5 13.8

N (number of pairs of data) 8,403 842

*The values in parentheses represent the standard deviation of that sample.

Figure 2: Comparison between average (a) and maximum wind speed (b) for one-minute time interval.

The frequency distributions of the average and maximum wind speed are presented at Figures 4 and 5 for one and ten-minute time interval, respectively. For the one-minute


Fisch, G.

time interval, the peak of these distributions is different: for the average wind speed, the aerovane´s peak is one class prior to the sonic (Fig. 4a), increasing this difference for two classes for the maximum wind speed (Fig. 4b). The ten-minute time interval results also presented the same behavior. Each class interval represents 0.5 m/s of wind speed difference, and these situations is coherent with the statistics showed in Table 1 and Figures 2 and 3. For both cases, the wind speed distribution is close to a normal (Gaussian) statistic distribution. Gisler (2009), using a different data set (winds observations from anemometric tower at ASC from the period of 1995 until 1999), showed that the wind flow may be represented by a normal/Gaussian distribution.

In order to analyze the time evolution of the difference between the two sensors, a time series for the average and maximum wind speed is showed in Figure 6 for one-minute time interval and at Figure 7 for ten-minute time interval. For most of the cases, the sonic measurements are higher than the aerovane. For the average wind speed, the difference ranged from -0.1 m/s to +1.0 m/s for one-minute and from +0.2 m/s up to +0.6 m/s for ten-minute time interval. These results for the maximum wind speed

Figure 3: Comparison between average (a) and maximum wind speed (b) for ten-minute time interval.

A

B

A

B

Figure 4: Frequency distribution for average (a) and maximum (b) wind speed for one-minute time interval.

ranged from -1.5 m/s to +4.5 m/s and from -0.1 to +3.3 m/s for one and ten-minute time interval, respectively.

CONCLUDING REMARKS AND FINAL COMMENTS

This study compared measurements of wind speed made with two different sensors (aerovane and sonic anemometer) during a field test at Alcântara Launch Center in the 2008 dry season. This analysis was motivated by the possible and future substitution of the aerovanes by sonic anemometer sensors installed at the anemometric tower at ASC. The analyses were made considering the average and maximum wind speed for one and ten-minute time interval. The results showed that the sonic measurements are mostly higher than the aerovane´s and the average differences between them were around 0.5 m/s. This difference increases to a value around 1.0 m/s considering the maximum wind speed. There is no significant difference between the results obtained for one and ten-minute time interval. The substitution of the sensors at the anemometric tower will lead to an increase of the average (and maximum) wind speed measurements.


Comparisons between aerovane and sonic anemometer wind measurements at Alcântara Launch Center

A

B

Figure 5: Frequency distribution for average (a) and maximum (b) wind speed for ten-minute time interval.

Figure 6: Time series of the difference between the average (a) and maximum wind speed (b) for one-minute time interval.

A

B

A

B

Figure 7: Time series of the difference between the average (a) and maximum (b) wind speed for ten-minute time in-terval.

As a draft procedure to joint the past (aerovane´s measurements) and the future (sonic´s measurement) data set, a fixed value (0.5 m/s for the average wind speed and 1.0 m/s for the maximum wind speed) must be added to the past data set in order to have it normalized with the new equipment. Additionally, an comparison between the sensors in a wind tunnel is highly desired in order to fulfill this analysis, as well as other measurements during different meteorological conditions (wet season) and several heights.

ACKNOWLEDGMENTS

The author would like to acknowledge the entire team involved in the field campaign from Operação Murici II, especially the meteorological technician Jorge Yamasaki, who prepared some of the statistics presented.

REFERENCES

Altino, K.M.; Barbré Jr., R.E., 2009, “Applications of Meteorological Tower Data at Kennedy Space Center”, 1st AIAA Atmospheric Space Environment Conference, 22-25 June 2009, San Antonio, TX, US (Paper AIAA 2009-3533).


Fisch, G.

Fisch, G., 1999, “Características do Perfil Vertical do Vento no Centro de Lançamento de Foguetes de Alcântara (CLA)”, Revista Brasileira de Meteorologia, Vol. 14, No. 1, pp. 11-21.

Fisch, G., 2009, “The Atmospheric Boundary Layer: Concepts and Measurements”, In: Moreira, D.M. and Vilhena, M.T. (org.), “Air Pollution and Turbulence: Modelling and Applications”, CRC Press, Boca Ratton, US, pp. 3-19.

Gisler, C.A.F., 2009, “Análise do Perfil do Vento na Camada Limite Superficial e Sistemas Meteorológicos Atuantes no Centro de Lançamento de Alcântara”, Dissertação de Mestrado em Meteorologia. 2009-05-25. [citado 24 fev 2010]. Available at: <http://urlib.net/sid.inpe.br/MCT-m18@80/2009/04.24.12.33>

Guedes, R. L; Oyama, M. D., 2004, “Aspectos observacionais das oscilações intra-sazonais de intensidade do vento em Alcântara usando ondeletas: análise preliminar”, In: XIII Congresso Brasileiro de Meteorologia, Meteorologia e o desenvolvimento sustentável. Anais de Fortaleza, CE, CD-ROM.

Johnson, D.L., 2008, “Terrestrial Environment (Climatic) Criteria Guidelines for Use in Aerospace Vehicle Development”, 2008 Revision (NASA/TM—2008–215633). D.L. Johnson, Editor, Marshall Space Flight Center, Marshall Space Flight Center, Alabama, December 2008. [cited 2 jul 2009], available at: http://ntrs.nasa.gov/search.jsp.

Leão, R.C., 2009, “Ajuste do Perfil Vertical de Vento no Centro de Lançamento de Alcântara com dados obtidos por torre anemométrica e radiossondagem no Centro de Lançamento de Alcântara (CLA)”, Dissertação de Mestrado em Engenharia Aeroespacial, Instituto Tecnológico de Aeronáutica, 85 p.

Pereira, E.I. (Org.), 2002, “Atlas Climatológico do Centro de Lançamento de Alcântara”, Relatório de Desenvolvimento ACA/RT 01/01 GDO-000000/B0047, 186 p.

Plate, E.J., “Engineering Meteorology: Fundamentals of Meteorology and their application to problems in environmental and civil engineering”, Elsevier Scientific Publishing Company, Studies in Wind Engineering and Industrial Aerodynamics, Vol 1, 733 p.

Roballo, S.T., Fisch, G., 2008, “Escoamento atmosférico no Centro de Lançamento de Alcântara (CLA): Parte I- aspectos observacionais”, Revista Brasileira de Meteorologia, Vol. 23, No. 4, pp. 510-519. doi: 10.1590/S0102-77862008000400010.

Short, D. A., Wheeler, M.M., 2006, “RSA/Legacy Wind Sensor Comparison. Part II: Eastern Range”, NASA Contract Report CR 2006-214205, 26 p, 2006. [cited 2010, mar 18] Available at http://science.ksc.nasa.gov/amu/.

Wastrack, K.G. et al., 2000, “Comparison of Wind Sensors – ultrasonic and Wind wane /anemometer”, In: Proceedings of NUMUG Meeting, Las Vegas, NV, 10 p.


Thesis abstractsThis section presents the abstract of most recent Master or PhD thesis related to aerospace technology and management

Study of internal boundary layer downwind of coastal cliffs with application to the Brazilian Launching Center of Alcântara

Luciana Bassi Marinho PiresThe University of [email protected]

Thesis submitted for PhD degree in Meteorology at National Institute for Space Research, INPE, São José dos Campos, São Paulo State, Brazil, 2009.

Advisors: Dr. Ralf Gielow and Dr. Gilberto Fisch

Key-words: Internal boundary layer, Alcântara Launching Center, Wind tunnel, Immersed boundary, Coastal cliffs.

Abstract: The development of the Internal Boundary Layer (IBL) generated inside the Atmospheric Boundary Layer (ABL), due to a neutral wind incident at 90o on a coastal cliff, and caused by step changes of both the surface level and roughness. Observational data, numerical simulations and wind tunnel experiments were used. Numerically, two-dimensional DNS simulations with the immersed boundaries method for ocean-cliffs of diverse heights and geometric forms were effected. The code was validated with wind profiles observed on a 70-meter anemometric tower (AT) and punctual velocities measures on masts up to 15 m. With the code validated, simulations for various cliff heights and wind velocities, plus a case study for the 40 m ocean-cliff of the Alcântara Launching Center (2°19’ S; 44°22’ W) were carried out. The Reynolds number (Re) varied from 102 to 107, and for the atmospheric cases it is greater than 106. Also, experiments in a wind tunnel (WT) adapted to emulate the ABL over coastal-cliffs were made, limited to Re equal to 7.5 x 104. These emulations were numerically well simulated, concerning the height of the IBL, and the occurrence of a re-circulation bubble (RB) near the edge of the cliff, as visualized with the Particle Imaging Velocimetry (PIV) technique. The experiments, including a model of the Mobile Integration Tower (TMI) at 150 m from the edge mentioned, showed another RB at the top of the TMI plus a less intense one upwind, which affected the flow starting at 125 m from the edge. In addition, experiments were carried out in the WT with wind incidences of 55o e 45o, which showed the 3D

nature of the flow, with results similar, but less severe, to those due to the 90o incidence. Thus, this demonstrates that the 2D simulations with the numeric code actually constitute the most extreme case concerning the wind incidence on ocean-cliffs. So, the results of this study are of great value to determine extreme scenarios caused by winds downwind of ocean-cliffs. Finally, this is the first numerical study of the mechanical IBL generated by a topographic step change which combines WT experiments and micrometeorological observations, and also presents empirical expressions for the results.

Barriers and facilitators in the technology transfer to the space sector: case study of partnership programs of the Brazil (AEB) and USA (NASA) space agencies

Roberto Roma de VasconcellosInstitute of Aeronautics and [email protected]

Thesis submitted for PhD degree in Production Engineering at the Polytechnic School of the University of São Paulo, USP, São Paulo, São Paulo State, Brazil, 2008.

Advisor: Prof. Dr. João Amato Neto

Keywords: Technology transfer, Technology innovation, Partnership programs, Space agencies.

Abstract: The level of requirement of the society in order to satisfy its needs has been increasing progressively, as well as the technology complexity of goods and services offered. In order to follow this evolution, the technology innovation process needs to achieve a certain level of efficiency and effectiveness that be able to articulate all players of the innovation process in the network cooperation, in other words, there is no place for solitary organizational work. Partnerships are required to produce new products and processes to achieve its goals and promote a better quality of life. The space sector has an important role, such as the earth climate monitoring and preventive medicine equipments that were developed


Thesis Abstracts

from technologies used for space applications. Therefore, similarly to other countries, Brazil has transferred technologies to its space sector through partnership programs, though sometimes without success. The assumption of this study was “the effectiveness of technology transfer in the partnership programs can be achieved by overcoming the barriers in the process through specific facilitators”, and it was based on the international experience of space programs and literature review. The aim of this dissertation was to identify critical factors between players in the technology transference process on the Brazilian space sector. The methodology used was based on case studies of five partnership projects and involved three universities and four R&D institutes in the Brazilian partnership program called Uniespaço, which is coordinated by the Brazilian Space Agency (AEB). The NASA’s innovative partnership program was also studied in order to know the organizational arrangement and the technology transfer facilitators between players in the US space sector system of innovation and production. The main results of this dissertation were two new conceptual models; the first was based on critical factors of TT between technology generators and users, such as technology maturity level, adaptation of new technology versus user’s technological culture, and the ability of absorbing technology and innovation; the second model was the result of the dynamics of partnership formation and the impact of social players involved in the TT process.

Development of SiC piezoresistive sensors aiming aerospace system applications

Mariana Amorim FragaTechnological Institute of Aeronautics [email protected]

Thesis submitted for PhD degree in Physics and Chemistry in Aerospace Materials at the Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2009.

Advisors: Prof. Dr. Marcos Massi and Dr. Ivo de Castro Oliveira

Keywords: Silicon carbide, Piezoresistive sensors, Microfabrication, MEMS (Micro Electro Mechanical Systems)

Abstract: This thesis evaluates the potential of silicon carbide (SiC) films produced by two techniques enhanced

by plasma, PECVD (plasma enhanced chemical vapor deposition) e RF magnetron sputtering, for the development of piezoresistive sensors. The developed works covered all steps of synthesis and characterization of the films as well as the study processing steps for making resistors and pressure sensors. PECVD technique was used to produce a set of five samples of SiC films using a SiH4, CH4 and Ar gas mixture under different SiH4 flow. In situ doping of the film was performed by the introduction of nitrogen gas during the deposition process. A set of six samples was produced by RF magnetron sputtering of a stoichiometric SiC (99.5% purity) in Ar and N2 atmosphere. During the depositions, only the nitrogen flow was varied. SiC films obtained by two techniques were submitted to thermal annealing under argon atmosphere at 1000ºC for 1h. Chemical, structural, morphological, electrical, mechanical and optical properties of the SiC films, before and after thermal annealing, were investigated by Rutherford backscattering spectrometry (RBS), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), atomic force microscopy (AFM), four points probe, nanoindentation and transmission/reflection measurements in order to determine the films with suitable characteristics for the development of sensors. The etching process by RIE (reactive ion etching) plasma of the films using a SF6 and O2 gas mixtures to produce the structures of the sensors was studied. In order to study the piezoresistive properties of the films deposited, SiC resistors with Ti/Au electrical contacts were fabricated. An experimental setup was mounted to determine the electrical resistance changes as a function of applied mechanical stress. One SiC resistor was glued near the clamped end of a steel beam and on free end were applied different forces. The electrical resistance of the SiC resistor was measured for each force applied on the beam. This experiment allowed to determine the piezoresistive coefficient and gauge factor of the films deposited. The influence of temperature on the electrical resistance of the resistors was evaluated for temperatures up to 250ºC. Finally, a methodology for the design, fabrication and packaging of a prototype of piezoresistive pressure sensor based on SiC film is showed. The developed prototype was tested and presented an average sensitivity of 2.7 mV/psi.

Proposed model to simulate faults in the electrical network service used by sounding rockets

Fábio Duarte SpinaInstitute of Aeronautics and [email protected]


Thesis abstracts

Thesis submitted for Masters in Mechanical Engineering at University of Taubaté, UNITAU, São Paulo State, Brazil, 2009.

Advisor: Prof. Dr. Francisco Carlos Parquet Bizarria

Key-words: Airborne systems, Electrical networks, Sounding rockets.

Abstract: This work presents the proposals for computational models to represent the main grounding schemes and equipment used in the electrical network service used by sounding rockets with the goal of enabling the operational verification and technical viability in the context of electrical power distribution. In these models, the conditions of nominal operation and in fault are simulated, and the latter is carried out at strategic points in the electrical network with the purpose of determining maximum power achieved by the system under these conditions. The current values obtained in these simulations are mainly used as a guide in choosing the distribution of power best suited to be used by the electrical network service and the determination of electrical characteristic requirements that the equipment should possess in order to meet the nominal conditions and support the possible faults that can affect the system. The satisfactory results obtained in the simulations of the computer models designed to represent the grounding schemes and equipment belonging to the electrical network service used by sounding rockets presented in this paper indicate that the models are consistent with and appropriate to the intended purposes.

Operational analysis of the solid propellant mixer system by Petri nets

Alexandre Pereira RangelInstitute of Aeronautics and [email protected]

Thesis submitted for Masters in Aerospace Engineering at Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2009.


Keywords: Mixer system, Solid propellant, Petri nets.

Abstract: In the current process of composite solid propellant manufactory used in rockets like VLS, developed by the Aeronautics and Space Institute, two systems are dedicated to mix and homogenize the raw material present

in the propellant. These systems are called Macerador I and Macerador II. With the objective of modernizing the process, we chose to automate the operation of Macerador II. In this context, this work presents the use of Petri’s Net, to represent the current architecture of automation used in the operation and control of Macerador II. These models are tested in various sequences of simulations to discover if this model works according to original process of manufacture. In these simulations, the properties of Petri nets related to conservation, vivacity and conflicts of “confusion” and “death” are evaluated. The results of these evaluations show that the proposed models are able to represent the main states achieved by the equipments used to mix and homogenize, and accordingly changes are suggested to prioritize safety and efficiency in the use of this architecture.

Petri nets applied to algorithm analysis for self-test of spatial vehicles integration tower

Rodrigo PetterleTechnological Institute of [email protected]


Advisors: Prof. Dr. Francisco Carlos Parquet Bizarria and Prof. Dr. Alfredo Rocha de Faria

Keywords: Self-test, Integration tower for spatial vehicles, Petri nets.

Abstract: The Satellite Launcher Vehicle (VLS) designed in Brazil needs to be integrated in a special pad named Launch Pad. The structure of this pad has much equipment such as Rolling Bridge, Elevator, Platforms, Sliding Doors, Trucks and other to support the tasks of integration, tests and launch. The procedures of these tasks expose people to danger (risks) inherent to aerospace sector, building a situation where it is strategic to ensure security by the test of each equipment before it is use by the control system. This work presents the algorithm and the model to represent a proposal of a system that runs the Built-in Self Test (BIST) in actuator and sensors of each piece of equipment of the launch pad by Petri Nets. Computational simulations are done on this model to test properties of Petri nets like conservation, liveness and conflicts. The positive results obtained by these simulations ensure


Thesis Abstracts

that the proposed algorithm will be capable of detecting failures during the execution of the BIST on the equipment of the Launch Pad.

Development of a pressure sensitive paint technique to measure surface pressure in aerodynamic models

Mauricio PedrassiTechnological Institute of [email protected]

Thesis submitted for Masters in Aeronautical Engineering at Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2009.

Advisor: Prof. Dr. Roberto da Mota Girardi

Keywords: Pressure sensitive paint, aerodynamics, impingement jet, flat plate.

Abstract: An optical technique of pressure measurements known as Pressure Sensitive Paint appears in the 1980s to promote a directing breakthrough on surface pressure field measurement. This technology, already developed on the main research centers, has proved to provide accurate results with high spatial resolution, which is the biggest advance in terms of conventional pressure tap measurements. Since its early studies, the PSP technique development has been continuous and progressive, part due to the improvements on the paint formulation but mostly because of the technology advances on equipment, such as CCD cameras and computers which enabled not only capturing a series of high precision images but also increasing the data-processing speed. The main objective of this work is to understand how the PSP technique performs applying it for experimental procedures development on FENG Laboratory and to add expertise to the pressure measurement techniques. The work is divided into two parts. The first one is focused on calibration procedures (a priori calibration) when the PSP system is evaluated specially in the view of the paint behavior. During this phase, some limitations on the experimental apparatus were noticed such as the low full well capacity by the CCD camera which interferes directly in the final uncertainty measurement, producing an error of at least 0,74% on the measurement of light intensity. The direct relation between the paint and the temperature which impacts the results of the pressure fields was also confirmed. The second and final phase is related to an experimental investigation of the oblique impingement jet applied to a flat plate and

compared to the conventional pressure tap measurements. The major variations of pressure were around 3000Pa to 5500Pa. The results were compared to the gross measures of the PSP system with absolute uncertainty of 1000Pa (25%). When the PSP system was smoothed by a median filter, which is very representative of the gross measurements, it presented a decrease of the measurement of uncertainty of the PSP system by around 400Pa (10%), reaching a minimum level of 225Pa (3%). The result is quite below when compared to the absolute uncertainties around 22Pa obtained for researchers abroad. The long path ahead was pointed out in order to obtain precise pressure measurements with the PSP system for low speed flows. However, the improvement demands investments mainly on the experimental apparatus, making it more sensitive and capable of measuring small variations in the luminescence intensities resulted from the small pressure variations near to the atmosphere pressure. The main result that can be applied immediately is the pressure maps provided by the high spatial resolution of the PSP technique. Despite the uncertainty figures presented in the measurement procedures, the pressure maps described efficiently the behavior of the air flow.

Characterization of the interlaminar fracture toughness of carbon/epoxy composite

José Calixto FarahTechnological Institute of [email protected]


Advisor: Prof. Dr. Luiz Claudio Pardini

Keywords: Composites, Carbon fiber, Delamination, Interlaminar fracture toughness

Abstract: Composites are considered, for the aeronautical and aerospace industry, strategic materials since they allow reduction of structural weight of the aircraft or space vehicles keeping the performance in load bearing applications. It is essential, therefore, to obtain parameters that define the mechanical properties of the several types of composites that will be used by engineers in several application areas. The mechanical properties of structural composites are a function, among other factors, of the reinforcement and the matrix from which they are


Thesis abstracts

manufactured. For laminar composites, the stacking of reinforcement fiber layers is such that the interlaminar region is the weakest in terms of mechanical properties for aerospace composites. This leads to the fact that the properties of polymer composites and the ones made with carbon or ceramic matrices have been characterized by a low interlaminar shear strength and, as a consequence, a low interlaminar fracture toughness. The present work uses the methodology described in the ASTM D 5528 standard to evaluate the interlaminar fracture toughness of carbon fiber/epoxy composite having different formulations for the epoxy matrix and different directions of crack propagation in relation to the main fiber axis.

Investigation of the mechanism of functioning of the Gas Dynamic Igniter (GDI)

Leonardo Bartholomeu do NascimentoInstitute of Aeronautics and [email protected]


Advisors: Prof. Dr. Amilcar Porto Pimenta and Prof. Dr. Khoze Vassilievitch Kessaev

Keywords: Resonance tube, Gas dynamic igniter, Ignition systems, L15 Motor, Liquid propellant rocket engines, Propulsion.

Abstract: The main objective of this dissertation is to investigate the physical mechanism of operation of the gas dynamic igniter to enable a smooth start of the L15 engine and, also, to know the properties of the torch generated by the igniter, which will make possible to change operation parameters of the igniter to be used in other engines. A theoretical investigation of the heating mechanism of the gas injected into the resonator of the gas dynamic igniter, a mathematical model for this mechanism, including a routine of calculation and the comparison with test results will be presented in this paper. Experimentally, the resonance time and how to decrease it, the mixture ratio of the torch generated by the igniter, and how to reach a fuel-rich torch will be investigated.


Thesis abstractsThis section presents the abstract of most recent Master or PhD thesis related to aerospace technology and management

Study of internal boundary layer downwind of coastal cliffs with application to the Brazilian Launching Center of Alcântara

Luciana Bassi Marinho PiresThe University of [email protected]

Thesis submitted for PhD degree in Meteorology at National Institute for Space Research, INPE, São José dos Campos, São Paulo State, Brazil, 2009.

Advisors: Dr. Ralf Gielow and Dr. Gilberto Fisch

Key-words: Internal boundary layer, Alcântara Launching Center, Wind tunnel, Immersed boundary, Coastal cliffs.

Abstract: The development of the Internal Boundary Layer (IBL) generated inside the Atmospheric Boundary Layer (ABL), due to a neutral wind incident at 90o on a coastal cliff, and caused by step changes of both the surface level and roughness. Observational data, numerical simulations and wind tunnel experiments were used. Numerically, two-dimensional DNS simulations with the immersed boundaries method for ocean-cliffs of diverse heights and geometric forms were effected. The code was validated with wind profiles observed on a 70-meter anemometric tower (AT) and punctual velocities measures on masts up to 15 m. With the code validated, simulations for various cliff heights and wind velocities, plus a case study for the 40 m ocean-cliff of the Alcântara Launching Center (2°19’ S; 44°22’ W) were carried out. The Reynolds number (Re) varied from 102 to 107, and for the atmospheric cases it is greater than 106. Also, experiments in a wind tunnel (WT) adapted to emulate the ABL over coastal-cliffs were made, limited to Re equal to 7.5 x 104. These emulations were numerically well simulated, concerning the height of the IBL, and the occurrence of a re-circulation bubble (RB) near the edge of the cliff, as visualized with the Particle Imaging Velocimetry (PIV) technique. The experiments, including a model of the Mobile Integration Tower (TMI) at 150 m from the edge mentioned, showed another RB at the top of the TMI plus a less intense one upwind, which affected the flow starting at 125 m from the edge. In addition, experiments were carried out in the WT with wind incidences of 55o e 45o, which showed the 3D

nature of the flow, with results similar, but less severe, to those due to the 90o incidence. Thus, this demonstrates that the 2D simulations with the numeric code actually constitute the most extreme case concerning the wind incidence on ocean-cliffs. So, the results of this study are of great value to determine extreme scenarios caused by winds downwind of ocean-cliffs. Finally, this is the first numerical study of the mechanical IBL generated by a topographic step change which combines WT experiments and micrometeorological observations, and also presents empirical expressions for the results.

Barriers and facilitators in the technology transfer to the space sector: case study of partnership programs of the Brazil (AEB) and USA (NASA) space agencies

Roberto Roma de VasconcellosInstitute of Aeronautics and [email protected]

Thesis submitted for PhD degree in Production Engineering at the Polytechnic School of the University of São Paulo, USP, São Paulo, São Paulo State, Brazil, 2008.

Advisor: Prof. Dr. João Amato Neto

Keywords: Technology transfer, Technology innovation, Partnership programs, Space agencies.

Abstract: The level of requirement of the society in order to satisfy its needs has been increasing progressively, as well as the technology complexity of goods and services offered. In order to follow this evolution, the technology innovation process needs to achieve a certain level of efficiency and effectiveness that be able to articulate all players of the innovation process in the network cooperation, in other words, there is no place for solitary organizational work. Partnerships are required to produce new products and processes to achieve its goals and promote a better quality of life. The space sector has an important role, such as the earth climate monitoring and preventive medicine equipments that were developed


Thesis Abstracts

from technologies used for space applications. Therefore, similarly to other countries, Brazil has transferred technologies to its space sector through partnership programs, though sometimes without success. The assumption of this study was “the effectiveness of technology transfer in the partnership programs can be achieved by overcoming the barriers in the process through specific facilitators”, and it was based on the international experience of space programs and literature review. The aim of this dissertation was to identify critical factors between players in the technology transference process on the Brazilian space sector. The methodology used was based on case studies of five partnership projects and involved three universities and four R&D institutes in the Brazilian partnership program called Uniespaço, which is coordinated by the Brazilian Space Agency (AEB). The NASA’s innovative partnership program was also studied in order to know the organizational arrangement and the technology transfer facilitators between players in the US space sector system of innovation and production. The main results of this dissertation were two new conceptual models; the first was based on critical factors of TT between technology generators and users, such as technology maturity level, adaptation of new technology versus user’s technological culture, and the ability of absorbing technology and innovation; the second model was the result of the dynamics of partnership formation and the impact of social players involved in the TT process.

Development of SiC piezoresistive sensors aiming aerospace system applications

Mariana Amorim FragaTechnological Institute of Aeronautics [email protected]

Thesis submitted for PhD degree in Physics and Chemistry in Aerospace Materials at the Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2009.

Advisors: Prof. Dr. Marcos Massi and Dr. Ivo de Castro Oliveira

Keywords: Silicon carbide, Piezoresistive sensors, Microfabrication, MEMS (Micro Electro Mechanical Systems)

Abstract: This thesis evaluates the potential of silicon carbide (SiC) films produced by two techniques enhanced

by plasma, PECVD (plasma enhanced chemical vapor deposition) e RF magnetron sputtering, for the development of piezoresistive sensors. The developed works covered all steps of synthesis and characterization of the films as well as the study processing steps for making resistors and pressure sensors. PECVD technique was used to produce a set of five samples of SiC films using a SiH4, CH4 and Ar gas mixture under different SiH4 flow. In situ doping of the film was performed by the introduction of nitrogen gas during the deposition process. A set of six samples was produced by RF magnetron sputtering of a stoichiometric SiC (99.5% purity) in Ar and N2 atmosphere. During the depositions, only the nitrogen flow was varied. SiC films obtained by two techniques were submitted to thermal annealing under argon atmosphere at 1000ºC for 1h. Chemical, structural, morphological, electrical, mechanical and optical properties of the SiC films, before and after thermal annealing, were investigated by Rutherford backscattering spectrometry (RBS), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), atomic force microscopy (AFM), four points probe, nanoindentation and transmission/reflection measurements in order to determine the films with suitable characteristics for the development of sensors. The etching process by RIE (reactive ion etching) plasma of the films using a SF6 and O2 gas mixtures to produce the structures of the sensors was studied. In order to study the piezoresistive properties of the films deposited, SiC resistors with Ti/Au electrical contacts were fabricated. An experimental setup was mounted to determine the electrical resistance changes as a function of applied mechanical stress. One SiC resistor was glued near the clamped end of a steel beam and on free end were applied different forces. The electrical resistance of the SiC resistor was measured for each force applied on the beam. This experiment allowed to determine the piezoresistive coefficient and gauge factor of the films deposited. The influence of temperature on the electrical resistance of the resistors was evaluated for temperatures up to 250ºC. Finally, a methodology for the design, fabrication and packaging of a prototype of piezoresistive pressure sensor based on SiC film is showed. The developed prototype was tested and presented an average sensitivity of 2.7 mV/psi.

Proposed model to simulate faults in the electrical network service used by sounding rockets

Fábio Duarte SpinaInstitute of Aeronautics and [email protected]


Thesis abstracts

Thesis submitted for Masters in Mechanical Engineering at University of Taubaté, UNITAU, São Paulo State, Brazil, 2009.


Key-words: Airborne systems, Electrical networks, Sounding rockets.

Abstract: This work presents the proposals for computational models to represent the main grounding schemes and equipment used in the electrical network service used by sounding rockets with the goal of enabling the operational verification and technical viability in the context of electrical power distribution. In these models, the conditions of nominal operation and in fault are simulated, and the latter is carried out at strategic points in the electrical network with the purpose of determining maximum power achieved by the system under these conditions. The current values obtained in these simulations are mainly used as a guide in choosing the distribution of power best suited to be used by the electrical network service and the determination of electrical characteristic requirements that the equipment should possess in order to meet the nominal conditions and support the possible faults that can affect the system. The satisfactory results obtained in the simulations of the computer models designed to represent the grounding schemes and equipment belonging to the electrical network service used by sounding rockets presented in this paper indicate that the models are consistent with and appropriate to the intended purposes.

Operational analysis of the solid propellant mixer system by Petri nets

Alexandre Pereira RangelInstitute of Aeronautics and [email protected]



Keywords: Mixer system, Solid propellant, Petri nets.

Abstract: In the current process of composite solid propellant manufactory used in rockets like VLS, developed by the Aeronautics and Space Institute, two systems are dedicated to mix and homogenize the raw material present

in the propellant. These systems are called Macerador I and Macerador II. With the objective of modernizing the process, we chose to automate the operation of Macerador II. In this context, this work presents the use of Petri’s Net, to represent the current architecture of automation used in the operation and control of Macerador II. These models are tested in various sequences of simulations to discover if this model works according to original process of manufacture. In these simulations, the properties of Petri nets related to conservation, vivacity and conflicts of “confusion” and “death” are evaluated. The results of these evaluations show that the proposed models are able to represent the main states achieved by the equipments used to mix and homogenize, and accordingly changes are suggested to prioritize safety and efficiency in the use of this architecture.

Petri nets applied to algorithm analysis for self-test of spatial vehicles integration tower

Rodrigo PetterleTechnological Institute of [email protected]


Advisors: Prof. Dr. Francisco Carlos Parquet Bizarria and Prof. Dr. Alfredo Rocha de Faria

Keywords: Self-test, Integration tower for spatial vehicles, Petri nets.

Abstract: The Satellite Launcher Vehicle (VLS) designed in Brazil needs to be integrated in a special pad named Launch Pad. The structure of this pad has much equipment such as Rolling Bridge, Elevator, Platforms, Sliding Doors, Trucks and other to support the tasks of integration, tests and launch. The procedures of these tasks expose people to danger (risks) inherent to aerospace sector, building a situation where it is strategic to ensure security by the test of each equipment before it is use by the control system. This work presents the algorithm and the model to represent a proposal of a system that runs the Built-in Self Test (BIST) in actuator and sensors of each piece of equipment of the launch pad by Petri Nets. Computational simulations are done on this model to test properties of Petri nets like conservation, liveness and conflicts. The positive results obtained by these simulations ensure


Thesis Abstracts

that the proposed algorithm will be capable of detecting failures during the execution of the BIST on the equipment of the Launch Pad.

Development of a pressure sensitive paint technique to measure surface pressure in aerodynamic models

Mauricio PedrassiTechnological Institute of [email protected]

Thesis submitted for Masters in Aeronautical Engineering at Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2009.

Advisor: Prof. Dr. Roberto da Mota Girardi

Keywords: Pressure sensitive paint, aerodynamics, impingement jet, flat plate.

Abstract: An optical technique of pressure measurements known as Pressure Sensitive Paint appears in the 1980s to promote a directing breakthrough on surface pressure field measurement. This technology, already developed on the main research centers, has proved to provide accurate results with high spatial resolution, which is the biggest advance in terms of conventional pressure tap measurements. Since its early studies, the PSP technique development has been continuous and progressive, part due to the improvements on the paint formulation but mostly because of the technology advances on equipment, such as CCD cameras and computers which enabled not only capturing a series of high precision images but also increasing the data-processing speed. The main objective of this work is to understand how the PSP technique performs applying it for experimental procedures development on FENG Laboratory and to add expertise to the pressure measurement techniques. The work is divided into two parts. The first one is focused on calibration procedures (a priori calibration) when the PSP system is evaluated specially in the view of the paint behavior. During this phase, some limitations on the experimental apparatus were noticed such as the low full well capacity by the CCD camera which interferes directly in the final uncertainty measurement, producing an error of at least 0,74% on the measurement of light intensity. The direct relation between the paint and the temperature which impacts the results of the pressure fields was also confirmed. The second and final phase is related to an experimental investigation of the oblique impingement jet applied to a flat plate and

compared to the conventional pressure tap measurements. The major variations of pressure were around 3000Pa to 5500Pa. The results were compared to the gross measures of the PSP system with absolute uncertainty of 1000Pa (25%). When the PSP system was smoothed by a median filter, which is very representative of the gross measurements, it presented a decrease of the measurement of uncertainty of the PSP system by around 400Pa (10%), reaching a minimum level of 225Pa (3%). The result is quite below when compared to the absolute uncertainties around 22Pa obtained for researchers abroad. The long path ahead was pointed out in order to obtain precise pressure measurements with the PSP system for low speed flows. However, the improvement demands investments mainly on the experimental apparatus, making it more sensitive and capable of measuring small variations in the luminescence intensities resulted from the small pressure variations near to the atmosphere pressure. The main result that can be applied immediately is the pressure maps provided by the high spatial resolution of the PSP technique. Despite the uncertainty figures presented in the measurement procedures, the pressure maps described efficiently the behavior of the air flow.

Characterization of the interlaminar fracture toughness of carbon/epoxy composite

José Calixto FarahTechnological Institute of [email protected]


Advisor: Prof. Dr. Luiz Claudio Pardini

Keywords: Composites, Carbon fiber, Delamination, Interlaminar fracture toughness

Abstract: Composites are considered, for the aeronautical and aerospace industry, strategic materials since they allow reduction of structural weight of the aircraft or space vehicles keeping the performance in load bearing applications. It is essential, therefore, to obtain parameters that define the mechanical properties of the several types of composites that will be used by engineers in several application areas. The mechanical properties of structural composites are a function, among other factors, of the reinforcement and the matrix from which they are


Thesis abstracts

manufactured. For laminar composites, the stacking of reinforcement fiber layers is such that the interlaminar region is the weakest in terms of mechanical properties for aerospace composites. This leads to the fact that the properties of polymer composites and the ones made with carbon or ceramic matrices have been characterized by a low interlaminar shear strength and, as a consequence, a low interlaminar fracture toughness. The present work uses the methodology described in the ASTM D 5528 standard to evaluate the interlaminar fracture toughness of carbon fiber/epoxy composite having different formulations for the epoxy matrix and different directions of crack propagation in relation to the main fiber axis.

Investigation of the mechanism of functioning of the Gas Dynamic Igniter (GDI)

Leonardo Bartholomeu do NascimentoInstitute of Aeronautics and [email protected]


Advisors: Prof. Dr. Amilcar Porto Pimenta and Prof. Dr. Khoze Vassilievitch Kessaev

Keywords: Resonance tube, Gas dynamic igniter, Ignition systems, L15 Motor, Liquid propellant rocket engines, Propulsion.

Abstract: The main objective of this dissertation is to investigate the physical mechanism of operation of the gas dynamic igniter to enable a smooth start of the L15 engine and, also, to know the properties of the torch generated by the igniter, which will make possible to change operation parameters of the igniter to be used in other engines. A theoretical investigation of the heating mechanism of the gas injected into the resonator of the gas dynamic igniter, a mathematical model for this mechanism, including a routine of calculation and the comparison with test results will be presented in this paper. Experimentally, the resonance time and how to decrease it, the mixture ratio of the torch generated by the igniter, and how to reach a fuel-rich torch will be investigated.

Journal of Aerospace Technology and ManagementV. 2, n. 1, Jan. - Apr. 2010116

INSTRUCTIONS TO THE AUTHORS

Scope and editorial policy

The Journal of Aerospace Technology and Management is the official publication of Institute of Aeronautics and Space (IAE) of the Department of Aerospace Science and Technology (DCTA), São José dos Campos, São Paulo State, Brazil.

The journal is published three times a year (April, August and December) and is devoted to research and management on different aspects of aerospace technologies. The authors are solely responsible for the contents of their contribution. It is assumed that they have the necessary authority for publication.

When submitting the contribution the author should classify it according to the area selected from the topics.

• Acoustics• Aerodynamics• Aerospace Systems• Applied Computation• Automation • Chemistry• Defense• Electronics

• Management Systems• Materials• Mechanical Engineering• Meteorology• Propulsion• Structures • Vibration

The submissions, except thesis and book reviews, will be peer reviewed by three Editorial board members and selected for publication according to the editorial policy of the journal. Copyrights on all material published belong to IAE. Permission must be requested prior to use.

Mandatory requirements

All papers must include: type of contribution (review article, original paper, short communication, case report, book reviews or theses), title, authors’ names, electronic addresses and affiliations, abstract, key words (three to six items that should be based on NASA Thesaurus volume 2 – Access Vocabulary), and indication of the author responsible for correspondence.

Contents

Editorial

Any researcher may write the editorial on the invitation of the editor-in-chief. The article should not exceed two pages.

Review articles

They should cover subjects falling within the scope of the journal. These contributions should be presented in the same format as a full paper, except that they should not be divided into sections such as introduction, methods, results and discussion. However, they must include a 150 to 200-word abstract, key words, concluding remarks, acknowledgment and references. The article should not exceed 18 pages.

Technical papers

These articles should report the results of original research and need to include: a 150 to 200-word abstract, key words, introduction, methods, results and discussion, acknowledgment, references, tables and/or figures. The article should not exceed 12 pages.

Communications

They should include a 150 to 200-word abstract, key words, tables and/or figures acknowledgment and references. The communication should not exceed eight pages.

Thesis abstracts

The journal welcomes Masters and PhD thesis abstracts for publication.

Journal of Aerospace Technology and Management V. 2, n. 1, Jan. - Apr. 2010 117

Paper submission

Manuscript should be written in English or Portuguese and submitted electronically. See the instructions on www.jatm.com.br/papersubmission.

References

References should be cited in the text by giving the last name of the author(s) and the year of publication. Either use “Recent work (Smith and Farias, 1997)” or “Recently Smith and Farias (1997)”. With four or more names, use the form “Smith et al. (1997)”. If two or more references would have the same identification, distinguish them by appending “a”, “b”, etc., to the year of publication.

Acceptable references include journal articles, numbered papers, dissertations, thesis, published conference proceedings, preprints from conferences, books, submitted articles, if the journal is identified, and private communications.

References should be listed in alphabetical order, according to the last name of the first author, at the end of the article. Some sample references follow:

Bordalo, S.N., Ferziger, J.H. and Kline, S.J., 1989, “The Development of Zonal Models for Turbulence”, Proceedings of the 10th Brazilian Congress of Mechanical Engineering, Vol. 1, Rio de Janeiro, Brazil, pp. 41-44.

Coimbra, A.L., 1978, “Lessons of Continuum Mechanics”, Ed. Edgard Blücher, S.Paulo, Brazil, 428 p.

Clark, J.A., 1986, Private Communication, University of Michigan, Ann Harbor.

Silva, L.H.M., 1988, “New Integral Formulation for Problems in Mechanics” (In Portuguese), Ph.D. Thesis, Federal University of Santa Catarina, Florianópolis, S.C., Brazil, 223 p.

Soviero, P.A.O. and Lavagna, L.G.M., 1997, “ANumerical Model for Thin Airfoils in Unsteady Motion”, RBCM- J. of the Brazilian Soc. Mechanical Sciences, Vol. 19, No. 3, pp. 332-340. Sparrow, E.M., 1980a, “Forced Convection Heat Transfer in a Duct Having Spanwise-Periodic Rectangular Protuberances”, Numerical Heat Transfer, Vol. 3, pp. 149-167.

Sparrow, E.M., 1980b, “Fluid-to-Fluid Conjugate Heat Transfer for a Vertical Pipe-Internal and External Natural Convection”, ASME Journal of Heat Transfer, Vol. 102, pp. 402-407.

Associação Brasileira de Normas Técnicas, 2002, NBR6032: “Abreviação de títulos de periódicos e publicações seriadas”, Rio de Janeiro, Brazil 14p.

BRASIL, 1993, “Relatório de atividades”, Ministério da Justiça, Brasília, D.F. Brazil 28p.

Garcia,A., 2005, “Estudo Preliminar de Concepção de Performance de Veículos Lançadores Referentes aos Estudos do Grupo de Trabalho VLS-2010”, IAE, São José dos Campos, Brazil. (ASE-RT-006-2005).

EMBRAPA, 1995, “Unidade de Apoio, Pesquisa e Desenvolvimento de Instrumentação Agropecuária”. Medidor digital multissensor de temperatura para solos, BR n. PI 8903105-9, 26 Jun. 1989, 30 maio 1995.

Illustrations

All illustrations (line drawings, photographs and graphs) should be submitted, preferably in .jpg, .tiff or .xls format, with good definition (1 to 2 megapixels). References should be made in the text to each illustration. Explanations should be given in the figure legends, so that illustrations are kept clean.

Tables

Authors should take notice of the limitations set by the size and layout of the journal. Therefore, large tables should be avoided. All tables must be mentioned in the text.

Sponsors

This publication is sponsored by IAE.

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