itjemast v2(3) 2011:: international transaction journal of engineering, management, & applied...

IN THIS ISSUE

Thermal Comfort Assessment to Building Envelope: A Case Study for New Mosque Design in Baghdad

A Practical Step towards Integrating Elderly Pathway Design into Museum Space Planning: Framework of Satisfaction Assessment

Validating Measurements of Perceived Ease Comprehension and Ease of Navigation of an Online Learning Technology: Improving Web Based Learning Tool Adoption and Use

A Land Data Assimilation System Utilizing Low Frequency Passive Microwave Remote Sensing: A Case Study of the Tibetan Plateau

Prediction of Weld Pool Geometry in Pulsed Current Micro Plasma Arc Welding of SS304L Stainless Steel Sheets

Habitability Study on Low-Cost House Design of Modern and Traditional Mid-rise House Units in the City of Mukalla, Yemen

Interrelationships between Characteristic Lengths of Local Scour Hole

Oxygen Excess Control of Industrial Combustion Through the Use of Automotive Lambda Sensor

International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies

Cover photo is copyrighted by Dr. Wataru Takano and Professor Dr. Yoshihiko Nakamura. Humanoid robots, NAO, are being used for Undergraduate Mechanical Engineering Seminar at Department of Mechano-Informatics, University of Tokyo. (Photo is used with permission).

Volume 2 Issue 3 (July, 2011) ISSN 2228-9860 eISSN 1906-9642 http://TuEngr.com http://Go.to/Research


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International Editorial Board

Editor-in-Chief Boonsap Witchayangkoon, PhD

Associate Professor, Thammasat University, THAILAND

Honorary Board: Professor Dr.Mikio SATOMURA (Shizuoka University, JAPAN) Professor Dr.Chuen-Sheng Cheng (Yuan Ze University, TAIWAN) Professor Dr.I Nyoman Pujawan (Sepuluh Nopember Institute of Technology, INDONESIA) Professor Dr.Neven Duić (University of Zagreb, CROATIA) Professor Dr.Lee, Yong-Chang (Incheon City College SOUTH KOREA) Professor Dr.Phadungsak Ratanadecho (Thammasat University, THAILAND) Associate Prof. Dr.Uruya Weesakul (Dean of Faculty of Engineering, Thammasat University, THAILAND )

Associate Editors: Associate Prof.Dr. Ahmad Sanusi Hassan (Universiti Sains Malaysia, MALAYSIA ) Associate Prof. Dr. Paulo Cesar Lima Segantine (University of São Paulo, BRASIL) Associate Prof. Dr. Kurt B. Wurm (New Mexico State University, USA ) Associate Prof. Dr. Truong Vu Bang Giang (Vietnam National University, Hanoi, VIETNAM ) Associate Prof. Dr.Narin Watanakul (Thammasat University, THAILAND) Dr.H. Mustafa Palancıoğlu (Erciyes University, TURKEY)

Editorial Research Board Members Associate Prof.Dr.Peter Kuntu-Mensah (Texas A&M University-Corpus Christi, USA) Associate Prof.Dr. Anchalee Jala (Thammasat University, THAILAND ) Associate Prof. Dr. Masato SAITOH (Saitama University, JAPAN ) Assistant Prof.Dr. Zoe D. Ziaka (International Hellenic University, GREECE ) Associate Prof.Dr. Supornchai Utainarumol (King Mongkut's University of Technology North-Bangkok, THAILAND) Associate Prof.Dr.Chavalit Chaleeraktrakul (Thammasat University, THAILAND ) Associate Prof.Dr.Krittiya Lertpocasombut (Thammasat University, THAILAND ) Associate Prof.Dr. Bovornchok Poopat (King Mongkut's University of Technology Thonburi, THAILAND ) Assistant Prof.Dr. Akeel Noori Abdul Hameed (University of Sharjah, UAE) Assistant Prof.Dr. Atch Sreshthaputra (Chulalongkorn University, THAILAND) Assistant Prof.Dr. Rohit Srivastava (Indian Institute of Technology Bombay, INDIA) Assistant Prof.Dr. Watanachai Smittakorn (Chulalongkorn University, THAILAND ) Assistant Prof.Dr. Kitjapat Phuvoravan (Kasetsart University, THAILAND) Assistant Prof.Dr. Khiensak Seangklieng (Thammasat University, THAILAND ) Assistant Prof.Dr. Chainarong Chaktranond (Thammasat University, THAILAND ) Assistant Prof.Dr.Kridayut Chompoming (Thammasat University, THAILAND ) Assistant Prof.Dr. Nopporn Leeprechanon (Thammasat University, THAILAND ) Assistant Prof.Dr. Sawat Pararach (Thammasat University, THAILAND ) Assistant Prof.Dr.Winai Raksuntorn (Thammasat University, THAILAND ) Assistant Prof.Dr. Watit Pakdee (Thammasat University, THAILAND ) Assistant Prof.Dr. Cattaleeya Pattamaprom (Thammasat University, THAILAND ) Dr. David Kuria (Kimathi University College of Technology, KENYA ) Dr.Isares Duchallaya (Thammasat University, THAILAND ) Dr.Puttipol Dumrongchai (Chiangmai University, THAILAND ) Dr.Bandit Suksawat (King Mongkut's University of Technology North-Bangkok, THAILAND ) Dr. Foong Swee Yeok (Universiti Sains Malaysia, MALAYSIA) Dr.Orawan Chunhachart (Kasetsart University Kamphaengsaen Campus, THAILAND) Dr. C. Raza Mirza (UK )

2011 International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies.

International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies (ITJEMAST) (ISSN 2228-9860) is published quarterly by TuEngr Group @ Faculty of Engineering, Thammasat University, Klong-Luang, Pathumtani, THAILAND 12120. Periodicals postage paid at Pathumtani, THAILAND. Correspondence: All correspondence should be addressed to Dr.Boonsap Witchayangkoon, Faculty of Engineering,

Thammasat University, Klong-Luang, Pathumtani, THAILAND 12120 or [email protected].

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:: International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies

Volume 2 Issue 3 (July, 2011) ISSN 2228-9860 http://TuEngr.com, http://Go.To/Research eISSN 1906-9642

FEATURE PEER-REVIEWED ARTICLES

Thermal Comfort Assessment to Building Envelope: A Case Study for New Mosque Design in Baghdad 249

A Practical Step towards Integrating Elderly Pathway Design into Museum Space Planning: Framework of Satisfaction Assessment 265

Validating Measurements of Perceived Ease Comprehension and Ease of Navigation of an Online Learning Technology: Improving Web Based Learning Tool Adoption and Use 287 A Land Data Assimilation System Utilizing Low Frequency Passive Microwave Remote Sensing: A Case Study of the Tibetan Plateau 303

Prediction of Weld Pool Geometry in Pulsed Current Micro Plasma Arc Welding of SS304L Stainless Steel Sheets 325

Habitability Study on Low-Cost House Design of Modern and Traditional Mid-rise House Units in the City of Mukalla, Yemen 337

Interrelationships between Characteristic Lengths of Local Scour Hole 355

Oxygen Excess Control of Industrial Combustion Through The Use of Automotive Lambda Sensor 365



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*Corresponding author (Dr. Akeel Noori Abdul Hameed). Tel: 0097165050992. Fax: 0097165050982 E-mail addresses: [email protected]. 2011. International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. Volume 2 No.3. ISSN 2228-9860. eISSN 1906-9642. Online Available at http://TuEngr.com/V02/249-264.pdf

249


http://www.TuEngr.com, http://go.to/Research

Thermal Comfort Assessment to Building Envelope: A Case Study

for New Mosque Design in Baghdad

Akeel Noori Abdul Hameed a*

a Department of Architectural Engineering, College of Engineering, University of Sharjah, UAE

A R T I C L E I N F O

A B S T RA C T

Article history: Received 12 February 2011 Received in revised form 13 April 2011 Accepted 20 April 2011 Available online 01 May 2011 Keywords: Thermal Comfort; Building Envelope Assessment

The work is carried out with an objective of first, evaluating: the thermal characteristics of opaque and transparent parts of the building envelope in hot dry climate of case study “new mosque” building in Baghdad, the impact of sol-air temperatures, heat gain factors and the u-value of envelope section components. Second, it aims to assess the architectural criteria for appropriate passive design of new mosques in hot dry climates. Architectural design and construction of the new mosque (musalla) envelope in Baghdad are thermally inefficient in protecting the indoor space from climatic fluctuations. Therefore, the existing new mosques are not within thermal comfort level. To achieve and maintain that, applying architectural and construction alternatives on the mosque envelope contributes to controlling heat exchange through it as well as enhancing its thermal behaviors that contribute to getting internal thermal balance. The research covers survey of design, construction features, comfort levels in new mosques, and definition of the “model mosque”, as well as identification and thermal assessment of the typical “model mosque”. Computer simulations for building thermal behavior and design modification of building construction components also covered by the research. The findings and conclusion of the impact of simulation changes stated as well as recommendations for possible future mosque and design strategy. The findings show that HVAC systems entail capital, functional and maintenance costs whereas the passive mosque (musallas) building consumes less energy as well as being more likely to be in sympathy with the environment.

2011 International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. Some Rights Reserved.

2011 International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. 2011 International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies.

250 Akeel Noori Abdul Hameed

1. Introduction Architectural design is influenced by the actual thermal behavior of building components,

and this depends not only on their steady and periodic thermal characteristics but also on

exposure effects, orientation, surface features and the climate parameters of the location.

The main issue of this research is “the thermal comfort for internal space of the modern

mosque in Baghdad”. The mechanical and electrical systems of heating and cooling encourage

architects to implement new construction techniques and using wide openings in buildings'

facades as well as employing new constructional materials, which are not suit local hot climate.

All this makes people depends on HVAC systems, which consume high amounts of energy

annually in an attempt to provide a comfortable indoor environment. The mosque buildings are

affected by the adoption of new materials and new urban planning as well as new architectural

designs, which are not sensitive to the environment, the actual needs of occupants, and the

building function or comfort criteria. (Tappuni, 1973).

The new city of Baghdad nowadays includes individual multi-storey buildings. Wide

streets and open spaces expose those buildings more to solar radiation and other types of

climatic impact more than the other traditional buildings, which are surrounded by narrow

alleyways. It can be concluded that for buildings in a hot-dry climate, minimizing the external

heat gain through the building envelope would be a good strategy to reduce the dependence on

energy in conditions of necessity. That can be achieved by means of appropriate design for the

building envelope.

The research is carried out with the objectives of evaluating thermal characteristics of the

new mosque “musalla” envelope in Baghdad, the impact of sol-air temperatures, heat gain

factors and the U-value of envelope section in aims to assess the generational architectural

criteria for appropriate passive design of mosques.

The research discusses the thermal comfort in the new “musalla” in Baghdad, which is

effected by heat exchange that influenced by its orientation, envelope design, structural and

constructional components as well as the specifications and use of materials in order to:

i. Investigate the impact of envelope components on the heat exchange and thermal

comfort of the users of inner environment of the new mosque (musalla).

ii. Investigate the thermal efficiency of the present new mosque envelope in Baghdad.


251

iii. Study how to minimize the “environmental impact” by revising the design and

materials of the envelope.

iv. Identify the optimum thermal design “passive design” and construction materials

specifications and details for the new mosque envelope.

v. Propose other suitable treatments, which affect thermal design for the mosque that

provides thermal comfort for the occupants and reduces energy consumption at the

same time.

vi. Optimize comfort level for occupants for five prayer times.

As beginning a new paragraph, a line is leaved blank before starting a new paragraph

(Satomura et al., 2013). All references must be mentioned in the writing article.

2. Background of the Research

2.1 Baghdad Climate Generally, the climate of Iraq is characterized by a large diurnal air temperature range

coupled with a high intensity of incident solar radiation as shown in Figure 1 On the other

hand, in such widely fluctuating climates, building envelope has great potential in providing

thermal comfort and reducing energy consumption. An efficient thermal design of a building

envelope should consider three main parameters which are; First the form and orientation of

the building, Second; the fenestration, which relate to the size, orientation and exposure of the

windows to the sun and the type of glazing and Third; the thermal properties of the opaque

elements. This includes the solar absorptance of the external surfaces and the thermal capacity

and conductance of the elements as well.

Climatic information, including air temperature and solar intensity in the Baghdad region,

as well as thermal air rates, humidity and other parameters were obtained from the Iraq

Forecast Directory-Baghdad. It has been arranged with the Building Research Center in

Baghdad to get the outputs of some tests carried out by the center’s instruments, which help in

furnishing this research with some important information.

2.2 Problem Statement Due to the defined daily uses of mosques, the problem facing architects and engineers is

how to achieve thermal comfort during prayer times when the mosque building is occupied.

The short time of each of the five daily prayers (almost 30 minutes per prayer) gives rise to


serious problems in terms of providing comfort. It is noticed that it is not enough to reach

comfort level even though an HVAC system is used and just operates before each prayer time.

It would be too costly also to operate it for a long period before prayer times to provide

comfort for very short periods of prayer.

One of the important characteristics of the mosque design is the orientation of Mecca

(Qibla direction), which considered as a constant design parameter for the mosque.

Figure 1: Annual Temperature in Baghdad, Source: Baghdad Metrological Dept.2000.

The thermal properties of the envelope are determined by the combination of wall mass,

thermal resistance; insulation location, external surface colour and texture, and the size and

location of glazing. All of those affect energy consumption differently according to weather

conditions. The design of the building envelope can also greatly affect infiltration rates.

Based on the previous highlighted design features and specific climate parameters, the

problems of the new mosque in Baghdad may be summarized as following:

i. Lack of optimum passive design guidelines for the mosque’s envelope which influence

the comfort level of the inner environment and contribute for energy conservation.

ii. Ignoring comfort level requirements for occupants which influenced by construction

materials and details used in buildings as well as the suitable architectural treatments in the

new mosques building design in Baghdad.


253

3. Research Method The research has considered the following steps:

i. Achieving specific survey to ascertain whether it is true or not that the new mosque

building in Baghdad is not comfortable thermally for occupants.

ii. Defining the weaknesses in the design and construction components of the mosque

through the following strategy:

a. Collecting data from 50 new mosques in Baghdad that represent 65% of the new

mosques in the Baghdad vicinity in July 2008.

b. Identification of the typical new mosque, “Model Mosque”, in Baghdad.

ii. Applying an analytic study and assessment for architectural and construction

components relating to heat exchange through the envelope of the “Model Mosque” in

Baghdad, which is determined according to the common architectural and constructional

elements in fifty new mosques in Baghdad, using heat balance equation.

iv. Assessment for the “Model Mosque” using a computer simulation program (BLAST

program) before and after introducing changes to the total transparent area of its envelope and

the construction features.

The BLAST (Building Loads Analysis and System Thermodynamics) system is a set of

computer programs for predicting heating and cooling energy consumption in building.

One of the BLAST processors, Heat Balance Loads Calculator (HBLC), is used to

interactively create BLAST input files with a minimum of input required from the user.

4. Definition of “Model Mosque” A survey to define the “Model mosque “musalla” and determine the architectural and

constructional features of the new mosque envelope as well as thermal comfort response for the

praying people in those fifty new mosques is the main aim before starting thermal assessment.

The conclusion of the survey output gave the architectural characteristics and other

constructional details of the typical new mosque in the Baghdad vicinity the “Model Musalla”,

which is considered as representative the typical design of new mosques for use in the

computer simulations.

The typical “musalla” or “praying area hall” within mosque “complex” that has other

facilities”, has the same specifications as all the modern types in Baghdad. It was found that


these specifications are the following:

i. The musalla has a detached rectangular form with inside net-dimensions in general

22mx11mx6m in height. It includes a central dome at the roof, the diameter of which is 7.0m

and the height of which from the base to the top of the cone is 6.5m. This rectangular shape has

one attached arcade laid at the same longitudinal wall, which is parallel to that which faces the

“qibla” or Mecca (the holy city in Saudi Arabia) see Figure 3.

ii. The main feature of the musalla mass is the dome which lies in the center of the roof.

The dome has three levels from bottom to top. The first part is the drum (dome base). Its height

is 2.00m. Above it there is a spherical part and the upper part is the cone.

13

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4

67 8

9

1 0

1 1

1 2

1 4

1 51 6

1 7

1 8

2 0

2 12 2

2 3

2 4 2 5

2 6

2 7

2 8

2 9

3 0

3 13 2

3 3

3 4

3 5

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4 04 1

4 2

4 3

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F in d e n c lo se d f t h e d e ta i ls o t h e M o sq u e s s u rv e y f ro m 1 to 5 0

S U R V E Y O F F IF T Y N E W M O S Q U E S IN B A G H D A D

IN 1 9 9 7

IR A Q

Figure 2: Location of fifty surveyed new mosques in Baghdad.

All these components are usually found in the typical Baghdadi mosque’s dome. Four

columns support the dome from inside praying hall; the average thickness of its concrete slab is

0.15m and includes eight small arcade windows normally situated on the drum part of the

dome.

iii. The musalla is usually constructed from a reinforced concrete skeleton structure with

brick wall partitions. The roofing slab thickness is 0.15m, and the brick wall is 0.24m thick.

Above the concrete slab of the roof there are many layers which consist of the waterproof layer

(0.07m), natural clean sand (0.15m) and rough sand (0.05m) and cement tiles (0.03m). The

dimensions of each cement tile are 0.80mx0.80m. The interior finishing of the dome and the


255

walls is fine gypsum, and its thickness is 0.025m.

Figure 2a: Plan for the Model Mosque “Musalla”.

5. Research Considerations Fundamental research considerations for the “Model Mosque” features are:

1. musalla envelope is one piece.

2. The collected data did not refer to the existence of any space beneath the musalla.

3. The musalla envelope consists of just external Walls, Roof and Floor.

4. Sub-parameters, windows, and doors “Transparent Part” are represented as part of the

envelope.

5. Air vents, as uncontrolled openings do not exist.

6. The minaret “the tower” still has no role in the thermal behavior of the new musalla

envelope.

7. Average number of praying persons per prayer time for the five daily prayers is 30,

becoming sometimes 45 at peak time at sunset prayer “maghrib prayer”.

8. Air cubage is represented by the human comfort zone that is within 8 feet in height and

the remaining volume of the internal space of the musalla.

9. It is proposed that the inner environment of the “Model musalla” is in thermal balance

to estimate the actual ability of the musalla envelope to maintain that balance. The

present research discussed, by means of geometrical analytical study, all parts of the

musalla envelope to highlight the role of each, area of opaque and transparent parts, and


study for the dome parts as well as defining the air cubage.

10. Heat exchange estimate by heat flow mean per sq.m through walls, windows and roof

as well as heat flow mean by ventilation per m³ owing to the successful results from

thermal computer simulations and approach, which have been considered.

The new mosque type in Baghdad is representative of the mosques built after World War

II and shares the following characteristics:

1. Located in the Baghdad vicinity.

2. Used usually on five short occasions daily.

3. Its building is passive designed.

6. Results

6.1 Computer Simulation The “Model musalla” building as shown in Figure 3 has been simulated for the four

different roof and five different walls structures. To make the simulations comparable, the size

of one huge space or praying hall (musalla) and its direction to Mecca at 10 degree southwest

has been treated as a constant.

6.2 Simulation Alternatives Applications

6.2.1 Walls Simulation Analysis a. The computer simulation proved that the massive envelope behaves as a “Thermos

Flask”. So, there is no an actual enhancement for thermal comfort level of the inner

environment after increasing wall thickness more than 36cm or even using cavity walls with

the same specifications of the “Model Musalla” envelope, Figures 4, 5, and 7.

b. It appears that the musalla building is dialectically balanced with the outside climate for

a wall thickness of 36 cm because as the wall thickness decreases below 36cm its effectiveness

in damping outside temperature fluctuations also decreases. On the other hand, for wall

thickness more than 36cm, the heat received during the long summer day cannot be released

during the shorter nighttime according to expected long “Time Lag”, which causes bad

envelope behaviors in terms of “Thermos Flask” manner. In this case, there is overlapping heat

gain occurrence which a raises the inner air temperature.

c. The inner environment of the musalla’s building is balanced with the outside climate


257

when the wall thickness is 36cm, but it is influenced more by climatic fluctuations when there

is a thin envelope of 12cm thickness.

6.2.2 Roof Simulation Analysis The computer simulation also indicates, that the traditional RC (Reinforced Concrete) flat

roof still perform the best thermally, and has positive heat exchange after the applying of

additional insulation material (15cm), Figures 6, 8 and 9.

Figure 3 This graph shows that the radiation peak time in Baghdad starts at 10.30 am and increases gradually to reach a maximum at 3.00 pm, and reduces gradually after that to reach starting point at 7.00pm. However, the inner temperature increases from 1.00 pm gradually till 10.00 pm, that indicates the important role of the envelope in delaying the heat gain from reaching the inner space, or what is called –Time lag period–which depends on the envelope section in terms of the specifications of material and constructional details. The lowest curve indicating the comfort level ranges

Figure 4a: Building envelope behavior before applying simulation.

Figure 4 Range of Comfort Level in Iraq


Figure 4b: Building envelope behavior before applying simulation.

Figure 5: Building envelope behavior after reducing glazing area to half.

Figure 6: Building envelope behavior after reducing glazing area to half.


259

Figure 7: Building envelope behavior using different types of roof.




Figure 10 Building envelope behavior using no glass area at west& east

7. Discussion Achieving and maintaining thermal comfort level for the indoor environment of the

mosque “musalla” by applying architectural and construction alternatives on the musalla

envelope will contribute controlling heat exchange through it as well as enhancing the thermal

behaviors of its construction components.

The findings are showing that HVAC systems mean capital, functional and maintenance

costs for passive musalla building consumes less energy. It is more likely to be in sympathy

with the environment also.

The specific research findings are concluded as follows:

1. Architectural Design of the present new mosque “musalla” envelope in Baghdad is

thermally inefficient according to the previous analytical assessment and computer simulation.

2. Materials used in the construction of the envelope of the new musalla are not thermally

efficient in protecting the indoor environment from climatic fluctuations.

3. Then, the indoor environment of the present new musalla is not recently within thermal

comfort level.

4. It appears that the indoor environment of the musalla building is thermally balanced

with the local climate for a wall thickness of 36cm; highly insulated typical RC flat roof, avoid

the transparent area at west and east as well as reducing it at South-west orientation to be half

of transparent area of the “model musalla”.

5. It is found also that the indoor environment of the musalla’s building is influenced more


261

by climatic fluctuations when there is a thin envelope (less than 30cm thickness), and the

envelope’s behaves as a “Thermos Flask” when there is a massive envelope (more than 36cm

thickness).

6. During the past ten years it has not been economically feasible to invest in HVAC plant

for mosques to meet the running costs. It is not likely that this economic situation in Iraq will

change in the near future and undoubtedly many mosques will have to be built with these

economic constraints. So, this study has not considered the totally dependence on centralized

HVAC systems as part of any strategy to achieve thermal comfort.

7. Achieving as well as maintaining thermal comfort for the indoor environment of the

present new musalla should come from controlling heat gain and enhancing external

microclimate. The following factors should be taken into consideration as recommendations

and techniques to be applied:

i. Selecting materials and construction system on the basis of low thermal transmittance

(low U-value) and high thermal mass in addition to the implementation of

constructional treatments and alternatives to get a desired time lag within 8 to 14 hours

for walls, and 20 to 30 hours for the roof. Using well-insulated roofing materials to

provide high time lag, low thermal transmittance and high thermal capacity (like local

fershi brick 30cmx30cmx5cm) and 0.36m walls thickness to replace 0.24m walls, or

foaming Portland cement mixture with a foaming agent such as aluminum dust to make

insulated light concrete roof slab could be also more effective in controlling heat flow.

ii. Using the most common economical thermal insulation materials in Baghdad, that is,

polystyrene (11 cm) thick for the roof; (7 cm) thick for south-facing walls;(8 cm) for

southeast walls; and (10 cm) for other orientations. Insulation material should be

located near the external layer of the walls, which should be smooth and painted

externally in light colors.

iii. Designing well-shaded walls and windows, selecting suitable window insulating Low-

e-glass and size for each orientation, these areas should be minimal on the east and west

elevations.

v. Raising the roof enables cooling by ventilation; the best U-value for the whole roof and

ceiling construction should be 0.8 W/sq.mc.

v. Using double roof, double walls skin and the early development ideas on "Filter"

Architecture" to get high thermal protection will give an additional protection for

indoor environment.

vi. Designing the musalla to be in thermal contact with the earth, the idea of (sub ground


level–basement) enables benefits from the cooled humid space more than is possible at

ground level.

vii. Additional ventilation is required in summer using fans. This can be beneficial,

particularly at nighttime, and daytime in shaded spaces. Further research is needed on

the optimal mix of natural ventilation, the simple mechanical fan, and water nozzle fan.

viii. Employment of an L-shape or U-shape Riwaq (semi-covered arcade area) attached to

the musalla envelope gives it more shade, and enhances the microclimate. In addition,

an increase in the numbers of domes is thermally desirable for more benefits from

buoyancy phenomena occurrences that generate more passive ventilation through the

dome and envelope openings.

ix. Employing of minarets as external breeze catchers (Air Scoop). The inlet openings of

minarets should face the prevailing pleasant northwest wind in Baghdad to promote

airflow into the musalla, using the convective and evaporative cooling techniques for

elevating internal comfort level in such harsh summer in Baghdad.

x. Microclimate planning controls can have a major effect over the musalla design. In

addition to providing shade, plants can assist cooling by evaportranspiration. Plants also

enhance the visual environment and create pleasant filtered light.

xi. The study will be transferable for other parts of Iraq with certain limitations. For

example, in the southern part of Iraq increase in temperature could be consummated

either by introduction of some cooling or an increase in the thermal mass. In the north,

which is generally cool, this may be consummated of some heating or an increase in

insulation and a reduction in glazed area.

8. Conclusion The existing musalla is effectively a passive building. Based on that, there is no

consideration for HVAC systems. The musalla building will be dialectically balanced with the

outside climate for a wall thickness 36 cm because as the wall thickness decrees below 36cm

its effectiveness in damping outside temperature fluctuations also decreases.

For wall thickness more than 36cm, the heat received during the long summer day can not

be released during the shorter nighttime that brings overlapping heat gain occurrence which

raises the indoor air temperature. The computer simulation also indicates, that the traditional

RC (Reinforced Concrete) flat roof still the best thermally in terms of cost, available labor skill

in Baghdad, and positive heat exchange as well that will be more suitable after applying of

additional insulation material (15 cm ).


263

Passive Mosque (Musalla) building design must take into account the following;

i. Indoor Thermal comfort requirements.

ii. Limitations of local construction, climate, available materials and labor skills.

iii. Specific nature of activity.

v. Capability of building envelope for protecting the indoor environment of the musalla

from climatic fluctuations.

vi. Consideration of high thermal mass envelope, insulation and other criteria that

influence heat exchange and Time-Lag.

vii. Microclimate impacts as well the pattern of the surrounding urban fabric, vegetation

and landscape.

viii. Construction capability that play direct role in heat flow.

ix. How all the previous criteria affect the economic factor that represents a major

parameter in taking design decisions?

9. Acknowledgements First of all, I would like to thank my university for providing full support including

financial support, which is the most needed for this project to be achieved. My sincere thanks

go also to all the field assistants, without whom this research would not have been realized.

Very special thanks are due to Professor Dr. Peter Woods (Malaya University, Malaysia), as

well as Associate Professor Dr. Ahmad Sanusi Hassan (Universiti Sains Malaysia), and

Assistant Professor Dr. Atch Sreshthaputra (Chulalongkorn University, Thailand) for their

insightful comments, helping clarifying and improving the manuscript.

10. References Al-Azawi, Muhyi.(1984). The Passive Internal Temperature of Buildings for Different Design

Conditions in Iraq. (Proceeding of Scientific Research Council-Baghdad Research Center, Building Materials Department-Baghdad-Iraq, Vol.2. Symposium of Thermal Insulation in Hot-Dry Climate, 26-28 Nov. 1984), Baghdad.

Al-Riyahi, Mehdi and Akrawi, A. (1995). Evaluation of Direct and Total Solar Radiation on Surfaces with Different Orientation in Baghdad during Cloudless Days. Journal of Solar Energy Research, Vol.3, No.1, Building Research Center, Baghdad.

Al-Umary, Hafsah Ramzy (1988).Modern Architecture of Mosques in Iraq: Analytic Field Study for Baghdad Mosques since Second World War, Unpublished M. Sc. Thesis (in Arabic) submitted to the University of Baghdad.

ASHRAE 55-1992,(1992). ASHRAE standard-Thermal Environmental Conditions for Human Occupancy, Atlanta: American Society of Heating, Refrigerating and Air-conditioning


Engineers, Inc.

Bomberg, M. & W.C. Brown, (1993). Building Envelope and Environmental Control, Part I & II, published in ,construction Canada35 (1),1993,P.15-18.

CIBSE AM13 (2000) .Chartered Institute of Building Services Engineers, UK

Climatology Atlas No.II for Iraq (2006), Baghdad. Metrological Department, Ministry of Communications, Baghdad

Dawud, Azhar J.(1983). Passive Approaches to Solar Architectural Design for Iraq, Unpublished M.A. thesis submitted to the University of Sheffield,UK.

Fanger, P.O (1970). Thermal Comfort: Analysis and Applications in Environmental Engineering, McGraw-Hill Book Company, Kopinhagen.

Shaaban, Dr. A.C. and Jawadi, Dr. M.(1973). Analysis of the Climate of Iraq: It's Impact on the Building Character, R.p. 21/73., Building Research Center, Baghdad.

Straube, J.F., Burnett, E.F.P(2005). Building Science for Building Enclosures, Building Science Press, Westford.

Tappuni, R. A.(1973). Generative Approach to the Thermal Design of Buildings in Hot Dry Climate, Unpublished Ph.D. thesis submitted to the University of Edinburgh.

Wasim Y, Saman & Khamis S. Gasim, (1984),Thermal Performance of Iraqi Building Construction, Proceeding of scientific Research Council- Baghdad, Research Center, Building Materials Department, Vol 2. Symposium Thermal Insulation of Hot-Dry Climate 26-28 Nov. 1984.

Dr.Akeel Noori AH is currently an Assist. Professor of the Architectural Engineering Department at the College of Engineering, University of Sharjah, UAE (2009~). He holds a PhD in Architecture & Environmental Impact Assessment (2004) from Faculty of Built Environment, Malaya University, Malaysia. He is a fully licensed consultant Architect since (1996). He has worked at Faculty of Architecture & Environmental Design, International University Malaysia 1998-2008, Guest lecturer in the Architectural Design Dept., University Putra Malaysia. He successfully combines professional and academic roles and has a particular interest in Heat Exchange in Building, EIA, Passive & Green Architecture. Dr. Akeel has been an active role in many important international environmental-related conferences such as the International Environmetrics Society, TIES 2005 Conference. He is also an author of number of papers and books; chapters in books, journal papers, and technical reports & has many papers presented in many international conferences as well. He has a distinguished professional experience and known by reputed international Architectural companies as a consultant, and designer on both public and private architectural projects in Malaysia, Iraq, Saudi Arabia and the UAE.

Peer Review: This article has been internationally peer-reviewed and accepted for publication

according to the guidelines given at the journal’s website.

*Corresponding author (Raed M. A. Elottol). Tel/Fax: +60174405868 . E-mail addresses: [email protected]. 2011. International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. Volume 2 No.3. ISSN 2228-9860 eISSN 1906-9642. Online Available at http://TuEngr.com/V02/265-285.pdf

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A Practical Step towards Integrating Elderly Pathway Design into Museum Space Planning: Framework of Satisfaction Assessment Raed M. A. Elottol a* and Azizi Bahauddina

a School of Housing, Building and Planning, Universiti Sains Malaysia, MALAYSIA A R T I C L E I N F O

A B S T R A C T

Article history: Received 12 February 2011 Received in revised form 26 March 2011 Accepted 10 April 2011 Available online 01 May 2011 Keywords: Interior Environment, Museums’ Design, Pathway Design, Elderly, Satisfaction

The study examines how elderly visitors’ perception, interior environment, pathway design quality, and satisfaction are related in the context of interior environment and space planning of museums. This paper explores a theoretical as well as practical key issue in elderly pathway design in museums in Malaysia. The research intends to explore the elderly pathway design that interacts with the interior environment and space planning in museums. This is to fully understand the relationship between elderly visitors’ satisfaction and pathway design. This paper plans to answer critical questions; what is interior pathway design? How does the pathway design relate to the elderly visitors’ satisfaction? And what is the relationship between elderly visitors’ satisfaction, and pathway design quality? This study is one of the few studies focus on elderly people and pathway design. The empirical analysis carried out on 509 of elderly visitors in 21 museums in Malaysia allows us to confirm that the quality of interior pathway design is a direct determinant of elderly satisfaction. The results also reveal that there is a significant relationship between elderly satisfaction and quality perception. Finally, the interior environment elements of museums such as lighting design, furniture arrangement and finishes materials are also considered.


1. Introduction This study concerns about the pathway design of the museums and the elderly visitors’


266 Raed M. A. Elottol and Azizi Bahauddin

satisfaction in Malaysia, and to assess the adequacy of the circulation design of the museums,

the study uses the confirmation and disconfirmation process as a reference point to investigate

the overall satisfaction of the elderly visitors. Wener (2002) discusses the issues of

circulation, orientation and pathway design. According to him, there is growing evidence that

the interior designers of museums are either unconcerned or largely ignorant of the needs of

users and visitors. He considers pathway design in museums and orientation as the first, and

possibly the most basic behavioral need of visitors upon entering the museum. Wener also

highlights the nature of visitors in the museum and the questions of place orientation and

pathway, such as "where am I?" and "how do I get from here to there?" as well as the function of

pathway and circulation, such as "how does this pathway system work?". Elderly visitors in

museum will try to answer all these questions efficiently and fast to enjoy the visit and to spend

the rest of the time focusing on the objects in the museum (Weissmann. and Islam. 1996).

Richard (2002) states that if the pathway in buildings are insufficiently designed, the remaining

options for user will be asking others for help, observing the actions of others or spending much

time just to find the direction. He considers each option as a source of capriciousness and

therefore stressful in and of itself which may lead to dissatisfaction. The remaining option for

visitors is self-exploration, which can be even more frustrating (Wener, Richard et al. 1982;

Wener 2002). Weisman ( 1983) also finds in his study that experts' ratings of the complexity of

floor plans correlated highly with the likelihood of space users getting lost (Weisman 1983).

Reussner (2004) finds that, from the late 1980s, continuous criticism regarding to the lack of

studies and audience research for museums, as well as the lack of proper guidelines can

consider all genders and ages of visitors (Reussner 2004).

Until now there are no researches have been conducted to measure the attendance of

elderly people in museums, but some studies (Bitgood 1991; Weissmann. and Islam. 1996;

Rogers 1998; Tufts and Milne 1999; Rojas and Camarero 2008; Webb 2010) give indications

that elderly visitors are very interested in visiting museums. Based on Roger’s research (1998)

most of the museums visitors in his study are ranged from age 50 -70 (elderly), and as a result

of his study also, elderly visitors of museum have a high expectations concerning museums’

interior design and comfort level in terms of interior pathway and circulation system. Roger

explains that elderly attendance could be based on (a) personal characteristics such as nostalgia,

(b) experiences, and (c) general levels of satisfaction with the museum itself and interior design.

In different study Rojas and Camarero (2008) also state that in order to use museum resources


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and design in the most successful and advantageous manner, museums need more studies to

identify what factors have to be considered for the visitors’ circulation and pathway in

museums (Rogers 1998; Rojas and Camarero 2008). Throughout museums’ basics, museum

design must emphasis the relationship between visitors and space. In Malaysia, the absence of

interior pathway design’s strategy for elderly visitors is noticeable, where at the museums in

Malaysia it is easy to get tired and old people may tire particularly quickly (Researcher 2009).

To achieve efficient interior circulation and pathway design of museums for elderly people,

designers must understand the nature of elderly visitors, behaviour, design data and their needs.

According to several studies (Wener 1998; Wavell, Baxter et al. 2002; Yin 2003) many of

the elderly visitors have impaired mobility, and some of them are in wheelchairs, but more

simply walk slowly and painfully. Some also use a stick or simply find stairs very difficult. In

order to overcome this problem, Malaysian government endorsed the Biwako Millennium

Framework for Action (BMF) in the year 2002. It announced the extension of the Asian and

Pacific Decade of Disabled and Elderly Persons (Meng 2009). Accessibility to built

environment and pathway design are some of the areas out of 7 priorities in the policy which

Biwako Millennium Framework for Action would like to achieve. The policy reflects the

consequence of implementing a barrier-free in order to accommodate the involvement of

disabled people and elderly in the society (Meng 2009). Thus Meng (2009) also states in his

study that, “The design strategy for pathway design and accessibility for elderly and disabled in

museums’ buildings in Malaysia needs to be ascertained” (Meng 2009). Mohamed and Mustafa

(2005) in their study also find that, designers are still unfamiliar with the needs of the elderly

people which are of great importance. They state that, In Malaysia, until now there is no source

or study which can give a great source of information related to the elderly user’s needs,

capabilities, and interior pathway design. However holding these sessions may be a challenge

for several reasons. These challenges involve adjusting for diversity of the older population and

their physical and cognitive differences, dealing with the attention characteristics of this

population (Black 2005; Black 2008).

Finally, several studies (Ching 2004; Department of Statistics in Malaysia 2009; Cusiima

2010; Department of Finance and Personnel 2010) highlight that understanding of museum

space planning and form of pathway is a very important factor affects the visitors’ circulation

and satisfaction with museums. So, it is believed that the desired outcomes of this study should

assist designers to consider better ways for museum space planning and pathway design by


making them aware about the true level of elderly satisfaction with museums’ design in

Malaysia.

2. Interior Pathway and Circulation Design Bitgood (1988) highlights the importance of pathway design in museums. He states that,

the museums’ interior design and the layout of the exhibitions in the building that constrain

visitor circulation may determine visitors' methods of interaction with display objects (Bitgood

1994; Bitgood 2005; Bitgood 2010; Bitgood 2010). Therefore, the way in which pathway is

designed is the major question of museums’ interior design. Nowadays, It becomes a fact that

the interior pathway is the key issue for exhibition and museums’ design (Hall, Basarin et al.

2010; Haywood and Cairns 2010; Heath and Lehn 2010; Hendon 2010; Holjevac, Marković et

al. 2010; Holl’s 2010). At the same time designers must understand that all elements of

circulation and pathway are important, so in museum design process, pathway is the main key

of decisions regarding how the collection will be displayed and viewed for visitors. On the

whole, pathway design becomes critical for moving the museum’s visitors through the building

(The International Council of Museums 2009). Several studies state that interior design of

museums must meet the specific needs of elderly or disable visitors, such as accessibility,

pathway design quality, space planning, comfort level and visitors’ satisfaction (Foster 2010;

Goodman, Gallant et al. 2010; Goor-balk, Warmerdam et al. 2010; Hall, Basarin et al. 2010;

Haywood and Cairns 2010; John J. Koran, Jr. et al. 2010). So to design a museum properly the

interior pathway must be considered and involves the creation of solutions of all problems.

Therefore, elderly movement in space/time also to be resolved in the ultimate sustainable plan

(Yalowitz 2002; Yenawine 2002; Wunsch, Jones et al. 2010; Hsu 2004). Moreover, Hsu

(2004) and others highlight a very important issue that visitors may not be mindful of how their

bodies and movement are in continuous dialogue with the pathway and interior environment. In

different meaning, how visitors practice the three dimensionality of a building (perceptual

function) is mainly through movement of our bodies through time, sequence and space

(Zelanski and Fisher 2010; Zorloni and Wien 2010; Hsu 2004). Few researchers only wrote

about the pathway and the interior circulation within buildings. Beirne (2003) stresses that the

horizontal circulation and pathway can be considered as, “all walking areas on all floors of a

building required for physical access to some spaces”. This is including to the horizontal

features such as corridors, lobbies, verandas, porches, doors, entrance foyers, and balconies. He

also defines vertical circulation as; “all walking areas and mechanical tools installed in all


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floors of a building required for vertical physical access to some space” This is also including to

staircases, ramps, elevators and escalators (Beirne 2003). Moreover, G. Black (2005) in his

research defines interior circulation in buildings as:

“The all walking areas on all floors of a building required for physical access to some subdivision of space, whether physically bounded by partitions or not. Included Horizontal and Vertical circulation, which should be but is not limited to, public corridors, exhibition spaces, entrance foyers, elevator lobbies, tunnels, bridges, and each floor's footprint of elevator shafts, escalators and stairways. Also included are corridors, whether walled or not, provided they are within the outside facelines of the buildings to the extent of the roof drop line.” (G. Black, 2005: 12).

Finally, Stephen (2009) explains clearly the interior circulation in the buildings as;

“A term describes how visitors make their way through the facility. What pathways do they take? Do visitors circulate the way the designers intended? Do visitors miss key exhibits because of the architectural design of the facility? Which direction do visitors turn when they reach choice points? Do visitors have a circulation strategy (e.g., "Turn right and follow the perimeter") or do they simply wander more or less aimlessly?” (Stephen, 2009: 44).

Ching (2004) discusses in detail the configuration of pathway design , he states that:

“All paths of movement, whether of people or services are linear in nature. And all paths have a starting point, from which we are taken through a sequence of spaces to our destination. The contour of path depends on our made of transportation. While we, as pedestrians, can turn, pause, stop, and rest at will” (Ching, 2004:134). In addition, Ching (2004) discusses the nature of a path’s configuration influences, the

factors affect path’s configuration. Ching thinks that the most important factor affects pathway

configuration is the visitors’ orientation within the building. According to Ching, there are

many types of circulation paths in buildings, Ching also lists down the most popular types such

as: Linear Circulation Path, Radial Circulation Path, Spiral Circulation Path, Grid Circulation

Path, Network Circulation Path and Composite Circulation Path (Ching 2004).

3. Elements of Interior Pathway Design and Circulations The efficiency of interior pathway and circulation system in museums determined by the

basic shape and form of building. Buildings of the same internal floor area and same function

differ in the proportion of space taken by elements of interior circulation and pathway. It differs

also in the design style of circulation and pathway elements such as lifts, corridors and other

mechanical equipment (Sookhanaphibarn and Thawonmas 2009.; Bitgood 2010; Bitgood 2010;

Bitgood 2010; Bolton 2010). The time needed by a visitor to move from one area within the


building to another area and the enjoyment of doing this by visitors are affected by the building

form, pathway design and circulation style that is designed (Khan and Syed 2009;

Martı´n-Ruiz, Castellanos-Verdugo et al. 2009; Mattsson 2009; Meng 2009; Rohloff, Psarra et

al. 2009). The design of interior circulation elements such as stairs, corridors and mechanical

circulation elements are very important issue for interior designers. In addition, the design

quality of a building depends at first on the basic analysis of the traffic flow of visitors or users

and the follow-on decisions on the primary form of the building (Canada Science and

Technology Museum Corporation 2009; Carney 2009; Department of Statistics in Malaysia

2009; Foster, Koran et al. 2009; Guidlines 2009). In general, the elements of interior circulation

and pathway at a building such as lifts and escalators, stairs and corridors differ in visitors’

carrying capacity and design requirements. Moreover, the interior designers must consider and

match the characteristics of each element with those of the traffic generated in buildings

(Roberts, McKay et al. 2008; Rojas and Camarero 2008; Satoh 2008; Taha 2008; Tran 2008).

For example, the main entrance area in buildings is considered small but it is carrying a major

quantity of traffic, as become principal nodes of the pathway and circulation design, with the

optimum shape of the building dependent on the ratio between internal traffic and movement to

and from the outside (Abaci and Kamaraj 2009; Board of Directors of the Hawaii Public

Housing Authority 2009; British Standard 2009; Brititsh Standard 2009; Burns and Bowling

2009).

4. Aspects of Interior Pathway and Circulation Design Kaynar (2010) points out that, the designer must meets the pathway and circulation

function in buildings, and the architectural design should embrace appropriate space to house

and to improve traffic from area to area. Aspects of interior pathway determine the criteria for

the success of the design and evaluation criteria. According to Hsu (2004) this includes at least

five aspects: approach, entrance, configuration of the path, path/space relationship and form of

the circulation space. By using any museum as example, one can appreciate the relevance of

each following component of pathway and circulation (Amburg 2007; Banning and Schoen

2007; Brock 2007; Butterworth 2007; Rojas and Camarero 2007).

4.1 Approach The axial general view of the interior design and entrance lobby form the approach of the

interior circulation and pathway design in museums’ spaces. Based on the study of Kaynar


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(2010) the distant view before entering the building is very important to prepare the visitors for

the experience of the spaces in the museums (Kaynar 2010; Hsu 2004).

4.2 Entrance The entrance of a museum is the start point where the visitors move from the outside space

to the interior space. Kaynar (2010) points out that Museum’s entrances are usually highlighted

by very visible items or attractive patterns, decorative or structural components. Finally, in

modern museums, great effects linked with the entrance design have served as a preview of

what the visitor can expect, which increase the expectation levels of visitors (Code 2003;

Communities 2003; Community Council of Devon 2006; Kaynar 2010).

4.3 Pathway Configuration Based on study of Kaynar (2010), he finds that pathway configuration is a term refers to

the path of movement from a starting point to the end point within the museum. In any building,

the configuration of the path is strong-minded by some conditions, such as the overall shape of

building, the form of the pathway, the volume of space selected to the path and organizational

pattern of the spaces it links. However, researchers (Pearlmutter, Berliner et al. 2006; Rounds

2006; Sakkas and Pe´rez 2006; Sharma and Dhariya 2006; Sheeks 2006) consider all paths as

linear, and the configuration or shape can take on other forms.

4.4 Path/Space Relationship According to several studies (Bitgood 1992; Bitgood 1999; Ching 2004; Black 2005;

Canadian Museums Association 2006; Community Council of Devon 2006; Foster 2010; John

J. Koran, Jr. et al. 2010) the relationship between the path and space in a museum can be linked

in three different ways. First, the path passes by the exhibitions and spaces, ensuring the

connectivity for each space. Second the path passes through spaces. In turn, the intervening of

spaces trespassed creates patterns of rest and movement. Third, the path terminates in a space,

often as a way of emphasizing the importance of the final destination. Kavangah (1991), in his

research highlights the importance of locations of facilities, and according to him, it is the time

now to consider the location of facilities in museums.

4.5 Form of the Circulation Space Form of the circulation, is how the pathways for movement are integrated into the spatial

organization of a building. So the form and size of the circulation space must to be considered

in museums. A circulation space may be enclosed, open on one side or open on both sides (Han


and Cho 2006; J.A.Renshaw 2006; Jeong and Lee 2006; Jun, Kyle et al. 2006; Khattar 2006). It

also can be narrowed to encourage forward motion or widened to create spaces for waiting or

stopping. The form of the circulation space can be adjusted to distinguish the rote of the

pathway as either for visitors or service corridor (Community Council of Devon 2006; Crayford

2006; Dalke, Little et al. 2006; Davey 2006; Gutwill 2006). Ching (1979) discusses in detail the

configuration of path and the form of circulation space. According to him the form of pathway

depends on our design of transportation and building form. Several studies (Ching 2004;

Department of Statistics in Malaysia 2009; Cusiima 2010; Department of Finance and

Personnel 2010) highlight that understanding of museum space planning and form of pathway

is a very important factor which affects the visitors’ circulation and satisfaction with museums.

5. Elderly People and Satisfaction The definition of 'elderly' has differed among institutions and researchers. According to

Mat and Taha study (2003) The United Nations World Assembly On Ageing held in Vienna,

1982, used '60 years and over' as the cut-off in deliberating ageing trends (Mat and Taha 2003).

Immediately, Malaysian policy makers have adopted this demarcation and are officially used in

planning for senior citizens. This research has thus used the same age cut-off to refer to senior

citizens in Malaysia (Mat and Taha 2003; Wong, Rajikan et al. 2010). Recently, the populations

are growing older more and more in all countries all over the world. According to Kinsella &

Phillips (2005) by 2030, almost 1.2 billion of the expected 1.5 billion people age 65 or older

will inhabit in less developed regions and more will be in developed countries. The ratio of

aging 65-80 or older will reach to 14.3% while in Europe the ration will be 30% of all

populations which is very high. Therefore, just 22 % of the world’s older citizens will live in

developed countries (Kinsella and Phillips 2005). This demographic change will extremely

affect the health services, socioeconomic development, design requirements and sustainability

of all nations. The reason for that is the population aging may be seen as a human success story

of the country and a strong indication toward the strength of the level of public health, medical

advancements, and economic development over diseases. But the common phenomenon of

aging also brought an acknowledgement by the United Nations (UN) of the many challenges

such as, aging and design criteria, general development, issues concerning the sustainability

and the ability of states and communities to consider aging populations and to consider their

satisfaction (Kinsella and Phillips 2005). Figures 1 and 2 show population age-sex structure in

developed and less developed countries. A review of the population for the past four censuses


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find a visible decreasing proportion of population in the younger ages and a sharp increase in

the older age groups (Kinsella and Phillips 2005).

Figure 1: Population age-sex structure in less developed countries, 1950, 1990, and 2030

(Kinsella and Phillips 2005).

Figure 2: Population age-sex structure in more developed countries, 1950, 1990, and 2030. (Kinsella and Phillips 2005).

It becomes a fact that the elderly people in Malaysia are increasing at a faster rate than the

total population growth and will more than double in numbers from the current 1.4 million to 5

million or more in 2030 (Mat and Taha 2003). Malaysia is considered as a fast developing

nation (Mat and Taha 2003), so recording the needs of elderly people is a crucial to balanced the

growth of the nation and to consider past, present and future trends of the elderly people in

Malaysia. According to Mat and Taha (2003) this is the time to create awareness of the space

planning and implementation of interior design for the elderly population in Malaysia (Mat and

Taha 2003). However, until now there are no studies measuring the level of elderly attendance

at museums in Malaysia. Researchers in Malaysia don’t know if elderly people are interested to

visit museums or not. Internationally, several studies (Gotlieb and Brown 1994; Korn 1994;

Parasuraman, Berry et al. 1994; Ritchie 1994; Katz 1994,) show that, elderly people are very

interested in visiting museums. In a study for a botanical garden museum, Hood and Roberts


(1994) find that the group with the largest attendance was aged 55 and older. This group is

considered for one-third to one-half of the visitors on any given day. Studies find also that

elderly visitors were more interested in purchasing in the souvenir shops in museums (Gotlieb

and Brown 1994; Korn 1994; Parasuraman, Berry et al. 1994; Ritchie 1994; Katz 1994,).

6. Research Hypotheses According to Gronroos (2000) design quality can be defined from two perspectives. They

are technical quality (what is delivered to the visitors) and the functional service quality (how it

is delivered) (Rojas and Camarero 2007; Pile 2010). In another study, Brady and Cronin (2001)

figure out that the design quality can be outlined by three perspectives. They are outcome

quality, interaction quality, and physical environment quality in buildings. As the environment

quality refers to the ambient conditions(Rojas and Camarero 2007). Oliver (1997) states that

visitors’ interpretation is related to the level of expectations. According to (Rojas and Camarero

2007) expectations is known as previous predictions or beliefs of visitors before they enter the

building. According to Oliver (1997), the quality of design is based on perceptions of

excellence. Oliver (1997) also states that it is logical to believe that perceived quality is

influenced by the expectations of the visitors (Rojas and Camarero 2007). It becomes a fact that

visitors use their expectations to evaluate design quality and performance. Therefore,

researchers propose the first hypothesis:

(H1. Visitors’ expectations positively influence visitors’ perception of interior pathway

design quality and interior environment of museums.)

Recently, design quality is believed to be the right judgment exposed by visitors who

estimating the quality level of design. So, satisfaction and design quality are highly interrelated

(Rojas and Camarero 2007). Researchers accept the theory said that quality leads to

satisfaction. On this basis, we propose the second hypothesis:

(H2. Interior Pathway design and space planning of museums positively influence the

elderly visitors’ satisfaction.)

Disconfirmation happens when interior pathway design quality is lower or higher than

what visitors expected after they made the final decisions (Oliver 1996). If the interior designs

higher or lower that the visitors’ expectations, a positive or negative disconfirmation occurs and

this will increase or decrease the level of satisfaction. According to Oliver (1996):


275

“Consumer satisfaction is a function of expectations and disconfirmation, and prior expectations are used as the comparable standard. Past empirical research has shown that expectations have a significant effect on disconfirmation”(Oliver 1996; Rojas and Camarero 2007).

7. Methodology In order to test the proposed hypotheses, the empirical study performed is based on

information collected by means of a questionnaire presented to visitors of 21 selected museums.

The 21 Museums are located in Kuala Lumpur, Terengganu, Selangor and Kedah in Malaysia.

The museums have been selected based on the following criteria: (a) State history theme, (b)

Geographic location, (c) Annual attendance, and (d) Quality of interior design & environment.

After proceeding to the quantitative study of 21 museums, interviews and observations

(qualitative study) conducted for four selected museums. The four museums have been selected

based on the following criteria; the importance and the value of the museum, number of visitors

per year, style of design, and location of museum (Figure 1).

Figure 1: Locations of selected museums in Malaysia.

Interviews with the museums’ managers, employees and visitors were performed in order

to know visitors’ reactions and emotions during their visits. A questionnaire was developed to

test the aforementioned hypotheses. The questionnaire was divided into two parts. The first part

covered the experience, mood and the expectations before the visit. The second part referred to

the design quality, the disconfirmation of expectations, the pleasure and the satisfaction after

the visit. The first survey was conducted during the months of July to October 2009 and the

total number of questionnaires distributed was 800. A second set of data was collected through

observations and interviews during October, and November 2009, providing valid data for

analysis. Those surveyed were asked to answer the first part of the questionnaire, (i.e. the

questions referring to their experience, mood and expectations). After answering these


questions, the visitor held onto the questionnaire during the visit, and the second part of the

questionnaire was completed upon exit. Of these 800 questionnaires, 613 were returned. One

hundred and four questionnaires were excluded (40 incomplete and 64 the age of participants

were under 65 years old). The total numbers of questionnaires analysed were 509

questionnaires with observed response rate of 76.6%. Analysis was conducted using the

statistical software package SPSS version 17.0 with a sample size of 509, α (the probability of

making a correct retention is 0.95) =0.05, df (degree of freedom) = 1.0. Of the 509 respondents,

290 were men (57.4%) and 215 were women (42.6%). Three hundred and forty eight visitors

(69.3%) were 65-70 years old, one hundred and forty eight visitors (29.7%) were equal or more

71 to 90 years old. Of the 509 respondents, 271 (53.9%) were locals, and 229 (45.5%)

foreigners. Of the locals, 162 were Malay (32.2%), 61 were Chinese (12.1%), 76 were Indian

(15.1%), indicating that Malay visitors are more interested in visiting museums than others.

Of the 509 Participants, only 43 (8.5%) of elderly visitors came alone to the museum, while 212

(42.1 %) came with friends and 185 (36.7%) came with their families. The rest of participants

60 (11.9%) visited museums with organizations. The scale of expectations is constructed of

five items were adapted from the scale proposed by (Rojas and Camarero 2007) and also was

applied to the case of museums and exhibition centres. The scale of perceived quality (six

items) was prepared from the proposal of Brady and Cronin (2001). All of the included items

of expectations were adapted to reflect the context of interior pathway and circulation in

museums. The results of the responses (either agree or disagree) were presented under the

check-list of three categories obtained from literature review; a) horizontal pathway &

circulation design, b) vertical pathway & circulation design, and c) Interior environment and

space planning. In horizontal pathway item, the results of the responses (either agree or

disagree) were presented under the check-list of six factors based on the literature review such

as; horizontal accessibility, halls’ arrangement and spaces, corridors and entrance lobbies,

waiting areas, orientation system, furniture arrangement and interior layout. In vertical

pathway design, the results of the responses (either agree or disagree) were presented under the

check-list of three factors based on the literature review such as; vertical accessibility, position,

visibility and capacity of lifts, ramps and staircases, and interior paths and circulation. In

interior environment item, the results of the responses (either agree or disagree) are presented

under the check-list of four factors based on the literature review such as; creativity and interior

environment, interior materials and textures, interior lights and interior colours. To measure

satisfaction (five items) the Oliver (1996) scale was used and included additional items that


277

measured the intention to repeat the visit and word-of-mouth recommendation. All scales were

validated the values of reliability were calculated by the Cronbach alpha in each case. The

data in this study have been obtained in three ways: (a) personal observations (qualitative study

without a formal survey) on the museums of the study areas, (c) personal oral interviews with

the elderly visitors in the study areas, and (c) a survey (quantitative study) of the study area

using questionnaires. All the qualitative factors of the circulation and pathway design in the

museums are adopted from the previous studies. The answer for satisfactory is "Yes", but when

it is unsatisfactory, the answer is "No".

8. Analysis and Results The first hypothesis (H1) states that there will be significant relationship between elderly

visitors’ expectation in museum, and design quality perception. The correlation coefficient is

-.083- . As the result suggests, a significant negative relationship does not exist ( Sig= 0.061);

therefore, this can be concluded from these result, that elderly visitors' expectation before they

entering the museum don’t determine or affect the elderly visitors’ perception of the design

quality of the interior pathway and circulation in museums. The second hypothesis (H2) stated

that the interior pathway design and space planning of museums positively influence the elderly

visitors’ satisfaction. From the result the correlation coefficient is 0.685 . Sig (2-tailed) or P

value is 0.000 ≤ α 0.05 which can be concluded from these result that there is a positive

significant relationship between elderly visitors’ satisfaction in museum and interior pathway

and circulation design, thus H2 is confirmed that the interior pathway design and space

planning of museums positively affect the level of the elderly satisfaction. Results also state

that there will be a positive significant relationship between elderly visitors’ satisfaction, and

time spent within museums. The correlation coefficient is 0.404. As the result, a significant

relationship exists; therefore, this can be concluded from these result, that time spent within the

museum influenced by elderly visitors' satisfaction , thus time spent within museums consider

as a good an indicator of satisfaction. In other words, satisfied visitors tend to spend more time

walking in museums. As illustrated in table 1, a whole, it is overwhelmingly clear that in all of

the factors under all the different categories, the respondents have until today a far greater

negative perception towards interior pathway and circulation design of museums in Malaysia.

Such negatively weak perception of the pathway and circulation design towards museums in

Malaysia is an expression of their dissatisfaction level in the nature of the circulation designs of

these museums. Finally, in the three categories, the respondents have scored 41.03 % < 50% for


qualitative and 43.26 % < 50% for quantitative analysis, suggesting a clear feeling of

dissatisfaction towards the interior pathway and circulation design and the interior

environments of the selected museums. Table 1, presents a combination of the results of the

analyses via a qualitative method with those results obtained via a quantitative method. An

integrative examination of the composite data via a combination of methods (in this case

quantitative and quantitative procedures) in this way is termed as "triangulation" in this study.

Researchers subject data to such a triangulation procedure because such procedure helps

counteract threats to validity.

Table 1: Overall composite averages in all categories.

Categories of Factors Selected 21 Museums

"Satisfactory" scores from Qualitative survey

( )

"Satisfactory" scores from Quantitative survey

Interior Pathway Design 41.725 % 44.225 % Interior Environment and Space Planning 39.66 % 41.33 %

Overall composite average 41.03 % 43.26 %

9. Discussion and Conclusions This study began with the aim of analyzing a specific aspect of interior design and space

planning applied to museums in Malaysia, and the formation of visitors’ satisfaction. The first

implication of this research is the confirmation of hypotheses due to its high validity and

explanatory power. In particular, the respondents selected from the museums in Malaysia

have a high level of expectation towards the interior pathway, circulation design and interior

environment in museums. Such positively strong expectation is undoubtedly an expression of

their level of experience and trust towards the design industry in Malaysia. Moreover, the

Interior pathway and circulation design quality appears to be multidimensional consisting of

different three dimensions. The Three dimensions are horizontal pathway design, vertical

pathway design, and interior environment of museums. Under each dimension there are many

different components. The scores from the survey have demonstrated overwhelmingly same

low perceptions and bad expression about the interior pathway design and interior environment

in museums in Malaysia. These negative design qualities of the circulation design in museums

together with the positive and high expectations of the elderly visitors compositely justify the

low level of general satisfaction of the elderly visitors in museums. This being the case, the

dissatisfaction seems to have arisen from :The absence of design creativity, the absence or


279

disregard the elderly needs, the insufficient accessibility to interior halls and other spaces, the

inflexibility of the halls arrangement and use of the spaces, the lack of waiting areas and

comfort seats, the use of poor or inappropriate interior materials and textures, the insufficient

design of corridors and pathway design, the insufficient design of orientation system within the

museums, the use of poor or inappropriate interior position and design of staircases ramps and

lifts, the insufficient design of interior lighting system, the use of poor or inappropriate interior

colours, insufficient furniture arrangement and interior layout, interior pathway and

circulations in general are not suitable for elderly visitors. The ideas that interior pathway

design and interior environment must be good, as a high percentage of the elderly visitors find it

useful and can enhance their satisfaction level. Yet, little thought seems to have been given to

what interior pathway is, what is necessary to achieve visitors' circulation efficiency, and what

benefits can be expected. Interior designers in Malaysia have not considered effectively the

interior pathway design of elderly visitors. Elderly visitors learn more and are to be more

satisfied when they are properly circulated and oriented to an exhibition and when the

exhibition is designed with an understanding of their needs and abilities.

This will require us to re-think again about interior pathway and circulation design quality

of museums in Malaysia. This study has several limitations, as some of the them are: 1) First

study - this is the first study of its type and additional research is needed to confirm the results,

2) The results were mixed and full support wasn't obtained for all factors, 3) Unit of Analysis

-While it is appeared that the notion of interior circulation design was universal regardless of

industry or size, this research limited itself to the study of interior circulation quality at

museums environment in Malaysia, 4) Lack of prior relevant research, 5) Generalizing the

findings of this study - Due to geographical limitations, participants may possess certain

attributes that differ from those in other parts of the world.

Future research may use more diversified random samples to verify the dimensions

developed in this study. Interior pathway design could be the trend in museums and visitors'

studies in the future, so more studies of this nature should be carried out. However, the interior

designers are invited to continue this initial investigation of interior pathway design quality

within museums, especially in new areas of design where we knew our user elderly preferences,

needs and abilities. Interior circulation elements are a design strategy, a success value and

quality indicator of museums design. It is the communication and circulation tools, strategy and


technology that permit the combination of all museums' services and visitors.

10. Acknowledgment A very special thank you is due to Dr.Siriporn Kobnithikulwong for insightful comments,

helping clarify and improve the manuscript.

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Dr.AZIZI BAHAUDDIN is currently Associate Professor in Interior Design at the School of Housing, Building & Planning, Universiti Sains Malaysia. His main research areas are focusing on Exhibition Design/Interior Design; Art and Design especially researching on Cultural Issues and Ethnography, and in Architectural and Cultural Heritage in Tourism.

RAED M. A. Elottol is currently a PhD candidate in Interior Design at the School of Housing, Building & Planning, Universiti Sains Malaysia. His main research areas are focusing on Museums; Space Planning/Interior Design; Architecture especially researching on Cultural Issues and Building Technology.




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Validating Measurements of Perceived Ease Comprehension and Ease of Navigation of an Online Learning Technology: Improving Web Based Learning Tool Adoption and Use Bangaly KABAa*

a Schools of Business, International Relations and Economic Policy (BIREP), International University of Grand-Bassam, IVORY COAST A R T I C L E I N F O

A B S T RA C T

Article history: Received 21 March 2011 Received in revised form 27 May 2011 Accepted 31 May 2011 Available online 01 June 2011 Keywords: Technology; Acceptance; Model; WebCT (Web course tools); Measurement; E-learning.

Many universities are realizing that the implementation and use of online learning tool become a competitive advantage to address the actual learning needs. The purpose of this study is to determine the factors that influence users’ perceived ease of use of Webct an online learning tool. We administrated a questionnaire to undergraduate students from an university in Quebec, Canada. The results tend to corroborate that ease of comprehension and ease of navigation are the key factors which influence the perceived ease of use of WebCT. More specifically, the terms used in educational web applications must be as simple and relevant as possible. Jargon and technical terms in the wording of text used for links should be carefully avoided. This research is extending the finding of IT adoption studies by specifying what make an online tool easy to use.


1. Introduction Recently, following the example of other organizations, a large number of universities

have been giving primary importance to the use of information and communication

technologies (ICTs), allocating substantial resources to their acquisition. ICTs are used on a


288 Bangaly KABA

daily basis in universities to build students and employees’ databases, to carry out statistical

analyses, to conduct refined bibliographical research, to send e-mails, to permit multimedia

animation in classrooms, etc. (Bradley et al., 2006; Mbarika et al., 2003a, 2003b). In addition to

these uses, ICTs have become the preferred media for distance learning services (Mbarika,

2004), thus considerably reducing temporal and spatial constraints (geographical disparities).

The current trend is for distance learning to become an option for a great number of instructors

to respond to the new needs of students.

The investments made in order to acquire, implement and use ICT for educational purposes

should be expected to result in positive impacts for the quality of instruction. More specifically,

these investments should materialize in the form of increased productivity, a reduction in

transaction costs, and therefore; in improved performance (Goodhue et al. 2000; Mathieson,

1991).

Many models have allowed researchers to determine and measure the factors involved in

the adoption of a technological innovation (Goodhue et al., 2000; Mathieson, 1991; Taylor and

Todd, 1995). Among these, Davis (1989)’s technology acceptance model (TAM) figures as a

classic in the field of the adoption of technological innovations. TAM is generally referred to as

the most influential and commonly employed theoretical model in information systems

research (Lee et al. 2003). This theory is of particular interest in explaining user behavior with

regard to IT. TAM has been consistently validated by a number of empirical studies (Davis et

al., 1989; Kwon and Chidambaram, 2000; Mathieson, 1991; Taylor and Todd, 1995; Venkatesh

et al., 2003).

However, since most of these studies aim to test the model, opportunities for the

information systems and information technology (IS/IT) community to contribute become

more and more restricted if serious theoretical modifications are not made to the fundamental

model. At least two possible criticisms of TAM can be made. First, TAM is a generalized

theory which does not always seem to take into account particular types of technological

innovations. In fact, the process of acceptance depends upon the nature of the IT (Igbaria, 1994;

Mahler and Rogers 2000; Markus, 1997). Secondly, TAM fails to provide useful explanations

which could help those who design or manufacture IT to increase the level of acceptance of

their products by end users (Venkatesh and Davis, 2000, Benbasat and Barki, 2007).


289

This situation considerably limits the practical application of TAM (Benbasat and Barki,

2007). In light of this finding, we intend in this study to validate new scales of measurement of

the ease of use of WebCT, which is a course management system for online learning.

This study based on technology acceptance model (TAM) is initiated to validate the

measurement of the factor that influence users’ perceived ease of use of WebcT in order to

enhance our understanding of online learning tools use. TAM stated that easier is to use a

system or a technology high is the probability of its adoption and use. Unfortunately, the model

does not indicate what make practically a technology easy to use. Our main research question

is: what are the practical factors or measures which could be considered as alternative of users’

perceived ease of use? We consider that perceived ease of comprehension and perceived ease of

navigation as good alternatives which could serve as measurements of the ease of use of

WebCT even other online learning tools. Before outlining the conceptual framework of this

study, we consider it is useful to present the characteristics and the attractions of WebCT which

may be unfamiliar to the general public.

2. Overview of WebCT Among internet and Web-based applications for online courseware, WebCT emerges as a

leader (Clark, 2002). This application was designed by the information systems department of

the University of British Columbia about a decade ago. Since then, the functionality of WebCT

has constantly improved, and it is now used by more than 2,200 institutions in more than 70

countries (WebCT, 2005). WebCT is a powerful tool for the creation of a distance learning

environment. It provides a complete set of tools for the delivery of an online course (Palloff

and Pratt, 2001 ; Mioduser et al. 2000). Once instructors and students become familiar with the

software, it can be used for e-learning. WebCT offers the possibility of synchronous and

asynchronous communication, sending e-mails, file sharing, student evaluations, access to

course materials, and access to outside resources dedicated to learning.

3. Theoretical Framework Chris et al. (2004) emphasize the importance of the online knowledge management tool’s

user interface as a critical factor for its adoption and for online learning. Indeed, as a link

290 Bangaly KABA

between the user and the system, the user interface allows a reduction of effort by making the

navigation among the different components of the system easier.

The success of an online application also relies upon the terminology used. The

terminology of a system refers to all words, phrases, and abbreviations it uses (Lindgaard,

1994). For example, a frequent problem with online courseware systems has to do with the

technical jargon used. This jargon includes technical or professional vocabularies with which

general users are often unfamiliar. In such cases, great effort must be made by end users in order

to utilize the system to its full potential. A clear and comprehensible terminology can thus

reduce the effort necessary to master the system and to make users more productive.

Consequently, it may be concluded that clarity of terminology is a good measurement of

perceived ease of use.

Davis et al. (1989) states that a technology or a system designed in such a way as to allow

its potential user to expend little time or energy (avoiding the constant need to refer to the user’s

manual or to contact the provider for help, etc.) will encounter few obstacles to its adoption.

These authors predict that the more a technology is perceived to be easy to use, the greater the

likelihood of its adoption. According to Davis et al. (1989), ease of use corresponds to the

degree to which a person believes that using a new IT will be easy. It is measured by the

following three indicators using Likert scales: the technology is easy to master, the technology

is user-friendly, the technology, in general, is easy to use. These measurements are for general

purposes and do not always appear to take into account the specific characteristics of a given

type of technology. This lack of specificity is susceptible to make the task of IS designers more

arduous when it comes time to determine the specific aspects of the system which could

influence users’ perceptions.

The previous shortcoming has led Moore and Benbasat (1991) to argue that one of the

problems facing the theories related to the adoption of technological innovations is the lack of

valid, trustworthy instruments to measure users’ perceptions in the context of adoption of these

innovations. Our intent in the current study is to identify and validate measurements of the

perception of ease of use which takes into account the features of a specific technological

innovation, which is WebCT.

The concept of ease of use is generally used in the literature on user acceptance of


291

technology and on user behavior. As previously mentioned, Davis et al. (1989) identify ease of

use as one of the important determinants of the use of ICTs. Davis (1989) suggests that the

perceived ease of use can in fact determine the perceived usefulness. Mathieson (1991) and

Szajna (1996) report that ease of use accounts in large part for variations in perceived

usefulness. Therefore, in light of the aforementioned contributions, we can assert that a better

comprehension of the measurements of ease of use of WebCT constitutes a worthwhile domain

to investigate, because it could have a beneficial effect on the other determinants of ICT

success.

Inspired by the study of Lederer et al. (2000), we propose in the current research, the ease

of comprehension and the ease of navigation as alternative measurements of WebCT’s ease of

use. However, unlike Lederer et al. (2000), we consider that these two variables are rather

measurements of perceived ease of use, not the antecedents.

After having pinpointed the various theoretical contributions that are relevant to our

analysis, the next section focuses on the methodology adopted in this research.

4. Methodology

4.1 Questionnaire Development The data for this study was collected through a questionnaire survey that was divided into

different sections. Each section was devoted to each variable of the research model: Task

characteristics, group characteristics, facilitating conditions, social influence, and the intention

of the users. A seven-point Likert scale, where 1 indicates “strongly disagree” and 7 “strongly

agree” (see questionnaire in appendix) was used to measure the latent variables used in the

study, with the exception of socio-demographic factors. These latent variables included:

perceived ease of use, perceived ease of comprehension, perceived ease of navigation,

perceived competency, computer anxiety, technical support and user help, and experience using

the internet. Variables measurements were inspired by Lederer et al. (2000) and Davis et al.

(1989), and adapted to the context of this study. Each variable’s was measured using multiple

items. Aside from demographic factors, the present analysis is only concerned with two

variables, “perceived ease of use” and “ease of navigation”. In the following section we

present the results obtained by our analysis.

292 Bangaly KABA

A pre-test of the questionnaire was performed in order to assure its content validity before

its final distribution to the respondents. First, we designed a preliminary version of the

questionnaire. This version was given to researchers in the field of IT and information systems

(IS), and to experts in the industry familiar with the African context. Each individual provided

some comments on the formulation, the syntax, and the number of items included in the

questionnaire. Taking into account the various comments, we made minor changes to the

questionnaire. The various comments also permitted us to eliminate biases which could exist in

the questionnaire. .

4.2 Data Collection

Data in this study were collected using a questionnaire survey. Orlikowski and Baroudi

(1991) maintain that the questionnaire survey is the method of data collection mostly used in IT

research. This method is often indicated for gathering data, describing and explaining people’s

perceptions, attitudes, or behaviors. Questionnaires have the advantage of being structured and

assuring standardization in the formulation of questions and in their sequence. We administered

a survey to undergraduate students at a French-speaking university in Canada that use WebCT

in their course of studies. It should be noted that in this university, WebCT served as an

instructional supportive tool.

In order to be assured of a high response rate, we administered the survey by direct contact.

This mode of communication is very demanding in terms of investment, both in the time it takes

and in the amount of travel required. However, it seems to be the richest data collection

technique (Emory, 1980). With the instructors’ assistance, we solicited students’ direct

participation in their classrooms. The questionnaires were filled out on a voluntary basis before

the beginning of courses. We obtained 172 usable responses out of 230 questionnaires

administered, yielding a 75% response rate.

4.3 Data Analysis

The statistical analysis for this study employed the SPSS statistical software. The

assessment of the collected data’s descriptive statistics, construct validity and the testing of the

indicators’ reliabilities were conducted in SPSS. The factor analysis of principal component

was mainly applied to validate the measurement of easy of comprehension and easy of

navigation.


293

5. Results Details of the socio-demographic variables chosen for this study are given in Table 1.

Table 1: Socio-demographic profiles.

Variables Characteristics Absolute Frequencies

Percentage

Gender Male Female

57 115

33.1% 66.9%

Age 16 - 21 years 22 - 27 years 28 - 33 years 34 - 39 years 40 or older

67 87 10 6 2

39% 50.6% 5.8% 3.6% 1.2%

Years of experience using the internet

Less than 1 year 1 year 1 to 2 years 2 to 3 years 3 to 4 years 4 to 5 years 5 or more years

1 1 7

15 27 33 88

0.6% 0.6% 4.1% 8.7%

15.7% 19.2% 51.2%

Different uses of the internet

Information seeking Downloading Sending email Chat Forum

6.32 5.10 6.61 3.29 2.92

1.04 1.84 0.93 2.16 1.87

The socio-demographic variables examined in this study are concerned with gender, age,

years of experience using the internet, and the uses made of the internet. Only a third of the 172

respondents were men. The predominance of women in university programs is a reality which

cannot be ignored. The respondents were relatively young, since 154 of the respondents

(89.6%) are less than 30 years old. According to Paré (2002), the new generation of students has

an unprecedented level of mastery of ICTs (computers and the Internet). It is interesting, but not

surprising in the North American context, that the vast majority of respondents seem to be

familiar with the use of the internet. Indeed, 70.4% of respondents possess more than four

years’ experience using the internet, which could favor their acceptance of WebCT which is a

web-based application.

However, the respondents show a very weak score in terms of their use of the online chat

and of discussion forum. This low score is a bad sign of WebCT usage as these functionalities

are nonetheless among the essential components of the application, since they permit both

synchronous and asynchronous communication among learners as well as with the instructor.

294 Bangaly KABA

5.1 Validation of the scales of measurement used Variables measurements were validated through convergent and discriminant validity

testing. A principal components factorial analysis (PCA) was performed on each variables

measurement items in order to verify both types of validity. Additionally, the reliability of

each variable measurement was established by calculating Cronbach’s Alpha coefficient. The

tests of convergent and discriminant validity and of reliability are three measures necessary for

the validation of a scale of measurement. In the following section, the results of these three tests

are presented.

5.1.1. Test of convergent validity

An analysis of the correlations among the items measuring each variable was first carried

out, followed by a principal components analysis (PCA) with Varimax rotation when more than

one factorial axis was found.

The use of this method must satisfy three criteria. The first one is the criterion relative to

the eigenvalue which aids in identifying the number of components (factors) to retain. In this

study, we refer to Kaiser (1958)’s rule according to which only the axes whose eigenvalue is

higher than 1 are retained. The second criteria is related to the factorial contributions (loadings)

which aims at identifying relevant items or indicators that better explain a factor. According to

this criterion, only items with factorial contributions greater than 0.3 are accepted (Blau et al.,

1993). The last criterion deals with the communalities of items and it indicates the proportion of

explained variance in the combination of each factor. This criterion allows the assessment of

the level of representation of each item in the principal components. In this study, an item

whose communality was inferior to 0.4 was dropped from the analysis, in compliance with the

suggestions of Evrard et al. (2003).

5.1.1. Measurement of Perceived Ease of Comprehension

Table 2 includes items measuring the ease of comprehension. Results in Table 3 show

that the correlations among the items of measuring the ease of comprehension are positive and


295

significant, which might be a manifestation of the uniqueness of this measurement. The PCA

yields a factor which explains 68.36% of the total variance, with important positive factorial

contributions (loadings) and a good quality of representation for each item (>0.4) (see Table 4).

Based on the above results, we can state that the unidimensionality of this measurement has

been proven.

Table 2: Presentation of items measuring the ease of comprehension. Variable Codification Items description

Ease of comprehension

3.1 WebCT uses relevant terms

3.2 WebCT uses simple terms

3.3 WebCT includes links that give detailed information

3.4 WebCT has a pleasant design

3.5 WebCT posts pages that are easy to read

Table 3: Correlations matrix of ease of comprehension. Items 3.1 3.2 3.3 3.4 3.5 3.1 3.2 3.3 3.4 3.5

1 0.753** 0.646** 0.486** 0.587**

1

0.555** 0.490** 0.589**

1 0.573** 0.608**

1 0.750**

1 *** p< 0.01; ** p<0.05; *p<0.1 ns: not significant

Table 4: Factorial solution of ease of comprehension. Variables (Ease of

comprehension) Quality of representation Items

3.1 3.2 3.3 3.4 3.5

0.842 0.820 0.818 0.795 0.857

0.709 0.673 0.668 0.633 0.734

Eigenvalue 3.418 Explained variation 68.356

5.1.1 Measurement of perceived ease of navigation Table 5 shows items measuring the ease of navigation. The correlations among the items

of the perceived ease of navigation variable are all positive and significant (Table 6) and

296 Bangaly KABA

demonstrate the uniqueness of measurement of this variable. The PCA results in Table 7 show a

unique factor explaining 79.65% of the variance. All the items have a very good quality of

representation (>0.4).

Table 5: Presentation Items measuring the ease of navigation Variable Codification Items description

Ease of Navigation

4.1 WebCT allows me to easily return to previously-viewed pages

4.2 I can always tell where I am when navigating WebCT

4.3 WebCT is an easy site to navigate

Table 6: Correlations matrix of ease of navigation Items 4.1 4.2 4.3

4.1 4.2 4.3

1 0.715** 0.647**

1

0.721**

1 *** p< 0,01; ** p<0,05; *p<0,1 ns: not significant

Table 7: Factorial solution of ease of navigation Variables (Perceived ease of navigation) Quality of representation

Items 4.1 4..2 4.3

0.881 0.912 0.884

0.776 0.832 0.781

Eigenvalue 2.389 Explained variation 79.649%

5.1.2 Discriminant Validity The objective of this test is to verify the independence of the variables. Like for the test of

convergent validity, a principal components analysis was carried out on the items measuring

each variable. Three items were dropped from the analyses because each of them had a loading

greater than 0.3 on the two selected factors. These items are: Item 3.3 (WebCT includes links

that give detailed information) and item 3.4 (WebCT has a pleasant and agreeable design) for

the variable ease of comprehension; and item 4.3 (WebCT is an easy site to navigate) for ease of

navigation. According to the results discussed above and shown in table 8, we can assume the

independence of the two variables of the research.


297

The reliability test will conclude this validation of scales. The results appear in the

following table:

Table 8: Results of the test of discriminant validity Variables Ease of

comprehension Ease of

navigation Items 3.1 3.2 3.5 4.1 4.2

0.887 0.872 0.809

0.924 0.884

Eigenvalue 2.894 1.139 Explained variation 57.888% 22.783%

5.1.3 Analysis of the Reliability of the Measurement In order to ascertain the degree to which the measurement instrument (the questionnaire)

used in this study evaluates the perceptions of respondents in a consistent manner, we

performed a reliability analysis by calculating Cronbach’s Alpha coefficient. The results for the

two constructs of the study appear in the Table 9.

Table 9: Results of the reliability test.

Variables of the study Variables Items Cronbach’s Alpha

Wording Ease of comprehension 3.1.; 3.2; 3.5 0.8367 Ease of navigation 4.1; 4.2 0.8315

Throughout these results, we notice that the value of Cronbach’s Alpha for all the variables

is superior to 0.7, which shows the reliability of the adopted measurement instrument (Evrard et

al., 2003 ; Teo et al., 1999).

6. Conclusion, Limits, and Directions for Future Research The goal of the present study was to determine and validate measurements of the

perception of ease of use which takes into account the features of an online tool, which is

298 Bangaly KABA

WebCT. According to the analysis carried out in this work, perceived ease of comprehension

and perceived ease of navigation emerge as good alternatives which could serve as

measurements of the ease of use of WebCT, and indeed of other online interaction and learning

tools.

The implications of these results, for the designers of Web-based educational applications

in general and for those of WebCT in particular, are to continue to work toward making their

product as user-friendly as possible. More specifically, the terms used in educational web

applications must be as simple and relevant as possible. Jargon and technical terms in the

wording of text used for links should be carefully avoided. These recommendations are equally

valid for the academic content on WebCT. The results of this study can also be of benefit to

those individuals responsible for selecting online applications, in that they would know in

advance the relevant factors to take into account in order to increase the likelihood of success of

the chosen technologies.

Nevertheless, this research has its limits. For a better assessment of the face validity or the

content validity of the measurement used, it would have been helpful to recruit experts to

examine them. Increasing the survey sample size would also have been quite useful to ensure

that the study’s findings could be generalized. In the future, this study could be extended to

include other departments or universities where the level of ICT use is heterogeneous in order

to evaluate and understand possible differences in results. Further, the extension of the research

to other countries where the level of students’ access to e-learning tools is limited or at least is

still at an embryonic stage would constitute a relevant basis for comparison of the external

validity of the measurement instrument validated by this study. In such a study, it would be

beneficial to proceed with a confirmatory factor analysis.


299

7. Acknowledgment A very special thank you is due to Associate Professor Dr. Boonsap Witchayangkoon for

insightful comments, helping clarify and improve the manuscript.

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WebCT (2005). http://WebCT.com/entrypage, visited September 2007

Dr. Bangaly Kaba earned his PhD degree in Information Systems from a joint PhD program administered by the four largest universities in Montreal (UQAM, HEC, Concordia University and McGill University). He is a visiting professor at International university of Grand-Bassam. His research interests include the adoption and implementation of information and communication technologies (ICT), especially mobile technologies, the impact of ICT on organizations, cultural issues in ICT adoption and use, tele-education, multimedia learning case study, quantitative methods, and management of international projects.




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*Corresponding author (David Kuria). Tel: +254-727-399208. E-mail addresses: [email protected]. 2011. International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. Volume 2 No.3. ISSN 2228-9860. eISSN 1906-9642. Online Available at http://TuEngr.com/V02/303-324.pdf

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A Land Data Assimilation System Utilizing Low Frequency Passive Microwave Remote Sensing: A Case Study of the Tibetan Plateau David Kuriaa*, Toshio Koike b, Moses Gachari a, and Souhail Boussetta b, c a Department of Geomatic Engineering and Geospatial Information Science, Kimathi University College of Technology, KENYA b River and Environmental Engineering Laboratory, Department of Civil Engineering, Faculty of Engineering, The University of Tokyo, JAPAN c Currently at: European Centre for Medium-Range Weather Forecasts, UNITED KINGDOM A R T I C L E I N F O

A B S T RA C T

Article history: Received 15 March 2011 Received in revised form 2 June 2011 Accepted 3 June 2011 Available online 6 June 2011 Keywords: Soil moisture retrieval, Land Surface Modelling, Data assimilation, Passive microwaves, AMSR-E, Tibetan Plateau, Surface emission model

To address the gap in bridging global and smaller modelling scales, downscaling approaches have been reported as an appropriate solution. Downscaling on its own is not wholly adequate in the quest to produce local phenomena, and in this paper we use a physical downscaling method combined with data assimilation strategies, to obtain physically consistent land surface condition prediction. Using data assimilation strategies, it has been demonstrated that by minimizing a cost function, a solution utilizing imperfect models and observation data including observation errors is feasible. We demonstrate that by assimilating lower frequency passive microwave brightness temperature data using a validated theoretical radiative transfer model, we can obtain very good predictions that agree well with observed conditions.


1. Introduction While General Circulation Models (GCMs) are best at simulating evolving and future

changes in climate systems, they are unable to produce mesoscale and local atmospheric


304 David Kuria, Toshio Koike, Moses Gachari, and Souhail Boussetta

phenomena (Wilks, 1999). Thus downscaling methods are necessary to bridge the gap between

global scales and other smaller modelling scales. In this paper we use a high resolution

mesoscale model and nest it within a GCM. This nesting is realized by using initial and

boundary conditions from GCM output. This approach alone is not adequate for reproducing

local phenomena and extreme events because nesting does not include accurate land surface

initial and boundary conditions, missing important physical processes such as convection and

local circulation (Boussetta, 2005).

Many satellite based microwave imaging systems have been launched in space. Some of

the recent ones include the Scanning Multichannel Microwave Radiometer (SMMR) launched

in 1978 and Special Sensor Microwave Imager (SSM/I) launched in 1987. More recent sensors

launched include Advanced Microwave Scanning Radiometer on board Earth Observing

Satellite (AMSRE) and Tropical Rainfall Monitoring Mission (TRMM). These systems

provide observations of variables that describe the earth’s atmosphere, ocean, cryosphere and

land surface (Njoku, 1999). To aid in the interpretation of imagery from such sensors,

microwave radiative transfer models have been developed, which are used to express

propagation of microwaves in media, such as in Ulaby et al. (1981), Tsang et al. (1985), and

Wilheit et al. (1999).

Data assimilation employs models and observations exploiting the strengths of each.

Models are approximations of physical processes, and these approximations introduce errors

due to varying degrees of inaccuracy in representing these processes. On the other hand,

observations while recording actual situations include random observations errors. In addition,

due to costs incurred in obtaining these observations, they are more often than not inadequate,

and are not uniformly distributed in time and space. Thus, models or observations on their own

are not adequate in representing actual physical systems being studied or monitored. By

applying data assimilation approaches, these limitations in model representation and in

obtaining observations can be offset.

Data assimilation techniques have evolved within meteorology and physical oceanography

and in operational numerical weather prediction for atmospheric and oceanic flows (Ide et al.,

1997). These concepts have recently been applied to small scales, but this has largely been in

attempts to improve estimation of soil moisture by assimilation of microwave TBs (Mahadevan


305

et al., 2003, 2007; Reichle et al., 2001). In mesoscale modelling, it is critical to provide reliable

initial and boundary conditions. GCM forecast and analysis products can provide such data, but

these have to be downscaled to the mesoscale before they can be used. By combining

downscaling and data assimilation techniques, better initial conditions can be obtained, which

can thereafter be used to run the mesoscale model, giving better forecasts. Sensitivity of L-X

microwave bands to surface conditions has been exploited in the past in retrieving soil moisture

conditions (Njoku, 1999). Since at these frequencies the atmosphere can be assumed

transparent, clarification of surface emission heterogeneity through field experiment has a

potential of supporting a retrieval scheme for land surface conditions.

By exploiting data assimilation approaches and using a physically based surface emission

model as observation operator, there is potential to obtain better land surface condition

prediction by assimilating lower frequency microwave brightness temperatures. To physically

address the mechanisms of land-atmosphere interactions based on land surface conditions, the

Land Data Assimilation System developed by Boussetta (2005) is used to augment the

stand-alone mesoscale model. While this system addresses land surface heterogeneities, it does

not address atmospheric components in a direct way. This is not critical since this research is

restricted to using lower frequency brightness temperatures in the data assimilation exercise.

This system assimilates lower frequency (6.925 – 18.7 GHz) microwave TBs to improve

estimation of land surface conditions. In this paper we build on the work done by Boussetta

(2005), by including as observation operator an improved surface emission model that was

validated by Kuria et al. (2007).

Data assimilation is a method of estimating a set of parameters by optimizing the fit

between the solution and a set of observations which the model is meant to predict (Bannister,

2001). In this context, the procedure of adjusting the model parameters until the model ‘best

predicts’ the observables is referred to as optimization. The observations used for data

assimilation can be very heterogeneous with respect to their temporal and spatial resolution,

and their type. The results of an assimilation scheme are a continuous data set, which represents

the best estimate for the state of the system. This is done by optimizing the state vector of the

system using available observations and dynamic constraint of the numerical model, specified

by the governing dynamical equations.


In variational data assimilation not only is a a close fit to one observation (the last one)

required but additionally, consistency with a dynamic model over a defined period of time

(Daley, 1991). This means that in variational data assimilation, one tries to adjust the model

globally to fit all observations during the assimilation period.

A discrete model for the evolution of an atmospheric, coupled system from time ti to time ti+1 is

governed by the equation

(1)

where x and M are the model’s state vector and its corresponding dynamics (model) operator,

respectively. The state vector x has dimension n. M represents the model simulation or

prediction, and may differ from equation (1) if the model is nonlinear and/or deterministic. The

state vector x describes the state variables.

Observations y0 at time ti are defined by

(2)

where H is an observation operator, and ε is noise or observation errors. The observation vector

has dimension pi. A major problem of data assimilation is that, typically, .

The observation operator H, can be nonlinear, like M, and both can contain explicit time

dependence - denoted by subscript i - in addition to the implicit dependence via the state vector

. The error ε is assumed to have a normal distribution with mean 0. Its covariance

matrix is denoted by R, consisting of instrumental and observation errors.

In variational data assimilation one tries to adjust the model’s initial parameters x0,

globally to all observations available during the assimilation period. Therefore it is necessary to

introduce a scalar quantity J, which represents the difference between the model and observed

states. The objective function is a function of the state vector x. J is the sum of the background

error JB, which gives the difference between the model state and the background xb and an

observation error J0, which gives the difference between the model state and observations The

complete cost function can be written as;


307

(3)

The common form of JB is expressed as

(4)

where, x0 is the analysis variable, or state vector, is the background field, and B is the

background error covariance matrix.

The common form of J0 is given as

12

, (5)

where, y0 represents all of the satellite observations, H is the observation operator, M is the

model operator, and R is the observational error covariance matrix. In this paper, y0 represents

remotely sensed microwave brightness temperatures, and H is a radiative transfer model, which

computes corresponding brightness temperatures. N is the length of an assimilation window.

Thus, relatively accurate observations are used directly to correct model-estimated values, and

these corrections are fed back in the solution process.

The total cost function can be rewritten in as follows:

12

(6)

Various assumptions have been made when formulating the above cost function. The first

assumption is that the models are ‘perfect’ over the assimilation period, which leads to the


so-called strong-constraint formalism. An alternative cost function could be written with a third

term, as an additional constraint to penalize model errors. This would be an example of a weak

constraint formalism (Mahadevan et al., 2007). Due to its compactness, we adopt this

strong-constraint approach in this paper.

2. Meso scale model run Figure 1 shows the Tibet Coordinated Enhance Observing Period (CEOP) site. The Tibetan

plateau is located in Asia with an area of approximately 3000 × 1000 km2 and a mean elevation

of more than 4 km above mean sea level.

(a) (b)

Figure 1: CEOP Tibet Site: (a) Satellite imagery, with red pegs marking the extents

corresponding to AMSR-E image. Marked with small yellow pegs are 4 in-situ stations. This

image was obtained from Google Earth. (b) Terrain map generated by ARPS.

It is bounded by the highest mountains in the world (Himalayas, Kunlun shan, Pamir). It is

considered an important component of the global water and energy cycle as it exerts

appreciable thermal and dynamic influences on the local and regional meteorology as well as on

the Northern Hemisphere atmospheric circulations (Yang et al., 2009).


309

Table 1: Model domain specifications.

Variable Description Setting

Δx East West spacing 5560 m (0.05°)

Δy North South spacing 5643 m (0.05°)

λm Central longitude 91.9°E

φm Central latitude 32.0°N

nx East West grids 70

ny North South grids 70

nz Vertical levels 41

While there are other mesoscale models such as the Weather Research and Forecasting

(WRF) model and the Fifth-Generation Penn State Mesoscale Model (MM5), the Advanced

Regional Prediction System (ARPS) developed at the Center for Analysis and Prediction of

Storms (CAPS) (Xue et al., 2003) as the mesoscale model for simulating surface and

atmospheric evolution of Tibetan Plateau conditions. ARPS was used since a coupling of this

model had been done with Simple Biosphere Model (SiB2) and had demonstrated good results

in simulating land surface conditions (Boussetta, 2005). Table 1 defines the domain settings of

Tibet area used in the simulation and validation exercise. This area is about 390 × 390 km2

providing ample overlap over an AMSR-E brightness image covering an area of about 280 ×

280 km2 with central position defined as (32°N, 91.9°E). The z- dimension is staggered with

higher resolution provided near surface (30 m) and smoothly transitioning to lower resolution at

higher elevations (1.2 km). This is to significantly improve simulation of near surface features

which vary rapidly over time. The simulation were undertaken to simulate three days evolution

of land and atmosphere condition. This period was from 19th August 2004 00:00 UTC – 22nd

August 2004 00:00 UTC. The integration time steps were as follows: (i) evolution of surface

condition (120 seconds) (ii) small time step (1 second) and (iii) big time step (6 seconds).

2.1 Initial and Boundary conditions For this paper, we used National Centers for Environmental Prediction (NCEP) Global

Forecast System (GFS) reanalysis data to provide initial and boundary conditions for running

the Mesoscale model. The GFS is a global spectral data assimilation and forecast system. GFS

forecasts are produced every 6 hour. The output product has a horizontal resolution of 1° and


vertically it has 64 layers with model top layer at 0.2 hPa.

We used the EXT2ARPS package to generate the required lateral boundary forcing,

linearly interpolated in time to the domain of our model run. This GFS generated boundary

conditions were updated every 6 hours. The package ARPSTRN generated terrain data from

30”× 30” global topographic dataset provided by Center for Analysis and Prediction of Storms

(CAPS) University of Oklahoma. Temporal invariant surface condition was interpolated from

30” soil maps, land use maps and 10’ Normalized Difference Vegetation Index (NDVI) data

using ARPSSFC package.

2.2 Model parameters used To sufficiently simulate smaller scale atmospheric features related to land surface effect,

our domain horizontal resolution was set to 0.05° × 0.05° while for the vertical grid ARPS uses

a hyperbolic tangent function to stretch the grid interval in this case from 30 m at the surface to

nearly 1.2 km at the top (18 km).

The physics parameterization options include a 1.5-order Turbulent Kinetic Energy-based

subgrid scale closure scheme turbulence, and a planetary boundary layer parameterization.

Radiative forcing is computed according to an atmospheric radiation transfer parameterization

and is updated each 10 minutes.

The Simplified Biosphere (SiB) model, developed by Sellers et al. (1986) and

subsequently revised to SiB2 in Sellers et al. (1996), is used as surface scheme, and the Lin Ice

Microphysics parameterization (Lin et al., 1983) to parameterize cloud and precipitation. For

explicitly resolving convection, the modified Kain-Fritsch convective scheme is better suited

for resolving convection (Truong et al, 2009), the original Kain-Fritsch convective

parameterization (Kain and Fritsch, 1993) was adopted, since LDAS is mainly sensitive to land

surface conditions. The model domain topography is derived from 1 km resolution global

dataset. Land cover was obtained from the global dataset based on the global ecosystem

classification with a spatial resolution of 30” × 30” while its associated static parameters were

derived according to Sellers et al. (1996). Soil types were obtained from global dataset with a

resolution of 30” × 30” and vegetation types were obtained from a 100 resolution global


311

dataset. All these datasets were obtained from CAPS

3. Land Data Assimilation Scheme Boussetta (2005) validated Land Data Assimilation Scheme (LDAS) by assimilating

satellite data and assessed its dynamic downscaling ability. He applied it in a three dimensional

configuration on a mesoscale area of the Tibetan plateau. In his case, he used GEWEX Asian

Monsoon Experiment (GAME) Tibet dataset for 1998. This system combines a land data

assimilation scheme with a coupled land-atmosphere mesoscale model in a recursive cycle. The

system runs by first introducing the initial and boundary atmospheric conditions from NCEP

GFS into the coupled land-atmosphere mesoscale model (ARPSSiB2). This coupled model

then produces forcing for one assimilation window to the land data assimilation system which

optimizes the initial surface variables and feeds them back to the coupled land-atmosphere

model (Figure 2).

Figure 2: Land Data Assimilation Scheme.

Figure 3 shows LDAS assimilation cycle. A typical LDAS assimilation cycle comprises of

the following steps.

Step 1 : ARPS-SiB2 is run for an assimilation window time T to obtain an initial guess and

forcing parameters for LDAS.

Step 2 : LDAS runs for one assimilation window, which feeds back new initial surface

condition for ARPS-SiB2 at time t = t − T.


Figure 3: LDAS Assimilation Cycle.

Step 3 : ARPS-SiB2 runs for two assimilation window time 2T, the first window output

being considered as optimal, while the second one serves as forcing for the LDAS run.

In this paper, we used a 24 hour assimilation window (T = 24h). This was due to the need to

have at least one satellite observation to be assimilated during the assimilation period.

3.1 Model operator SiB2 is used as the model operator in the assimilation scheme. It is a dual source model

with fluxes originating from soil surface and canopy. It incorporates simple representations of

vertical soil moisture transport, plant controlled transpiration, interception, evaporation,

infiltration, sensible and heat fluxes through physically based mechanisms.

SiB2 includes three soil layers; a surface soil layer of a few centimeters which acts as a

significant source of direct evaporation when moist; a root zone which is the supplier of soil

moisture to the roots and accounts for transpiration; and a deep soil layer acting as a source for

hydrological base flow and upward recharge to the root zone.

3.2 Observation operator Boussetta (2005) assimilated TRMM Microwave Imager (TMI) satellite brightness

temperature (TB) observations at 10.7 and 19.4 GHz, both polarizations. In this paper, we used

AMSR-E TB observations at 10.7 and 18.7 GHz both polarizations. Additionally, assimilation

of two surrogate observations, namely Polarization Index (PI) proposed by Paloscia and

Pampaloni (1988) at 6.9 GHz, and Index of Soil Wetness (ISW) developed by Fujii and Koike


313

(2001), derived using 18.7 and 6.9 GHz horizontal polarization. These three frequencies’ data

were chosen due to their relative insensitivity to atmospheric conditions. These two

relationships are given as,

(7)

(8)

where v or h in the subscript denote polarization i.e vertical and horizontal respectively at the

given frequency.

Boussetta (2005) used a first order radiative transfer model (RTM) coupled with QH model

of Choudhury et al. (1979) for addressing surface roughness effects. In Kuria et al. (2007) it was

shown that the QH model is not fit for use with high frequency data. Although it has been

widely used, its roughness parameters have to be ‘calibrated’ first, and are thus not physically

based. While this is sufficient in most cases when dealing with frequencies lower than 20 GHz,

the lack of a physical basis in determining these parameters motivated us to consider using the

improved surface emission model validated by Kuria et al. (2007). This surface emission model

is used as the observation operator. Compared to that used in Boussetta (2005), it uses a

physically based treatment of surface roughness effects, thereby improving confidence of

forward modelling. A further refinement was by introducing Polarization Index (PI) and Index

of Soil Wetness (ISW) that describe roughness and moisture conditions as surrogate

observations. We use the variance matrix of the following form to describe the background

co-variance matrix B, used in equation 4.

0 0 0 00 0 0 00 0 0 00 0 0 00 0 0 0

(9)

The observation error covariance matrix (R), used in equation 5, follows a similar form


0 0 0 0 00 0 0 0 00 0 0 0 00 0 0 0 00 0 0 0 00 0 0 0 0

(10)

In these cases we assume that all observations are uncorrelated, and model state variables

are uncorrelated too. In Table 2, we list values of observation errors, and in Table 3, values of

background errors used in the observation and background error matrices, respectively as used

in this research. The background covariance matrix was assumed static for simplicity, though

ideally it should be allowed to evolve with the assimilation process, being updated with new

values for use in subsequent steps.

Table 2: Observation errors

Tb10h Tb10v Tb18h Tb18v PI6 ISW618

4K 3K 5K 4K 0.01 0.01

Simulated Annealing was used to minimize the cost function J. It is a heuristic

optimization approach capable of minimizing the variational cost function without using

adjoint models (Ingber, 1993). It avoids problems due to strong non-linearities and

discontinuities in finding the global minimum in the hilly structure of the cost function. It is

based on the analogous approach of metal annealing in thermodynamics (Kirkpatrick et al.,

1983).

Table 3: Background errors

Tg Td Mvsfc Mvrt Mvdp

3K 2K 0.04 0.03 0.02

4. Results and discussion We use ARPS/LDAS to simulate land surface conditions using AMSR-E lower frequency

(6.925, 10.65, and 18.7 GHz) brightness temperatures (TBs) for Tibetan plateau. This


315

simulation was for three days from 00:00 UTC on 19th August 2004 – 00:00 UTC on 22nd

August 2004.

(a)

(b)

Figure 4: Comparison of time-series land surface variables (a) surface temperature and (b)

surface soil moisture at BJ site

4.1 Time series comparison We run ARPS/LDAS assimilation as one case, and plain ARPS as second case. Both

models were run for 72 hours from 00:00 UTC 19/08/2004 to 00:00 UTC 22/08/2004. In Figure

4 we show comparisons of retrieved surface variables at BJ site.


(a)

(b)

Figure 5: Time series soil moisture product comparison along 91.9°E (a) ARPS case and

(b) LDAS case

We prepared a time series plot covering the duration 0 – 48h, and we compare this with an

in-situ dataset. This in-situ data set comprises hourly soil moisture records at 3cm and 10cm

depth, and soil temperature at the same depths. Since we are using Microwave observations

which sense shallow depths, we will analyze only near surface variables (3cm depth). During


317

this time period, we have two AMSR-E overpasses, descending overpass at 19:41 UTC on 19th

August and ascending overpass 06:42 UTC on 20th August.

(a)

(b)

Figure 6: Time series surface precipitation comparison along 91.9°E (a) ARPS case and (b)

LDAS case


We begin by considering surface temperature (Figure 4(a)).While bearing in mind the fact

that we are comparing grid averaged values with point observations, we note that (i) the diurnal

variation of near surface temperature observed is simulated by both cases, (ii) ARPS derived

surface temperature have much higher peaks and valleys than ARPS/LDAS case and (iii) in

general, the ARPS/LDAS configuration gives better agreement with the in-situ dataset, though

the gap between peaks/valley can vary by as much as 5 K.

Considering near surface soil moisture (Figure 4(b)), there is remarkable agreement with

in-situ dataset for ARPS/LDAS case. ARPS case is over-predicting soil moisture by as much as

5%. At the time slots corresponding to AMSR-E overpass times it can be noted that

ARPS/LDAS and in-situ datasets match perfectly, and also that in the interval between these

times, the simulations follows observations almost perfectly.

In Figure 5 we show comparison of time series moisture product along longitude 91°E.We take

the same period (0 – 48h) for this analysis. It is clear that the ARPS case (Figure 5(a)) is wetter

than the corresponding ARPS/LDAS case. We note that ARPS case is wettest at the edges,

alluding to the strong influence of initial and boundary conditions from GFS reanalysis data.

The situation is different in ARPS/LDAS case. ARPS seems to get wetter implying heavy

precipitation events at the beginning (6 hours after start) and about 30 hours after start. We have

similar events in ARPS/LDAS but their duration and intensity is not as high as in ARPS case.

Figure 6 depicts time series precipitation for the same period. As mentioned above, it can be

seen that ARPS is producing higher precipitation, in intensity and distribution. We note too that

ARPS precipitating durations are longer than ARPS/LDAS precipitation durations.

4.2 Comparison of simulation at hour closest AMSRE overpass time We consider 07:00 UTC on August 20th 2004 for analysis of soil moisture retrieval. Figure

7 shows simulation following the same convention, i.e. ARPS case (Figure 7(a)) and

ARPS/LDAS case (Figure 7(b)). Soil moisture distribution in ARPS case is strongly influenced

by the initial conditions giving rather high forecasts of soil moisture.

Its soil moisture distribution follows GFS soil moisture distribution (not shown). Soil

moisture distribution in ARPS/LDAS case by assimilating observed TBs shows improved

distribution.


319

(a)

(b)

Figure 7: Moisture comparison (a) ARPS and (b) LDAS for August 20th 2004.

Figure 8: GPCP Cumulative surface precipitation

To validate this hypothesis, we consider the relationship between precipitation and soil

moisture. It is known that the occurrence of a precipitation event invariably leads to an increase

in soil moisture, thus in the absence of quantitative soil moisture observations or estimates,


observed precipitation (or precipitation deduced from observations) can be used to give a

qualitative assessment of soil moisture.

We include Global Precipitation Climatology Project (GPCP) daily cumulative

precipitation data for the site on August 20th, to assist in verifying our hypothesis that

ARPS/LDAS case is significantly better than ARPS case. GPCP provides daily global gridded

values of cumulative precipitation, for the period from October 1996 – December 2006

(Huffman et al., 2001). The product considered for this validation exercise is the 1° resolution

daily precipitation dataset. Figure 8 shows this GPCP dataset for the spatial domain considered

in this paper. Comparing this with our simulations, it can be noted that while the resolution of

GPCP is very coarse, we have similar pattern with the ARPS/LDAS case. The ARPS case is

completely different with the observed precipitation pattern.

Considering surface temperature simulations (Figure 9), surface temperature

representation in both cases follows similar patterns, but on closer inspection, it can be noted

that ARPS simulated generally higher temperatures than ARPS/LDAS case.

(a) (b)

Figure 9: Surface temperature comparison (a) ARPS and (b) LDAS for August 20th 2004

Additionally, when we compare ARPS/LDAS case with terrain map (Figure 1), we note

that the temperature distribution shows agreement with terrain map (high temperature


321

corresponding to valley area, and low temperatures corresponding to mountain areas).

We also note that in the central region of ARPS/LDAS case we have colder temperatures.

This region corresponds could be experiencing a precipitation event at this time (bearing in

mind the time series results shown in Figure 6). It can thus be argued that ARPS/LDAS

simulated surface temperatures, while not matching observed conditions perfectly (see Figure

4(a)), does provide a much improved estimation of surface temperatures.

5. Conclusion Data Assimilation potential in improving model predictability has been investigated in this

paper. We have shown that by using a physically based surface emission model as the

observation operator we have improved estimation of near surface conditions. Near surface soil

moisture retrievals using ARPS/LDAS was shown to follow observed situation well. Surface

temperature retrieval was shown to be better when we use the assimilation system than if we did

not. While the match between observations and assimilated simulations is not perfect, there is

nevertheless a good agreement with the discrepancies being attributed to the fact that the in-situ

measurements were made at point locations while the assimilated TBs were obtained over areal

extents representing the satellite footprint resampled to a 10km spatial resolution.

From the results presented, we showed that in general, soil moisture estimation without

assimilation is higher than the corresponding assimilation case. This can be in part due to the

uncertainties in modelling microphysics and convection in the adopted mesoscale model. We

have demonstrated that by using LDAS, satellite TB observations can be used to improve soil

moisture and surface temperature estimations. While both cases depend on initial conditions,

poor initial conditions were demonstrated as severely impacting the non assimilation case as the

assimilation case is able to recover by assimilating passive microwave TBs. This means that if

uncertainties in mesoscale modelling are resolved, then assimilation of lower frequency

microwave TBs will yield much more reliable soil moisture estimates.

It has been demonstrated that by improving the land surface conditions, the surface

precipitation rates also improve which if therefore used to feed the atmosphere component of a

mesoscale model will in turn yield improved estimation of the atmosphere conditions. In such a


scheme, the modified Kain-Fritsch convection scheme can address convection while a

microphysics scheme such as the Schultz scheme (Schultz, 1995) addressing the five main

hydrometeor categories can be used.

Other satellite platforms operating at microwave frequencies such as the Tropical Rainfall

Monitoring Mission and the future Global Precipitation Mission, together with AMSR-E can

provide periodic passive microwave data (brightness temperatures) which can be used in the

LDAS presents, to improve estimation and forecasting the evolution of surface conditions (soil

moisture, surface temperature among others).

6. Acknowledgement This study was carried out as part of the CEOP and Verification Experiment for

AMSR/AMSR-E. Model validation data were provided by the CEOP University of Tokyo

Data Archiving Manager Mr. Katsunori Tamagawa. Dr. Kenji Taniguchi provided in-situ

dataset. The authors would like to thank them for their support towards this research effort.

A very special thank you is due to Associate Professor Dr. Mirza Raza and Dr. Mohammed

Rasmy for insightful comments, helping clarify and improve the manuscript.

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Boussetta, S., (2005). Development of a Land-Atmosphere Coupled Data Assimilation System for physical downscaling. PhD thesis, University of Tokyo.

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Fujii, H. and Koike, T., (2001). Development of a TRMM/TMI algorithm for precipitation in the Tibetan Plateau by considering effects of land surface emissivity. Journal of the Meteorological Society of Japan, 79, 475–483.

Huffman, G.J., Adler, R., Morrissey, M., Curtis, S., Joyce, R., McGavock, B. and Susskind, J., (2001). Global precipitation at one-degree daily resolution from multi-satellite observations. Journal of Hydrometeorology, 2, 36–50.

Ide, K., Courtier, P., Gill, M. and Lorenc, A.C., (1997). Unified Notation for Data Assimilation: Operational, Sequential and Variational. Journal of the Meteorological Society of


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Ingber, L., (1993). Simulated annealing: Practice versus theory. Mathematical and Computer Modelling, 18, 29–57.

Kain, J.S. and Fritsch, J.M., (1993). Convective parameterization for mesoscale models: The Kain-Fritsch scheme, the representation of cumulus convection in Numerical Models, Meteorology Monogram . American Meteorology Society.

Kirkpatrick, S.C., Jr., C.D.G. and Vecchi, M.P., (1983). Optimization by Simulated Annealing. Science, 220, 671–680.

Kuria, D., Koike, T., Lu, H., Tsutsui, H. and Graf, T., 2007, Field-supported verification and improvement of a passive microwave surface emission model for rough, bare and wet soil surfaces by incorporating shadowing effects. IEEE Transactions on Geoscience and Remote Sensing, 45, 1207–1216.

Lin, Y.L., Farley, R.D. and Orville, H.D., (1983). Bulk parameterization of the snow field in a cloud model. Journal of Climate and Applied Meteorology, 22, 1065–1089.

Mahadevan, P., Koike, T., Fujii, H., Tamagawa, K., Li, X. and Kaihotsu, I., (2007). Modification and application of the satellite based Land Data Assimilation Scheme for very dry soil regions using AMSR-E images: Model validation for Mongolia — a CEOP data platform. Journal of the Meteorological Society of Japan, 85A, 243–260.

Mahadevan, P., Koike, T. and Li, X., 2003, A New Satellite-Based Data Assimilation Algorithm to Determine Spatial and Temporal Variations of Soil Moisture and Temperature Profiles. Journal of the Meteorological Society of Japan, 81, 1111–1135.

Njoku, E.G., (1999). AMSR Land surface parameters: Algorithm theoretical basis document, NASA JPL.

Paloscia, S. and Pampaloni, P., (1988). Microwave Polarization Index for Monitoring Vegetation Growth. IEEE Transactions on Geoscience and Remote Sensing, 26, 617–621.

Reichle, R.H., Entekhabi, D. and McLaughlin, D.B., (2001). Downscaling of radio brightness measurements for soil moisture estimation: A four-dimensional variational data assimilation approach. Water Resources Research, 37, 2353–2364.

Sellers, P.J., Los, S.O., Tucker, C.J., Justice, C.O., Dazlich, D.A., Collatz, G.J. and Randall, D.A., 1996, A revised land surface parameterization (SiB2) for atmospheric GCMs, Part II: the generation of global fields of terrestrial biophysical parameters from satellite data. Journal of Climate, 9, 706–737.

Sellers, P.J., Sud, Y.C. and Dalcher, A., 1986, A simple biosphere model (SiB) for use within General Circulation Models. Journal of the Atmospheric Sciences, 43, 505–531.

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Tsang, L., Kong, J.A.U. and Shin, R.T., 1985, Theory of Microwave remote sensing. Wiley and Sons, New York.

Truong, N. M., Tien, T. T., Pielke Sr., R. A., Castro, C. L. and Leoncini, G., (2009). A modified Kain-Fritsch scheme and its application for the simulation of an extreme precipitation event in Vietnam. Monthly Weather Review, 137, 766 – 789.

Ulaby, F.T., Moore, R.K. and Fung, A.K., (1981). Microwave remote sensing: Fundamentals and radiometry, Vol. 1. Artech House, Norwood, MA.

Wilheit, T., Kummerow, C. and Ferraro, R., (1999). EOS/AMSR Rainfall. Algorithm theoretical basis document.

Wilks, D.S., (1999). Multisite downscaling of daily precipitation with a stochastic weather generator. Climate Research, 11, 125–136.

Xue, M., Wang, D., Gao, J., Brewster, K. and Droegemeier, K.K., (2003). The Advanced Regional Prediction System (ARPS), storm-scale numerical weather prediction and data assimilation. Meteorology and Atmospheric Physics, 82, 139–170.

Yang, K., Chen, Y.Y. and Qin, J., (2009). Some practical notes on the land surface modeling in the Tibetan Plateau. Hydrology and Earth System Sciences Discussions, 6, 1291–1320.

David Kuria is a Senior Lecturer in the department of Geomatic Engineering and Geospatial Information Science of the Kimathi University College of Technology. He received his B. Sc (Surveying) with Honors from the University of Nairobi (Kenya) in 1998. He holds an M. Sc (Photogrammetry and Geoinformatics) from the Stuttgart University of Applied Sciences (Germany) awarded in 2003. He undertook Ph.D. studies at the University of Tokyo (Japan) completing it in 2007. He has lectured for more than 4 year at the Jomo Kenyatta University of Agriculture and Technology. Dr. Kuria’s current interests are in webmapping, climate research and geospatial application development.

Toshio Koike received the B.Eng., M.Eng., and D.Eng. degrees from the University of Tokyo, Tokyo, Japan, in 1980, 1982, and 1985, respectively. He was a Research Associate at the University of Tokyo in 1985 and was appointed as an Assistant Professor at the same university in 1986. He was also appointed as an Associate Professor at Nagaoka University of Technology, Nagaoka, Japan in 1992. He has been a Professor at the River and Environmental Engineering Laboratory, Department of Civil Engineering, University of Tokyo since 2000. He is the Lead Scientist of the Coordinated Enhanced Observing Period project. Prof. Koike’s research interests are in hydrology, water resources, satellite remote sensing, climate change, and Asian monsoons.

Souhail Boussetta received B.Eng, and M.Eng degrees from the National school of Engineering of Tunis at the University of Tunis in 1991 and 1993 respectively, and a Ph.D from the University of Tokyo, Japan in 2005. He was a Research Associate at the University of Tokyo in 2006 and was appointed as Assistant Professor for EDITORIA at the University of Tokyo in 2007. He is currently a scientist at the European Centre for Medium range Weather Forecast. Dr. Boussetta’s research interests include Land surface parameterization, land data assimilation, and satellite remote sensing applied to water resources.



*Corresponding author (Kondapalli Siva Prasad). Tel/Fax: +91-9849212391 E-mail addresses: [email protected] 2011. International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. Volume 2 No.3. ISSN 2228-9860. eISSN 1906-9642. Online Available at http://TuEngr.com/V02/325-336.pdf

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Prediction of Weld Pool Geometry in Pulsed Current Micro Plasma Arc Welding of SS304L Stainless Steel Sheets Kondapalli Siva Prasada*, Ch. Srinivasa Raob, D. Nageswara Raob

a Department of Mechanical Engineering, Anil Neerukonda Institute of Technology & Sciences, INDIA b Department of Mechanical Engineering, Andhra University, INDIA A R T I C L E I N F O

A B S T RA C T

Article history: Received 21 March 2011 Received in revised form 27 May 2011 Accepted 13 June 2011 Available online 14 June 2011 Keywords: Pulsed Current MPAW, SS304L, ANOVA, Bead Geometry

Pulsed Micro Plasma Arc Welding (MPAW) is a metal joining technique widely used in manufacturing of thin sheet components due to its inherent properties. The weld quality and productivity are controlled by the process parameters. The paper discuses about development of mathematical models for weld pool geometry of stainless steel 304L sheets. Design of experiments based on full factorial design is employed for the development of a mathematical model correlating the important controlled pulsed MPAW process parameters like peak current, background current, pulse and pulse width with front width, back width, front height and back height. The developed mode has been checked for adequacy based on ANOVA analysis. Weld bead parameters obtained by the models are found to confirm actual values with high accuracy. Using these models effect of pulsed MPAW process parameters on weld pool geometry are studied.


1. Introduction The plasma welding process was introduced to the welding industry in 1964 as a method

of bringing better control to the arc welding process in lower current ranges (Modern

Application News, 1999 ). Today, plasma retains the original advantages it brought to the


326 K. Siva Prasad, Ch.Srinivasa Rao, D.Nageswara Rao

industry by providing an advanced level of control and accuracy to produce high quality

welds in both miniature and pre precision applications and to provide long electrode life for

high production requirements at all levels of amperage. Plasma welding is equally suited to

manual and automatic applications. It is used in a variety of joining operations ranging from

welding of miniature components to seam welding to high volume production welding and

many others.

The welding optimization literature frequently reveals correlation among responses.

(D.K.Zhang et.al,2010) studied the influence of welding current, arc voltage, welding speed,

wire feed rate and magnitude of ion gas flow on front melting width, back melting width and

weld reinforcement of Alternating Current Plasma Arc Welding process of LF6 Aluminum

alloy of thickness 3mm using Artificial Neural Network- Back Propagation algorithm.

(Sheng-Chai Chi et. al ,2001) developed an intelligent decision support system for Plasma

Arc Welding of stainless steel plates of thickness range from 3 to 9 mm based on fuzzy Radial

Basis Function (RBF) neural network by performing experiments using Taguchi method. (Y.

F. Hsiao et. Al,2008) studied the optimal parameters process of plasma arc welding of SS316

of thickness 4mm by Taguchi method with Grey relational analysis is studied. Torch stand-

off, welding current, welding speed and plasma gas flow rate (Argon) were chosen as input

variables and welding groove root penetration, welding groove width, front-side undercut

were measured as output parameters. (K.Siva et.al, 2008) used central composite rotatable full

factorial design matrix and conducted experiments in optimization of weld bead geometry in

Plasma arc hardfaced austenitic stainless steel plates using Genetic Algorithm.

(A.K.Lakshminarayan et.al, 2008) predicted the Dilution of Plasma Transferred Arc

Hardfacing of Stellite on Carbon Steel using Response Surface Methodology (RSM). (V

Balasubramanian et.al, 2009) used Response Surface Methodology to predict and optimize the

percentage of dilution of iron-based hardfaced surface produced by the Plasma transferred arc

welding process.

From the earlier works, it has been observed that much work is not reported so far to

investigate the effect of pulsed current MPAW process parameters on stainless steel weld

characteristics; and developing the related mathematical models to predict the same especially

for welding of thin stainless steel sheets. Hence an attempt was made to correlate important

pulsed MPAW process parameters to bead geometry of thin AISI 304L stainless steel welds


327

by developing mathematical models. The models developed will be very useful to predict the

weld pool geometry parameters for desired bead geometry. A statistically designed

experiment based on full factorial design has employed for the development of mathematical

models (Montgomery DC ,2005).

Figure 1: Typical weld pool geometry.

2. Experimental procedure Austenitic stainless steel sheets of type AISI 304L 100×50×0.25 mm are welded

autogenously with square butt joint without edge preparation. To evaluate the quality of

MPAW welds, measurements of the front width, back width, front height and back height of

the weld pool are considered. Figure 1 indicates the typical weld pool geometry. Table 1

indicates the chemical composition of AISI 304L stainless steel sheet. Experiments are

conducted using the Pulsed Micro Plasma Arc Welding (MPAW) process with pulse DCEN.

Industrial pure and commercial grade argon gases are used for shielding and back purging,

respectively. Automatic voltage control available in the welding equipment is used. Fixture

variation effects are not considered as the same setup has been used throughout the

experiment. Some of the welding process parameters are fixed based on earlier work and also

from the trial run so as to obtain full penetration weld. Trial runs are conducted to find the

limits of each controllable process parameter so as to obtain full penetration weld, free from

any visible defects. Because of computational ease and enhanced interpretability of the

models, parameters are converted to coded form for developing mathematical models

(Giridharan PK et.al, 2007). The upper limit of a factor is coded as +1 and the lower limit as


−1. Table 2 represents the levels determined for process variables with their levels, units and

notations for the pulsed MPAW process. Table 3 represents the fixed pulsed MPAW process

parameters and their values.

Table 1: Chemical composition of austenitic stainless steel (AISI 304L) sheet.

Elements Chromium Silicon Nickel Carbon Manganese Iron

% by weight

18.2% 0.5%

8.5% 0.015%

1.6% Balance

Table 2: Input variables and their levels

Levels SI No Input Factor Units -1 +1 1 Peak Current Amps 6.5 7.5 2 Back Current Amps 3.5 4.5 3 Pulse No’s /Sec 30 50 4 Pulse width % 40 60

Table 3: Fixed pulsed MPAW process parameters and their values.

Power source Secheron Micro Plasma Arc Machine (Model: PLASMAFIX 50E)

Polarity DCEN Mode of operation Pulse mode Electrode 2% thoriated tungsten electrode Electrode Diameter 1mm Plasma gas Argon & Hydrogen Plasma gas flow rate 6 Lpm Shielding gas Argon Shielding gas flow rate 0.4 Lpm Purging gas Argon Purging gas flow rate 0.4 Lpm Copper Nozzle diameter 1mm Nozzle to plate distance 1mm Welding speed 260mm/min Torch Position Vertical Operation type Automatic

From the Design of Experiments and due to wide range of input process parameters, the

present work is limited to use four factors, two levels, full factorial design matrix in order to

simplify the present problem. Table 4 shows the measured values of output response by

taking an average value of three samples of 16 sets of coded conditions used in the form of

design matrix. The 16 experiments have been formulated as per 24 (two levels and four

factors) factorial design.


329

3. Recording the Responses Three samples are cut from the welded specimens at an interval of 25mm and mounted in

Bakelite powder, polished and etched with Oxalic acid as per ASTM E3 and ASTM E340.

Weld pool geometries are measured using Metallurgical Microscope make Dewinter

Technologie, Model No. DMI-CROWN-II. Figure 2 represents the Photomacrographs of a

typical weld specimen showing the bead profile at 100X magnification.

Figure 2: Photomacrographs of a typical weld specimen.

Table 4: Welding parameters and responses for the full factorial design.

Exp No

Peak Current

(PC)

Back Current

(BC)

Pulse (P)

Pulse Width (PW)

Front Width

Back Width

Front Height

Back Height

Amperes Amperes No’s % Microns Microns Microns Microns 1 7.5 3.5 30 60 1579.22 1499.50 63.209 57.775 2 6.5 4.5 30 60 1486.59 1361.64 59.137 49.443 3 7.5 4.5 50 60 1383.04 1301.22 53.953 48.422 4 6.5 3.5 50 40 1539.88 1480.60 54.191 49.422 5 7.5 4.5 30 60 1582.92 1506.41 76.886 71.209 6 7.5 3.5 50 40 1404.63 1283.25 71.247 65.947 7 6.5 3.5 30 60 1477.09 1393.14 60.583 54.737 8 6.5 3.5 50 60 1451.98 1372.69 61.896 54.251 9 6.5 3.5 30 40 1530.30 1453.96 57.514 52.538 10 6.5 4.5 50 60 1382.42 1305.11 63.619 58.265 11 7.5 3.5 50 60 1392.70 1337.14 59.083 54.855 12 6.5 4.5 30 40 1543.53 1466.85 42.855 36.559 13 7.5 3.5 30 40 1581.70 1537.70 48.824 42.514 14 7.5 4.5 50 40 1503.05 1436.88 64.101 59.595 15 7.5 4.5 30 40 1547.92 1474.37 52.275 46.553 16 6.5 4.5 50 40 1486.94 1408.72 65.613 58.092

4. Development of Mathematical Models A low-order polynomial is employed for developing the mathematical model for

predicting weld pool geometry. Equation (1) represents a typical mathematical model, in

which the response is well modeled by a linear function of the independent variables.


Table 5: ANOVA test results.

ANOVA for Front Width Source Main Effects 2-Way Interactions 3-Way Interactions Residual Error Total R2 Value =94.05

DF 4 6 4 1

15

Seq SS 25659 23462 23142 4575

76837

Adj SS 25659 23462 23142 4575

Adj MS 6415 3910 5785 4575

F 1.40 0.85 1.26

ANOVA for Back Width Source Main Effects 2-Way Interactions 3-Way Interactions Residual Error Total R2 Value = 96.24

DF 4 6 4 1

15

Seq SS 35868 38078 19057 3633

96636

Adj SS 35868 38078 9057 3633

Adj MS 8967 6346 4764 3633

F 2.47 1.75 1.31

ANOVA for Front Height Source Main Effects 2-Way Interactions 3-Way Interactions Residual Error Total R2 Value = 95.18

DF 4 6 4 1

15

Seq SS 499.22 335.64 157.23 50.23

1042.32

Adj SS 499.22 335.64 157.23 50.23

Adj MS 124.80 55.94 39.31 50.23

F 2.48 1.11 0.78

ANOVA for Back Height Source Main Effects 2-Way Interactions 3-Way Interactions Residual Error Total R2 value = 97.39

DF 4 6 4 1

15

Seq SS 487.77 336.44 233.81 28.32

1086.34

Adj SS 487.77 336.44 233.81

32

Adj MS 121.94 56.07 58.45 28.32

F 4.31 1.98 2.06

Where SS =Sum of Squares, MS=Mean Square, F=Fishers ratio

Y = β + β1 x1 + β2 x2 + …._ βx xx + ∈ (1)

The regression coefficients were calculated using MINITAB14 software and Equations

(2), (3), (4), and (5) represent the developed mathematical models with welding parameters in

coded form.

Front Width =1492.12+(38.45*X1)-(6.42*X2)+(7.07*X3)+(5.85*X4) +(26.12*X1*X2)

+(9.6*X1*X3)+(24.67*X1*X4)+(2.1*X2*X3)+(4.17*X2*X4)-(7.86*X3*X4)+

(16.27*X1*X2*X3)+(28.66*X1*X2*X4)-(10.35*X1*X3*X4)-(15.91*X2*X3*X4) (2)


331

Back Width =1413.7+(46.21*X1)-(5.53*X2)-(1.79*X3)+(8.53*X4)-(34.34*X1*X2)

+(15.69*X2*X3)+(27.73*X1*X4)+(9.46*X2*X3)-(1.52*X2*X4)-(9.7*X3*X4)+

(10.7*X1*X2*X3)+(28.4*X1*X2*X4)-(10.32*X1*X3*X4)-(12.8*X2*X3*X4) (3)

Front Height = 59.687-(1.253*X1)-(0.756*X2)+(3.032*X3)-(4.457*X4)

+(1.146*X1*X2)+(3.509*X1*X3)-(1.707*X1*X4)-(1.891*X2*X3)+(0.676*X2*X4)

-(0.639*X3*X4)+(0.937*X1*X2*X3)-(0.304*X1*X2*X4)+(0.529*X1*X3*X4)+

(2.929*X2*X3*X4) (4)

Back Height = 53.761-(1.212*X1)-(0.513*X2)+(2.845*X3)-(4.545*X4)

+(0.637*X1*X2)+(3.731*X1*X3)-(1.436*X1*X4)-(1.886*X2*X3)+(0.671*X2*X4)

-(0.795*X3*X4)+(0.571*X1*X2*X3)-(0.195*X1*X2*X4)+(1.25*X1*X3*X4)

+(3.562*X2*X3*X4) (5)

Table 6: Comparison of actual and predicted values of responses.

Front Width Back Width Front Height Back Height Run

Order Actual Predicted Actual Predicted Actual Predicted Actual Predicted

1 1579.22 1562.31 1499.5 1484.43 63.209 61.4371 57.775 56.4446 2 1486.59 1469.68 1361.64 1346.57 59.137 57.3651 49.443 48.1126 3 1383.04 1399.94 1301.22 1316.28 53.953 55.7249 48.422 49.7524 4 1539.88 1556.79 1480.6 1495.67 54.191 55.9629 49.422 50.7524 5 1582.92 1566.01 1506.41 1491.34 76.886 75.1141 71.209 69.8786 6 1404.63 1421.54 1283.25 1298.32 71.247 73.0189 65.947 67.2774 7 1477.09 1460.18 1393.14 1378.07 60.583 58.8111 54.737 53.4066 8 1451.98 1435.07 1372.69 1357.62 61.896 60.1241 54.251 52.9206 9 1530.3 1513.39 1453.96 1438.89 57.514 55.7421 52.538 51.2076

10 1382.42 1365.51 1305.11 1290.04 63.619 61.8471 58.265 56.9346 11 1392.7 1409.60 1337.14 1352.21 59.083 60.8549 54.855 56.1854 12 1543.53 1560.44 1466.85 1481.92 42.855 44.6269 36.559 37.8894 13 1581.7 1564.79 1537.7 1522.63 48.824 47.0521 42.514 41.1836 14 1503.05 1519.95 1436.88 1451.95 64.101 65.8729 59.595 60.9254 15 1547.92 1564.83 1474.37 1489.44 52.275 54.0469 46.553 47.8834 16 1486.94 1503.85 1408.72 1423.79 65.613 67.3849 58.092 59.4224

5. Checking the Adequacy of the Mathematical Models The adequacy of the developed models is tested using Analysis of Variance (ANOVA)

technique. As per this technique, if the calculated value of Fratio of the developed model is less


than the standard Fratio (from F-table) value at a desired level of confidence (say 99%), then

the model is said to be adequate within the confidence limit. ANOVA test results of all the

responses are presented in Table 5.

The ANOVA table (Table 5) reveals that all the calculated F values are less than standard

table F value; hence developed mathematical models are adequate.

6. Results & Discussion Table 6 represents the predicted values of weld pool geometry. Figures 3, 4, 5, and 6

represents the scatter plots of weld bead parameters, indicating that the actual and predicted

values of Weld pool geometry parameters are very close to each other.

Predicted

Act

ua

l

160015501500145014001350

1600

1550

1500

1450

1400

1350

Scatterplot of Front Width

Predicted

Act

ua

l

8070605040

80

70

60

50

40

Scatterplot of Front Height

Figure 3: Scatter plot of Front Width Figure 5: Scatter plot of Front Height

Predicted

Act

ua

l

1550150014501400135013001250

1550

1500

1450

1400

1350

1300

1250

Scatterplot of Back Width

Predicted

Act

ua

l

757065605550454035

70

65

60

55

50

45

40

35

Scatterplot of Back Height

Figure 4: Scatter plot of Back Width Figure 6: Scatter plot of Back Height

Figures 7, 8, 9, 10, 11, 12, 13, and 14 represent the main and interaction effects of

different pulsed MPAW process parameters on the weld pool geometry. From Figures 7, 8, 9,

and 10, it is understood from the results that peak current & pulse had more significant effect

on weld pool geometry compared to back current and pulse width.


333

Me

an

of

FR

ON

T W

IDT

H

1-1

1525

1500

1475

14501-1

1-1

1525

1500

1475

14501-1

PEAK CURRENT BACK CURRENT

PULSE PULSE WIDTH

Main Effects Plot (data means) for FRONT WIDT H

Me

an

of

BA

CK

WID

TH

1-1

14601440142014001380

1-1

1-1

14601440142014001380

1-1


PULSE PULSE WIDTH

Main Effects Plot (data means) for BA CK WIDT H

Figure 7: Main effects for Front Width. Figure 8: Main effects for Back Width.

Me

an

of

FR

ON

T H

EIG

HT

1-1

64626058

561-1

1-1

6462605856

1-1


PULSE PULSE WIDTH

Main Effects P lot (data means) for FRONT HEIGHT

Me

an

of

BA

CK

HE

IGH

T

1-1

58

5654

5250

1-1

1-1

5856

54

5250

1-1


PULSE PULSE WIDTH

Main Effects Plot (data means) for BA CK HEIGHT

Figure 9: Main effects for Front Height. Figure 10: Main effects for Back Height.

As the peak current and number of pulses increases, heat input also increases, which

leads to higher penetration and hence wider front and back widths. As the widths become

wider the slopes become smaller, thereby decreasing the front and back heights. As the pulse

with increases the weld pool geometry parameters decreases because of lower cooling rate of

weld metal.

Back current is helpful in maintain the continuous arc, however increasing the back

current decrease the weld pool geometry parameters because of large variation in pulse/sec.


PEAK CURRENT

PULSE

PULSE WIDTH

BACK CURRENT

1-1 1-1 1-1

1550

1500

1450

1550

1500

1450

1550

1500

1450

PEAKCURRENT

-11

BACKCURRENT

-11

PULSE-11

Interaction Plot (data means) for FRONT WIDT H

PEAK CURRENT

PULSE

PULSE WIDTH

BACK CURRENT

1-1 1-1 1-11500

1400

1500

1400

1500

1400

PEAKCURRENT

-11

BACKCURRENT

-11

PULSE-11

Interaction Plot (data means) for BA CK WIDT H

Figure 11: Main effects for Back Height. Figure 12: Interaction effect for Front Width.

PEAK CURRENT

PULSE

PULSE WIDTH

BACK CURRENT

1-1 1-1 1-1

65

60

55

65

60

55

65

60

55

PEAKCURRENT

-11

BACKCURRENT

-11

PULSE-11

Interaction Plot (data means) for FRONT HEIGHT

PEAK CURRENT

PULSE

PULSE WIDTH

BACK CURRENT

1-1 1-1 1-1

60

55

50

60

55

50

60

55

50

PEAKCURRENT

-11

BACKCURRENT

-11

PULSE-11

Interaction Plot (data means) for BA CK HEIGHT

Figure 13: Interaction effect for Front Height. Figure 14: Interaction effect for Back Height.

From Figures 11 and 12, it is understood that the interaction effect on Front Width and

Back Width are almost same i.e. the combined effect peak current and back current decrease

in Front Width and Back Width, the combined effect of Peak Current and pulse increase the

Front and Back Width and the combined effect of peak current and pulse width decrease in

Front and Back Width.

From Figures 13 and 14 it is understood that the interaction effect on Front Width and

Back Width are almost same i.e. the combined effect peak current and back current decrease

in Front Width and Back Width, the combined effect of Peak Current and pulse decrease the

Front and Back Width and the combined effect of peak current and pulse width increase in

Front and Back Width.

Finally from Figures 11 to 14, it is understood that peak current and number of pulses has

more significant effect on weld pool geometry parameters over other weld parameters.


335

7. Conclusion From the developed mathematical models predicted values of weld pool geometry

parameters were computed and found to be very close to actual values. Front Width & Back

Width increases with Peak Current & Pulse, where as it decreases with Back Current and

Pulse Width. Front Height and Back Height decreases with Peak Current, Back Current, Pulse

and Pulse Width. The present study is limited to four process parameters namely peak

current, back current, pulse and pulse width for predicting the weld pool geometry. One may

consider other factors like welding speed, nozzle stand of distance, plasma and shielding gas

flow rates and more levels for improving the statistical mathematical model.

8. Acknowledgements We express our sincere thanks to Shri. R.Gopla Krishnan, Director, M/s Metallic Bellows

(I) Pvt Ltd, Chennai, INDIA and management of MVGR Engineering College, Vizianagaram,

INDIA for their support to carry out experimentation. A very special thank you is due to

Associate Professor Dr. Bovornchok Poopat for insightful comments, helping clarify and

improve the manuscript.

9. References Lakshinarayana.A.K, Balasubramanian.V, Varahamoorthy.R and Babu.S. (2008). Predicted

the Dilution of Plasma Transferred Arc Hardfacing of Stellite on Carbon Steel using Response Surface Methodology, Metals and Materials International, Vol.14, No.6, pp.779-789.

Balasubramanian.V, Lakshminarayanan.A.K, Varahamoorthy.R and Babu.S. (2009). Application of Response Surface Methodolody to Prediction of Dilution in Plasma Transferred Arc Hardfacing of Stainless Steel on Carbon Steel, Science Direct, Volume 16, Issue 1, pp.44-53.

Giridharan P.K, Murugan N. (2007). Effect of pulsed gas tungsten arc welding process parameters on pitting corrosion resistance of type 304L stainless steel welds, Corros J,63(5),pp.433–441.

Hsiao.Y.F, Tarng.Y.S and Huang.W.J. (2008). Optimization of Plasma Arc Welding Parameters by Using the Taguchi Method with the Grey Relational Analysis, Journal of Materials and Manufacturing Processes, 23, pp.51–58.

Montgomery DC, Design and analysis of experiments, 6th Ed. Wiley, New York, 2005.


Plasma Welding: more accurate, better control at lower currents, Modern Application News, December 1999.

Siva.K, Muragan.N, Logesh.R. (2008). Optimization of weld bead geometry in Plasma transferred arc hardfacing austenitic stainless steel plates using genetic algorithm, Int J Adv Manuf Technol, Volume 41,Numbers 1-2, pp.24-30.

Sheng-Chai Chi, LI-Chang Hsu. (2001). A fuzzy Radial Basis Function Neural Network for Predicting Multiple Quality characteristics of Plasma Arc Welding, IEEE,0-7803-7078-3/01,pp.2807 -2812.

Zhang. D.K. and Niu.J.T. (2010). Application of Artificial Neural Network modeling to Plasma Arc Welding of Aluminum alloys, Journal of Advanced Metallurgical Sciences, Vol.13, No.1,pp.194-200.

K.Siva Prasad is an Assistant Professor of Department of Mechanical Engineering at Anil Neerukonda Institute of Technology & Sciences, Visakhapatnam, India. He received his Bachelors degree from Osmania University, India and Master Degree from JNTU, Hyderabad, India. He is also a part time scholar at Andhra University. He is a member of various professional bodies like ISTE, FPSI, ISHRAE etc. His area of research is micro welding processes.

Dr.Ch.Srinivasa Rao is an Associate Professor in the Mechanical Engineering Department at Andhra University, Visakhapatnam, India. He obtained his PhD degree from Andhra University, Visakhapatnam, India. He has published his research papers in various International Journals and conferences proceedings. He is a member of various professional bodies like ISTE, IE etc. His area of interest is manufacturing sciences, rapid prototyping and robotics.

Dr.D.Nageswara Rao is a Professor in the Mechanical Engineering Department at Andhra University, Visakhapatnam, India. He obtained his PhD degree from Indian Institute of Technology Delhi, India. He is the coordinator for Centre for Nanotechnology at Andhra University. He has successfully completed various projects sponsored by DST, UGC, AICTE, NRB etc. His area of research is manufacturing sciences and nanotechnology.



*Corresponding author (Ahmad Sanusi Hassan). Tel/Fax: +6-04-6532835. E-mail addresses: [email protected]. 2011. International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. Volume 2 No.3. ISSN 2228-9860. eISSN 1906-9642. Online Available at http://TuEngr.com/V02/337-353.pdf

337



Habitability Study on Low-Cost House Design of Modern and

Traditional Mid-rise House Units in the City of Mukalla, Yemen Anwar Ahmed Baeissaa, and Ahmad Sanusi Hassanb*

a Department of Architecture and Environmental Planning, Faculty of Engineering and Petroleum,

Hadhramout University of Science and Technology, YEMEN b School of Housing, Building and Planning, Universiti Sains Malaysia,11800 Penang, MALAYSIA A R T I C L E I N F O

A B S T RA C T

Article history: Received 06 April 2011 Received in revised form 24 June 2011 Accepted 25 June 2011 Available online 27 June 2011 Keywords: Habitability, House design, Low-cost houses, Traditional style

This study investigates the measurable factors which influence the residential level of satisfaction in low-cost house units in Mukalla, Yemen. The importance of this study is due to the development of this city that has been influenced by modern architecture since colonial period. It is the tradition in Mukalla that most population live in traditional (known as tower houses) and modern mid-rise houses. The work aims to examine the level of habitability of modern house design in comparison to the level of habitability of house design of the traditional houses. The result shows that levels of satisfaction of the respondents who live at traditional house units are generally higher than those in modern house units. The finding of the study indicates house design as an important factor that determines the level of residential satisfaction. This research contributes several proposals from the research findings considered for house design guideline for the local authority to improve quality of modern house layout units with reference to the traditional house design layout in the present and future development.


International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies 2011 International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. 2011 International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies.

338 Anwar Ahmed Baeissa and Ahmad Sanusi Hassan

1. Introduction Allen (1987: 355-356) in Oxford Dictionary argued that a house is defined as “…a

building for human habitation.” It covers the “…dwelling of houses as a provision of shelter

or lodging.’ The United Nations (United Nations, 1977: 4) defines a house as not simply as

shelter but also as a mean of the creation of communities considering the functions a house

has to perform. By house design, it means the quality of the house in terms of the

organization and the allocation of space areas relative to the key functions that a household

requires which is space planning and function. Caudill (1978) noted that an adequate house

layout always takes care of both the current and the future needs; and such needs may be

evaluated on the basis of quality rather than cost, size, light and building that make up the

physical environment the residents interact with. Therefore, layout space in house design that

man creates should meet a kind of needs, and the design adequacy calls for the ability of the

designer to put all the required elements within a defined and clear relationships. Landau et

al. (1988: 1453) in Chambers English Dictionary defines the term habitable as ‘…appropriate,

proper, and fit’. Habitability therefore, can be defined as the state of being habitable,

appropriate, or proper. Habitability, however, is relative term. In the context of a house, its

habitability can be viewed in terms of its fulfilment to certain needs. Habitability in

appropriate term is said to exist when needs are being fulfilled, or there is a match between

what is needed and what is being supplied by a house, and inhabitability arises when there is a

mismatch between the two. Habitable house plays a vital role in fulfilling the key functions

that a household require. House plans must be set to measure the quality of house design that

may be achieved by using quality indicators allowing future or current house layout to be

evaluated based on quality rather than cost, site, size, light, and building that make up the

physical environment they interact with (Caudill, 1978). This article does not provide a new

idea but it is a social based house unit research topic which provides additional contribution

of the existing knowledge supported with social survey on the house unit.

2. Issues on House Design in the Case Study This habitability’s study tackles low-cost housing development in Mukalla, Yemen. In

particular, it will look at the problem of inhabitable living conditions due to inappropriate

house design as argued by UN-HABITAT (2002). This issue has always been

underestimated by both the architects and the house builders due to the influence of modern


339

styles as noted by Damluji (1992:10) frequently considered as the solution. There has been a

proposal by the United Nations (1977) that housing should be integrated with the functions of

the interior house design for a habitable living condition. This aspect is as important as the

quality of the materials that have been used towards its development. The public low-cost

housing programmes are undertaken by the federal governments with supervision and

monitoring under the Ministry of Housing and Local Government. The architects should

focus on house designs that are based on the traditional Yemeni houses. They further assert

that when designing houses for the habitation of the low-income groups, such a focus could

serve as a guiding policy towards appropriate house design. Also they suggest that strict

adherence to such a policy-guideline would certainly makes the finished houses not only

friendly to the environment but are also able to sustain the local needs and traditions. Benton

and Benton (1975:111) have mentioned the importance of this point. The purpose of this

study is to examine the level of residential satisfaction level and factors affecting in low-cost

housing in Mukalla, Yemen. Residential satisfaction reflects the degree to which individuals’

human needs are fulfilled. Therefore, it acts a guide to policy makers to monitor the

implementation of housing policies. Since no study of residential satisfaction level in low-

cost housing in Mukalla, Yemen. The study hopes to fill the gap in this area. The results of

the study will help in understanding of overall satisfaction level with low-cost housing built

by government and monitoring the implementation of housing policy in the country. The

relationships of theoretical factors are grouped into five components, namely dwelling units.

3. Methodology The methodology of this study is derived from the aim of this paper which is to examine

the level of habitability of modern house design in comparison to the level of habitability of

house design of the traditional houses. Following the ideas of Johnson and Christensen

(2000:136), these definitions have been identified as mentioned in the previous discussion on

habitability. The same factors have been used in the qualitative and the quantitative surveys.

The data obtained have been used in the qualitative and the quantitative analyses. The

adoption of the two analyses is congruent with Badar's (1982: 314-343) contention that it is

better to follow more than one method to get to the truth and to avoid biased data, such as the

respondents' bias. Finally, the control sample has been selected by the same method used

when selecting the practical sample (random/stratified/survey). Therefore, all the different


elements represent both the control and the practical samples with the same percentage. This

has been done in order to be able to compute the impact of factors under study which we

need. There are two types of analyses: qualitative and quantitative.

3.1 Measurable Scale According to Hanks (1977) in Collins English Dictionary, satisfaction is defined as the,

‘…act of satisfying; the state of being satisfied; the fulfilment of a desire; the pleasure

obtained from such fulfilment; a source of fulfilment…’ (1977: 1297).

The opposite of satisfaction is dissatisfaction, which means ‘…lack of satisfaction or

contentment’ (Allen, 1984: 212). According to the Oxford Dictionary, the concept of level of

satisfaction cannot be measured in absolute terms; instead, it is usually measured in a

continuum ranging from very satisfied to very dissatisfied, and that the level of satisfaction

varies in relation to several factors such as circumstances, time or between person-to-person

depending on each individual background. Residential level of satisfaction first is recognised

as important component of individuals' quality of life and second individuals' evaluation of

house design determine the way they respond to residential environment. Therefore, the

knowledge about factors that figure residential level of satisfaction is critical for

understanding of household moving decision process (Lu, 1999). Residential level of

satisfaction is based on the notion that residential satisfaction measures the difference

between households’ actual and desired house design layout and situations. They make their

decisions about residential conditions based on their needs and aspirations. Satisfaction with

their residential conditions indicates the absence of complaints as their needs meet their

aspirations. On the other hand, they are likely to feel dissatisfied if their house design does

not meet their residential needs and aspirations. Morris and Winter (1978) presented the idea

of ‘‘housing shortage’’ to conceptualise residential satisfaction. Their housing adequate

theory contends that if a household’s current housing meets the norms; the household is likely

to express a high level of satisfaction with housing needs.

4. House Design in Mukalla The architecture of Mukalla is dominated by white painted houses and buildings, (Figure

2). The architectural styles are a mixture of Arabic, Yemeni and Indian patterns. It is

characterized by unique architectural designs of the 18th and 19th centuries. The space


341

planning in the traditional houses in Mukalla has been moulded by the culture, values and

lifestyles of the Hadhrami people. In addition, the space planning has been influenced by

their attitude to give priority to privacy. At the same time they have emphasised their

preference for community intimacy, their needs for seasonal feasting and other cultural

activities. The study of the interior space is focused on the following factors:

a. Diwan, dining area and bedrooms

b. Bathrooms

c. Corridor and storage

d. Courtyard and balcony

e. Compositions of the rooms' layout

Figure1: View of Old Picture’s Part of Mukalla showing a typical traditional mid-rise houses

(right) and an example of a house facade (left).

a. Bathrooms

In a traditional house in Mukalla, usually the diwan is a space located in front of a house

and which is essentially for males and is separated from the private areas of the house which

visitors or strangers do not see. In this respect the location of the diwan plays an important

role in the layout of the house design unit as a whole. An analysis of the survey revealed that

this factor seems to have been recognized in the design of most of the houses. Some interior

spaces of a traditional house are generally not named by the conventional labels such as

diwan, dining room, but rather by the actual activities in the space at a particular time. The

only exceptions where the spaces are named permanently by their uses are the kitchen and the

toilets. There are, therefore, no permanent spaces with specific labels such as the living room,

the bedroom, the dining room, the hall or the study room, which are directly named after


certain activities as in the case of Western and modern houses. This reflects the multi-

functional nature and the non-specialised uses of the spaces in the modern houses in Mukalla

(Figure 2). This definition of space leads to inappropriate use of space and is consistent with

the inclinations towards inhabitable living conditions.

Figure 2: Example of Plan (left) and Axonometric (right showing the activities) of a Small-

Sized Interior Space in One Floor Level of One Unit Modern Apartments for Low-Income

Group.

The inhabitable space layout in the modern houses is basically found in houses in the

urban areas. The poor design and the construction seem have created physical problems on

the buildings themselves and some psychological problems on the residents. These seem to

have arisen from designs that have ignored the separation of males and the females, and also

not being sufficiently sensitive to the basis Islamic needs such as orientating the house to the

Kiblah. In addition, modern houses (apartments and flats) are considered to have many

disadvantages for local Mukalla people as such premises create a feeling of loneliness and

isolation. First the sizes are small. Second, the space functions in the modern apartments and

flats reflect the poor design and the distribution of the spaces, (Figure 2). There are rooms

that are used for various functions; for example, a diwan for women during the day time is

also transformed into a living room, a visitor room for many people during the day time.

Dining area is also transformed into a kitchen, and in a case a house unit with top floor

room/terrace is used by family members during the dining time. Bedrooms are transformed

into master’s bedroom, bedroom for males, and bedroom for females for family members

during the night.

Entrance door

Kitchen

Toilet

Hall

Visitor room

Bedroom

Living room

Entrance door


343

In contrast to the above, the life style in the traditional houses in Mukalla is unique and

exceptional. Indeed, the social functions behind the general aspect of the house design have

become private within the family. In a Mukalla traditional house, the other diwan is usually

located on the first floor. It is for accommodating visitors according to the gender (males and

females), (Figure 3). In the secluded diwan for women, the women do not need to cover

themselves and they are free from unforeseen visitors when they come in. Sometimes, the

rooms in the first floor are lent to the neighbours when they have important social activities.

The use of minimal furniture in a traditional house also helps to create a more flexible use of

the interior spaces. Bulky furniture not only cluster and break up interior spaces, they also

define and confine the spaces for certain uses only.

Figure 3: Floor Plans of a Traditional House Unit in Old Zone Scale 1/200 metres

Shows First Floor Level (right plan), Second Floor Level (middle plan) and Third Floor Level

(left plan).

The second floor, however, is to accommodate the elders and the relatives to live in.

Some rooms in this floor are designed for different functions, for instance a room which is

occupied by women in the day time as a diwan could be a bedroom at night for many people.

The third floor is entirely private as it places the bedroom for the head of the family and his

wife. Here the wife can receive, in private, her intimate friends. Children have their own

rooms on the third floor as well; they are not secluded and are free to move anywhere in the

house. Figure 4 depicts the first floor of a tradition house which is "socially" closed. It a

sense, it is only a semi- public space of the house. All visitors are not allowed to enter

Third floor Second floor First floor


directly. Only family members or close friends are allowed to enter the diwan (Figure 3 and

4). Strangers, if they are expected, can stay and wait for a while in the corridor, which is a

transition space. In the case of women visitors, the diwan is used but the men have to leave

the floor or even the house.

Figure 4: Diwan Interior Space (photo-left) and axonometric layout (right) of a Traditional

House Unit in Old Zone of Mukalla.

Figure 5: Illustrating the Absence of a Diwan in Low Income House Unit showing

Main Facade (top left), Axonometric Layout (top right) and Floor Plan (bottom) of Modern

One Unit Low-Income Modern Apartment.

Diwan

Visitor room

Dining room

Bathroom Kitchen

Visitor room

Dining room

Entrance Door


345

The second floor is reserved for the children and use during the day as the diwan for the

women of the family. The third floor is used by the parents. This floor keeps its original

function (bedroom) all day long (Figure 4). The foot bridge at the first floor which is used to

communicate with the next mid-rise house units is not used any more. The top floor

room/terrace which is an open spatial area is used for sleeping area during the hot summer

season. There is a traditional house in old zone which is more than 100 years old. It is one of

the best examples of a traditional house built in a traditional way with supporting walls in

freestones and flag in clay maintained by wooden grids and beams. In fact Old traditional

houses are very unique in their constructions as they are commonly adorned with purified

ornaments, come with special openings, built with terraces of parapet type and decorated with

wooden sculpture. This may be attributed to the division of the old buildings (previously

lodging a single family) into separate small apartments. In modern zones, the houses are

small due to economic grounds. One seemingly critical problem to a comfortable living life

style is that in all these small houses, (Figure 5), there is a significant absence of a diwan and

other spaces which are multifunctional in the traditional houses mentioned above.

b. Bathrooms

The design of modern houses does not cater a separate bathroom for the male and the

female members of the family. Instead, they have a common bathroom for both genders. This

is due to a dire shortage of space for any extra bathroom facilities. The lack of these facilities

is partly attributable to the apparent erosion of the religious values with respect to the social

interaction between a male and a female. In contrast to the above modern houses, the

traditional houses in the old zones contain their conventional sewage system that permits

them to possess flexible access to these facilities. That is, male and female members of the

family are assigned with separate bathrooms and toilets (Mukalla Master Plan, 1982).

c. Corridor and Storage

The corridor spaces and the space for the stairs in a modern house (apartments/flats) is

unsatisfactory by dimension and lighting and by the regular needs to move masses of goods.

Also, there is no storage and basement due to a limited area within the apartment. In a

traditional house, on the other hand, the main entrance provides sufficient space for the traffic

flow of the pedestrians in the house. Usually the entrance leads into a narrow passage to a


staircase which opens to a corridor space which in turn ushers the user to other spaces.

Therefore, the specific space layout in the traditional houses is sufficient. In particular, the

stairs are built around a huge pillar at the entrance or the main support of the house. In

addition, in the traditional houses there is sufficient storage space and a basement floor.

d. Courtyard and Balcony

Modern houses do not have any allocation of space for a courtyard and a balcony due to a

limited area and also due to the fact that their construction is from reinforced concrete. In

contrast, in a traditional house, the courtyards are very significant components as they provide

the ventilation and the cooling system. Costa (1995) mentioned that courtyards are built with

the intention of generating a constructive link between the external and internal environments.

Also they are designed to accommodate the different social activities such as the family

gatherings, a reception of guests and other related social occasions

e. Compositions of the Rooms' Layout

The arrangement of space between each pair of rooms and the rate of movement between

them play very important role in the locations and in the layout of the rooms. In modern

houses, the location of the rooms is very poorly laid-out due the limited space that is available

in them. However, in the traditional houses the location and the layout of house design

account the interior space elements like the doors, the windows, the interior walls, the floors,

and the ceilings. Usually, in a traditional house, the entrance leads into a narrow passage and

then to a staircase that leads to a corridor space which opens up to other spaces. The ground

floor is usually reserved for storage purposes while the first floor is allocated for social

activities. Such a composition of the space takes into account the emotions of the inhabitants

and accommodates their daily needs, wishes and ambitions. Therefore, in a traditional house

space layout is the central consideration as it accommodates the basic needs of the inhabitants

in organized and systematic ways which have been carefully thought out by the local master

builders.

5. Space Planning and Function This category has following factors: (a) Diwan (living room, visitor room and furniture

setting), (b) dining area, (c) bedrooms, (d) bathrooms, (c) corridor and storage, (e) courtyard


347

and the balcony, (f) compositions and layout of the rooms. In this qualitative study, the

criteria for evaluation are on qualitative analysis from checklist factors as discussed in the

literature review based on the researcher’s observation on the house design during the site’s

visit. The answer "Yes" represents as satisfactory and "No" as unsatisfactory. For example, if

the visitor’s room is satisfactory, the answer "Yes” will be marked as ‘x’, but when it is

unsatisfactory, the answer is "No" will be marked as ‘x’.

Table1: Items of Factors on House-Design.

Item

The Space planning and

function

Qualitative survey of

Modern Mukalla

Quantitative survey of Modern Mukalla

(% respondents)

Qualitative survey of Old Mukalla

Quantitative survey of Old Mukalla

(% respondents) Yes No Yes No

a

Diwan 55% 72% (a) living room x 53% x 70% (b) visitor room x 56% x 73% (c) furniture setting x 57% x 74%

b

Dining Area 42% 64% (a) Dining room x 40% x 62% (b) Kitchen x 42% x 65% (c) Top floor room/terrace

x 43% x 66%

c

Bedrooms 54% 67% (a) master bedroom x 52% x 65% (b) Bedroom for male x 55% x 68% (c) Bedroom for female x 56% x 69%

d

Bathroom 62% 70% (a) Bathroom for male x 60% x 69% (b) Bathroom for female x 64% x 71%

e

Corridor and Storage 45% 73% (a) Corridor Space x 42% x 71% (b) Stairs Space x 46% x 74% (c) Storage and basement floor

x 47% x 75%

f

Courtyard and Balcony

35% 46%

(a) Courtyard x 33% x 44% (b) Balcony x 37% x 48%

g The Composition of the room's layout

x 58% x 70%

N=17

Total

8

9

7

15

2

7

Total number of positive answers over

the total number of the items

8/17

9/17

351/7

15/17

2/17

462/7

Overall answers in percentages 47%

53%

50%

88%

12%

66%


On the other hand, the quantitative analysis is from the respondents’ answers (300

respondents) on their satisfaction level from questionnaires related to the same checklist

factors. The measurable scale is based on five rating scales of preferences in which each

respondent is required to identify by ticking only one answer ranging from 1 to 5 for each

question. These ranging scales are: No. 1: worst, No. 2: bad, No.3: no comment, No. 4: good

and No.5: best. According the Likert Scale (2006) an important distinction must be made

between a Likert scale and item (respondents’ answers from questions in the questionnaires).

The Likert scale is the sum of the responses (respondents’ answers) on Likert items

(questions). The total answers from each question are converted to obtain the mean average

ranging from 1 to 5 (x1 + x2 + x3 + …. xn divided by 5 = Mean Average). Finally, this mean

average of each question is converted to percentage scale to represent the percentage of the

respondents’ answers. The objective of the quantitative survey in this study is to identify the

factors of the level of satisfaction as perceived by the respondents represented with

percentages. The results of the qualitative and the quantitative analysis of the data are

presented in subsection of space planning and function, as in Table 1.

6. Results

6.1 Qualitative Analysis by Factors a. Diwan

i. The furniture setting in modern house design is unsatisfactory compared to the same items

in the traditional house due to the limited floor area for such purpose in the traditional

house design.

ii. The living and visitor rooms in the modern house design are found to be less satisfactory

than the same items in the traditional house design.

b. Dining area

i. The dining room and top floor room/ terrace in the modern house design are found to be

unsatisfactory compared to the similar items in the traditional house design due to a

limited floor area.

ii. The modern and the traditional house for kitchen have a similar level of satisfaction.

c. Bedrooms


349

i. The residents of the traditional houses find satisfaction with the house design of the

bedroom for the males and the females, while the residents of the modern houses find

these same items unsatisfactory. Both residents, however, find the house design of the

master’s bedroom as satisfactory.

d. Bathroom

i. In the modern house design, there is no allocation for separate bathroom for the male and

the female members of the family; hence the residents find this situation unsatisfactory. In

comparison, the residents of the traditional house design enjoy different allocation of

separate bathrooms for the males and the females.

e. Corridor and Storage

i. The residents of the modern houses find the allocation of space for the stairs satisfactory.

In comparison, the stairs in the traditional house design and the allocation of the basement

space are found unsatisfactory by its residents.

f. Courtyard and Balcony

i. No courtyard is found in the modern houses, and the residents find its absence

unsatisfactory. In comparison, the residents of the traditional house find enjoyment and

satisfaction in the availability and use of the courtyards there.

ii. The modern houses have balconies, and the residents find satisfaction in using them. The

traditional houses, however, do not have such similar balconies as they have regarded

them as a way of exposing the women to the areas outside the house which is counter to

the Islamic teachings. In fact the residents prefer the traditional premises to be without the

balconies, although some find its absence wanting.

g. Composition of the room's layout

i. On the whole, the residents regard the composition of the layout of the rooms in the

modern houses as unsatisfactory due to the limited built-up area in the modern house

designs. As a comparison, the residents of the traditional houses find satisfaction with the

nature of the layout and the organization of the interior spaces.


6.2 Qualitative Analysis by Category Table 1: shows that under the category of space planning and function, the average result

of Old Mukalla is 88%. Hence, it can be regarded that the residents there have considered the

factors within that category to be satisfactory. However, modern Mukalla has 47%. So,

relatively the residents seem to have felt that the traditional house designs on space planning

in the old zone have been considered as more habitable than those same factors in the modern

houses.

6.3 Quantitative Analysis by Factors For the quantitative analysis of the factors the relevant interpretation of the above

responses are as in (a) through (g) below:

a. The diwan

72% of the respondents from Old Mukalla are satisfied with the diwan (the living,

visitors’ rooms and furniture setting) as compared to merely 55% of the respondents from

Modern Mukalla find the diwan there satisfactory. In another words, generally the residents of

Modern Mukalla only slightly satisfied with the diwan of their houses.

b. The dining area

The analysis finds that 64% of the respondents from Old Mukalla perceive the dining

area facility in their houses to be satisfactory and that they are habitable. On the same factor,

the respondents from Modern Mukalla score only 42% suggesting they are not as satisfied as

their counterparts in Old Mukalla towards their dining area.

c. The bedrooms

With respect to the bedrooms, 67% of the respondents from Old Mukalla see their

bedrooms as satisfactory, while their counterparts in Modern Mukalla score only 54% on the

same factor suggesting that they find their bedrooms not as satisfactory as the respondents of

Old Mukalla find them.

d. The bathrooms

With a score of 70% on this factor, there is no doubt that the respondents of Old Mukalla

are more satisfied with their bathrooms than the respondents from Modern Mukalla who score

much less, which is 62%.


351

e. Corridor spaces and storage

On this factor, with a score of 73% the respondents of Old Mukalla clearly have

expressed much more satisfaction towards them than the respondents from Modern Mukalla

have as they score poorly with 45%.

f. Courtyard and balcony

With a score of 46% satisfactory answers for the courtyards and a score of only 35%

satisfactory answers for the balconies, the Old Mukalla residents are apparently more satisfied

with the courtyards than with the balconies. This is quite understandable as generally, the

traditional houses do not have balconies. The level of satisfaction on these two factors seems

to be the reverse in the case of the residents of Modern Mukalla. That is, with a satisfactory

score of 51% for the balconies as compared to a mere score of 19.5% for the courtyards, they

obviously have successfully expressed their displeasure and dissatisfaction towards the

absence of any courtyards in Modern Mukalla.

g. Composition of the house's layout

70% of the respondents of Old Mukalla have expressed satisfaction towards the

composition of the layout of spaces as compared to 58% of the respondents of Modern

Mukalla who have expressed similar satisfaction on the same factor. If these figures are any

positive indication of their perception, apparently the residents of Old Mukalla have perceived

their traditional houses to be more habitable with respect to this factor than their counterparts

have with their houses in Modern Mukalla.

7. Conclusion The perception of satisfaction on the nature of space planning of house layout, the

traditional houses of Old Mukalla were to be considered already have given more level of

satisfaction to its residents more than residents who live in Modern Mukalla. However,

relative to these perceptions, with a composite score of 88% from respondents’ answer for

Old Mukalla and 47% for Modern Mukalla. The residents of Modern Mukalla have expressed

dissatisfaction towards most of the factors. The main problems seem to have stemmed from

those aspects surrounding the feelings of discomfort and dissatisfaction due to limited space

areas, the absence of a diwan. In contrast, the residents of the traditional houses of Mukalla


seem to have expressed better views and more satisfied towards all the factors. On Old

Mukalla, from the qualitative survey high scores in the column of Table 1 for all the factors, it

is quite apparent that the respondents from Old Mukalla have rated highly all the factors. As

such these high average scores undoubtedly have served as expressions of much satisfaction

towards the house designs and the nature of the amenities there. In that light, within the ambit

of this study, the house designs in Old Mukalla can and do serve as references for the houses

in Yemen. The study has used the layout of the house design of the traditional houses of Old

Mukalla as the reference model.

At the end of the study, it is suggested here that the study has made the contributions

below with respect to people’s perception on the habitability of house design for the low

income group in Yemen in particular and some general ideas about habitability of house

design in the field of architecture in general. It has provided the definitions of the terms

house, designs and habitable within the ambit of the perception of the low-income group of

Yemenis.

8. Acknowledgements A very special thank you is due to Dr. Wijitbusaba Ann Marome for insightful

comments, helping clarify and improve the manuscript.

9. References Allen, R.E. (ed.). (1984). Oxford Dictionary. Oxford: Oxford University Press.

Allen, R.E. (ed.). (1987). The Oxford Dictionary of Current English. Oxford: Oxford University Press.

Badar, Ahmed. (1982). Ausul Al-Bahat Al-Elmi wa Manaheejh, (Methods of Scientific Research and Curriculum). (Arabic version). Al-Kuwait: Abdullah Hazami Agency Publications.

Benton, Tim and Benton, Charlotte. (1975). Form and Function. London: The Open University with Dennis Sharp.

Caudill, W. et al. (1978). Architecture and You: How to Experience and Enjoy Buildings. New York: Watson-Guptill Publications.

Damluji, S. S. (1991). A Yemen Architecture Sculptured in Mud and Stone. Reading: Garnet Publishing Limited.


353

Damluji, S. S. (1992). The Valley of Mud Brick Architecture Shibam, Tharim and Wadi Hadhramout. London: Garnet Publishing.

Damluji, S. S. (2007). The Architecture of Yemen: From Yafi to Hadhramout. London: Laurence King Publishing Ltd.

Hanks, Patrick (ed.) (1977). Collins Dictionary of the English Language. London: William Collins Sons & Co.Ltd.

Landau, Sidney. I., et. al. (eds.). (1988). Chambers English Dictionary. Cambridge: Cambridge University Press.

Lu, M. (1999). Determinants of Residential Satisfaction: Ordered Regression Models, Growth and Change, 30, 264–287.

Morris, Earl and Winters, Mary. (1978). Housing, Family, and Society. New York. John Wiley & Sons, Inc.

Mukalla Master Plan (1982). Arab Institute for Design and Studies. Peoples Democratic Republic of Yemen. Beirut: 65 Emile Bustany Street.

UN-HABITAT (2002), United Nations Human Settlements Programme [Online], [Accessed 12 May 2006]. Available from World Wide: file:///E:/anwar/Desktop/Yemen.htm

United Nations, (1977). The Social Impact of Housing: Goals, Standards. Social. Indicators, and Population Participation. New York: Department of Economic and social Affairs.

Dr. Anwar Ahmed Baeissa is an assistant professor at Department of Architecture & Environmental Planning, Faculty of Engineering & Petroleum, Hadhramout University of Science & Technology (HUST), Yemen. He earned a Bachelor and a Master of Architecture (B. Arch & M. Arch) degrees in 1998 from the Odessa State Academy of Civil Engineering and Architecture, Ukraine, USSR. He worked from 1999-2003 as instructor at department of Architecture & Environmental, Planning and he had been awarded a PhD degree in 2009 from the University of Science Malaysia (USM), Penang, Malaysia. His research is focused on evaluations of space planning towards habitable house designs for low-income group.

Dr. Ahmad Sanusi bin Hassan is an associate professor in the Architecture Programme at the School of Housing, Building and Planning, University of Science Malaysia (USM), Penang, Malaysia. He earned a Bachelor and a Master of Architecture (B. Arch & M. Arch) degrees in 1993 and 1995 respectively from the University of Houston, Texas, USA. At the age of 29, he was awarded a PhD degree in 1998 from the University of Nottingham, United Kingdom. His research is focused on sustainable architecture and construction, and urban design. He is one of the nine regional writers, three of each from Asia, Africa and South America, who have been involved in the preparation of Guideline: Agenda 21 for Sustainable Construction in Developing Countries: A Discussion Document edited by Chrisna du Plessis, published by The International Council for Research and Innovation in Building and Construction (CIB), and United Nations Environment Programme International and Environmental Technology Centre (UNEP-IETC), which was launched at The Earth/World Summit, Johannesburg in September, 2002. At the university, he lectures in courses related to sustainable urban design, sustainable architecture and construction, Computer Aided Design (CAD), and computer movie animation. He has integrated all these specialisations into his research, teaching, consultation and publications.




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*Corresponding author (H. Hamidifar). Tel/Fax: +982612231787. E-mail addresses: [email protected] . 2011. International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. Volume 2 No.3. ISSN 2228-9860. eISSN 1906-9642. Online Available at http://TuEngr.com/V02/355-364.pdf

355



Interrelationships between Characteristic Lengths of Local Scour

Hole Hossein Hamidifara*

a Department of Irrigation and Reclamation Engineering, University of Tehran, Karaj, Iran. A R T I C L E I N F O

A B S T RA C T

Article history: Received 12 May 2011 Received in revised form 21 June 2011 Accepted 28 June 2011 Available online 29 June 2011 Keywords: Local scour, Hydraulic structures, Characteristic lengths, Sediment, Sluice gate, Horizontal apron

This paper presents the results of an experimental study on local scour of noncohesive sediments downstream of a horizontal rigid apron. The experiments were carried out in a rectangular flume with 9m length, 0.5m width and 0.6m height which includes an alluvial test reach of 1.65m length and 0.2m depth at the end of the apron. Two types of uniform sediment with median diameters of 0.73mm and 1.85mm were used in the experiments. Time variations of the maximum scour depth was measured for some experiments. It was found that the scour hole does not reach the equilibrium state even after 48 hours. However, after the first 12 hours, the rate of extension of the maximum scour depth is found to be less than 0.001 cm/min. Although the scour profile seems to be three dimensional in nature, it was found that there is a geometrical similarity between the scour holes in all of the experiments. Variations of the characteristic lengths of the scour hole such as the maximum scour depth, dsm, the maximum extension of hole, L0, and the dune height, hd, are related to each other. Nondimensional graphs and formulas are suggested to determine the variation of these parameters in different conditions.


International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies 2011 International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies.

356 Hossein Hamidifar

1. Introduction When jets impinge upon loose beds of granular material downstream of hydraulic

structures such as weirs or sluice gates, they can lead to significant local scour and may cause

stability problems of the structure. Constructing a rigid apron adjacent the structure is a

typical engineering solution to protect the structure. Over the last three decades, several

experimental studies have been conducted to investigate the local scour process caused by

submerged and unsubmerged two-dimensional (2D) and three-dimensional (3D) jets. Results

indicate that the maximum scour depth not only depends on the impinging flow velocity,

characteristics of bed material, but also the apron length and apron surface roughness.

The limit of the scour pattern can be considered to be an isoline of constant shear stress

with a value equivalent to the threshold bottom stress. However, estimating the threshold

shear stress of a certain material presents uncertainties.

An approach to characterize the response of the sediment to jet flow, in the case of non-

cohesive sediment, is to use the densimetric Froude number associated with a representative

diameter. The densimetric Froude number F0 is defined as U0/(gdiΔρ/ρ)0.5, where U0 is the jet

velocity at the nozzle, g the acceleration due to gravity, di a representative size of the bed

material, and Δρ is the difference between the density of the bed material ρs and the density of

the fluid ρ. From dimensional considerations, F0 is a measure of the ratio of the tractive force

acting on the bed particle to the submerged specific weight of the particle.

Due to the practical importance，local scour caused by the jets has been a topic of

continued interest to the researchers and the design engineers as well. Farhoudi and Smith

(1985) studied the development of scour holes downstream of a spillway due to hydraulic

jump over an apron. Ali and Lim (1986) conducted experimental investigations to study the

localized scour caused by two- and three-dimensional turbulent wall jets. Recently published

results indicate that the scour hole develops rapidly in the early stages and progresses towards

an asymptotic stage beyond which the scour profile does not change significantly with time

and reaches an equilibrium state (Balachandar et al., 2000; Kells et al., 2001; Lim and Yu,

2002; Sarkar and Dey, 2004; Dey and Sarkar, 2006; Alihosseini et al., 2008; Oliveto et al.,

2008, Sarathi et al., 2008, Hamidifar et al., 2010, 2011; Omid et al., 2009).


357

Dey and Westrich (2003) investigated the flow characteristics of submerged jets over an

apron and in an equilibrium scour hole in cohesive beds. Moghim et al. (2008) developed an

empirical equation by using regression analysis to predict the maximum scour depth

downstream of aprons. In a more recent study Khwairakpam and Mazumdar (2009) conducted

a review on local scour around hydraulic structures.

However, nowadays many criteria are proposed to determine dimensions of the scour

hole. The research reported in this paper focused on finding the interrelations between

characteristic lengths of local scour hole downstream of an apron.

2. Materials and Methods Experiments were carried out in a recirculating glass-sided flume in the central laboratory

of water researches in University of Tehran. The flume was 9m long (the test reach being 3 m

long), 0.5m wide and 0.6m deep. Water was continuously pumped from the downstream

reservoir into the upstream head tank with a maximum capacity of 25 l/s. A calibrated

rectangular sharp crested weir was used to measure the discharge.

Figure 1: Experimental setup.

A submerged horizontal jet was produced by flowing water through a sluice gate opening

equal to 2cm over an apron of 1m length followed by a 0.2m deep sediment bed container.

The initial bed slope was adjusted to zero for each run using a carriage system riding on the


rails over the flume. At the downstream end, a tailgate allows the regulation of the flow depth

in the flume. The discharge Q, was set constant for each run and a constant tailwater depth

Tw, 10 times the gate opening Y1, was also set in order to satisfy the conditions of deeply

submerged horizontal jet.

3. Results and Discussion As soon as the water flowing from the sluice opening reached the erodible bed, the

movement of bed materials from the end of the rigid apron started and the geometry of the

scour hole started changing with time. The scour profiles at various times were marked on one

of the glass walls of the flume. It was observed that during the initial stage the rate of scouring

was very high. It then gradually tapered off as time elapsed. Ultimately the equilibrium stage

was reached when no movement of grains was observed at the location of maximum scour.

For each type of bed material, experimental runs have been undertaken for different

tailwater depths and for various discharges. Before starting a particular run, the initial bed

surface was leveled. To avoid the disturbance of the bed before regulating the tailwater depth

and discharge, the alluvial bed surface was covered with a Plexiglas plate with the same width

as the flume. After the desired conditions were established, the plate was removed gently

from the downstream.

Before starting the next run, the disturbed bed was leveled after dewatering and drying

the bed. The whole procedure was then repeated, and a new scour profile was obtained. The

scour profiles have been used to determine the characteristic lengths of the scour hole at the

equilibrium state.

Time variations of the maximum scour depth was measured for some experiments. It was

found that the scour hole does not reach the equilibrium state even after 48 hours. However,

after the first 12 hours, the rate of extension of the maximum scour depth is found to be less

than 0.05cmh-1.

From the scour profiles, the maximum scour depth dsm, the location of maximum scour

depth Xm, the maximum scour point L0, the maximum dune height hd and the location of

maximum height of the dune Xd for all the test runs has been measured. To obtain relationship


359

between the characteristic lengths of the scour hole, these parameters were plotted against the

dimensionless maximum scour depth.

Figure 2 shows the variation of the maximum dune height hd. It is observed from this

figure that the variations of these two parameters follow a linear trend which can be expressed

as Eq. (1):

84.8827.25050

−⎟⎟⎠

⎞⎜⎜⎝

⎛=

dd

dh smd R2=0.96 (1)

In Figure 3 variations of the maximum scour point L0 is plotted against the maximum

scour depth. It is clear that the variation trend is not linear and a quadratic equation as Eq. (2)

can fit the experimental data.

863.7839.1025.050

2

501

0 −⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟⎟

⎠

⎞⎜⎜⎝

⎛−=

dd

dd

YL smsm R2=0.95 (2)

In Figure 4 the variations of the location of the maximum dune height Xd, is shown. By

examination of different parameter to nondimensionalize Xd, it was found that the gate

opening Y1 is more appropriate than the particle median size d50. So, a new dimensionless

equation is proposed as below to determine Xd when dsm is known.

51.10198.3043.050

2

501−⎟⎟

⎠

⎞⎜⎜⎝

⎛+⎟⎟

⎠

⎞⎜⎜⎝

⎛−=

dd

dd

YX smsmd R2=0.88 (3)

Variations of Xm, against dsm is plotted in Figure 5 where Xm is the location of the

maximum scour depth downstream of the apron. As figure 5, the gate opening Y1 was used to

nondimensionalize this parameter as shown in Eq. (4). However, using Y1 was not remedial to

cover scattering of the data as well as figure 5.

338.0417.0004.050

2

501−⎟⎟

⎠

⎞⎜⎜⎝

⎛+⎟⎟

⎠

⎞⎜⎜⎝

⎛−=

dd

dd

YX smsmm R2=0.74 (4)


Figure 2: The relation between maximum scour depth and maximum dune height.

Figure 3: Variations of maximum length of the scour hole against maximum scour depth.


361

Figure 4: Relation between the location of the dune maximum heigth against dsm.

Figure 5: Variation of the location of maximum scour depth against dsm.

A comparison between the results of the present and previous studies is shown in Figure

(6). A dimensionless parameter, r, is defined as Eq. (5) to find the relative error between the

results. It is seen from Figure (6) that as the dimensionless parameter dsm/Y1 increases, the

relative error decreases and the results of the different studies come close to each other.


However there is considerable scatter in data for small values of the dimensionless scour

depth.

( ) ( )( ) studypresentsm

udypreviousstsmstudypresentsm

Yd

YdYdr

1

11 −= (5)

Figure 6: comparison of the results of the present and previous studies.

4. Conclusion The interrelationships between different parameters of local scour hole downstream of a

rigid apron is studied experimentally. The experiments were conducted in the wide range of

tailwater depths and different flow discharges. Results showed that there are good

correlations between scour hole parameters. So, some experimental equations were presented

by using regression analysis. It was found that the maximum dune height, the maximum

extension of the scour hole, the maximum extension of the dune, the distance between end of

the apron and both the maximum scour depth and the maximum dune height will increase if

the maximum scour depth increases. These proposed criteria can help hydraulic structure

enginners to design structures more safely.

5. Acknowledgement A very special thank you is due to Associate Professor Dr. Chavalit Chaleerakthrakul for

insightful comments, helping clarify and improve the manuscript.


363

6. References Ali, K.H.M. and S.Y. Lim, 1986. Local scour caused by submerged wall jets. Proceedings of

the Institute of Civil Engineers Part 2 (81):607–645.

Alihosseini, P., K. Ebrahimi, M. Sanei and M. Mashaal, 2008. Experimental investigation of temporal variation of scour profile downstream of submerged hydraulic jumps. Proceedings of the 7th Iranian Conference on Hydraulic. Nov. 11- 13. Sh. Abbaspour University. Tehran. Iran (in Farsi).

Balachandar, R., J. Kells, and R. Thiessen, 2000. The Effect of Tailwater Depth on the Dynamics of Local Scour. Canadaian Journal of Civil Engineering, Vol. 27, 138-150.

Dey, S. and A. Sarkar, 2006. Scour Downstream of an Apron due to Submerged Horizontal Jets. Journal of Hydraulic Engineering, Vol. 132, No. 3, 246-257.

Dey, S. and B. Westrich, 2003. Hydraulics of Submerged Jet Subject to Change in Cohesive Bed Geometry. Journal of Hydraulic Engineering, Vol. 129, No. 1, 42-53.

Farhoudi, J. and K. Smith, 1985. Local Scour Profiles Downstream of Hydraulic Jump. Journal of Hydraulic Research, Vol. 23, No. 4, 343-359.

Hamidifar, H., M.H. Omid, and M. Nasrabadi, 2010. Bed Scour Downstream of Sluice Gates. Journal of Water and Soil, Vol. 24(4), 728-736.

Hamidifar, H., M.H. Omid, and M. Nasrabadi, 2011. Scour downstream of a rough rigid apron. World Applied Science Journal, (Accepted).

Khwairakpam, P., and A. Mazumdar, 2009. Local scour around hydraulic structures. International Journal of Recent Trends in Engineering, 1(6), 59-61.

Kells, J. A., Balachandar, R., and K. P. Hagel, 2001. Effect of Grain Size on Local Channel Scour Below a Sluice Gate. Can. J. Civ. Eng, 28, 440–451.

Lim, S. and G. Yu, 2002. Scouring Downstream of Sluice Gate. First International Conference on Scour of Foundation, Texas Transportation Institute, Nov. 17-20, Texas A & M University, College Station, Texas, USA.

Moghim, M. N., Dorsangi, M. G. and M. Ghodsian, 2008. Prediction of maximum scour depth due to wall jets by using neural networks, 4th National Congress on Civil Engineering, Tehran, Iran. (in Persian)

Oliveto, G., V. Comuniello, and B. Onorati, 2008. Temporal development of local scour downstream of positive-step stilling basins. Proceedings of River Flows. Sep. 3-5. Izmir. Turkey. 1673-1678.

Omid, M. H., H. Hamidifar, and A. Reisi, 2009. Effect of tailwater depth on local scour downstream of an apron. Proceedings of 8th International Congress on Civil Engineering. May 11-13. Shiraz, Iran (in Persian).


Sarathi, P., M.A.A. Faruque and R. Balachandar, 2008. Influence of tailwater depth, sediment size and densimetric Froude number on scour by submerged square wall jets. J. Hydra. Res. 46(2): 158-175.

Sarkar, A. and S. Dey, 2004. Review on local scour due to jets, International Journal of Sediment Research 19(3), pp. 210–238.



H. Hamidifar is a PhD candidate of Water Structures at the Department of Irrigation and Reclamation Engineering at University of Tehran. He received his B.Sc. from Shiraz University. He continued his M.Sc. study at University of Tehran where he obtained his M.Sc. in Water Structures. He focuses on local scour (cohesive and non-cohesive sediments), Hydraulic jump and energy dissipaters.


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