phd symposium 2017...prof.dr. dick simons director of faculty graduate school chair of aircraft...

PhD Symposium 2017

Graduate School AE

Faculty of Aerospace Engineering

Delft University of Technology

19th of January 2017

PhD Symposium 2017

Academic Event

Organised by

Graduate School of Aerospace Engineering PhD Board Aerospace Engineering

January 19th , 2017 Faculty of Aerospace Engineering, Delft University of Technology

Delft, The Netherlands

Faculty Graduate School director: Prof.dr. Dick Simons Faculty Graduate School coordinator: Geeta van der Zaken PhD Board Members: Dirk van Baelen Fardin Esrail Koen Groot

Roberto Merino Martinez Fabrício Ribeiro Tomas Sinnige

Svenja Woicke

Graduate School AE Faculty of Aerospace Engineering Delft University of Technology Room 3.07 Kluyverweg 1 / P.O.Box 5058 2629 HS Delft / 2600 GB Delft T: +31 (0)15 27 88288 E: [email protected] or [email protected]

Colophon: Editor: Fardin Esrail Email: [email protected] Publication date: January 2017

Contents

Preface .................................................................................................................... 7

1. Programme ....................................................................................................... 9

2. Jury Members ................................................................................................. 13

3. Topics & Schedule....................................................................................................................... 15

Topics................................................................................................................................................. 15

List of participants ........................................................................................................................ 16

4. Abstracts ......................................................................................................................................... 19

4.1 Observation Techniques ...................................................................................................... 20

4.2 Gas Dynamics ........................................................................................................................ 28

4.3 Numerical Modelling ............................................................................................................. 33

4.4 Propulsion................................................................................................................................. 44

4.5 Control ....................................................................................................................................... 46

4.6 Performance ............................................................................................................................. 51

4.7 RAMS: Reliability, Availability, Maintainability & Safety .......................................... 58

4.8 Design and Manufacturing ................................................................................................. 67

4.9 Trajectories ............................................................................................................................... 76

4.10 Extreme Environments ...................................................................................................... 83

4.11 Environmental Impact ....................................................................................................... 89

4.12 Aeroacoustics and Climate Effects ................................................................................ 91

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The newest computer can merely compound, at speed, the oldest problem in the relations between human beings, and in the end the communicator will be confronted with

the old problem of what to say and how to say it.

- Edward R. Murrow

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Preface

The Graduate School of the faculty of Aerospace Engineering organizes a yearly PhD academic event. The aim of this event is to bring PhD students from different disciplines of the faculty together and stimulate collaboration among the students. In this respect, a symposium is organised for this year, where every PhD student will give a short presentation about his/her work. The presentations are divided into several sessions, where each session is aimed at highlighting a specific application and/or expertise in the field of the research conducted. The first PhD symposium takes place on January 19th, 2017 at the faculty of Aerospace Engineering in Delft, the Netherlands. On behalf of the FGS (Faculty Graduate School), prof. Dick Simons will open the symposium with an introductory talk about the goals of the Graduate School and the benefit of the academic event. Furthermore, four main sessions are organized, encompassing a total of 12 different topics. During each of the four sessions, parallel presentations will be given in five different lecture rooms. The topics of this year’s symposium are:

• Observation Techniques

• Gas Dynamics

• Numerical Modelling

• Propulsion

• Control

• Performance

• RAMS: Reliability, Availability, Maintenance and Safety

• Design and Manufacturing

• Trajectories

• Extreme Environments

• Environmental Impact

• Aeroacoustics & Climate Effects These topics are found to be the most representative of the research conducted by PhD students at the faculty. Each topic is shortly introduced by a PhD Board member before the presentations, who will also be chairing the presentation sessions. Each of the four main sessions takes between 1.5 - 2 hours, during which PhD students give presentation of 10 minutes, followed by a 5 minute question round. Each main session is followed by a 15 minute coffee break. After a jury evaluation of the presentations, the best candidate of each session will be determined, followed by an award ceremony.

Finally, the day is concluded with a socializing drink in the faculty lounge, the “Atmosfeer”.

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The eleven different sections/disciplines of the faculty and the corresponding PhD Board representatives are shown below:

Acronym Section PhD Board Representative

ASM Astrodynamics and Space Missions Svenja Woicke SSE Space Systems Engineering ,,

SI&C Structural Integrity and Composites Fabrício Ribeiro NovAM Novel Aerospace Materials ,,

C&S Control & Simulation Dirk van Baelen

ATO Air Transport & Operations Roberto Merino Martinez ANCE Aircraft Noise and Climate Effects ,,

AERO Aerodynamics Koen Groot FPP Flight Performance and Propulsion Tomas Sinnige

WE Wind Energy Tomas Sinnige & Koen Groot ASCM Aerospace Structures & Computational Fardin Esrail

Mechanics

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1. Programme

10

Thursday, January 19th 2017

Opening

08:30-08:45 Registration: collection of badges, lunch vouchers and booklets

Main Hall

08:45-09:00 Opening by Prof.dr. Dick Simons Main Hall

Session 1 Presentations by PhD candidates

09:00-10.30

LR E, F, G, H, K

10:30-10:45 Coffee break Main Hall


10.45-12.30

LR E, F, G, H, K

12:30-13:30 Lunch LR J


13.30-15.00

LR E, F, G, H, K

15:00-15:15 Coffee break Main Hall


15.15-17.00

LR E, F, G, H, K

17:00-18:00 Jury Evaluation, Closure and Award ceremony Main Hall

18:00-19:00 Drinks Atmosfeer

Time Room LR-E Name Room LR-F Name Room LR-G Name Room LR-H Name Room LR-K Name

9.00-9.15 Gas dynamics

Brandsen, J.D.

Numerical

Modelling

Athayde Costa e

Silva, de M.

Design &

Manufacturing Belligoli, Z. RAMS Ewald, V. Trajectories Ho, H.W.

9.15-9.30 Gas dynamics

Cordeiro

Guerrieri, D.

Numerical

Modelling Baptista, C.F.

Design &

Manufacturing Bley, A. RAMS Anand, C. Trajectories

Jaime Junell,

J.L.

9.30-9.45 Gas dynamics Groot, K. Numerical Modelling Blank, B.

Design & Manufacturing Candade, A.A. RAMS Deng, Q. Trajectories Mao, X.

9.45-10:00 Gas dynamics Hu, W.

Numerical Modelling

Cabral Santos Pestana, T.

Design & Manufacturing Farahani, H. RAMS Dhanisetty, V.S.V. Trajectories McGuire, K.N.

10.00-10.15 Gas dynamics March, G.

Numerical Modelling Coppola, M.

Design & Manufacturing Gent, van I. RAMS Eleftheroglou, N. Trajectories Rudnyk, I.

10.15-

10.30 Gas dynamics Tang, J.

Numerical

Modelling El, van der K.

Design &

Manufacturing Jovanov, K. RAMS Esrail, F.S. Trajectories Sun, J.

Break

10.45-11.00 Gas dynamics Tol, H.J.

Numerical Modelling Hoorn, van N.

Design & Manufacturing Kupski, J.A. RAMS Koornneef, H. Trajectories Sunil, E.

11.00-

11.15 Gas dynamics Visser, T.

Numerical

Modelling Folkersma, M.A.M.

Design &

Manufacturing Lavalette, N.P. RAMS Koutras, N. Trajectories Tijmons, S.

11.15-

11.30 Gas dynamics Zhang, Yi (AERO)

Numerical

Modelling Geul, J.

Design &

Manufacturing Natella, M. RAMS Mannucci, T. Trajectories Verbeek, R.J.D.

11.30-

11.45 Performance Dighe, V.V.

Numerical

Modelling Gillebaart, E.

Design &

Manufacturing Peeters, D.M.J. RAMS Rajabzadehdizaji, A. Trajectories Liu, Y.

11.45-12:00 Performance Fu, W.

Numerical Modelling Janssen, S.A.M.

Design & Manufacturing Post, W. RAMS Ribeiro, F.

Observation Techniques Caridi, G.

12.00-12.15 Performance Hong, Z.

Numerical Modelling Jain, V.

Design & Manufacturing

Sanchez Perez Moreno, S. RAMS Uriol Balbin, I.

Observation Techniques Dolkens, D.

12.15-12.30 Performance Huang, Y.

Numerical Modelling Lancelot, P.M.G.J.

Design & Manufacturing Susa, A. RAMS

Viegas Ochoa de Carvalho, P.A.

Observation Techniques Gaida, T.C.

Lunch

13.30-13.45 Performance Li, Y.

Numerical Modelling Mahapatra, G.

Design & Manufacturing Tsiangou, E. RAMS Walker, M.S.

Observation Techniques Giyanani, A.

13.45-14.00 Performance Lu, T.

Numerical Modelling Mooij, de C.

Design & Manufacturing Wang, Z. RAMS Zhang, Ye (C&S)

Observation Techniques Jatiningrum, D.

14.00-

14.15 Performance Miletović, I.

Numerical

Modelling Steinke, T.

Design &

Manufacturing Yu, H.

Extreme

Environments Baelen, van D.

Observation

Techniques

Kadathanad,

S.R.

14.15-

14.30 Performance Rajan, N.K.

Numerical

Modelling

Bos, van den

L.M.M.

Design &

Manufacturing Zhong, N.

Extreme

Environments Denissen, P.J.

Observation

Techniques Koop, L.

14.30-

14.45 Performance Smisek, J. Control Carvajal Godinez, J. Propulsion Nie, J.

Extreme

Environments Gutierrez Alvarez, J.

Observation

Techniques

Mohammadloo,

T.

Time Room LR-E Name Room LR-F Name Room LR-G Name Room LR-H Name Room LR-K Name

14.45-

15.00 Performance Udluft, H. Control LeBlanc, B.P. Propulsion Perpignan, A.A.V.

Extreme

Environments Hasan, Z.

Observation

Techniques Sambell, K.A.M.

Break

15.15-

15.30

Aeroacoustics &

Climate Effects Alves Vieira, A.E. Control Michelis, T. Propulsion Sanadi, D.S.

Extreme

Environments Krishnasamy, J.

Observation

Techniques

Schneiders,

J.F.G.

15.30-

15.45

Aeroacoustics &

Climate Effects Arnhem, van N. Control Rapp, S. Propulsion

Stokkermans,

T.C.A.

Extreme

Environments Landman, H.M.

Observation

Techniques Woicke, S.

15.45-

16.00

Aeroacoustics &

Climate Effects

Malgoezar,

A.M.N. Control Serpieri, J.

Environmental

Impact Ho Huu, V.

Extreme

Environments Sauvage, L.L.F.

Observation

Techniques Terra, W.

16.00-16.15

Aeroacoustics & Climate Effects

Merino Martinez, R. Control Smeur, E.J.J.

Environmental Impact Rajpal, D.

Extreme Environments Tapeinos, I.

Observation Techniques Ligterink, F.

16.15-16.30

Aeroacoustics & Climate Effects Sinnige, T. Control Zhu, L.

Environmental Impact Reurings, C.

16.30-16.45

Aeroacoustics & Climate Effects

Velden, van der W.C.P. Control Zong, H.

16.45-

17.00

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2. Jury Members

Prof.dr. Dick Simons Director of Faculty Graduate School

Chair of Aircraft Noise and Climate Effects Faculty of Aerospace Engineering, TU Delft

Prof.dr.ir. Rinze Benedictus Interim Dean

Department of Aerospace Structures and Materials Faculty of Aerospace Engineering, TU Delft

Prof.dr.ir. Jan van Ingen Former Dean and Professor of Aerodynamics Faculty of Aerospace Engineering, TU Delft

Prof.dr.ing.habil Stefan Hickel Chair of Aerodynamics Faculty of Aerospace Engineering, TU Delft

Prof.dr.ir. Pieter Visser Chair of Astrodynamics & Space Missions Faculty of Aerospace Engineering, TU Delft

Drs. Ineke Boneschansker Communication Department Faculty of Aerospace Engineering, TU Delft

Dr. Bernhard R. Brandl Professor of Infrared Astronomy Sterrewacht Leiden, Leiden University

Rebecca Cottrell, M.Eng. Researcher, Aston STEM Education Centre Aston University, Birmingham, U.K.

Ir. Javad Fatemi Systems Engineer Airbus Defence and Space Netherlands B.V.

Dr. Rene Pecnik Department of Energy Technology Faculty of Mechanical, Maritime and Materials Engineering, TU Delft

Dr.ir. Sonell Shroff Chair of Structural Integrity & Composites Faculty of Aerospace Engineering, TU Delft

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Dr. Mirjam Snellen Chair of Aircraft Noise and Climate Effects Faculty of Aerospace Engineering, TU Delft Dr. Daphne Stam Chair of Astrodynamics & Space Missions Faculty of Aerospace Engineering, TU Delft

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3. Topics & Schedule

Topics

Topic nr. Topic description

1 Observation Techniques

2 Gas Dynamics

3 Numerical Modelling

4 Propulsion

5 Control

6 Performance

7 RAMS: Reliability, Availability, Maintenance and Safety

8 Design and Manufacturing

9 Trajectories

10 Extreme Environments

11 Environmental Impact

12 Aeroacoustics & Climate Effects

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List of participants

Topic Name Section

12 Alves Vieira, A.E. ANCE

7 Anand, C. SI&C

12 Arnhem, van N. FPP

3 Athayde Costa e Silva,

de M. SSE

10 Baelen, van D. C&S

3 Baptista, C.F. WE

8 Belligoli, Z. AERO

3 Blank, B. ASM

8 Bley, A. WE

3 Bos, van den L.M.M. WE

2 Brandsen, J.D. ASCM

3 Cabral Santos

Pestana, T. AERO

8 Candade, A.A. WE

1 Caridi, G. AERO

5 Carvajal Godinez, J. SSE

3 Coppola, M. SSE

2 Cordeiro Guerrieri, D. SSE

7 Deng, Q. ATO

10 Denissen, P.J. NovAM

7 Dhanisetty, V.S.V. ATO

6 Dighe, V.V. WE

1 Dolkens, D. SSE

3 El, van der K. C&S

7 Eleftheroglou, N. SI&C

7 Esrail, F.S. ASCM

7 Ewald, V. SI&C

8 Farahani, H. NovAM

3 Folkersma, M.A.M. WE

6 Fu, W. C&S

1 Gaida, T.C. ANCE

8 Gent, van I. FPP

3 Geul, J. ASM

3 Gillebaart, E. ASCM

1 Giyanani, A. WE

2 Groot, K. AERO

10 Gutierrez Alvarez, J. ASCM

10 Hasan, Z. SI&C

11 Ho Huu, V. ATO

9 Ho, H.W. C&S

6 Hong, Z. ASCM

6 Huang, Y. C&S

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3 Hoorn, van N. ASCM

2 Hu, W. AERO

3 Janssen, S.A.M. ATO

3 Jain, V. AERO

1 Jatiningrum, D. C&S

8 Jovanov, K. ASCM

9 Junell, J.L. C&S

1 Kadathanad, S.R. ASM

1 Koop, L. ANCE

7 Koornneef, H. ATO

7 Koutras, N. SI&C

10 Krishnasamy, J. ASCM

8 Kupski, J.A. SI&C

3 Lancelot, P.M.G.J. ASCM

10 Landman, H.M. C&S

8 Lavalette, N.P. SI&C

5 LeBlanc, B.P. WE

6 Li, Y. ATO

1 Ligterink, F. SI&C

9 Liu, Y. ASM

6 Lu, T. C&S

3 Mahapatra, G. ASM

12 Malgoezar, A.M.N. ANCE

7 Mannucci, T. C&S

9 Mao, X. ASM

2 March, G. ASM

9 McGuire, K.N. C&S

12 Merino Martinez, R. ANCE

5 Michelis, T. AERO

6 Miletović, I. C&S

1 Mohammadloo, T. ANCE

3 Mooij, de C. SI&C

8 Natella, M. ASCM

4 Nie, J. AERO

8 Peeters, D.M.J. ASCM

4 Perpignan, A.A.V. FPP

8 Post, W. NovAM

7 Rajabzadehdizaji, A. SI&C

6 Rajan, N.K. WE

11 Rajpal, D. ASCM

5 Rapp, S. WE

11 Reurings, C. SI&C

7 Ribeiro, F. SI&C

9 Rudnyk, I. C&S

1 Sambell, K.A.M. ANCE

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4 Sanadi, D.S. FPP

8 Sanchez Perez

Moreno, S. WE

10 Sauvage, L.L.F. SI&C

1 Schneiders, J.F.G. AERO

5 Serpieri, J. AERO

12 Sinnige, T. FPP

5 Smeur, E.J.J. C&S

6 Smisek, J. C&S

3 Steinke, T. ASM

4 Stokkermans, T.C.A. FPP

9 Sun, J. C&S

9 Sunil, E. C&S

8 Susa, A. NovAM

2 Tang, J. WE

10 Tapeinos, I. SI&C

1 Terra, W. AERO

9 Tijmons, S. C&S

2 Tol, H.J. C&S

8 Tsiangou, E. SI&C

6 Udluft, H. ATO

7 Uriol Balbin, I. ASCM

12 Velden, van der W.C.P. AERO

9 Verbeek, R.J.D. ATO

7 Viegas Ochoa de Carvalho, P.A.

SI&C

2 Visser, T. ASM

7 Walker, M.S. SI&C

8 Wang, Z. WE

1 Woicke, S. ASM

8 Yu, H. NovAM

7 Zhang, Y. C&S

2 Zhang, Y. AERO

8 Zhong, N. NovAM

5 Zhu, L. SSE

5 Zong, H. AERO

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4. Abstracts

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4.1 Observation Techniques

On the use of HFSB for large-scale experiments in aerodynamics

Giuseppe Caridi

Chair of Aerodynamics, TU Delft

Keywords: Large-scale experiments, Tomographic PIV, Helium-filled soap bubbles, Delta Wing, Vertical Axis Wind Turbine Tomographic PIV has been employed in a wide range of small-scale applications since its introduction in 2006. One of the recognized limitations of this technique is the extent of the measurement volume, limited to a typical size of a few hundreds of cubic centimeters, especially in airflow experiments with micron-size particle tracers. This hampers its use in industrial applications. Most of the constraints are related to the flow seeding, scene illumination and imaging of the particles. The purpose of the present project is to overcome these limitations in order to develop image based techniques for industrial wind tunnel applications. The research will focus on the use of a new type of flow tracer in the PIV scenario, the Helium Filled Soap Bubbles (HFSB). The neutral buoyancy condition reached with HFSB tracers has been recently shown to combine the higher scattered intensity with good tracing fidelity. The time response of HFSB was measured in the range of 10-30 µs and proves that these tracers are deemed suitable for quantitative studies in low-speed aerodynamics. Moreover, the neutrally buoyant condition avoids that the tracers are centrifuged out of the vortex core, as in the case of micron-size droplets (oil- and water-based). Experiments performed on Leading Edge Vortices over a Delta Wing at Re=105 show that the use of HFSB can improve vortex core velocimetry. Finally, the HFSB are used to study the structure and dynamic evolution of a tip vortex released by a Vertical Axis Wind Turbine (VAWT) of 1 m diameter.

In-Orbit Phasing of a Segmented Deployable Telescope

Dennis Dolkens

Chair of Space Systems Engineering, TU Delft

Keywords: Optics, Earth-Observation, Telescopes, Calibration, Active Optics Deployable optics have the potential of revolutionizing the field of high resolution Earth Observation. When the primary mirror of a telescope is split up into smaller segments, it will be possible to offer the same resolutions as a conventional telescope, while using a much smaller launch volume and mass. As such, the costs of high resolution image data can be brought down drastically. In addition, the technology

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will ultimately enable resolutions that are currently unattainable due to limitations imposed by the size of launcher fairings. One of the critical technological challenges that must be faced to enable diffraction limited imaging is the phasing of the primary mirror segments. To reach a diffraction limited performance while operating in orbit, the relative position of each individual mirror segment must be controlled to a fraction of a wavelength. Reaching such accuracies with deployable telescope are challenging, due to inherent uncertainties in the deployment mechanisms. Adding to the complexity is the fact that the telescope will be operating in a Low Earth Orbit (LEO) where it will be exposed to very dynamic thermal conditions. Therefore, the telescope will be equipped with a robust calibration system. In this presentation, the characteristics of such a system will be discussed.

Innovation in acoustic data processing for seabed classification

Timo Gaida

Chair of Aircraft Noise and Climate Effects, TU Delft

Keywords: Seabed classification, multi-beam echo-sounder, marine geophysics, underwater acoustic The composition of the seabed is of high interest for several different environmental and economic disciplines. A variety of acoustic remote sensing systems such as side scan sonar, single- or multi-beam echo-sounder provide the opportunity to investigate the composition of the seabed. These marine systems emit short acoustic pulses interacting with the seabed. Specific processing techniques for the acoustic data is required to obtain the seabed composition. The PhD research is about the development of innovative data processing methods to increase the performance of seafloor classification using acoustic remote sensing systems.

Study of Lidar configurations for wind turbine control

Ashim Giyanani

Chair of Wind Energy, TU Delft

Keywords: remote sensing, Lidar data, wind resource assessment, wind data analysis

Remote sensing of the atmospheric variables with the use of LiDAR is a relatively new technology field for wind resource assessment in wind energy. The validation of LiDAR measurements and configurations is of high importance for further applications of the data. Within the framework of LAWINE (Lidar Applications for Wind farm Efficiency) project initiated by ECN, The Netherlands in cooperation with XEMC Darwind, AventLidar Technology and TU Delft under the framework of Top consortium for Knowledge and Innovation Offshore Wind (TKI‐WoZ), two measurement campaigns are carried out to evaluate the applications of LiDAR in wind energy. The project lays emphasis on testing and developing the LiDAR technology, optimisation of wind turbine control, load reduction and optimisation of wind farm operation.

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Different configurations of Lidars are available for different purposes. The vertical pulsed and continuous wave Lidars are suitable for wind resource assessment, while the scanning and the forward/back looking Lidars provide the wind speed measurements for prediction of the wind speed at the wind turbine and downwind of the turbine i.e. wakes. There are certain limitations in different configurations and hence, a study to determine the most optimal Lidar configuration based on the synthetic wind field and LES wind data is performed. The pattern of scanning, the temporal and spatial resolution and the type of the Lidar used are the main parameters to determine the applicability to control purposes based on the meteorological viewpoint are studied. In addition to these parameters, the study of effect of weighting functions and the uncertainty in the wind speed predictions are also studied.

In this paper, the optimal configurations for estimating the wind speeds at the wind turbine are suggested. Efficient wind turbine control mechanisms are required in order to reduce the fatigue and bending loads on the wind turbines and to keep the wind turbine in operation at the same time. The measurement of atmospheric turbulence and it’s evolution towards the wind turbine has been critical for the success of Lidars for their application for control over other measurement techniques and hence, the possibility of accurate turbulence estimations are studied with the help of Lidar measurements, synthetic wind field and LES wind fields. This study will thus provide a basis for understanding the configurations of Lidar necessary for future wind turbines commercial and research applications.

Investigating Misalignment in a 3-Axis Angular Accelerometer Measurement Unit

Dyah Jatiningrum

Chair of Control & Simulation, TU Delft

Sensitive axis misalignment of an Angular Accelerometer Measurement Unit (AAMU) is investigated using a standard multi-position test and a particular misalignment test. The AAMU new concept constitutes an array of single-axis angular accelerometers, mounted in a 3-axis orientation, perpendicular to each other. The angular accelerometer sensor response is acquired both in the sensor sensitive and non-sensitive axes using a specified oscillatory input. The cross-axis sensitivity then determined from the spectral components in the frequency domain data and subsequently employed to calculate the angular misalignment. The misalignment characteristics will govern the AAMU implementation in the future flight control systems.

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Coastal Ocean Application of CryoSat - 2 SAR Mode

Sowmini Kadathanad

Chair of Astrodynamics and Space Missions, TU Delft

Keywords: CryoSat-2 SIRAL, Delay Doppler Altimetry, land contamination, coastal ocean, North Sea

Satellite Altimetry, a matured and proven methodology, has contributed greatly to the field of earth observation. Within that space, the success of several radar altimetry missions, starting from GEOSAT, Topex till the recent CryoSat-2, confirms the possibilities this technique has to offer. Earlier missions relied on pulse limited altimetry - which is well studied and investigated whereas the recent missions like CryoSat-2, Sentinel-3 and the upcoming mission Jason-CS, are based on an advanced technique namely Delay Doppler Altimetry (DDA). Altimetry above open ocean is considered simple whereas altimetry for the coastal region can be challenging. Thus, coastal altimetry using DDA is quite interesting and demanding and it is in this respect that the use and optimisation of CryoSat-2 SAR data becomes relevant. The amount of potentially usable, un-utilized data that is generated from the various operational altimetry missions is significant. A big chunk of those data are altimetry measurements recorded from the coastal regions. Coastal areas are densely populated and, at the same time are more prone to the impacts of climate change. This triggers the need to better utilise the altimetry data closer to the coast more efficiently and productively. The main goal of this research is to develop signal processing algorithms that can eliminate or reduce the effect of land contamination from the SAR mode Full Bit Rate (FBR) data from CryoSat-2. This should then lead to a more realistic resolution of geophysical parameters like sea level, significant wave height and wind speed along the coast of North Sea.

Using acoustic remote sensing for seafloor habitat and sediment mapping

Leo Koop


Keywords: Multi-beam echo-sounder, Habitat mapping , Sediment mapping, Dutch North Sea, Acoustic remote sensing This study aims to improve the methods for benthic habitat mapping in the Dutch North Sea based on acoustic remote sensing. Since the introduction of the multi-beam echo-sounder there is the means to create full-coverage bathymetry and backscatter maps of the ocean floor. But standardized data interpretation tools for sediment and habitat mapping are lacking. As a first step to solve this problem the current mapping tools are examined with the view toward monitoring, maximizing the extraction of information from a dataset, and providing the means for a multi-sensor approach. Early results indicate that good monitoring tools exist, but there is a need for increased information extraction, as well as, the need to combine data from multiple sensors.

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Assessing the need to account for the use of FM signals in predicting the MBES bathymetric

uncertainties

Tannaz Mohammadloo


Keywords: baseline decorrelation, CW pulses, Doppler effect, degradation in bathymetry measurement performance, FM pulse, total bathymetry uncertainty

Modern MBES systems have the option to use FM signals, whereas in the past only CW signals were employed. FM signals enable emitting long pulse lengths allowing for measurements at larger ranges (increase in the attainable swath). However, in contrary to the expectations, the performance of the bathymetry measurements has been decreased when switching from CW to FM pulse. Doppler effect and baseline decorrelation have been identified as the error sources deteriorating the depth uncertainties in case of using FM. The objective of the present contribution is twofold: i) quantifying the bathymetry error for FM and CW pulse shapes due to the two sources in case of using high frequency MBES with large bandwidth in shallow water and ii) comparing the contribution of these error sources to the total uncertainty budget and assessing whether the modification of the bathymetry uncertainty model is required. The bathymetry uncertainty induced by the Doppler effect can be categorized into beamsteering and Dopplerized matched filter errors. The former exists both for FM and CW pulses and is approximately 80% of the total error budget predicted. However, the error due to Dopplerized matched filter exists only for FM pulse and can be as large as half of the error budget. Neither of these contributions have been taken into account in the current model describing the depth uncertainty. To take them into consideration and obtain a more realistic description of the bathymetry uncertainty, models describing random depth error due to the uncertainty in roll and steering angle and range measurements are to be modified. The Baseline decorrelation induces an error on the phase difference when using either pulse shapes resulting in the bathymetry uncertainty. The magnitude of this error source depends on the pulse shape and its parameters. For the CW and FM pulses the bathymetry uncertainty due to baseline decorrelation decreases with shortening pulse length and widening bandwidth. Although baseline decorrelation has not been considered in the current model for the bathymetry uncertainty, the term describing the random depth error due to uncertainty in the measurement of the impact angle can be related to this error source. Its contribution to the total depth uncertainty is insignificant and current approach gives a reliable description of depth uncertainty.

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Deriving deep ocean temperature changes from the ambient acoustic noise field

Karlien Sambell


Keywords: ambient noise, hydroacoustics, deep ocean temperature, interferometry, acoustic velocity Passively deriving the deep ocean temperature is a challenge. However, knowledge about changes in the deep ocean temperature are important in relation to climate change. In-situ observations and satellite observations are hardly applicable. Low-frequency sound waves of a few hertz can penetrate the deep oceans over long distances. As their propagation is temperature dependent, these waves contain valuable information that can be used for temperature monitoring. In this study, the use of interferometry is demonstrated by applying this technique to ambient noise measured at two hydrophone arrays located near Robinson Crusoe Island in the South Pacific Ocean. The arrays are separated by 40 km and located at a depth of 800 m. Both arrays consist of three hydrophones with an interstation distance of 2 km. It is shown that the acoustic velocity, and with this the temperature variation, can be derived from measured hydro-acoustic data. Furthermore, the findings are supported by ocean models that describe the propagation of sound between the hydrophone arrays. This study shows the potential of using the ambient noise field for temperature monitoring in the deep ocean.

Beyond Nyquist

Jan Schneiders


Keywords: aerodynamics, measurements, data assimilation, Navier-Stokes, pressure A novel flow measurement system for time-resolved volumetric measurements in wind tunnels at industry scale and high spatial resolution is proposed. The presentation covers the hardware aspects of such a system and focusses on advanced data processing techniques that make use of the flow governing equations. In particular, the ‘vortex-in-cell plus’ (VIC+, Schneiders and Scarano 2016, Exp. Fluids) is presented that recovers instantaneous flow properties at high spatial resolution by making use of the vorticity transport equations and particle tracking measurements, thereby bridging the gaps between computational and experimental fluid dynamics.

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Stereo vision landing system for increased autonomy and robustness during planetary

landings

Svenja Woicke

Chair of Astrodynamics & Space Missions, TU Delft

Keywords: computer vision, planetary landings, safety, hazard detection and avoidance, camera Landing a vehicle on a planet or moon is never a trivial task. To date we have only mastered to perform this task on a couple of bodies in our solar system. And even for those bodies where we successfully delivered landers to the surface, our capabilities are still not such that we can go to any desired location with high accuracy. We are therefore developing a system which can enable the lander to see and make autonomous, real-time, decisions. This can increase the navigation accuracy as well as the landing safety. We are using stereo cameras to reconstruct a 3D model of the planetary surface, which is then used to assess the safety of the landing site. By this hazardous landing regions become feasible targets. But not only are the cameras used for hazard detection, the cameras are also used to localise the lander with respect to the surface, which allows for more precise landings. Our system will therefore make more accurate and safer landings possible.

Evaluation of aerodynamic drag of a full-scale cyclist model by large-scale tomographic-PIV

Wouter Terra


Keywords: Tomographic PIV, aerodynamic drag, HFSB, large-scale measurements, cycling aerodynamics Experiments are conducted to determine the drag of a full-scale cyclist model in a wind tunnel at 4 m/s. The aerodynamic drag is evaluated from tomo-PIV measurements in the wake of the model applying the conservation of momentum within a control volume. The measurements are conducted in a thin volume of 100 x 170 x 3 cubic centimeters using helium-filled soap bubbles as flow tracers. The aerodynamic drag from PIV measurements is compared to standard balance measurements, obtaining an agreement between the two results within 2%.

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Rembrandt’s ink drawings Reconstructing the past, analyzing the present and predicting the future

condition of Rembrandt’s ink drawings

Frank Ligterink

Chair of Structural Integrity & Composites, TU Delft

Keywords: Rembrandt's ink drawings, hyperspectral imaging, physical modelling, visualisation

Rembrandt's ink drawings on paper represent an important core of his oeuvre as a continuously experimenting artist. Until recently their material characteristics could not be studied as a result of the limited suitability of available analytical techniques. Due to recent technical advances new opportunities arise. For the first time, Rembrandt’s drawings from several of the world’s most important collections are focus of an integrated trans-disciplinary research. This (dual PhD) project aims to develop novel ways of looking at these drawings by answering scientific questions that are key to a deeper appreciation of the drawings and a better informed conservation decision making.

To explore the making and aging of the drawings, in this research state-of-the-art techniques such as hyper spectral imaging, micro-sampling, chemical characterization, physical modelling and data visualization are merged with historic research and experimental art technology. All types of data acquisition in this project, ranging from analytical measurements to historic research, will be targeted to feed into an integral material-biography model of Rembrandt's ink drawings.

Visual reconstruction of their genesis, their past, and prognosis of their future will help museums to keep these precious but highly sensitive artworks optimally accessible to future generations and will shed light on their hidden stories.

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4.2 Gas Dynamics

Shape Optimisation for Dynamic Fluid-Structure Interaction Problems

Jaco Brandsen

Chair of Aerospace Structures & Computational Mechanics, TU Delft Chair of Wind Energy, TU Delft

Keywords: Fluid-structure interaction, transient shape optimisation Behaviour driven by fluid-structure interaction (FSI) is exhibited by many systems in aerospace engineering. Examples include both onshore and offshore wind turbines, airborne wind energy systems and aircraft wings. Furthermore, each of these devices operates under conditions that are transient. The goal of the present PhD project is to utilise transient shape optimisation techniques to enhance the performance of aerodynamic devices, such as these, by optimising the aerodynamically active shapes of each device with respect to its unsteady operating conditions.

The first part of the project is currently in progress and involves developing a FSI simulation tool. The simulation tool consists of the open-source, computational fluid dynamics (CFD) code, Fluidity, coupled to a rigid body dynamics code that represents the geometry of the structure using methods found in computer-aided design (CAD) software (specifically non-uniform rational basis splines (NURBS)). The second part will consist of integrating the simulation tool with a transient shape optimisation algorithm to form a FSI shape optimisation tool. The FSI shape optimisation tool will then be used to modify the shapes of devices from the field of aerospace engineering, especially those from wind energy, to improve their aerodynamic performance.

Development Status of a Low Pressure Micro-Resistojet for Nano- and Pico-Satellites

Dadui Cordeiro Guerrieri


Keywords: Micro-resistojet, Low-Pressure, Rarefied Gas Dynamics, Water, MEMS

A Low Pressure Micro-Resistojet is under development at TU Delft with the intention to provide future nano- and pico-satellites with the necessary capability to execute formation flying maneuvers, orbit change maneuvers and/or station keeping. In this particular type of electro-thermal thruster, water, or another intrinsically safe propellant, is stored as a solid and operated at very low pressure, under sublimation conditions. The vapor formed at the surface flows to a series of hot microchannels (micronozzles) in a heater chip. In the hot micronozzles the flow is heated and expanded at high Knudsen numbers to a high exhaust velocity. This concept is very

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promising when associated to the typical Cubesat and pocketQube requirements that demand for low tank pressure, low system mass, intrinsic safety, “green” propellants – non-corrosive, non-flammable, non-toxic, with limited energetic content – and a sufficiently long operational life. The present work will show the current status of development of this promising micro-propulsion system, keeping an eye at the plans for its in-flight demonstration.

BiGlobal stability analysis of a micro-ramp wake using PIV base flows

Koen Groot


Keywords: laminar-turbulent transition, BiGlobal stability Micro-ramps are micro vortex generators that are applied to suppress Shock-Wave/Boundary-Layer Interaction (SWBLI), encountered in supersonic internal flows like supersonic inlet cones. Hairpin shaped Kelvin-Helmholtz waves are observed in tomographic PIV experiments on a wake of such a micro-ramp. In this study, these waves are reproduced by applying BiGlobal stability theory to base flows conceived with the measurement data. The stability results converge with the number of instantaneous snapshots used for the base flow. The most unstable wavelength lies in the experimentally observed range and the flow structure closely resembles that shown in the snapshots.

Introduction to Shock wave/boundary layer interactions

Weibo Hu


Shock wave/boundary layer interactions (SWBLIs) has been the focus of most concern for researchers since supersonic flight and become an important basic theoretical subject of fluid mechanics, aerodynamics and thermodynamics at present. There are still many open questions of SWBLIs to be solved in aerospace domain. American Air Force Office of Scientific Research (AFOSR), National Aeronautics and Space Administration (NASA) and Sandia National Laboratory (SNL) launched the National Hypersonic Foundational Research Plan in 2000 and SWBLIs are one of the major content. Europe, Australia and Japan have set about the related research and made great contributions in the last decades. SWBLIs are common in high speed flows, and they significantly degrade the performance of transonic aerofoils and supersonic inlets for the response of the low momentum regions of the boundary layer. For transonic aerofoils, shock wave in supersonic region interferes with boundary layer and induces the separation of flow which may degrade the aerodynamic performance of aerofoils. Moreover, the resonance of aerofoils can cause stall of aircrafts and failure of aerofoils structure due

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to unsteady shock wave vibration. For supersonic inlets, there is an adverse pressure gradient on the boundary layer due to the incident shock wave, thus causing the increase of boundary layer thickness and separation of flow. This can trigger decrease of the total pressure recovery coefficient of inlet, significant distortion and even unstart of inlet as a result of added aerodynamic blockage. Therefore, there is a strong need to study SWBLIs.

Thermosphere density data using satellite accelerometer observations and DSMC method

Guenter March


Keywords: Thermosphere, Density, Accelerometer, DSMC, Satellite Dataset, Geometry modelling. In the last years, the accelerometers on CHAMP, GRACE, GOCE and Swarm satellites provided high-resolution thermosphere density data. These observations considerably improved the knowledge on atmospheric dynamics. Because most of this research has focussed on relative changes in density, scale differences between these satellite datasets have been largely ignored. These scale differences originate from errors in the aerodynamic modelling, specifically in the modelling of the satellite outer surface geometry and of the gas-surface interactions. Through detailed 3-D satellite models, improved thermosphere density data are going to be provided as the outcome of this work. The detected errors are directly related to the use of closed-form solutions, which are only available for simple shapes. In this investigation, a more accurate approach for determining aerodynamic coefficients for complex satellites has been selected. Indeed, the accuracy of geometry modelling is improved using the Direct Simulation Monte Carlo method. This technique includes the possibility to investigate ow shadowing and complex concave geometries with different gas-surface interaction models. Scale differences of the density datasets are investigated for a group of satellites, which includes CHAMP, GRACE, GOCE and Swarm. Finally, the thermosphere density data are provided by processing satellite accelerometer observations. By making use of the proportionality between the density and the aerodynamic acceleration, datasets are compared and geometry modelling errors are reduced. This improvement provides the possibility to enhance the understanding of the atmospheric dynamics, its energy balance and the role of climate change in the upper atmosphere.

Experimental Investigation of a ducted wind turbine

Juan Tang


Keywords: actuator disc, axial momentum theory, diffuser, ducted wind turbine. This study presents an experimental investigation on a ducted wind turbine or shrouded wind turbine, also known as diffuser augmented wind turbine (DAWT). At the beginning, a screen mesh is used to simulate the energy extraction mechanisms of a wind turbine in experiment. Different screen porosities corresponding to different

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turbine loading coefficients are tested. Measurements of the thrust, of the velocity distribution in different planes and of the pressure distribution along the duct are reported. The general purpose is to highlight the dependency between the diffuser and the screen, and to compare the velocity distributions in the diffuser between unloaded and loaded conditions. It is shown that the thrust on an unshrouded screen is lower than on a shrouded screen, under the same inflow condition. Moreover, the thrust on the diffuser largely depends on the screen loading. For the present configuration, the thrust on the screen with high loading coefficient contributes for more than 70% of the total thrust on the ducted wind turbine. Smoke visualizations and radial velocity profiles reveal that the high loading screen induces flow separation on the outer surface of the diffuser, justifying the results of the thrust measurements. It is also inferred that the flow separation leads to loss of thrust and has a great effect on the total pressure drag. It should be emphasized that the experimental results indicate that the flow field around the diffuser is strongly affected by the choice of screen porosity, that is, turbine loading. And that, the thrust coefficient of the diffuser does not show a linear dependence on the thrust coefficient of the screen. The axial momentum theory, therefore, is not a solid predictor for DAWT performance with high loaded screens.

Active flow control for boundary layers

Henry Tol

Chair of Aerodynamics, TU Delft Chair of Control & Simulation, TU Delft

Keywords: Closed-loop flow control, hydrodynamic stability, transition, model reduction, drag reduction Active flow control (AFC) is considered as a viable route to further push the performance boundaries of transport aircraft for drag reduction, noise suppression and lift enhancement. In closed-loop AFC one utilizes sensor information regarding the state of the flow, along with a model of the flow, to devise controls that alter the flow in its desired state. Such systems are most promising for efficient flow control. This work focuses on maintaining laminar flow for drag reduction by delaying or preventing transition to turbulent flow. By applying control through actuators/sensors acting only on a small localized part of the flow, a laminar flow can be maintained by only minute amounts of control energy expense. A new approach is presented for modelling and control of instabilities in the localized control domain. A reduced order model is derived that captures the input-output behavior and the dominant perturbation dynamics. This model is used to design an optimal controller for suppressing the instability growth to delay transition. A channel flow and a boundary layer flow over a flat plate are considered as application cases. Disturbances are generated upstream of the control domain and the resulting flow perturbations are estimated/controlled using wall shear measurements and unsteady blowing and suction at the wall. It will be shown that the controller is able to cancel the perturbations and is robust to unmodelled disturbances.

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GOCE Torque Modelling and Thermospheric Density and Wind Extraction

Tim Visser


Keywords: Satellite aerodynamic modelling, Satellite torque modelling, Multivariate splines, System identification, Global optimization, Particle-surface interaction, Free molecular flow The Gravity field and steady-state Ocean Circulation Explorer (GOCE) was launched in 2009 to map the gravity field of the Earth in unprecedented detail. Four years later, the propellant for its ion thruster ran out, which ended GOCE’s drag free flight. Three weeks later, on November 11 2013, the 5 meter long ‘Space Ferrari’ re-entered the atmosphere.

At 250 kilometres altitude, the orbit altitude of GOCE, aerodynamic forces form the largest disturbance. Previous research into the measured accelerations has resulted in a detailed view of the exact scale of these forces. Due to the extremely high sensitivity of GOCE’s accelerometers, the measurements could even be used to derive thermospheric density and crosswind. Contrary to GOCE’s linear accelerations, the angular motion of the spacecraft has not been analysed in detail yet. Therefore we have developed a set of models to predict the torque exerted on the satellite by aerodynamic effects, magnetic disturbances, control systems, the gravity field, the ion thruster, and the solar radiation pressure. The residual torque shows signs of unmodeled aerodynamic signals, as well as extra magnetic or charging effects. To extract the remaining information, a multivariate spline based algorithm will be constructed. In this algorithm, each torque will be represented by a spline of a fixed structure, but with custom constraints. If constraints are set properly, a simultaneous global optimization of all spline models will allow for refining the thermospheric density data and estimating vertical wind and other aerodynamic parameters, while at the same time correcting any faults in the other models.

Development and application of spectral structure preserving discretization to boundary layer flows

Yi Zhang


Development, analysis and application of structure-preserving variational multi-scale methods to transitional boundary layer flow. Boundary layers play an important role in all flows. Resolution of all length and time scales in numerical calculations is necessary for the correct prediction of drag and moments. The strong interaction between small and large scales and the large ratio of large over small scales requires enormous computational resources. In this project, we want to set up separate models for the large and the small scales. These small and large scales need to be

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coupled in such a way that basic physical symmetries (momentum, kinetic energy, helicity, mass) are correctly transferred between them. In order to do this structure-preserving spectral element discretizations will be employed. The structure-preserving part of this research aims to represent the basic physical laws (conservation laws) exactly in the discrete setting, while the combination with spectral element methods provides high-resolution schemes. The variational multi-scale approach will reduce the computation times considerably.

4.3 Numerical Modelling

Proportional valve modelling and control for micropropulsion applications

Marsil de Athayde Costa e Silva


Keywords: Micropropulsion, microvalve, vaporizing-liquid-microresistojet, modelling, control Thrust control is an important feature for micropropulsion systems to be used in the next generation of nano- and pico-satellites. It concerns the ability of controlling the direction and magnitude of the thrust vector and will break the current dependency on the attitude control system (ACS) to correct disturbances allowing the development of propulsion systems that are able to independently perform precise attitude and orbital maneuvers. This will allow the execution of optimized maneuvers. On example of such maneuvers are velocity increments, that are very important in formation flying missions. Typical micropropulsion systems usually compensate the disturbances in the thrust direction using the ACS to constantly correct the attitude, which poses a limitation in the achievable performance of the propulsion system. The magnitude control can be achieved by controlling the mass flow in the system therefore affecting directly the thrust level. In propulsion systems using liquid propellants, including the resistojets, flow control is done by regulating the opening of a proportional valve in the feeding section thus increasing or decreasing the mass flow. In this paper we present the development of a mathematical model to represent the dynamics of a proportional valve to be used as a means for controlling the mass flow in a micro-resistojet. The modelling is considering a simple case in which the inlet volume is controllable and affects the volumetric flow and the outlet pressure. The equations for this case, although simple, are highly nonlinear and not solvable by means of standard analytical mathematical procedures, which requires a linearization around an operational point or a numerical solver approach. The model is compared to standard CFD (Computational Fluid Dynamics) solutions to validate it and then it is tested in a closed-loop simulation with a controller. Aspects such as controllability and observability are also evaluated since the boiling of propellant in the chosen device represents a source of disturbances that might produce unwanted behavior or degrade performance. Results are evaluated in terms of response time, stability, and

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levels of actuation compared to the typical performance required to micropropulsion applications and used to validate this innovative framework for micro flow control.

Hybrid Eulerian-Lagrangian flow solver for multi-body fluid-structure interactions

Carlos Baptista


Keywords: domain decomposition, mesh-particle methods, hybrid Eulerian-Lagrangian flow solver, CFD, vortex methods Current Eulerian flow solvers (i.e. mesh-based solvers like Finite-Volume and Finite-Element codes) are very efficient in accurately resolving near-body flow features. On the other hand, these flow solvers are not well suited for resolving vortical structures in wakes due to the numerical dissipation associated with mesh-based methods. Although, high-order methods and fine meshes can be used to diminish this problem, it comes at the expense of severely increased computational cost. An alternative is to apply Lagrangian flow solvers based on vortex methods. The computational elements carry circulation and convect along with the flow. This mesh-free approach does not suffer from numerical dissipation and is intrinsically adaptive since the computational elements propagate only to regions where vorticity exists. The downside, however, is related to the isotropic character of the computational elements which make them too expensive for resolving boundary layers, where the flow is predominantly anisotropic and uni-directional. A more effective approach follows from decomposing the computational domain into distinct sub-domains on basis of the flow features present in each region of the computational domain. This way, multiple flow solvers can be employed simultaneously, where each flow solver is applied only for the sub-domain it is best suited for. The resulting hybrid flow solver benefits from the aforementioned advantages of Eulerian and Lagrangian flow solvers, while not suffering from any of their disadvantages. The aim of this project is to develop a 3D hybrid Eulerian-Lagrangian flow solver which out- performs both full-Eulerian and full-Lagrangian ow solvers in simulating multi-body fluid-structure interactions like propeller-wing interactions and the interaction between wind turbines in a wind farm.

Saving GRACE, A new model to use GRACE data to monitor climate change

Bas Blank


Keywords: GRACE, GIA, FE / FEM, Gravity, Geophysics

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In these times of climate change, the phrase ‘keeping you head above the water’ seems to get new meaning. Melting glaciers and rising sea-levels are beginning to become a greater concern for governments as approximately 50% of the global population lives in coastal areas. For this reason it is of great importance to be able to accurately monitor the change in land ice. Fortunately technological progress has come far enough that we now have almost 15 years’ worth of direct mass measurements of the polar regions from the GRACE (Gravity Recovery and Climate Expert) satellite mission. There is one downside to using the GRACE data. As GRACE does not only measure changes in ice mass but the ambiguous nature of gravity data means GRACE measures all changes in mass, including the ones beneath the Earth’s crust. Therefore I am developing a new model that is able that is able to simulate the effect of ice mass changes on the entire Earth system. This ranges from sea-level changes to changing mantle flows as a consequence of so called Glacial Isostatic Adjustment. This model is constructed in the commercial Finite Element (FE) package ABAQUS. It will differentiate itself from previous similar models by providing a model with a higher resolution and a more complex model of the Earth’s interior. Also the effect of rotational dynamics on the gravity field will be included. Finally the effects of erosion will also be incorporated in this model. Not only will this model pave the way to monitor ice mass changes with a higher accuracy than ever before, but it will also help us to increase our understanding of the very planet where we are trying ‘to keep our heads above water’ on.

Bayesian Uncertainty Quantification of Wake Models

Laurent van den Bos


Keywords: Uncertainty Quantification, Wind Energy, Bayesian model calibration, Turbine wakes, Epistemic uncertainty In the field of Uncertainty Quantification two types of uncertainties can be considered: aleatory and epistemic uncertainty. The first describes uncertainties that are inherent to the problem and are often modelled using statistical distributions, such as random boundary conditions. Epistemic uncertainties describe uncertainties that are inherent to the model, such as model errors, assumptions, and numerical errors.

These two types of uncertainties are also present in modelling offshore wind farms. The uncertain weather conditions are typically modelled using statistical models and are therefore aleatory. Advanced models are used to predict the loads, and hence the lifetime of the wind farm. Despite the quality of these models, they are inaccurate due to assumptions and simplifications, which form a source of epistemic uncertainty.

In this talk we will address Bayesian model calibration, which captures the epistemic uncertainty of a model in the parameters of the model. The resulting distributions can be propagated through the model to make predictions under parameter uncertainty. As a specific case we will present the simulation of wakes of

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wind turbines using simple analytical models and calibrate these models using data obtained from Navier–Stokes simulations.

DNS of Rotating Turbulence

Tiago Cabral Santos Pestana


Keywords: Direct Numerical Simulation, Rotating Turbulence, Spectral Energy transfer, High-performance Computing Direct Numerical Simulations (DNS) of forced homogeneous turbulence with imposed background rotation on a grid with up to 1536^3 points is investigated. Results are presented for different rotation rates (Rossby numbers ranging from 0.15 down to 0.004) and compared to the equivalent isotropic turbulence data. In order to elaborate on how rotation redistributes energy within the system, a term-by-term balance in wavenumber space for the energy, dissipation and energy transfer spectra is shown. Due to its importance in turbulence modelling, a particular attention is given to the energy transfer spectrum by further investigating energy backscatter and the dynamics of non-linear triadic interactions. Furthermore aspects of Large Scale computing using High-performance computing are reported.

Designing provable swarms

Mario Coppola


Keywords: swarm, robotics, artificial intelligence, modelling A swarm features multiple homogeneous agents that perform a task in a distributed manner. Each agent only has local knowledge of itself and its surroundings, and makes localized decisions. This implies that individual agents are relatively simple compared to the global task. In fact, they do not even have explicit knowledge of what the global task even is. Nevertheless, when operating in a team, the swarm succeeds in its goal. This ability to fulfill the goal is called an emergent behavior - it emerges from the local interactions between the agents and the agents and the environment. In robotics, using a swarm as opposed to a single advanced unit would bring inherent scalability, robustness, and flexibility to the system, making it an attractive alternative. When it comes to swarm design, however, the link between local behaviors and global behavior is still not well understood. Performance is typically evaluated using simulations and/or real-life tests with often no proof that the swarm will achieve the intended final result, but only statistical measures. This research aims to: 1) better understand the link between local and global behaviors and 2) use that

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understanding to design local behaviors for the individual agents of the swarm. At the moment, the research is still in its infancy. Different paradigms for swarm modelling are being investigated.

Modelling Human Control Behavior in Preview Control Tasks

Kasper van der El


Keywords: Human-Machine Interaction, Manual Control, Modelling, Preview, System Identification Human pilots that are manually steering their aircraft are an integral part of the ``control-loop’’: the human’s control actions influence closed-loop stability and performance. By modelling the human controller in the same ``control-theoretical’’ terms as the aircraft, loss-of-control and pilot induced oscillations can be predicted offline, and aircraft controls and interfaces can be designed to optimally support the human. This research project focusses on modelling human control behavior, in tasks where the human controller can explicitly see the future track he needs his vehicle to follow (called preview). A clear example is when the pilot is approaching the runway with his aircraft, but car driving also involves preview, from the view of the road ahead. Through a series of human-in-the-loop experiments in the SIMONA research simulator and the Human-Machine Interaction Laboratory I will determine on which visual cues human controllers base their control actions. Moreover, I will apply system identification to determine the control dynamics that relate the human’s inputs (visual cues) and outputs (control stick deflections), which relation I will subsequently model using transfer functions. These models will provide new insights in human controller capabilities and limitations; they can predict dangerous modes of the closed-loop pilot-aircraft dynamics without the need for flight tests, and they can be used to optimize the human-machine interfaces of the future, like haptic control devices.

Impact Damage Tolerance of Thick Composite Structures

Niels van Hoorn

Chair of Aerospace Structures and Computational Mechanics, TU Delft

Keywords: Damage tolerance; Impact behavior; Damage mechanisms; Thick composites; Numerical modelling Composite structures are likely to lose a significant amount of their strength due to internal damage as a result of impact events. This low damage tolerance normally results in high knock-down factors to compensate for uncertainties. As a result, composite materials lose the advantages of their high specific strength properties over conventional materials. Beside impact itself, one of the most critical requirements that composite structures must meet is residual strength after impact. The aim of

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this thesis is predict the damage state as a result of such an impact event and subsequently the residual compressive strength in thick composite structures. For these thick composite structures, such as the composite drag brace used in landing gears, even more challenging aspects arise. The prediction will be performed by a numerical model that accurately describes the global and local behavior of a thick carbon fibre reinforced laminate. Global behavior includes response of the laminate such as the force and displacement history during impact. Because impact in a thick laminate normally results in a localised response, dynamic effects like stress waves have to be taken into account. If there is any external damage this will be at the impact location consisting of a small dent, matrix and fibre crushing or particles that are propelled away. The main damage will be internally in terms of matrix cracking and delaminations. Appropriate failure criteria and modelling techniques have to be selected to accurately describe the damage mechanisms. In addition the effects of manufacturing in terms of voids, waviness or residual stresses have to be incorporated in the model. The accuracy of the model will be validated by new and previously performed experiments. For thick composite structures in the range of 20-50mm the number of plies could result in a significant computational time. Therefore the efficiency of the model should be taken into account with a minimal decrease in accuracy. In terms of applicability the goal is to propose an implementation of the developed model in a certification approach.

Fluid-Structure Interaction simulations on kites

Mikko Folkersma Chair of Wind Energy, TU Delft

Keywords: airborne wind energy, leading edge inflatable kite, FSI, CFD, aerodynamic modelling

Airborne wind energy is a rather new concept in which tethered devices are used to harness wind energy. Common energy capturing devices are kites which fly in crosswind motion to increase the aerodynamic forces. Leading edge inflatable kites are investigated at TU Delft. They are made of a thin membrane wrapped around a tubular inflatable frame. The kite is a highly flexible structure and therefore the wind loads and structural deformation are strongly coupled which forms a complex fluid-structure interaction (FSI) problem. In this project the aerodynamic loads are calculated by running computational fluid dynamics (CFD) simulations. Finite element method (FEM) is used to calculate the structural deformation. The goal of this project is to develop an FSI simulation methodology for a kite operating in an airborne wind energy system. The simulations are used to understand better the aerodynamics and to improve and evaluate new kite designs.

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Improving satellite collision and re-entry predictions

Jacco Geul


Keywords: space debris, uncertainty analysis, error propagation, conjunction analysis, impact predictions Space is an ever more busy (over 35.000 objects) and dangerous environment. The problem of space debris challenges the very accessibility of Space for human endeavors and must be managed properly. Especially, predictions of collisions between satellites and the impact locations on Earth of re-entering objects are essential for proper risk management and avoidance. These activities are constrained by imperfect knowledge of the objects, computational efficiency (due to the sheer number of objects) and availability of data (i.e., only non-cooperative techniques, such as radar). The quality of these predictions are driven by the accuracy of the initial location (i.e., state), how well we know and model its inaccuracy (uncertainty), and the fidelity of subsequent predictions (error propagation). The state accuracy is dependent on the network of (mostly radar) sensors and estimation routines by the United States Air Force, and can therefore not be simply improved. Instead, the uncertainty modelling, estimation, and propagation are investigated. A novel method for estimating the initial uncertainty is developed. Next, special propagation methods are researched that offer significant improvements in computational efficiency over traditional methods.

Simultaneous Aeroelastic Shape and Stiffness Optimisation of Composite Wings

Erik Gillebaart


Keywords: aeroelasticity, aerostructural optimisation, isogeometric analysis, aeroelastic tailoring, numerical modelling

Conventional preliminary wing design can be described as a sequential process consisting of the following steps:

1. Optimise the airfoil, wing shape and planform for aerodynamic performance at 1g flight 2. Design a structure that provides the optimised shape of the wing at 1g flight 3. Analyse aeroelastic behaviour

Aircraft performance, however, is a delicate balance between aerodynamic efficiency and structural efficiency, as is demonstrated by, for example, the simple Breguet range equation:

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Together with the trends towards more use of composite materials, more slender wings and perhaps deviations from conventional wing designs, this calls for a different design approach. Including the three steps into a single, multidisciplinary optimisation framework enables the possibility to make a trade-off between aerodynamic and structural efficiency, to fully exploit the benefits of composite materials, and perhaps to use aeroelastic effects to benefit the performance. The objective of this research is to create a fast and efficient framework for the simultaneous aeroelastic shape and stiffness optimisation of a (non-)conventional wing, made out of anisotropic material. The isogeometric analysis concept is invoked in all the disciplines involved in the optimisation framework in order to create a unified design and optimisation approach based on the actual CAD geometry of the wing.

Agent-based modelling for airport efficiency and security

Stef Janssen

Chair of Air Transport & Operations, TU Delft

Keywords: Agent-based modelling, Airport terminal, Security, Efficiency, Simulation

Both airport security and airport efficiency are well studied in literature. They are often seen as two separate fields, but intuitively there is a link between them. For instance, if the security checkpoint were to be removed from the airport terminal, efficiency would increase (i.e. no more lines at the checkpoint, lower costs), but the airport would be less secure. This projects aims to find a relationship between airport security and airport efficiency, specifically focused on the airport terminal. It will do so by using a newly developed mathematical definition of airport security, and current definitions of airport efficiency. Using these definitions, the relationship between security and efficiency is studied by using an agent-based model that simulates operations at the airport terminal.

Affordable high resolution reservoir modelling using a multiscale approach

Varun Jain

Chair of Aerodynamics, TU Delft Chair of Wind Energy, TU Delft

Chair of Flight Performance & Propulsion, TU Delft

Keywords: Reservoir modelling, Darcy flow, Mixed finite element, Multiscale methods, Mimetic methods Modelling geological reservoirs is essential to overcome important challenges such as optimal use of hydrocarbon reservoirs, management of earth’s ground water

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resources, geological storage of CO2, etc. Accurate representation of geological features such as faults, fractures or erosion requires geometrically flexible grids. Additionally, highly resolved geological grid models are computationally expensive and coarse grid models based on upscaling techniques are used. Therefore, we intend to construct a numerical method that is geometrically flexible, presents minimal grid orientation effects, and constitutes an accurate and robust alternative for conventional upscaling techniques. The objective is to take the geometric flexibility of the mimetic approach plus the robustness of least-square methods, and extend it to efficiently capture the coarse scale on the primal grid behavior of the solution and the small scale features on the dual grid, in order to bridge the gap between the fine scale details of the geological models and the global flow simulation.

Integration of Active and Passive Load Alleviation Systems on Aircraft Wings

Paul Lancelot


Keywords: aeroelasticity, gust load, optimisation, wind tunnel test, numerical modelling

Load alleviation has been a field of research which has received increased attention over the past decade. This is thanks to the development of light-weight highly flexible wings for modern airliners, long endurance drones, and wind turbines. It has been identified as an efficient way to reduce structures weight and to improve aircraft handling as well as passenger safety and comfort. Current load alleviation strategies mainly rely on the use of ailerons and spoilers. In combination with these methods, the wing structure can also be tailored in such way that it will relieve itself from the loads. Active and passive load alleviation is achieved by a redistribution of the aerodynamics forces inward, caused by negative local angle of attack toward the wing tip, or by deflecting the control surfaces. The advantage of passive load alleviation systems over active ones is to be more reliable and less complex, however they are not as versatile. Therefore this PhD aims to cover the integration of current state of the art devices for load alleviation into an aeroelasticity tailored wing, in order to fulfil both weight reduction and manoeuvrability requirements. The outcome of this project is to obtain “industry ready” technologies, with innovative content for both load alleviation mechanism and design methodology.

Investigating occurrence of circular ring patterns in the ground based polarization signals from Venus

Gourav Mahapatra


Keywords: Venus, clouds, polarimetry, Venus Express, Radiative transfer

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Venus is the closest planet to us, when measured at its closest approach, and it is also approximately similar in size to Earth. It is believed that both planets started with approximately the same composition but the similarities end there because Venus has a very thick layer of atmosphere primarily made up of CO2, the surface temperatures are about 750 K everywhere on the planet primarily due to CO2 which acts as a virtual blanket absorbing the planets thermal radiation and keeping its local temperature high. Its atmosphere has almost no water and the clouds and hazes are made of sulphuric acid droplets. These clouds play an important role in shaping the atmosphere and climate of Venus by scattering and absorbing incident light as well as the internal thermal radiation. Light scattered from the planet’s atmosphere provides a wealth of information about the clouds, haze layers and also the dynamic circulation patterns in the atmosphere. The scattered light also undergoes a change in its polarization depending upon the size and type of droplets which scatter the light. Understanding these dynamic processes on Venus furthers our understanding of the evolution and workings of atmospheres on terrestrial planets. In this work we examine the occurrence of mysterious, narrow rings of varying degree of polarization over the clouds deck of Venus that have been observed from a ground based telescope. We use a radiative transfer code to model the scattered and reflected light in different polarizations due to the various layers of clouds and hazes and we attempt to explain this effect by describing the possible micro and macro-physical clouds and haze properties on Venus. This analysis is a precursor for our future analysis of polarization measurements by the SPICAV instrument that was on board of ESA's Venus Express mission.

Shape Sensing With iFEM

Cornelis de Mooij


Keywords: Shape sensing, iFEM, inverse finite element method, Rayleigh scatter fibre optic sensors, DIC, digital image correlation A new inverse finite element method (iFEM) was developed for shape sensing, to determine structural strain and displacement fields. Given sensor data and a numerical model of the structure, the method can produce an estimate of the deformation of the structure. Previous iFEM techniques have used only a single type of sensor; the new iFEM presented here can utilize data from multiple sensor types. It can also compensate for missing measurements, smoothing over areas of the structure where no sensors are located using Tikhonov regularization, and has been demonstrated for various structures experiencing several different types of load cases. The strain and displacement estimates are compared to predictions from finite element analyses, which showed that the new iFEM algorithm is able to determine structural deformation with greater accuracy than iFEM implementations that were found in the literature, using fewer sensors.

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Identifying Internal Sources of Evolving Volcanic Activity on Io

Teresa Steinke


Keywords: Io, volcanism, tidal dissipation, finite element modelling, viscoelastic rheology

Satellite flybys and recent Earth-based observations indicate that the innermost of the Galilean moons, Io, is by far the most volcanically active body of the Solar system. The reason for that is a strong tidal forcing exerted by Jupiter which leads to a significant internal heating of the body. The mechanism and the exact location of the tidal dissipation, both depending on Io’s interior structure and rheology, however, are not well known. To better understand how Io works, we develop a 3-D finite element model of Io's interior and apply the corresponding tidal forcing. Results show a complicated spatial varying heat flux pattern on the surface. We validate simple spherical symmetric finite elements models based on linear viscoelasticity with existing analytical 1-D models, and present first tests of non-spherical geometry and nonlinear rheology. At a later stage of this work, modelled maps of heat flux pattern shall be compared to available maps of observed heat flux and volcanic features on Io’s surface to provide important constrains on Io's evolution and recent interior properties.

Online Self-learning Adaptive Flight Control for Micro Air Vehicles

Ye Zhou


Keywords: Adaptive control, Incremental approach, Approximate Dynamic Programming, Heuristic Dynamic Programming, Hierarchical approach Abstract: The emerging field of Micro Air Vehicles which often require a high level of autonomy, agility, and reliability, relies heavily on recent advances in control theory, and miniaturization. This research project is to propose an online self-learning adaptive flight control system to allow reliable, autonomous operations of UAV. To meet the constraints of the limited on-board computational power, partial observability, and the ability to adapt to unexpected circumstances, a series of new and effective control methods are proposed based on Reinforcement Learning and incremental approaches: incremental Approximate Dynamic Programming, incremental model based Heuristic Dynamic Programming, and Hierarchical Q-learning.

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4.4 Propulsion

Uncertainty quantification of turbine blade with high-dimensional geometric uncertainties using

multi-level Monte Carlo method

Jun Nie


The geometric uncertainties in turbine blade due to the manufacturing tolerance have the potential to dramatically lower the aerodynamic performance and need to be taken into account in the design stage which leads to aerodynamic robust design. In order to accurately and efficiently quantify the variability of aerodynamic performance under the influence of high-dimensional uncertainties, which is a key procedure in aerodynamic robust design, recently developed Multi-level Monte Carlo(MLMC) method is introduced. MLMC combines the ideas of multi-grid and Monte Carlo method, and can significantly improve the computational efficiency. Along with linear elasticity based mesh deformation technique, MLMC is applied to VKI-LS89 turbine vane with geometric uncertainties to demonstrate its superiority in computational cost saving.

The use of Flameless Combustion in gas turbine engines

André Perpignan

Chair of Flight Performance and Propulsion, TU Delft

Alternatives to combustion for civil aviation are unlikely to be feasible in the next decades. Therefore, improvement of the current combustion systems regarding efficiency and especially pollutant emissions is required. Flameless Combustion (FC) is a combustion regime characterized by well-distributed reaction zones, low acoustic oscillations, and lower NOx emissions. Although its application to industrial furnaces is successful and relatively simple, the attainment of the regime within gas turbine engines is not straightforward. High reactants temperature and low oxygen concentration would require recirculation of combustion products, which is difficult to implement with the given restriction of pressure losses and volume. The PhD research herein presented investigates possible design approaches to successfully use the FC regime in gas turbine engines.

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Insights into Combustion diagnostics

Dilip Sanadi

Chair of Flight Performance and Propulsion, TU Delft Keywords: Combustion diagnostics, Coherent Anti-Stokes Raman Spectroscopy (CARS), temperature measurements

The understanding of intricate combustion physics is of fundamental and applied importance for plethora of industrial application ranging from gas turbine engines, I.C engines, industrial furnaces etc. In order to understand this combustion physics, two most important scalars; the temperature and the mixture fraction is vitally important. Advanced laser-based diagnostics may in general provide these scalers measurements with exceptionally high spatial- and temporal resolution, which is important in producing reliable and accurate experimental data. Coherent Anti-Stokes Raman Spectroscopy (CARS) is one such versatile technique, which has had a profound impact in temperature measurement in reactive flows. The present literature research is centred around understanding Coherent Anti-Stokes Raman Spectroscopy (CARS) technique.

The pusher propeller and its hub vortex drag

Tom Stokkermans


Keywords: Propellers, compound helicopter, aerodynamic interaction, hub vortex, boss cap fins One can view a propeller as an isolated system. While this view simplifies propeller analysis and design, it is in most circumstances not complete. In any realistic application, propellers are located in the vicinity of the airframe, being anything from fuselage to wing, from stators to other rotors. As a consequence of the proximity, aerodynamic interactions occur. This research is about propellers where these interactions are not small anymore. The direct incentive is the investigation of these interactions for a novel compound helicopter with stub wings for lift and two wing-tip mounted pusher propellers for thrust and anti-torque in the Clean Sky 2 PROPTER project. The presentation will be about a problem encountered with the pusher propellers: Hub vortex drag resulting from the low pressure by the formation of a hub vortex from the root vortices of the propeller blades. Investigation is ongoing into spinner design to mitigate this and boss cap fins to benefit from this phenomenon. These fins mounted on the spinner are exclusively found in maritime applications and result in a 3-5% power saving in actual ship operation. Conclusions on the aerial applications are still to be drawn.

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4.5 Control

Multi-Agent based Architectures for Reliable AOCS Software in Satellites

Johan Carvajal-Godinez


Keywords: FDIR, AOCS, Onboard Computers, Multi-Agent Systems, Software Architecture Space missions with satellites are changing. There are two major trends impacting satellite architecture and design. In one hand, the miniaturization of electronic and electromechanical devices is shrinking the size, while increasing the functionality of satellite’s components. In the other side, the adoption of artificial intelligence (AI) technology is needed to develop more autonomous systems. Deploying AI-based algorithms is not straight forward, especially in highly constrained navigation computers onboard the satellites. It requires new ways to organize and pack software components to satisfy the reliability and performance requirements. This project proposes the adoption of Multi-Agent Systems (MAS) based software architectures to deal with dynamic execution environments. The main advantage of MAS-based architectures is its flexibility of operation with little implementation overhead. This investigation focuses in the applicability of such design pattern to improve fault detection, isolation, and recovery (FDIR) of attitude and orbit control subsystem (AOCS) in small satellite missions.

Active Pitch Control of Vertical Axis Wind Turbines

Bruce LeBlanc


Wind turbines have accelerated growth in size and market reach in the last decade. The next frontier of wind energy involves better utilisation of the vast offshore resources that are available across the planet. However, a significantly large portion of this available resource exists in areas with water too deep for conventional driven pile foundations. This has required designers to explore floating platform options. Traditionally however, these floating platform designs incur very high costs due to the large bending moments, and angular tilt requirements of a traditional Horizontal Axis Wind Turbine (HAWT). Due to the many differences in working with a floating platform in an offshore environment compared to a land based turbine, it is necessary to re-examine the concept of the wind turbine from the ground up and see if a design that varies from the 3 bladed upwind HAWT is better for this new case.

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Research into the Vertical Axis Wind Turbine (VAWT) has been progressing over the last few years due to this large shift in design constraints by leveraging tools and experience from research beginning in the 1970s and lasting until the HAWT established market dominance in the 1990s. The beginning studies looking into the feasibility of large VAWT turbines on offshore floating platforms have been largely positive and suggest a large cost savings when comparing to equivalent HAWT turbines. These savings assume certain platform cost reductions as well as ease of operations and maintenance due to certain systems being removed, like the active yaw system, and ease of access to significant components such as the gearbox and generator. In order to realize these cost gains, and perhaps identify more, is to improve the aerodynamic control of the rotor. The most obvious method to control aerodynamic loads on the wind turbine is through control of the pitch of the turbine. With pitch control it will be possible to tailor the loading of the turbine throughout the azimuthal sweep of the blades allowing the possibility of such things as aerodynamic braking, and self-start capability, as well as providing the possibility for advanced control for greater power capture and wake manipulation. This work will outline the design of a test turbine in order to implement individual pitch control on a Vertical Axis Wind Turbine within a controlled environment and will highlight recent experimental results as to the controllability of thrust loads generated by the turbine with pitch control.

On laminar separation bubbles

Theodoros Michelis


The research topic involves understanding fundamental features of a flow phenomenon termed “Laminar separation bubble”. A laminar boundary layer developing along an aerodynamic surface may separate if exposed to sufficiently strong adverse pressure gradient. If the increase of momentum exchange due to laminar to turbulent transition is adequate, reattachment is observed, forming a closed recirculation region near the surface, the “Laminar Separation Bubble”. Due to the requirement of a laminar boundary layer state at the separation location, this phenomenon is usually observed at low to moderate Reynolds numbers, typical in applications such as glider or unmanned aerial vehicle wings. The transition process is highly susceptible to environmental disturbances and the resulting bubble is inherently unstable. As a result, this leads to unwanted impact on aerodynamic performance, such as stall, loss of lift, increase of drag and noise emission. Throughout this work, an AC-DBD plasma actuator is employed to introduce controlled disturbances and trace the response of the separation bubble in terms of dynamics and stability.

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Multicopter Based Launching of a Kite Power System

Sebastian Rapp


Keywords: Airborne Wind Energy, Renewable Energy, Multicopter, Flight control, Robust control For every flying system the most critical flight phases are take-off and landing. This does not only apply to common aircrafts but also to airborne wind energy systems. Therefore, current research effort within the airborne wind energy community focuses on the development of reliable launching and landing concepts. In this contribution a flight control architecture for a multicopter based launching system will be presented. The multicopter is used to pull the kite to the operational altitude. Afterwards the multicopter is disconnected from the kite and lands automatically. For the development of the controller, models for a flexible kite and tether as well as the rigid body dynamics of a quadrotor have been implemented. The performance of the control approach is assessed by means of simulations.

Primary and secondary cross-flow instability

Jacopo Serpieri


Keywords: laminar-turbulent transition, cross-flow instability, flow control Laminar to turbulent flow transition on aerodynamic bodies is of crucial relevance as it involves aerodynamic performances and heat fluxes flow-structure. Swept wings and axial-symmetric bodies inclined w.r.t. the flow or spinning about their axes feature three-dimensional flows. This causes, within the boundary layer, a secondary flow called cross-flow. The cross-flow makes the three-dimensional boundary layers intrinsically unstable. The cross-flow instability is therefore the main cause of transition for these flows. Its understanding captured much interest from the scientific community in the last 30 years. Nevertheless it involves complicated flow mechanisms and their interaction which require advanced flow diagnostic approaches. State of art experimental techniques are employed in the present research. Efforts have been done also towards controlling these mechanisms. Again more advanced, i.e. active, flow control devices are employed for this purpose in this project.

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Guidance and Control of a Swarm of Hybrid Drones

Ewoud Smeur


A swarm of drones can be used to perform measurements in an area. If the area is large, the drones need quite some range to cover it. However, to perform their measurements, they should be able to land anywhere. These two features are combined in a hybrid UAV. A hybrid UAV can take off an land vertically (VTOL) like a helicopter and transition into fast forward flight like an airplane. There are still challenges regarding hybrid UAVs. We work on control strategies for attitude stabilization as well as the guidance and navigation, with a focus on sensor-based strategies like INDI. This way, the hybrid is able to remain stable during hover, forward flight and in between. Furthermore, it is able to estimate the wind speed and compensate for it using a model of the flight dynamics, such that it can track any ground velocity reference. Finally, the swarm of hybrids should be able to perform measurements. To do this efficiently, the nodes that need to be visited should be distributed such that the total time needed to visit all nodes is minimized. In the optimization, we have to keep in mind that not all drones can come back to the depot at the same time, as it only has a limited capacity.

Reaction Sphere for Microsatellite Attitude Control

Linyu Zhu


Keywords: actuator, microsatellites, magnetic bearing, motor A reaction sphere is able to rotate about arbitrary axes. Compared with conventional reaction wheels, the innovative spherical actuator could enhance robustness of a spacecraft's attitude control system. For a satellite with certain targeting requirements, an assembly of three wheels is vulnerable. Non-functionality of any wheel would lead to mission degradation or even failure. However, for spherical wheels, reconfiguration of remaining wheels' momentum direction enables mission to continue operations. Presently, some designs about analogous spherical actuators have been proposed or even developed. Nevertheless, there is none suitable to be applied to small satellites. Limited mass, volume and power budget make desirable momentum storage capability and efficiency challenging to achieve. Here, a new design concept is investigated. Performed numerical simulations demonstrate its feasibility for microsatellites attitude control. Driving of the actuator is given special attention. Based on existing different types of motors' characteristics analysis, a proper principle working mechanism has been selected through the analytical hierarchy process. Motor's modification to sphere and magnetic geometry's optimization are presented. Furthermore, to facilitate the rotor's omnidirectional rotation, an active magnetic bearing is employed. The non-contact support method eliminates friction and wear issues. Feasibility of the proposed design is analysed through dynamic modelling and simulation. Decoupling of electromagnetic driving and levitation is also discussed. The spherical reaction wheel is expected to have a

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mass of less than 1 kg, with 4π rotational velocity up to 8,000 rpm. Power consumption will be limited within 10 W, including suspension and driving.

Electro-mechanical Efficiency of Plasma Synthetic Jet Actuator Driven by Capacitive Discharge

Haohua Zong


Keywords: plasma; synthetic jet; actuator; efficiency; capacitive discharge Plasma synthetic jet actuator (PSJA) is a novel flow control actuator, featured by high jet velocity (>400 m/s) and high working frequency (>5 kHz). A simplified model is established to estimate the jet exit density variation of PSJA driven by capacitive arc discharge. This model, in conjunction with phase-locked planar Particle Imaging Velocimetry (PIV) measurements, enables the calculation of jet mechanical energy for different operating conditions. Discharge energy is directly calculated based on waveforms of applied voltage and discharge current. The ratio of jet mechanical energy to discharge energy provides the absolute electro-mechanical efficiency. Results indicate that PSJA is characterized by a rather low electro-mechanical efficiency in the order of 0.1%, while the maximum observed value under tested conditions is 0.22%. Electro-mechanical efficiency improves significantly with non-dimensional energy deposition, and appears largely independent of jet exit diameter.

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4.6 Performance

Investigation into the aerodynamics of diffuser augmented wind turbines

Vinit Dighe


This study would investigate on the aerodynamics related to diffuser augmented wind turbines (DAWT) using theoretical, experimental and numerical methods; and explore possible ways of further power extraction by using flow augmentation devices. The idea is to maximize the sub-atmospheric pressure at the diffuser exit than the -0.33 found in the near wake of an ideal wind turbine. Numerical simulations would be validated against the experiments conducted in controlled environment. The following study will provide fundamental hints to increase the DAWT performances.

Modelling Human Haptic Threshold of

Control Inceptor Dynamics

Wei Fu


Keywords: Control Loading System, Control Inceptor, Just Noticeable Difference, Human perception threshold

The current requirements on the control loading system in flight simulator need further study. The time domain requirements, which focus on the zero crossings and the oscillations, lack sufficient motivation. The requirements consider the control device in isolation, while the tactile feel is most relevant when the pilot is actually touching the stick. With a pilot holding the control device, the control device and pilot hand become a coupled system. The performance of the control device by itself in the release task does not ensure that the control device will provide an accurate feel to the pilot. A better evaluation should base these requirements on the accuracy of the control loading device with which the pilot can sense the changes in device dynamics.

My research objective aims at a new criterion for the proper evaluation of the fidelity of control loading devices. As the CLS usually resembles the actual control device by a mass-spring-damper featured system, my research therefore started from the Just Notable Differences (JND) in the human perception of mass, damping and stiffness changes. An expected outcome would be a descriptive model of human perceptual thresholds on such featured systems.

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Efficient Sizing of Structures Under Stress Constraints

Zhi Hong


Keywords: sizing optimization; stress constraint; convex optimization; large scale structures; computational efficiency

Optimisation algorithms used to automatically size structural members commonly involve stress constraints to avoid material failure. However the cost of optimisation grows exponentially as the number of structural members is increased due to the corresponding increase in the number of constraints. Therefore the purpose of this PhD research is to design a numerical method to achieve the computational efficiency for large scale stress constrained structural sizing optimisation problems. A bottom-up approach is applied to build up the methodology layer by layer in the iterative framework. First of all, convex optimisation is employed to establish the framework for the proposed method. On the basis of the convex optimization, the predictor-corrector interior point method is utilized for the efficiency of the optimisation. Inside the interior point method, a convex, separable, and scalable approximation for stress constraints which splits the approximation into a local fully stressed term and a global load distribution term is introduced to set up the subproblem. Finally the efficient preconditioned conjugate gradient method (PCG) is used to solve the linear equation iteratively in the subproblem with a new preconditioner proposed. The core idea in this work is to achieve computational efficiency in the optimization procedure by avoiding the construction and the solution of the Schur complement system generated by the interior point method. Avoiding the Schur complement, and explicit sensitivity analysis, eliminates the high cost of solving stress constrained problems within the interior point optimisation. This can be obtained by combining the approximation and PCG together in the interior point method. The proposed method is tested first to work with different types of elements with homogeneous material before expanded to design composite structures. Real engineering problems will be attempted with the method eventually.

A Review of Control Schemes for Hydraulic Stewart

Platform Flight Simulator Motion Systems

Yingzhi Huang


Keywords: Motion control systems, Nonlinear control system, Robustness, Hydraulic robots, Parallel manipulators For current high performance research and training flight simulator motion systems, Stewart platform, also known as hexapod systems, are widely used due to the

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advantages of high stiffness and accuracy, as well as their simplicity. As relatively large forces are applied with actuators of flight simulators, hydraulic actuators dominated high payload simulators for the past decades, owning to their rapid response, high loading capabilities and smoothness. The control schemes on the motion system largely decide the performance of the simulators. Hydraulic systems, as well as hexapod robotic systems, are highly nonlinear and suffer seriously from model and parametric uncertainties, which will significantly degrade the performance of traditional model-based nonlinear controllers such as nonlinear dynamic inversion. The goal of this PhD topic is to apply an innovative sensor-based controller, known as incremental nonlinear dynamic inversion, to the studied systems. The proposed control technology uses less model information and is inherently insensitive to model uncertainties, with assumptions of accurate state measurement and high sampling rate. With a successful implementation, significant improvement of motion control performance of the motion system is expected in existence of model mismatches. The fidelity of flight simulation will thus be improved. The research work includes the development of a detailed fully nonlinear model for a hydraulic hexapod motion system, the development of the sensor-based robust controller for the hydraulic force tracking subsystem as well as the general parallel robotic systems, and the real world implementation of the proposed control system to the SIMONA Research Simulator.

Analysis of ATM features within a complex network model

Yalin Li


Keywords: ATM performance, complex network, network capacity, resilience, equity In the work presented, a simulation tool based on complex network theory is used to evaluate the ATM network performance. Several KPIs (Key Performance Indicators) have been chosen to investigate their relationships with complex network metrics. Preliminary trial to explore the relationship has been launched to investigate by using network scale (nodes number), degree and degree distribution. Consequently, ATM performance has been tested within a complex network developed model. We observed the KPIs of the network and find that they may not simply enhanced by enlarging the network and its capacity of nodes. Also by adding impact on the nodes’ capacity, we observed the performance of the network in order to investigate the importance of different nodes in the network. We also consider the standard deviation of delay to measure the equity of the airports in the network.

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Pilot-Centered Flight Simulator Aircraft Model Fidelity

Tao Lu


Flight simulators are widely used to train pilots not only before their first real flights but also during their full flight careers. Using flight simulators to train pilots are usually safer, cheaper and task-repeatable compared with the trainings using real aircraft. An ideal training effect means that pilots can transfer their skills obtained from the flight simulators to real aircraft seamlessly. It is not only time and cost efficient for airlines but also very crucial in the aspect of flight safety. For example, flight simulators can replicate some flight situations where the aircraft is malfunctioned, like engines shut down or landing gears unable to be withdrawn. In January 15th, 2009, an Airbus A320 (US Airways Flight 1549) was forced to make an emergency water landing after the bird strike induced engines failure in the Hudson River between New York City and Weehawken, New Jersey, and flight simulators played a crucial role in the investigation of this flight accident afterwards. To train pilots in flight situations like approaching or landing, the aircraft model of the flight simulators is a very important factor considering the fidelity of the flight simulators. Aircraft model is usually obtained by large amounts of real flight and wind tunnel tests, thus it is very expensive and increases the total expense of a flight simulator. However, it is unknown whether this high accuracy aircraft model is always necessary in training the pilots, or it is possible to simplify the aircraft model but still able to obtain a similar pilot control behavior. Thus a cybernetic approach is used to objectively quantify the pilot control behavior with different aircraft models. The control task is selected as a compensatory tracking task, which mimics the scenarios of aircraft approaching and landing. If pilot control behavior of the simplified aircraft model is similar from the one of the baseline aircraft model (which is more accurate), it suggests for specific flying tasks like approaching and landing the aircraft model could be built simpler and thus less expensive. The goal of the research is to find a mismatch boundary between the simpler aircraft model and high accuracy aircraft model within which the pilot control behavior remains similar. This boundary may help engineers to better judge the fidelity of the aircraft model for flight simulators in the future.

A Framework to Quantify Rotorcraft Flight Simulation Motion Fidelity

Ivan Miletović


Keywords: Flight Simulation, Motion Cueing, Rotorcraft, Manual Control & Cybernetics, Handling Qualities

Over the last decade, a strong incentive to develop objective metrics for the assessment of flight simulation fidelity has emerged. At the same time, however, it is recognised that the knowledge on human self-motion perception and manual control is too limited to warrant a full understanding of the effect of simulated environment characteristics on

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perceived fidelity. Subjective assessments made by qualified pilots therefore remain the most important measures of flight simulation fidelity demanded by regulatory bodies. A fundamental problem with subjective assessment of simulation fidelity, however, is the difficulty of obtaining reproducible results and, consequently, the lack of accepted standards. The problem is further aggravated by the complexity of the notion of simulation fidelity itself. Many subsystems in a modern flight simulator interact to produce a realistic flight environment to pilots. Often these interactions, and especially their effect on perceived fidelity, are poorly understood. Perhaps the most notorious example is the motion system of a full-flight simulator. In order to constrain the motion of simulators within the available workspace, the vehicle motion computed by a mathematical flight model is processed using so called Motion Cueing Algorithms (MCA’s). MCA’s insuperably affect the motion cues perceived by pilots, though objective standards regarding acceptable levels of mismatch are yet to be defined. The current research project, organised by TU Delft in collaboration with Desdemona B.V. at TNO Soesterberg, aims to formulate a more quantitative framework to approach the problem of motion cueing fidelity for rotorcraft flight simulation. The adopted approach relies heavily on the fundamental knowledge that can be obtained from first-principles rotorcraft flight mechanics models coupled with contemporary MCA’s. Validation of the proposed framework is to take place using pilot-in-the-loop experiments on the DESDEMONA and SIMONA flight simulators in Soesterberg and Delft, respectively.

Aerodynamic analysis of a rigid Leading-Edge-Inflatable Kite

Navi Rajan


Keywords: Immersed boundary, adaptive re-meshing, Airborne Wind Energy, Fluid-Structure-Interaction, Leading-Edge-Inflatable kites Airborne Wind Energy (AWE) is a relatively new name in renewable energy technologies. Flexible kites are used in several concepts that are under development. Leading-Edge-Inflatable (LEI) kites are a subclass of flexible kites. The complex geometry and high angle of attacks make the associated flow phenomena an interesting topic of study. Existing methods utilize approximated fluid-dynamics models to predict this behavior. The flow over an LEI kite has seldom been studied before. Nevertheless, membrane flows have been extensively studied on sail wings and ram air wings. The earliest studies on membrane wings used 2D strip theory. Potential flow models are often modified to account for minor nonlinear-viscous effects. However, potential flow methods are reliable only for attached flows at low angles of attack. To capture the nonlinear effects, mostly CFD has been used. Reynolds-Averaged –Navier-Stokes (RANS) simulations of upwind yacht sails have been validated with experimental results. Even for separated flows, the results agreed well with the experimental data. Both the leading-edge and trailing-edge separations were captured. At large angles of attack, flow separation is expected to occur on the suction side of the kite. From the available literature, it is clear that 2D finite strip approximations or

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potential flow methods are not suitable for separated flows. Previous researches seem to suggest that RANS methods are the best options for aerodynamic analysis of LEI kites. In this study, steady aerodynamic analysis is performed on a rigid LEI kite, which is used in traction based power generation. The TUD-25mV2 kite of the Kite Power group is considered. An Immersed Body (IB) method is applied for solving the flow field on an unstructured grid, and k-ω SST turbulence model is selected for the separated flow. Effects of grid-resolution, angle of attack, and the inflated-leading-edge are examined.

Shared control for teleoperation

Jan Smisek


Keywords: teleoperation, haptics, shared control, human-automation interaction, haptic guidance Teleoperation - performing tasks remotely by controlling a robot - permits the execution of many important tasks that would otherwise be infeasible for people to carry out directly. Nuclear accident recovery, deep water operations, and remote satellite servicing are just three examples. Remote task execution principally offers two extremes for control of the teleoperated robot: direct telemanipulation, which provides flexible task execution, but requires continuous operator attention, and automation, which lacks flexibility but offers superior performance in predictable and repetitive tasks (where the human assumes a supervisory role). My dissertation explores a third option, termed haptic shared control (HSC), which lies in between these extremes, and in which the control forces exerted by the human operator are continuously merged with "guidance" forces generated by the automation. In an HSC system, the operators continually contribute to the task execution, keeping their skills and situational awareness. In my dissertation, I aim to develop a system-theoretical framework that would improve the design and evaluation process of HSC systems.

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Agent-based simulation of decentralized control for taxiing aircraft

Heiko Udluft


Keywords: Agent-Based Simulation; Decentralization; Distributed Systems; Aircraft Taxiing; Airport Operations; Airport Performance The already high demand for air transportation is expected to continue to grow over the next decades. In busy areas and major hub airports, demand for the air transportation system is reaching its capacity limits and further demand cannot be accommodated by the current system. Multinational research initiatives such as SESAR are developing solutions to increase the system capacity, reduce cost and performance and keep the current level of safety. One factor that is known to limit system capacity is the coordination resource, specifically the Air Traffic Controller. Furthermore, the development of new systems challenges the centralized paradigm that is currently guiding top-down decision-making, responsibility, and control in the air transportation system. While it is modelled and addressed as a centralized system, actual performance and operations are governed by a combination of centralized and distributed processes, which can be too complex to capture and respond to by centralized coordination. In this work, we implement decentralized control for airport taxiing operations using the multi-agent systems paradigm. Shifting decision authority to distributed agents in the system allows taking local effects into account in the decision process. Furthermore, it allows responding to changing local conditions in a dynamic and timely manner without the need for central coordination. This approach can reduce the workload on centralized coordination resources and will result in a more flexible system. We test the influence of decentralized control on various performance metrics, such as aircraft taxi time, aircraft taxi speed and system throughput, using Monte Carlo simulations. In our setup, agents at each taxiway intersection use information about the current traffic situation to control aircraft routing. For the experiments, a generic taxiway layout under homogeneous traffic demand is simulated. The simulations were carried out by cumulatively adding aircraft to the system, i.e. through spawn rate, to investigate the system performance under varying demand conditions, and test the system capacity and its saturation levels. The simulation experiments undertaken were designed to explore the influence of decentralized decision making under a range of governing logic formulations. Our results demonstrate that local decision-making results in stable operations and explore the influence of information and coordination on system performance. The work highlights the potential for the decentralized control paradigm relative to the chosen application, investigates the influence of certain associated predominant parameters and rules, and finally, makes some more general observations.

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4.7 RAMS: Reliability, Availability, Maintainability & Safety

Imaging of defects in composite structures using ultrasonic arrays

Chirag Anand


Keywords: composite, ultrasonic array, NDT, defects, imaging There has been a significant increase in the use of composite materials as primary structures in many engineering applications. Extensive research has been done to study their mechanical properties and understand their failure mechanisms. Yet, the inspection of these materials forms a bottleneck that hinders technological progress in this field. New ultrasonic array imaging techniques have been developed for the optimum visualisation of defects in isotropic metals. Applying such techniques in multilayer anisotropic composites for defect detection and characterisation is not a trivial task. Hence the aim of this study is to develop an imaging algorithm which takes into account information provided by wave propagation phenomenon and can be used to inspect complex geometries and to use this algorithm to detect and characterize defects in a composite laminate.

A Remaining Useful Life Based Dynamic Programming Approach for Aircraft Heavy

Maintenance Scheduling

Qichen Deng


Keywords: C-Check, Dynamic Programming, Long-Term Scheduling A remaining useful life (RUL) based dynamic programming approach is proposed to schedule the long-term aircraft heavy maintenance. The heavy maintenance, or known as C-check, usually lasts 3-4 weeks, in which aircraft has to be grounded and removed from revenue schedule. An efficient long-term aircraft C-check schedule reduces the aircraft ground time, increases aircraft availability while keeping safety regulations. However, most of the current schedules are planned manually according to experience of maintenance engineers or maintenance operators. Very few research work had been carried out on the long-term aircraft scheduling optimization. Therefore, the proposed algorithm aims at optimizing long-term aircraft scheduling by minimizing the total unused flight hours between two C-checks. Aircraft age, type, status and operational constraints are taken into account in problem formulation.

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The proposed algorithm is evaluated using the C-check data from the airline Transportes Aéreos Portugueses (TAP). The outcomes show that the proposed algorithm can significantly reduce the total unused flight hours of a fleet of aircraft as well as the total number of C-check in a reasonable computation time.

Composite impact damage maintenance repair decision making in a limited data framework

Viswanath Dhanisetty


Keywords: composites, impact, damage, maintenance

Maintenance decisions are made on daily basis with the emphasis on increasing reliability with decreased costs. Large sets of historical data is used to build maintenance decision making models that output the optimal repair option for any given impact damage. The new-generation of wide-body jets are moving away from metals to composites as the dominant material. However, the novelty of the composites on such a large scale in recent years means that there is little historical data to utilise and build composite maintenance decision making models. To counter the limited composite data, a material damage characterization approach is taken. The metal structure damages exhibit dimensions that are predictable. Therefore for a given impactor size, the impact energy that caused the damage on a metal structure can be calculated. If the energy is known then it is applied to a composite structure to evaluate the resulting damage. Through this metal-to-composite damage conversion a purely metal damage dataset can be used to create a pseudo composite damage dataset. This pseudo dataset is now statistically significant enough to produce a composite maintenance decision making model, for an aircraft that has little to no real damage history.

Online remaining fatigue life prognosis for composite materials based on health monitoring

data and stochastic modelling

Nick Eleftheroglou


Keywords: composite materials, fatigue, structural health monitoring, stochastic

modelling

The aerospace industry promotes the use of composite materials widely nowadays. However, a comprehensive understanding of the damage accumulation behavior under fatigue loading is missing. This behavior is a complex phenomenon of stochastic nature and depends on a number of parameters such as type and frequency of loading, stacking sequence, material properties etc. Due to the stochastic nature of the damage accumulation, its mathematical modelling, parameterization and estimation are very difficult but also challenging and interesting

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problems. This study is going to combine stochastic modelling with online structural health monitoring (SHM) data, in order to assess the remaining useful life (RUL) in composite materials under fatigue loading. The degradation process is not direct observed but it is correlated with structural health monitoring (SHM) data. Due to this behaviour of the damage accumulation, Non-Homogenous Hidden Semi Markov model seems to be a suitable candidate for describing the composite’s damage evolution in time. The proposed model is applied to a coupon-level fatigue test campaign with SHM data from Acoustic Emission (AE), Digital Image Correlation (DIC) and fusion techniques. In conclusion, the RUL estimations of each SHM data should be compared with the actual RUL in order to verify the prognostic measures.

Impact Damage in Composites: An Analytical Methodology to Determine Damage and Effect on

Residual Strength

Fardin Esrail


Keywords: Impact, composites, analysis, damage resistance, damage tolerance

Impact damage is known to be a critical design aspect of composite laminates. Low velocity impacts, like dropped tools during manufacturing, are the major cause of impact damage in composites with barely visible impact damage (BVID) as a result. Over the years, various analytical and numerical approaches have been proposed to predict impact damage in composites. These methods are not sufficiently accurate or computationally too expensive to be used in an industry environment, where 10.000’s of composite parts with various stacking sequences need to be assessed for impact, for example, during the preliminary design of an aircraft structure. The goal of this PhD research is to create an efficient and analytical model to predict the damage types, sizes and locations during low velocity impact in composites and the effect on residual compression strength. The aim is also to do this by reducing the computational time from a couple of hours to a couple of minutes. This approach is an extension of a previous method developed by the PhD student for quasi-isotropic laminates. The extension will include the consideration of orthotropic laminates and a progressive damage model to improve the accuracy of the predicted damage and residual compression strength.

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Efficient Aircraft Maintenance by Ultrasonic SHM

Vincentius Ewald


Keywords: Ultrasonic Lamb wave, Structural Health Monitoring, Aircraft Maintenance, Damage Detection, Machine Learning To ensure continuing airworthiness, non-destructive testing (NDT) has been acknowledged as a valid method since more than a decade. The current range of NDT technologies such as Ultrasonic Phased Array, X-Ray Tomography, or Eddy Current Array are reliable enough to forecast the existence of microscale damage in a relatively short period. Nevertheless, along with the increase in demand for efficient aircraft maintenance, a trade-off between cost and technology becomes inevitable, and Structural Health Monitoring (SHM) is a promising methodology to improve this trade-off. In short, SHM is an automated process which collects, processes, and interprets damage information by integrated sensors in an engineering structure. SHM covers both diagnostic and prognostic aspects, the focus of this research lies on diagnostic tasks which are: 1). to detect, 2). to localize, 3). to classify, and 4). to quantify the structural damage based on information generated by piezoelectric transducers (PZT) mounted on complex aircraft structures. This project uses a physical effect of ultrasonic Lamb wave propagation. When a Lamb wave interacts with a structural damage, the damage acts a secondary wave source, and this “secondary wave” is captured by the PZT. The captured signal is processed to fulfill one or more of the four SHM tasks described above. A supervised machine learning algorithm will be developed to recognize the pattern in the captured signal change.

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An integrated framework for dispatch decision

and maintenance task support

Hemmo Koornneef


Keywords: aircraft maintenance, dispatch decision, Multi-Criteria Decision Making, Machine Learning, contextualized documentation With time-sensitive and growing amounts of data relevant for the dispatch decision, making a well-informed go/no-go assessment, based on all the available data, becomes a time-consuming process, leading to sub-optimal dispatch decisions. The goal of this research project is to develop a framework to automatically gather and analyze (real-time) data relevant for the dispatch decision and provide ranked dispatch options to stakeholders through a (mobile) application, in order to minimize flight disruptions. The framework will include methods to deal with data uncertainty and increase robustness of the solution by applying Machine Learning techniques. Additionally, methods for contextualized maintenance documentation will be integrated in the decision making framework in order to provide (line) maintenance technicians with a single source of access to relevant task support information and enable efficient maintenance task execution. The research is performed as part of the European AIRMES project, focusing on E2E solutions in aircraft maintenance in order to minimize flight disruptions. Based on the framework three prototypes will be developed to verify and validate the solution in an operational (test) environment during different stages of the research project.

Influence of temperature on the strength of resistance welded thermoplastic composites joints

Nikos Koutras


Keywords: Thermoplastic Composites, Resistance Welding, Temperature, Joint Strength, Failure Mechanism

In this work, the effect of temperature exposure on the strength of resistance welded joints is analysed. Glass fibre polyphenylene sulphide (GF/PPS) laminates were joined using the resistance welding technique and a stainless steel mesh as the heating element. Single lap shear tests were performed from -50°C to 150°C to evaluate the strength of the welded joints, and fractography was utilised in order to investigate the morphology of the fracture surfaces. The results showed that the strength decreased with increasing temperature, except for the region between 50°C and 90°C where the joint strength reached a plateau. Furthermore, fractographic inspection revealed that the main failure mode at all temperatures is fibre/matrix debonding and that the connection between the stainless steel mesh and the PPS matrix is not the weakest link at the interface.

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Robust Online Safe Exploration for Reinforcement Learning Aerial Vehicles

Tommaso Mannucci


Keywords: reinforcement learning, safety, adaptive control, machine learning, model-free control Model dependency of classical control such as PID control limits the applicability of such methods and is cause for significant expenditures in order to obtain hi-fi models. Reinforcement Learning (RL) is black-box solution to the problem of model dependency. In RL, optimal control is not the result of a predetermined policy, but is learned by trial-and-error interaction between the agent, i.e. the controller, and the platform, and can account for degradation and failures as well. However, a fully black-box approach with an inexperienced agent can result in damage to the platform at the beginning and during learning. The goal of this thesis is to solve the above by developing algorithms for online learning that can react to the insurgence of risk during learning with the aid of sensor information, uncertain models, and safety metrics. The result of the thesis would be one or more approaches that combine the advantages of model-free learning with the requirements of safety and cost of a typical aerospace platform.

Composite factories of the future

Aydin Rajabzadeh


Keywords: fibre Bragg gratings (FBG), glass-fibre composites, fatigue and static loading, classification, structural health monitoring (SHM)

Our objective in this project is damage identification and classification in composite structures and we have chosen embedded fibre Bragg grating (FBG) sensors as our method of inspection. FBG sensors are lightweight, miniature sized and flexible sensors that also have the multiplexing capabilities. These sensors are manufactured by creating a repetitive pattern of refractive index changes inside the core of an optical fibre, for lengths of less than 50 millimetres. These usually sinusoidal refractive index changes (also called Bragg gratings) act like a mirror for certain wavelengths of incident light. The output for these sensors are this very reflected light, and is recorded with an interrogator. The location of the peak of this reflected output is proportional to the period of the gratings, and therefore any change in the strain distribution along the length of the FBGs, would result in a change in these gratings, and hence in the reflected spectral graph. By designing some experiments using embedded FBG sensors inside GFRP coupons, we have analysed the reflected spectra and have been able to identify the damage, and also classify the type of load (static or fatigue) that the coupon is undergoing.

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Assessing the Fatigue of Adhesively-Bonded Composite Structures

Fabrício Ribeiro


Keywords: crack growth, mode II, composites, fiber optic sensing, bonded joint

Adhesively-bonded structural repairs present several advantages over classical mechanically fastened repairs. However, certification authorities still don’t allow the use of such repairs on primary aircraft structures due to the difficulty on predicting their durability when exposed to the typical airplane operational conditions. The issues arises because different environmental conditions act synergistically in degrading the durability of a repair. Thus, a holistic approach is necessary to assess the problem. The current research aims to understand the fatigue durability of adhesively-bonded composite joints by analyzing the problem under two operational conditions, variable amplitude loading and temperature. The shear loading condition (mode II) was chosen to be studied because it is the main loading case expected to be observed in a well-designed bonded joint. Thus, fatigue tests were performed using a carbon/epoxy Central Cut Plies (CCP) specimen. A distributed fiber optic system based on Rayleigh Backscattering was used to measure the strain distribution on the specimen’s surface. The results showed the need to improve the specimen for the bonded case and an optimization was done, suggesting a new CCP geometry. Combining the test results with a finite element method, a new approach was developed to obtain the crack growth curves from the specimen’s strain profiles.

Buckling in Launcher Structures: Scaling Approach

Inés Uriol Balbín


Keywords: Shell buckling, space launchers, composite materials, scaling models, mechanical testing Space launcher components are typically shell cylindrical structures prone to buckling. This phenomenon is initially difficult to predict and thus designers recur to, for the most cases, conservative safety factors. This strategy, though reliable, increases the launchers weight and the project cost. Moreover, composite materials design possibilities are not being fully exploited due to the lack of data. The objective is to tackle some of these issues, but given the problem non linearity and high dependence on imperfections, experimental validation is essential. However, due to the size and complexity of the launchers, full size tests are expensive. There is a need of scaled structures in order to test efficiently, where the results and conclusions are applicable to the large scale. To do so, our first step is the development of an analytical model that identifies the driving parameters. By keeping the values of these parameters through compromises in other areas two scaled sizes apt for laboratory

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purposes are selected. Secondly, the results are verified in the scaled models through finite element analysis. Finally, the results will be validated with experiments both in the large and small scale. In conclusion, by closely examining the buckling phenomenon through scaling, this work can have an influence in the new generation of safe but lighter launcher structures.

Reliable ultrasonic health monitoring of thermoplastic composite aircraft primary structures

Pedro Viegas Ochôa de Carvalho


Keywords: Composite, Structural health monitoring, Ultrasound, Guided wave Aviation industry has been struggling with uncertainty in the behaviour of damaged composites, hampering the implementation of maintenance programs for the new generation of composite aircraft. At the same time, transducer miniaturization and electronics have reached a very high technology readiness level which allows custom-made solutions for many different applications. These two scenarios represent a potentially successful symbiosis in which transducers can be permanently attached to critical zones of aircraft primary structures in order to constantly monitor their condition, and thereby assess when and where maintenance should be applied. However, according to the main aircraft manufacturers, the lack of robust characterization of structural health monitoring systems in representative environments is preventing their implementation. This research aims precisely at tackling this problem by developing and characterizing a structural health monitoring system for the most recent thermoplastic composite aircraft primary structures, based on the interrogation of ultrasonic guided waves with unobtrusive piezoelectric transducers.

Additively Manufactured Structures Which Facilitate Certification: Assessment of the crack propagation behaviour of laser sintered Ti-6Al-4V thin walled

lattice structures

Megan Walker


Keywords: Laser Sintering, Ti-6Al-4V, Lattice, Additive Manufacturing, Fatigue, Crack Growth Additive Manufacturing (AM) provides unique opportunities to produce complex geometries not possible with conventional manufacturing processes. Laser Sintering (LS) is an AM process capable of producing high quality metallic parts, in particular of Ti-6Al-4V, a popular alloy within the aerospace industry. The focus of this work is

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to assess the ability of a lattice structure to slow crack growth in thin walled additively manufactured structures. As such, research focuses primarily on the evaluation of fatigue and tensile behaviour of LS Ti-6Al-4V lattice structures. The objective is to produce a physics-based crack growth tool for thin-walled lattice reinforced structures.

Online Safe Flight Envelope Prediction for Fixed-Wing Aircraft

Ye Zhang


Keywords: safe flight envelopes; database; system identification; damage classification; level set method

Many endeavours have been made to prevent aircraft loss of control after sudden structural and aerodynamic failures, and one of which is safe flight envelope (SFE) prediction. Considering the unpredictable nature of such failures, many challenges and restrictions exist in the process of implementing such a prediction system. My research is to find a solution to the problem of safe flight envelope prediction after sudden damages based on a database-driven approach. The advantages of this approach can be generalized into two aspects. First, by reducing the online component into a database lookup and interpolation problem, it circumvent the challenges associated with direct online SFE prediction, and only local aerodynamic model is used to generate database keys to the lookup table. More importantly, a new method of using changed aerodynamic coefficients under the framework of machine learning as features to determine the structural damage condition of the aircraft is proposed and investigated. The research will mainly focus on the offline building and online retrieval of the database.

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4.8 Design and Manufacturing

A new design for the reduction of drag in wing-body junctions

Zeno Belligoli


Interference drag is that component of drag caused by flow phenomena at the wing-fuselage junction. Junction flow phenomena take place when a boundary layer developing on a surface encounters and obstacle in its path and separates due to the obstacle's adverse pressure gradient. In this study, a gradient-based shape optimization is carried out on a NACA 0015-flat plate geometry with the objective of reducing the interference drag. Some particular constraints are placed on the optimization that differentiate it from all the other optimizations carried out on similar geometries in the past. This results in an innovative design, completely different from the state-of-the-art, that permits a considerable drag reduction. Wind-tunnel experiments are then carried out to validate the numerical outcomes. Balance measurements and PIV are used to compute the drag and analyze the flow field in the wake of the wing. The experimental investigation confirms the numerical evidence and provided some indications on the working mechanism of the new design.

System-level Modelling, Optimization and Control

of Kite Power Systems and Parks

Anna Bley


Keywords: Airborne Wind Energy, Kite Power, Traction Power Generation, Cost Optimization, Quasi-Steady Model The concept of extracting wind energy by means of Kite Power Systems (KPS) is considered. Wind power increases with the cube of the wind speed and thus with height while crosswind motion potentially improves power production by the square of L/D. KPS exploit these two effects by using a tethered airfoil flying crosswind at high altitudes in a repeated pumping cycle. Forces are directly transferred to the ground making KPS particularly suitable for offshore deployment. Economic assessment of KPS is essential on the current path from technology demonstration to a fully commercial product. System-level analysis allows to estimate the power output and optimize w.r.t. cost, performance and design parameters. A quasi-steady analytic framework enables fast computational modelling of physical system aspects complemented i.a. by atmospheric and cost models. Experimental validation data is provided through wing towing-tests and real system operation.

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Multidisciplinary System Design, Safety and Cost Optimisation of Airborne Wind Energy

Ashwin Candade


In conventional wind turbines, during unfavourable conditions, the rotor can be stopped using mechanical or aerodynamic braking and the turbine can be put into “parking” mode. However, in comparison tethered AWE converters need an automated mechanism to either land or “park” the airborne element at the zenith. This one example already illustrates the level of complexity and automation that is required in AWE. These multi-disciplinary systems require high safety standards to ensure their fault free operation. In order to be economically viable for power generation, a balance between the level of safety, cost, and performance of the AWE converter needs to be achieved. This leads to the requirement of an overall system level model that incorporates models of the environment, the tethered wing, and the various electro-mechanical elements that comprise of the converter. While the focus of this research is at the overall system level, some aspects of the AWE requires detailed models that are integrated into the system model. This leads to the current focus of the PhD, which is on the structural model of the kite wing box. In order to minimise the weight of the composite wing box, a preliminary internal shape, and ply fiber orientation optimization is required. The methodology of this is detailed in this PhD symposium.

Analysis of the Critical Effect of Chemical Composition on Transformation Kinetics in Fe-C-Mn

Steels

Hussein Farahani

Chair of Novel Aerospace Materials, TU Delft

Keywords: Material science, steel, phase transformation, kinetics, modelling The effect of alloying element partitioning on the migration rate of austenite-ferrite interface and on the overall kinetics of austenite to ferrite phase transformations remains of great interest in the field of solid state ferrous phase transformations. Recently, cyclic partial phase transformation experiments have been successfully used to unravel the effect of Mn partitioning at austenite-ferrite interface in far more detail than conventional transformation studies. In this project, the effect of various Mn concentrations on the kinetics of cyclic austenite to ferrite transformation in Fe-C-Mn steels has been systematically investigated using different thermodynamic models. The results revealed a critical concentration range of 1.5-2 wt.% for Mn above which the kinetics of the phase transformations changes significantly. Analysis of the evolution of interfacial concentrations of C and Mn show that for low Mn concentrations, the transformation can progress with partitioning of C while for higher levels of Mn, transformation can only proceed with additional partitioning of

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Mn. Dilatometric cyclic transformation experiments confirm the critical Mn concentration range of 1.5-2 wt.% predicted by simulations.

Composing MDO symphonies: graph-based problem formulation to enable automated execution for large

MDO systems

Imco van Gent


In this presentation the current capabilities of a new software system will be presented. The system is called KADMOS (Knowledge- and graph-based Agile Design with Multidisciplinary Optimization System) and aims at increasing the agility of aircraft design teams that perform multidisciplinary design optimization (MDO). By increased agility, an MDO-based development process is meant that better fits the iterative nature of performing aircraft design. KADMOS has been developed on the notion that performing MDO is analogous to performing music with a large symphonic orchestra, however, in the MDO domain a music notation system is missing, which prevents us from composing large, complex pieces. This notation system is under development as part of the EU project AGILE where a new generation of aircraft MDO systems are investigated to support collaboration of heterogeneous teams of experts. KADMOS improves the agility of the design team in three ways: 1) reducing the set-up time required to compose large and complex MDO models, 2) enabling the systematic inspection and debugging of this model, and 3) manipulating the model for automated creation and reconfiguration of optimization strategies, including the accompanying executable workflow. This is achieved by means of a graph-based analysis system that combines different existing advantageous techniques for performing MDO, such as the use of a single sharable data schema containing a parametric representation of the aircraft under investigation, knowledge-based technologies, and simulation workflow (SWF) software packages. Two MDO case studies will be presented in the paper. The first case study is the well-known Sellar1 problem, which has been used to demonstrate a proof-of-concept of the graph-based system. The seconds case study concerns a detailed wing aerostructure design using a collection of wing design tools. Both cases demonstrate the capability of KADMOS to support quick formulation, (re)configuration, and execution of MDO workflows using distributed and heterogeneous sets of analysis tools.

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Multi-fidelity Analysis and Sensitivity Analysis for Aeroelastic Tailoring of Aircraft Wings

Kristofer Jovanov


Keywords: aeroelasticity, aircraft design, multi-fidelity modelling, optimisation, simulation

Aircraft components, and wings in particular, are subject to high aerodynamic loads during flights. The deformations often exceed the limits of linear behavior and the components encounter shocks and flow separation phenomena at transonic flight. In order to account for nonlinear effects, both structural as well as aerodynamic, high-fidelity models must be employed. These models, although computationally expensive, can estimate aerodynamic loads very close to wind-tunnel results. Low-fidelity models, on the other hand, allow for many simulations at a low computational cost. Nevertheless, what they make up for in cost savings they lack in accurate modelling capabilities in transonic flow. This indicates a clear trade-off between computational expense and physical accuracy when different models of varying fidelity are employed.

This research aims to incorporate high-fidelity aerodynamic models in an existing aeroelastic-tailoring framework. A stand-alone high-fidelity module is created that can be called upon whenever the user wants to compute high-fidelity loads and gradients. The high-fidelity model is based on the Euler or the RANS equations and the aerodynamic solver is the state-of-the art CFD solver elsA, developed by ONERA.

Flybond: Novel design concepts for adhesively bonded composite joints

Julian Kupski


Keywords: Adhesive bonding, composite layup optimization, lap joints, multi-objective optimization algorithm, Carbon fibre prepreg A suitable joining method is the missing puzzle piece to efficiently use composites in aircraft structures. The aim of this project is to investigate novel design concepts towards improvements in strength and damage tolerance performance by making use of the anisotropic behaviour of the composite materials. Reducing governing peel stresses at the edges of the bondline is approached through optimization of topology, stacking sequence, fibre direction and ply thickness. A Finite Element Model (Abaqus-Python) describing the structural behaviour will be validated by testing corresponding coupons at D-ASML.

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Optimization and rationalization of a composite truss structure

Nicolas Lavalette


Keywords: Truss, Topology optimization, Ground structure method, Composites, Joints In transportation engineering, and particularly in aerospace engineering, reducing the weight of structures has for decades been one of the primary concerns. A structure achieving the same mechanical properties, while being lighter than the currently used one, leads to a reduced fuel consumption, serving economics and environmental impact. With this goal in mind, the present research aims at developing truss structures made of composite materials, whose superior mechanical properties and lower weight would allow for existing structures to be replaced based on a higher structural efficiency. In order to develop those structures, truss optimization techniques are being used, however aspects such as manufacturing and joint design complicate the optimization, but are needed to prevent unrealistic solutions. The focus of this research project is therefore to conceive and optimize truss structures, with constraints leading to feasible solutions. Such constraints are for instance the properties of joints or the manufacturing costs. An envisioned application for this type of truss is to form the internal structure of aircraft wings.

Aeroelastic Tailoring for Composite Aircraft

Mario Natella

Chair of Aerospace Structures & Computational Mechanics, TU Delft

Keywords: aeroelasticity, aeroelastic tailoring, flight dynamics, flexible composite aircraft The modern trend in aircraft design features light, slender and flexible aircraft structures. A trend that requires a new paradigm for design, analysis and optimization. Among the optimization methods we focus on aeroelastic tailoring. This optimization approach modifies the thickness and stiffness distribution of composite structures for enhanced performance (e.g. minimum weight, increased flutter speed). Aeroelastic tailoring has also been shown to reduce the speed of another dynamic instability known as body-freedom flutter. Such an instability involves flight dynamic motions (e.g. aircraft pitch) and aeroelastic deformations and it is particularly crucial for flexible composite structures. Traditionally aeroelasticity and flight dynamics have been developed as separate disciplines, both subjected to a number of simplifying assumptions to permit large

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numerical solutions. However, the recent research efforts in the development of fast and reliable low-fidelity models in this field have made coupled approaches feasible. The goal of this research is to develop a novel approach to aeroelastic tailoring for flexible composite structures that couples non-linear aeroelasticity and flight dynamics. The novel approach will thoroughly model the important phenomena involving flexible composite structures and deliver aircraft structural designs at optimized performance.

Design Optimisation of Practical Variable Stiffness Laminates

Daniël Peeters


Keywords: optimisation, fibre placement, composites, manufacturing, variable stiffness By varying the fibre angle within a layer over the structure, the stiffness properties are varying, leading to variable stiffness laminates. For optimisation purposes, a three-step optimisation is used. In step one, the laminate stiffness, in terms of the lamination parameters, is optimised. In step two the fibre angle distribution of each layer is determined, and in step three the fibre paths are retrieved. During step two, the change in fibre angle variation from point to point is limited by a steering constraint to guarantee manufacturability. Furthermore, an equivalent 10% rule is implemented to increase industrial feasibility of the optimised design.

Self-healing fibre reinforced polymer composites characterized by destructive and non-destructive

techniques

Wouter Post


Keywords: Self-healing, fibre reinforced composites, polymers, non-destructive

techniques, mechanical characterization Fibre reinforced polymer (FRP) composites are being used more and more in structural lightweight applications such as wind turbines, sports equipment and aircrafts. However, due their complex geometry they are prone to small scale damage which can propagate to larger damages ultimately leading to full fracture of the composite. By introducing self-healing entities within the composite structure these small scale damages can be repaired thereby preventing failure of the structure and

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prolonging its overall lifetime. The self-healing entities can be introduced in the fibres, matrix or the fibre-matrix interface. In any case, the extent of healing needs to be measured using non-destructive testing techniques in order to validate that the healed component can be used again. This presentation gives an overview of several approaches to initiate self-healing within FRP composites and its quantification by conventional mechanical testing and state of the art non-destructive acoustic techniques.

Roadmap for designing optimal wind energy systems

Sebastian Sanchez


A research agenda is described to further encourage the application of Multidisciplinary Design Analysis and Optimisation (MDAO) methodologies to wind energy systems. As a group of researchers closely collaborating within the International Energy Agency (IEA) Wind Task 37 for Wind Energy Systems Engineering: Integrated Research, Design and Development, we have identified challenges that will be encountered by users building an MDAO framework. This roadmap comprises 17 research questions and activities recognised to belong to three research directions: model fidelity, system scope and workflow architecture. It is foreseen that sensible answers to all these questions will enable to more easily apply MDAO in the wind energy domain. Beyond the agenda, this work also promotes the use of systems engineering to design, analyse and optimise wind turbines and wind farms, to complement existing compartmentalized research and design paradigms.

Effect of the dianhydride/branched diamine ratio on the architecture and room temperature healing

behavior of polyetherimides

Arianna Susa


Keywords: polyetherimide, intrinsic self-healing, fatty dimer diamine, branches, interdiffusion Traditional polyetherimides (PEIs) are commonly synthesized from an aromatic diamine and an aromatic dianhydride leading to the imide linkage and outstanding chemical, thermal and mechanical properties yet lacking any self-healing functionality. In this work, we have developed a family of self-healing polymers capable of healing at room temperature yet maintaining very high elastomeric-like mechanical properties. Hereby we present the SH mechanism of the developed polymer. A dedicated analysis suggests that healing proceeds in three steps: (i) an initial adhesive step leading to the formation of a relatively weak interface; (ii) a second step at long healing times leading to the formation of an interphase and (iii)

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disappearance of the damaged zone leading to full healing. We argue that the fast interfacial adhesive step is due to van der Waals interactions of long dangling alkyl chains followed by an interphase formation due to polymer chain interdiffusion. The results here presented offer a new route for the development of room temperature self-healing thermoplastic elastomers with improved mechanical properties using fatty dimer diamines.

Up-Scaling Of the Welding Process for Joining and Disassembling Thermoplastic to Thermoset

Composites

Eirini Tsiangou


Keywords: Polymer-matrix composites (PMCs), joining/joints, up-scaling, welding, disassembly Ultrasonic welding (UW) is a superior welding process when it comes to welding thermoplastic to thermoset composites, as it is a really fast technique and that can prevent thermal degradation of the thermoset resin when subjected to the high temperature that is required for fusion bonding thermoplastic composites. However the welded area obtained is restricted and the joint that is created is permanent (separation of the adherents can be achieved only by destroying them). Therefore this research focuses on up scaling the UW procedure, shifting from static UW (the sonotrode can move only in a downward direction) to continuous UW (the sonotrode can move parallel to the welding line). Additionally, a disassembly process is investigated that will allow separation of welded adherents without causing degradation.

Development and Validation of an Integrated Tool for Aerodynamic And Structural Load Calculations

on Wind Turbine Rotor Blades

Zi Wang


The objectives of this project are to develop a combined aerodynamic and structural load calculation tool based on an unsteady lifting line code for the aerodynamics and a structural model using fully nonlinear beam models. The first approach assures detailed aerodynamic load determination, and the latter includes efficient cross-sectional stiffness and deflection calculation. The tool will be set up in such a way that a proper aero-elastic representation of a flexible rotor, including large, non-linear deflections is possible. The final goal is to determine and analyse unsteady loads on rotor blades with both conventional as well as unconventional plan forms (such as

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swept blade tips) including structural coupling between flap and pitch for dynamic load reduction.

On the Cobalt – Tungsten/Chromium balance in martensitic creep resistant steels

Hao Yu


Keywords: computational design, creep, Cobalt exchange, Laves phase, M23C6

precipitates Recently novel martensitic creep resistant steels strengthened by slowly coarsening Laves phase or stable M23C6 precipitates have been identified both computationally and experimentally. The coarsening kinetics of these precipitates, traditionally considered to be very detrimental in creep steels, can be suppressed to a degree which makes them attractive strengthening factors by alloying such steels to high Cobalt levels. As high Co levels are undesirable for various reasons, in the present work, the characteristics of Laves phase and M23C6, in particular the volume fraction, coarsening rate and precipitation strengthening factor, in newly designed alloys are computationally compared with those of existing Co-containing creep steels. The binary analyses of Co-M balance show that Co-W are highly coupled for creep steels strengthened by Laves phase deposits and W can partially replace Co to yield the same precipitation strengthening. For the M23C6 strengthened alloys, irrespective of the Cr level, a high Co concentration is necessary for a high creep resistance.

Self-healing Thermal Interface Materials

Nan Zhong


Keywords: thermal interface materials, self–healing, organic–inorganic polymer networks, fracture strength, thermal conductivity Thermal interface materials (TIMs) are widely used in all kinds of electronic devices to handle the heat dissipation and the mechanical anchoring of the heat producing component. The aging of TIMs may lead to delamination and internal crack formation causing a loss of heat transfer and mechanical integrity both leading to premature device failure. In the present work, a novel TIM system based on a self–healing organic–inorganic polymer matrix filled with spherical glass beads is presented which is capable of healing both the thermal conductivity and the mechanical properties upon thermal activation. The effect of particle volume concentration (PVC) and particle size on tensile strength and thermal conductivity healing behavior is investigated. The results show that higher PVC increases the mechanical property but decreases mechanical healing. For the same PVC, bigger particles lead to lower mechanical properties but higher thermal conductivities and higher mechanical healing efficiencies.

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4.9 Trajectories

Bio-inspired monocular vision for MAVs landing

Hann Woei Ho


Keywords: Bio-inspired monocular vision, MAVs, autonomous landing, visual servoing, self-supervised learning The capability of Micro Aerial Vehicles (MAVs) to perform landing task is essential for the autonomous operation, especially when they are outside line-of-sight. For autonomous landing, these vehicles need to know by themselves which areas are safe to be landed upon and how to approach the desired landing target. However, they have limited computing capability and on-board payloads. Therefore, bio-inspired vision solution is proposed due to the fact that biological systems, such as flying insects, have the capabilities to perform complex tasks by only using their bare eyes and a little amount of processing power of their brains. For instance, optical flow has been heavily used by honeybees and dragonflies to perceive the environment and avoid dangerous objects while flying. For application of optical flow in MAVs, it requires only a monocular camera which is small and lightweight, and measuring optical flow is computational inexpensive. This project aims for using bio-inspired computer vision algorithms to identify the safe landing areas, determine how to approach it, and perform smooth landing. These areas have to be a relatively flat surface with small inclination, and most importantly should be free of obstacles. To identify these areas, motion parallax perceived by the optical flow is utilized to estimate the surface slope and roughness which tells us the surface inclination and existence of objects in the field of view. Furthermore, the appearance of the obstacles can be easily identified using a machine learning technique with optical flow. Lastly, divergence measured from optical flow allows the MAVs to control its vertical dynamics in order to have a desired landing profile.

Reinforcement learning for autonomous UAV flight

Jaime Junell


Keywords: Reinforcement Learning, Micro Aerial Vehicles, high-level guidance, autonomous flight, model-free Autonomous flight for Micro Aerial Vehicles (MAVs) is appealing for many reasons. Small flying vehicles have the ability to survey indoor and outdoor areas, patrol streets, inspect bridges, deliver mail, or get to areas not accessible by humans or land based vehicles. An MAV in real life applications will encounter unforeseen and unpredictable situations which calls for fast and intelligent decision making. When a human is not available as the decision maker, a reliable, adaptable, and autonomous method must be in place for the mission to succeed.

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Reinforcement Learning is a promising approach to help with decision making aspect of autonomous flight. This type of machine learning algorithm is inspired by the way humans and animals learn: by interacting with its environment and learning the desirable behavior using feedback it receives from the environment and a reward or penalty structure. Reinforcement learning can be model-free, which means it can learn without a priori knowledge of the system. This approach is applicable to a large span of problems because it needs minimal to no information, is adaptable, and can learn complex behavior from a simple reward structure. In this research, reinforcement learning is applied to quadrotor MAV tasks in order to improve autonomy in flight. We hope to accomplish this by learning to find optimal guidance solutions in previously unknown environments while using only the sensors available on the vehicle.

Absolute and Relative Precise Orbit Determination of Satellite Constellations

Xinyuan Mao

Chair of Astrodynamics & Space Missions, TU Delft

Keywords: Precise Orbit Determination, Low Earth Orbiters, Global Positioning Systems, GPS Receivers, Baseline Determination An increasing number of space missions use a spacecraft formation or constellation in Low Earth Orbit (LEO) to meet certain scientific or operational objectives. In order to take full advantage of the data information content provided by these formations or constellations, absolute and relative Precise Orbit Determination (POD) is a prerequisite. In addition, a growing number of LEO satellites are equipped with high-quality, dual-frequency Global Positioning System (GPS) receivers. Typically, the orbit determination for such LEO satellites is done in single-satellite mode, i.e. for each satellite a separate absolute orbit determination is conducted where today cm-level precision levels can be achieved. The method for determining relative positions of LEO satellites has been further extended by fixing the so-called double-differenced integer ambiguities. Currently the most precise record is made at TU Delft for GRACE mission, which obtains a baseline determination precision at 0.5 mm level. The current research topics related to POD of LEO have been covered in this PhD project: (1). Antenna patterns research of GPS receivers, (2). The influence of different receiver tracking loops and (3) More robust baseline determination research for high-dynamic baselines.

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Swarm Exploration with Pocket Drones

Kimberly McGuire


Keywords: Exploration, Bio-robotics, pocket drones, swarm The study on micro air vehicles (MAVs) and their possibilities within our society is a new and emerging field. The contribution of this project is to investigate and design a swarm of tiny unmanned aerial vehicles, pocket drones, to perform multi-robot exploration of an unstructured indoor environment. These pocket drones are small quadroters with a mass in the order of 20 grams and a diameter of about 10 cm, so it can manoeuvre itself through small corridors, windows and is easily able to reach different levels. These pocket drones have strict limitations on their on-board energy, sensing and processing capabilities. The challenge is to efficiently combine the needed functionalities, in terms of obstacle avoidance, exploration and coordination with the other drones. Inspiration drawn from honeybees and other flying insects will be used to develop efficient algorithms for multi-robot exploration with the pocket drones.

Trajectory Prediction for Medium Term Conflict

Detection

Julia Rudnyk


Keywords: Trajectory Prediction, Trajectory Predictor, Medium Term Conflict Detection, Uncertainty, Air Traffic Control

The provision of a safe and expedited air traffic flow is ensured by an air traffic controller. Decision support tools are used to assist air traffic controllers in their duties and reduce congestion of and delays in air traffic. All decision support tools, whether they are used for traffic flow management or conflict detection purposes, rely on the information about a current and/or future aircraft position. While the current position is obtained from the surveillance radar or downlinked via ADS-B, the future position is predicted by a trajectory predictor. The trajectory predictor is a service that constructs a four-dimensional flight profile of an aircraft based on available input data, such as flight plan, aircraft performance and weather forecast. The accuracy of the predicted flight profile depends on fidelity of a mathematical model used and input data quality. The most of the present trajectory predictors rely on a Point Mass three degree-of-freedom model, which is considered to be sufficient for air traffic management purposes. On the other hand, system design solutions, like omission of a turn modelling, can create inaccuracies and errors in a lateral path prediction. Anyhow, the major source of errors in the trajectory prediction is input data. The acceptability of the trajectory prediction quality depends on the decision support tool purposes. What is considered to be tolerable for traffic flow management, may be unacceptable for conflict detection purposes. With respect to conflict detection, the quality of data for a short term look-ahead time is rather sufficient, while for a long term look-ahead time it is almost always incomplete. Input data can be wrong or

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unknown (at required time). For instance, a flight plan shall be filed prior to a flight and is the only source of information about the flight intent, however, it is generally known that flight plan is hardly ever followed. A sensitivity study is being carried on to investigate the contribution of erroneous input data to the trajectory prediction accuracy. Parameters chosen for the study are considered to have the biggest impact and include aircraft take-off mass, speed settings, weather forecast, top of descent placement, descent performance, turning performance, level-offs and ATC clearances.

Developing Open Aircraft Performance Models Using Data Mining

Junzi Sun


Keywords: aircraft performance, ADS-B, machine learning, data mining In the Air Traffic Management (ATM) community simulation plays a large role. Studies use different simulation platforms, often based on proprietary data. This inhibits comparison of validation results, which makes it difficult to compare the different options for future ATM technology and operational concepts. These issues reveal a need for standardized and open simulation programs, scenarios, as well as aircraft models. There are several opportunities to circumvent the limitations of closed data and models. They depend on freely available information such as technical textbooks and reports, and public websites. A second source of freely available information is that of historical data, such as ADS-B feeds. Several studies have shown that ADS-B broadcasts of position and velocity can be used to estimate real-time situation and configuration. In this research, similar methods will be developed to extract performance model parameters from much larger sets of historical data. The PhD research will primarily focus on data mining on ADS-B data, also investigate existing modelling methodologies using open data, to work towards creating open aircraft performance models. The results of this analysis shall provide the input for an open aircraft model database initiative, as an alternative to the traditionally closed ATM research approach.

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The Influence of Traffic Structure on Airspace Capacity

Emmanuel Sunil


Keywords: airspace structure; airspace capacity; en-route airspace design; air traffic control; air traffic management

Airspace structure can be used as a procedural mechanism for a priori separation and organization of en-route air traffic. Although many studies have explored novel structuring methods to increase en-route airspace capacity, the relationship between the level of structuring of traffic and airspace capacity is not well established. To better understand the influence of traffic structure on airspace capacity, in this research, four airspace concepts, representing discrete points along the dimension of structure, were compared using large-scale simulation experiments. By subjecting the concepts to multiple traffic demand scenarios, the structure-capacity relationship was inferred from the effect of traffic demand variations on safety, efficiency and stability metrics. These simulations were performed within the context of a future personal aerial transportation system, and considered both nominal and non-nominal conditions. Simulation results suggest that the structuring of traffic must take into account the expected traffic demand pattern to be beneficial in terms of capacity. Furthermore, for the heterogeneous, or uniformly distributed, traffic demand patterns considered in this work, a decentralized layered airspace concept, in which each altitude band limited horizontal travel to within a predefined heading range, led to the best balance of all the metrics considered.

Autonomous Indoor Navigation of Flapping Wing Micro Air Vehicles

Sjoerd Tijmons


Keywords: Flapping wing MAVs, computer vision, autonomous system, indoor navigation Micro Air Vehicles (MAVs) are becoming ever smaller and lighter. This opens new areas of application, mainly because of the capability to access small spaces. A straightforward example of such an application is building inspection. In such a case there is in general no prior knowledge about the environment. Furthermore there will be no direct communication between MAV and operator due to signal blocking, and GPS positioning is not possible for the same reason. These restrictions require the MAV to perform several autonomous tasks: attitude control, obstacle avoidance, navigation etc. Extremely light-weight MAVs are very limited in the amount of available on-board sensors and processing power.

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This project aims at developing an on-board system that provides the resources required for full autonomy. It should enable the MAV to perform the following tasks: determine safe directions of flight explore the environment efficiently and thoroughly find out how to enter new spaces to increase the exploration area find its way back to previously visited points. This system will be used for and tested on DelFly, a Flapping Wing MAV of less than 20 grams developed by TUDelft. The dimensions of this MAV demand a system that makes use of an extremely efficient combination of sensor types, data processing algorithms and control loops. This will lead to approaches that are more biologically inspired than current state-of-the-art avoidance and mapping methods. The main focus will be on using cameras and vision-based methods. The objective is to develop a vision-based system that can be carried on-board a light weight MAV (<20 grams) which enables fully autonomous operation in GPS-denied environments.

Flight planning within air traffic management studies

René Verbeek


Keywords: flight planning, cost index, oceanic operations, route charges, route network Airline dispatchers depend on tools generating optimized flight plans. The optimization takes into account the cost of fuel, travel time, and route charges. These commercial tools are unfortunately not available for public research, including in the field of air traffic management (ATM). Within ATM research therefore simplified flight planning methods are used when generating flight scenarios. A simple method is just using a shortest-path-algorithm. Effects of wind, aircraft weight and route charges are then not taken into account. In some types of ATM research these types of effects are not negligible. This is the case in studies studying effects of route charges, but also when trying to optimize the structure of the route network. For this reason a flight plan generation tool is in development that can be applied to ATM studies. The tool uses the Base of Aircraft Data (BADA) version 4 from Eurocontrol for representative aircraft performance behaviour. The underlying route network and sector layout is based on data available for the SAAM tool, also from Eurocontrol. Grib2-data is used for wind and temperature information. It is the objective that the tool will generate 4D flight plans that are optimized for fuel, time and route charges.

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Assessing Accessibility of Main-Belt Asteroids Based on Gaussian Process Regression

Yuxin Liu

Chair of Astrodynamics & Space Missions , TU Delft

Keywords: Main-belt asteroids; Trajectory optimization; Gravity assist; Machine learning; Model training

The main-belt asteroids are of great scientific interest and have become one of the

primary targets of planetary exploration. In this paper, the accessibility of more than 600,000 main-belt asteroids is investigated. A computationally efficient approach based on Gaussian Process Regression is proposed to assess the accessibility. Two transfer models consisting of globally optimal two-impulse and Mars gravity-assist transfers are established, which would serve as a source of training samples for Gaussian Process Regression. The multi-start and deflection technologies are incorporated into the numerical optimization solver to avoid local minima, thereby guaranteeing the quality of the training samples. The covariance function, as well as hyper-parameters, which dominate the regression process, are chosen elaborately in terms of the correlation between samples. Numerical simulations demonstrate that the proposed method can achieve the accessibility assessment within tens of seconds, while the average relative error is only 1.33%. Mars gravity-assist exhibits significant advantage in the accessibility of main-belt asteroids, as it reduces the total velocity increment by an average of 1.23 km/s compared with the two-impulse transfer. Furthermore, it is observed that 3,976 candidate targets have potential mission opportunities with a total velocity increment of less than 6 km/s.

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4.10 Extreme Environments

Haptic Feedback for Flight Envelope Protection

Dirk Van Baelen


Keywords: Human-machine interaction, Manual Control, Haptics, Force feedback, Flight Commercial airplanes nowadays use a very elaborate set of control laws to keep the aircraft within the operational limits (the flight envelope). Although this provides a valuable addition for safety to the aspect of flying, it is not always communicated clearly to the pilots. When this vital information on the limits of the aircraft is needed, mostly in stressful situations, the workload combined with a complicated set of control laws in different regions of the flight envelope, can result in confusing situations where wrong actions are imminent. To support the pilot in such situations, a haptic interface is designed which communicates the limits of the flight envelope to the pilot using the control device. It is hypothesized that this haptic interface provides a new and intuitive source of information to the pilot such that his/her situation awareness increases. Additionally, as the pilot has a more direct way of assessing the flight envelope, the workload is expected to decrease when the haptic feedback is applied.

Algae exoskeletons for active corrosion protection of AA2024-T3

Paul Denissen


Keywords: AA2024, Biosilica , Coating, Corrosion Inhibitor, Diatomaceous earth

In recent times the use of synthetically produced nano-carriers doped with environmentally friendly corrosion inhibitors has been proposed as an alternative to existing corrosion protective concepts using highly efficient but toxic corrosion inhibitors based on Cr VI. Despite the promising results using these nanocarriers, limitations related to their versatility, manufacturing, embedding in coating matrices, and efficient and time-sustained protection of damages makes the search for carrier alternatives a necessary step for a successful industrial implementation of the concept. In our work we explore the potential use of environmentally friendly and naturally produced diatom exoskeletons for the active corrosion protection of metallic structures.

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The proof-of-concept is demonstrated using Aulacoseira diatom frustules doped with the corrosion inhibitor Ce(NO3)3 for the active protection of aerospace aluminium alloy AA2024. In order to evaluate the doping degree and release kinetics of the diatom frustules a new in-situ UV/VIS detection system was developed and validated. The protection degree was then evaluated by oxygen mapping, Raman, and a newly made in-situ opto-electrochemical technique which combines crucial optical information about delamination and underfilm corrosion processes with electrochemical signals.

The work demonstrates that the use of diatom frustules as carriers for active corrosion inhibition in coatings is feasible and very promising. The results show that, without further optimization of the formulation or the doping and release mechanism, protection of AA2024 coated plates containing controlled damages immersed in 0.05 M NaCl is possible. Moreover, two in-situ evaluation set-ups have been proposed and validated allowing future research in a much more efficient and reliable manner. These first results are very promising and open a new research line using environmentally friendly and nature inspired concepts for active corrosion protection.

Thermomechanical Buckling in Supersonic Aircraft

Javier Gutierrez Alvarez


Keywords: Thermal Buckling, Composite Materials, Supersonic Aircraft, Load Alleviation, Morphing

Aerodynamic heating in supersonic aircrafts can trigger thermomechanical buckling, an occurrence that may cause aerodynamic and structural complications. In composite structures this is a rather counterintuitive phenomenon, highly dependent on material properties and layup distribution. Latest news indicate that the supersonic flight is returning; this is an opportunity to revise traditional structural conceptions. The starting point for this research is the hypothesis that combined thermomechanical buckling behavior in composites can, to some extent, be controlled and exploited through material, shape and stacking choice. Cases of gradually increasing complexity are considered, firstly flat metallic and composite plates under temperature increment and restricted expansions; secondly, long symmetrically laminated plates under thermomechanical loading and restricted expansions, and the extrapolation of these problems to pure mechanical buckling cases. The influence of laminate stacking, bending anisotropy and compliant foundations, both in buckling pattern and bifurcation temperature, is studied. Applications like passive load alleviation or local shape adaptability are some of the benefits that are pursued in this research. In summary, by further understanding thermomechanical buckling in aerostructures, this work will contribute to the supersonic aircrafts that will shape the future by making them safer, smarter and lighter.

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Icing, Electro-thermal De-and Anti-icing, and Thermo-Mechanical Life of a Heated GLARE Leading

Edge

Zahid Hasan


Keywords: multiphase flow, Eulerian film, ice accretion, water vaporization, species transport, power consumption, thermal expansion, inter-material constraint, interface failure, thermo-mechanical fatigue life

Ice accretion on aerodynamic surfaces can substantially degrade the aircraft performance by inducing wing or tail stall. The prevention of ice accretion demands the heating of an aerodynamic surface, i.e. a heat flux. As the next generation aircraft are getting more electrical, therefore, an intelligent heating concept for a GLARE made wing leading edge is developed based on the integrated heating strip. But the performance of such a heating system in a real icing condition is still unknown. Moreover, a substantial amount of heat gets lost from the leading edge due to the forced convective and evaporative cooling at sub-freezing temperatures. To investigate this issues, computational fluid dynamics models, based on the di-phase and species transport concepts, are designed which can predict the time-dependent ice accretion and power consumption by a GLARE leading edge in an icing cloud. Noticeably, the cyclic thermal heating of GLARE leads to thermal expansion of materials and inter-laminar stress, and eventually to thermo-mechanical fatigue due to different thermal expansion coefficients of adjacent laminae. Therefore, a methodology is formulated which couples the finite element and analytical methods to predict the thermo-mechanical fatigue life of GLARE.

Modelling the Fracture Behavior of Thermal Barrier Coatings in the Presence of Healing Particles

Jayaprakash Krishnasamy


Keywords: Thermal Barrier Coating (TBC), Self-healing, Failure, Microstructure, Numerical modelling

Thermal Barrier Coating (TBC) systems are applied on the external surface of critical structural components to protect them against melting and oxidation when exposed to high-temperature environments. However, under thermo-mechanical cyclic loading, micro-cracks nucleate and grow in the TBC system which, upon failure, leaves the substrate unprotected. A typical TBC system consists of three different layers, namely a ceramic top coat (TC), a thermally grown oxide (TGO) layer and a metallic bond coat (BC). In the self-healing TBC system examined here dispersed healing particles are contained in the TC layer. For the design of a robust healing

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system, it is important to understand the failure behavior of the TBC. In particular, the depth at which cracks are likely to initiate need to be identified to judiciously distribute the healing particles. To achieve this, cohesive element-based finite element fracture analyses are conducted. Distinct fracture properties and microstructural features such as interface roughness and porosity are considered in the modelling. Moreover, the interaction between cracks and healing particles are analysed under thermal loading and assuming the healing particles to be dispersed in the TC close to the interface between the TC and TGO layers. Several configurations for the healing particles have been analysed to assess the influence of the particle distribution. This study helps to identify the optimal configuration of the healing particles for successful activation of the healing mechanism.

Startle and Surprise in Flight Crew

Annemarie Landman


Keywords: Human factors, Cognition, Mental models, Sensemaking, Stress Today’s debate around loss of control in-flight events and the implementation of upset prevention and recovery training has highlighted the importance of pilots’ resilience, i.e., the ability to deal with unexpected events. Unexpected events, such as technical malfunctions, automation surprises, aircraft upsets or spatial disorientation, are said to induce a “startle factor” that may significantly impair performance. Based on the literature, we propose that what is in practice often called “startle” can involve two processes: 1) a true startle response, which is a more physiological and fast process, and 2) surprise, which is a more cognitive and slow process. By describing the processes in a conceptual model, we propose that surprise, not startle, is most problematic when unexpected events occur during flight. The model assumes that surprise indicates a mismatch between an active mental model or “frame” and new information, and that surprise elicits efforts to explain this mismatch (i.e., “sensemaking”). Whereas the appraisal processes following both startle or surprise may cause excessive stress, surprise may also impair performance through an excessive mental workload caused by sensemaking activities, and through a loss of frame-related resources.

The conceptual model is the basis for our 4-year research program on “managing surprise in flight crew”. The first experiment to validate the model was executed in March 2016. In this experiment, we tested the effect of surprise on the pilots’ performance in recovery from an aerodynamic stall, using the DESDEMONA flight simulator, equipped with an extended aerodynamic aircraft model (SUPRA). The preliminary data of this experiment will be discussed in relation to the model.

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Effects of hygrothermal conditions on the long-term performance of adhesively bonded composite-to-

steel joints

Romina Lopes Fernandes


Keywords: Adhesively bonded joints, durability, environment conditions, interfacial degradation, thick bondline There is an increasing need for reducing the weight in traditionally heavy loaded structures such as ships and bridges, demanding the development of durable and lightweight solutions that can survive the heavy loads under extreme conditions. The combination of high-strength steels and composites can significantly increase the strength-to-weight ratio towards lighter and stronger structures. Within this type of structures, hybrid composite-to-metal joints are unavoidable. Adhesive bonding is one of the most suitable joining methods for this application, since it can be used to bond dissimilar materials with different coefficients of thermal expansion because the adhesive’s flexibility can compensate this difference and help to withstand the residual thermal stresses. Moreover, this joining process does not require the adherents to be drilled and hence there is a significant reduction of stress concentrations in the adherents compared to e.g. bolding or riveting. The limited understanding of the long-term durability of composite-to-steel bonded joints under service conditions hinders its application in industry. Therefore, there is an immediate need of performing studies in this field. The main goal of this project is the development of a model that accurately predicts the long-term performance of adhesively bonded Glass Fibre Reinforced Polymer (GFRP) to under hygrothermal conditions. Mechanical tests will be performed in order to study the mechanical degradation of the bonded joints when exposed to the ageing conditions. The experimental results will be the input for the numerical model. The idea is to combine different computational modelling techniques (Continuum Damage Modelling and Cohesive Zone Modelling (CDM and CZM, respectively)) in order to simulate all the damage mechanisms that can occur with the ageing.

The prediction of fatigue damage for 18th-century pastels subjected to vibrations induced by transport

Leila Sauvage


Keywords: Conservation, damage, fatigue, vibration, holistic approach

What is the common point between a conservator and an aerospace engineer? They both focus on maintaining structures in good condition by preventing damage. In practice, the materials researched are different, but the question remains the same: “How long can this material be transported before damage occur?” Trained as a

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conservator, I could not answer it for pastel paintings so I brought it to the engineering field as Ph.D. research. Adopting a holistic approach to a conservation problem, I would like to introduce the concept of fatigue life to assess scientifically the long-term effect of transport on such fragile objects.

Multi-spherical Composite-Overwrapped Cryogenic Fuel Tanks for Hypersonic Aircraft

Ilias Tapeinos


Keywords: cryogenic storage, multi-cell tank, progressive failure analysis, volumetric efficiency, conformable geometry

Composite overwrapped pressure vessels (COPVs) are increasingly utilized in applications where high strength and stiffness-to-weight ratios are critical e.g. in the field of hydrogen storage. LH2 is known for its high gravimetric energy density (MJ/kg), and when used as a cryogenic propellant in the aerospace sector it leads to increased aircraft range, greater payload and lower carbon emissions. The use of LH2 as fuel is exploited in EU CHATT (Cryogenic Hypersonic Advanced Tank Technologies) where composite-overwrapped (LH2) tanks are employed in the two-stage hypersonic reusable launch system (RLV) Space-Liner. However the downside of having LH2 is its low volumetric energy density (MJ/liter)-which is only a quarter of kerosene- introducing a need for large capacity hydrogen storage.

Therefore a novel multi-cell pressure vessel design is developed throughout this work, that shows potential for higher volumetric efficiency when fitted in a prescribed envelope (e.g. wing-box, fuselage), and significant weight savings compared to the conventional cylindrical tanks. It consists of four co-planar, intersecting spherical cells with a plastic liner and composite-overwrapped, and with hoop reinforcements at the intersections. Issues such as identification of the tank design-space, effective insulation and support at the stress-concentration areas –as a result of thermal gradients and inner pressure from the cryogenic fuel-are addressed. The operating window of this structure needs to be fully understood based on progressive failure analysis -in terms of pressure and temperature allowables under cryogenic conditions- by taking into account temperature-material property sensitivity. Finally proof-of-concept sub-scale demonstrators are manufactured from optimized composite patches to assess tank behavior when exposed operation loads, obtain pressure allowables and study damage progression and the nature of failure patterns.

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4.11 Environmental Impact

A multi-level optimization methodology for minimizing environmental impacts of aircraft

terminal operations on near-airport communities

Vinh Ho-Huu


Keywords: departure/arrival routes, runway sequencing, gate allocation, integrated optimization problems and integrated optimization methods The aviation industry has been contributing importantly to the development of business, communication and tourism globally. However, the continuous growth of the aviation market results in increasing negative impacts on the environment and near-airport communities. Air transport produces around 2% global CO2 emissions, and causes a considerable noise, which directly impact on global climate change and the quality of life of communities surrounding airports. To reduce noise and pollutant emissions, many research activities on aircraft and airport operations such as departure and arrival routes, runway sequencing and gate allocation have been considered and obtained significant results. Nevertheless, most studies often considered only one of these operations at a time, while they are often linked together. Therefore, the PhD research project aims to develop a multi-level optimization methodology for minimizing environmental impacts of aircraft terminal operations on near-airport communities, which can link many operations of aircraft and airport as a whole. The project focuses on formulating and solving simultaneously the integrated optimization problems of departure and arrival routes, runway sequencing and gate allocation.

Inclusion of Critical Gust Loads and Fatigue in the Preliminary Aeroelastic Design Framework

Darwin Rajpal


Keywords: gust load, aeroelasticity, fatigue, optimization, aircraft design The goals set up by Flightpath 2050 includes among others a 75% reduction in CO2 ,90% reduction in NOx and 60% reduction in perceived noise. These objectives necessitate the need for new technologies combined with unconventional aircraft configurations. To compensate for the lack of empirical data during the design and analysis of novel configurations, it is essential to have increased understanding about the various influential parameters in the early stages of design process. With this in mind, the current research will focus on the

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influence of critical gust loads and fatigue requirements on the aeroelastic tailoring of composite wings. Knowledge about the effect of aforementioned parameters on the structural performance in the initial phases will lead us to a more realistic design space which will result in an improved and efficient conceptual/preliminary design. A reduction in the design cycle and thus development time and cost can be achieved.

Towards a composite car exhaust

Niels Reurings


Keywords: Fibre-reinforced plastic, design, porous-open flow, boundary layer, heat transfer The gases emitted from car exhaust pipes are currently a hot topic in both senses of the word. Apart from after treatment systems, in exhausts weight can be saved and thus emissions reduced, by replacing steel with a lighter alternative. Fibre-reinforced plastics could potentially be such an alternative, but only when a low-mass thermal insulation layer can fill the gap between the fast and hot gasses and the composite shell. But before such a system, with its superior corrosion and fatigue properties, can hit the market insight has to be gained into the complex interaction between the turbulent flow and the permeable insulation. Preliminary results from newly developed test setups provide insight into the validity of criteria for interaction for this configuration, and as such the strength of the no-slip and zero-wall normal velocity.

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4.12 Aeroacoustics and Climate Effects

Experimental validation of an engine noise shielding prediction tool for tube and wing aircraft

Ana Alves Vieira


Keywords: aircraft noise shielding, Kirchhoff integral, Modified Theory of Physical Optics

Recent research indicates engine noise shielding by the aircraft airframe as promising in the reduction of the noise footprint on ground. Previous work on noise shielding prediction for Blended Wing Body (BWB) configurations indicate high values of noise attenuation and some studies demonstrate that noise shielding can be also significant in conventional tube and wing aircraft if the engines are placed above the wings. Despite such encouraging results, experimental work is still very limited in this area and no work have been done in the correlation between numerical results and experimental data of full-scaled aircraft. A new tool for noise shielding prediction was developed in the scope of this work, based in a method that uses the Kirchhoff diffraction integral approach and the Modified Theory of Physical Optics. This method is more accurate for thin sharp-edged objects as is the case of wings and allows calculations at high frequencies. The correlation between computational results and experimental measurements of flyovers was performed for aircraft models in which noise shielding is expected to occur due to the location of the engines above the wings.

Aerodynamic installation effects of tail mounted tractor propellers

Nando van Arnhem


Keywords: propellers, aerodynamic interactions, aircraft configurations, CFD, fluid-structure interaction Tail mounted open-rotor propulsion has gained increased attention for potential cabin noise reduction and reduced propeller-wing interference effects compared with wing mounted propellers. The closely integrated horizontal and vertical tail with the propulsion system results in significant influence of the propeller slipstream on the aircraft’s stability, the trimmed condition and controllability. In addition, the downwash from the wing results in aerodynamic induced excitations to the structure due to the unsteady loads on the propeller blades. The relatively thin support

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structure requires special attention in the (preliminary) structural design (i.e. stiffness and damping) in order to have a safe operation and a certain level of passenger comfort. The first goal of the research is to obtain a better understanding of the influence of rear mounted propeller integration in different flight conditions on (a) the tail plane aerodynamics, (b) the sizing of the tail and (c) the effect on the aircrafts flight mechanics. The second goal is to investigate the bounds of a safe operation (e.g. whirl flutter issues) of tail mounted propellers relative to the passenger comfort (e.g. aerodynamic induced vibrations of the structure). As the research is yet to be started, the presentation will be an overview of the relevant phenomena and an introduction of the methods used by others.

Beamforming techniques for quantifying propeller sound

Anwar Malgoezar


Keywords: Acoustics, beamforming, propeller, optimization, microphone array In order to reduce noise pollution from aircrafts, detailed understanding for the noise mechanisms is needed. For aircrafts fitted with a turboprop, the propeller is the primary contributor to the overall noise. To quantify the noise originating from a propeller, beamforming methods can be used with the help of a microphone array. In this work optimization techniques will be presented to improve the localization and strength of the acoustics sources. Techniques to both optimize relative microphone positions and optimize post-processing will be presented.

Microphone arrays for aerospace applications

Roberto Merino Martinez


Keywords: aircraft noise, aeroacoustics, microphone arrays, beamforming. Noise generated by aircraft and onshore wind turbines is becoming increasingly annoying and stricter environmental regulations limit the air traffic and the wind power generated. Microphone arrays and beamforming algorithms are useful tools to localize and quantify noise sources. They provide essential information necessary for lowering the noise levels of aircraft components or assess the performance of low-noise measures, such as trailing edge serrations or porous materials. This is typically

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done with experiments with aircraft flyovers and wind tunnel experiments. Variability analyses within the same aircraft type can also be performed.

Mitigation of Pusher-Propeller Installation Effects by Pylon Trailing-Edge Blowing

Tomas Sinnige


Keywords: propellers, propulsion integration, aeroacoustics, applied aerodynamics, flow control The high propulsive efficiency of propeller propulsion systems offers significant economic and environmental benefits over current-generation turbofans. However, the integration of advanced propellers to the airframe poses challenges in terms of ground clearance and noise emissions. Experiments were carried out at DNW–LLF to characterize the pylon–propeller interaction occurring for fuselage-mounted pusher propellers. For such layouts, the propeller performance and noise emissions are adversely affected by the impingement of the pylon wake on the rotor disk. Therefore, pylon blowing was studied as a means to eliminate the installation penalties. The impulsive rise in blade loading during the pylon-wake encounter increased the noise by up to 24 dB. The application of pylon blowing successfully eliminated the unsteady propeller blade loading during the pylon-wake passage. As a result, the noise penalty due to pylon installation was eliminated, bringing the sound pressure levels back to those recorded for the isolated propeller.

Benefits of concave serrations on

broadband trailing-edge noise reduction

Wouter van der Velden


Keywords: concave trailing-edge serration, turbulent boundary-layer trailing-edge noise, aeroacoustics, noise reduction Far-field noise and hydrodynamic flow field over a novel trailing-edge serration shape made as a concave triangle (named “iron-like” shape) are investigated. Spectra of the far-field broadband noise, directivity plots and the hydrodynamic flow-field over the iron-shaped serrations are obtained from numerical computations performed using a compressible Lattice-Boltzmann solver. The iron-shaped serrations are compared to more conventional trailing-edge serrations with a sawtooth geometry. Both serration geometries were retrofitted to a NACA 0018 airfoil at zero-degree angle of attack. The iron-shaped geometry is found to reduce far-field broadband noise of approximately 2 dB more than the conventional sawtooth serrations for chord-based Strouhal numbers Stc < 15. At higher frequencies, the far-field broadband noise for the two serration geometries has comparable intensity. Near-wall velocity distribution and surface pressure fluctuations show that their intensity and spectra are

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independent on the serration geometry, but a function of the streamwise location. It is found that the larger noise reduction achieved by the iron-shaped trailing-edge serration is due to the mitigation of the scattered noise at the root. It is obtained mitigating the interaction between the two sides of the serrations by delaying toward the tip both the outward (i.e., the tendency of the flow to deviate from the centerline to the edge of the serration) and the downward (i.e., the tendency of the flow to merge between the two sides of the serration) flow motions present at the root of the sawtooth.

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