Table Of ContentMultiobjective Optimization in
Engineering Design
Applications to Fluid Power Systems
Linköping Studies in Science and Technology. Dissertations.
No. 675
Multiobjective Optimization in
Engineering Design
Applications to Fluid Power Systems
Johan Andersson
Division of Fluid and Mechanical Engineering Systems
Department of Mechanical Engineering
Linköpings universitet
SE-581 83 Linköping, Sweden
Linköping 2001
On the cover a set of chromosomes is depicted. Chromosomes are essential
for evolution as well as for genetic algorithms, which is an optimization algo-
rithm employed within this thesis.
ISBN 91-7219-943-1
ISSN 0345-7524
Copyright © 2001 by Johan Andersson
Department of Mechanical Engineering
Linköpings Universitet
SE-581 83 Linköping, Sweden
Printed in Sweden by UniTryck Linköping, 2001.
Abstract
T
HIS THESIS FOCUSES on how to improve design and development of complex
engineering systems by employing simulation and optimization techniques. Within the
thesis, methods are developed and applied to systems that combine mechanical, hydrau-
lical and electrical subsystems, so-called multi-domain systems. Studied systems in-
clude a landing gear system for a civil aircraft, electro-hydrostatic actuation systems for
aircraft applications as well as hydraulic actuation systems.
The usage of simulation and optimization in engineering design is gaining wider ac-
ceptance in all fields of industry as the computational capabilities of computers in-
crease. Therefore, the applications for numerical optimization have increased dramati-
cally. A great part of the design process is and will always be intuitive. Analytical
techniques as well as numerical optimization could however be of great value and can
permit vast improvements in design.
Within the thesis, a framework is presented in which modeling and simulation are
employed to predict the performance of a design. Additionally, non-gradient optimiza-
tion techniques are coupled to the simulation models to automate the search for the best
design.
Engineering design problems often consist of several conflicting objectives. In many
cases, the multiple objectives are aggregated into one single objective function. Optimi-
zation is then conducted with one optimal design as the result. The result is then
strongly dependent on how the objectives are aggregated. Here a method is presented in
which the Design Structure Matrix and the relationship matrix from the House of Qual-
ity method are applied to support the formulation of the objective function.
Another approach to tackle multiobjective design problems is to employ the concept
of Pareto optimality. Within this thesis a new multiobjective genetic algorithm is pro-
posed and applied to support the design of a hydraulic actuation system. The outcome
from such a multiobjective optimization is a set of Pareto optimal solutions that visual-
ize the trade-off between the competing objectives. The proposed method is capable of
handling a mix of continuous design variables and discrete selections of individual
components from catalogs or databases.
In real-world situations, system parameters will always include variations to some
extent, and this fact is likely to influence the performance of the system. Therefore we
need to answer not only the question “What is best?”, but also “What is sufficiently
robust?” Within this thesis, several approaches to handle these two different questions
are presented.
Acknowledgments
Nog finns det mål och mening med vår färd -
med det är resan som är mödan värd.
Karin Boye, ’I rörelse’.
T
HERE ARE SEVERAL people who have in one way or another made this thesis
possible, and to whom I whish to express my gratitude. First, I would like to thank asso-
ciate Professor Petter Krus for his great supervision, support and encouragement during
this work. I would also like to thank Professor Jan-Ove Palmberg, head of division, for
his support and for fruitful discussions during my work to complete this thesis.
My gratitude is extended to all members of the division of Fluid and Mechanical En-
gineering Systems for their help and support. The innumerable discussions, regarding
not only research but everything under the sun have created a stimulating and enjoyable
atmosphere to work in. I would like to express my special gratitude to Jochen Pohl, co-
author of a number of papers in this thesis. Thanks for the many valuable discussions
during the completion of this thesis and for the companionship in traveling the bumpy
road towards the Ph.D. degree.
I would also like to thank my other co-authors: Dr. Katarina Nilsson at CNS Systems
AB (formerly at Saab AB), for her help and support and for being an extraordinary in-
dustrial advisor. Professor Steven Eppinger at Massachusetts Institute of Technology
(MIT), Boston, for introducing me to a new discipline, and for his kind supervision.
During this work, I have had the pleasure to co-operate with Professor David
Wallace at the MIT CADlab, for which I am very grateful. The co-operation has been
very valuable and given birth to many new ideas. I would like to extend the gratitude to
all members of the CADlab and to Dr. Matthew Wall at Oculus Technologies Corpora-
tion for his support while using his GAlib genetic algorithm package.
Founding for this work was provided by the Swedish Foundation for Strategic Re-
search through the ENDREA research program and is gratefully acknowledged.
Last but not least I would like to express the warmest thank you to my family Eva,
Rolf and Anna and to my girlfriend, Kia, for always backing me up and encouraging me
to struggle on.
Linköping in March 2001
Johan Andersson
Bryt upp, bryt upp! Den nya dagen gryr.
Oändligt är vårt stora äventyr.
Karin Boye, ’I rörelse’.
Papers
T
HE FOLLOWING SEVEN papers are appended and will be referred to by their
Roman numerals. The papers are printed in their originally published state except for
changes in format and minor errata.
[I] ANDERSSON J., POHL J. AND EPPINGER S. D., “A Design Process Modeling Ap-
proach Incorporating non-Linear Elements”, in Proceedings of the ASME Design
Theory and Methodology Conference, Atlanta, USA, September 13-16, 1998.
[II] ANDERSSON J., POHL J. AND KRUS P., “Design of Objective Functions for Opti-
mization of Multidomain Systems”, in Proceedings of the ASME Annual Winter
meeting, Fluid Power System and Technology, Anaheim, USA, November 15-
20, 1998.
[III] NILSSON K., ANDERSSON J. AND KRUS P., “Method for Integrated Systems De-
sign – A Study of EHA Systems”, in Proceedings of Recent Advances in Aero-
space Hydraulics, Toulouse, France, November 24-25, 1998.
[IV] ANDERSSON J. AND WALLACE D., “Pareto Optimization Using the Struggle Ge-
netic Crowding Algorithm”, submitted for international publication, 2000.
[V] ANDERSSON J., KRUS P. AND WALLACE D., “Multiobjective Optimization of Hy-
draulic Actuation Systems, in Proceedings of ASME Design Automation Confer-
ence, Baltimore, USA, September 11-13, 2000.
[VI] ANDERSSON J. AND KRUS P., “Multiobjective Optimization of Mixed Variable
Design Problems”, in Proceedings of 1st International Conference on Evolution-
ary Multi Criteria Optimization, Zurich, Switzerland, March 7-9, 2001.
[VII] ANDERSSON J. AND KRUS P., “Metamodel Representations for Robustness As-
sessment in Multiobjective Optimization”, accepted publication in Proceedings
of the 13th International Conference on Engineering Design, ICED 01, Glasgow,
UK August 21-23, 2001.
The following papers are not included in the thesis but constitute an important part of
the background.
[VIII] ANDERSSON J., POHL J. AND KRUS P., “Design of Multi-Domain Systems Using
Optimization”, in Proceedings of NordDesign 98, Stockholm, Sweden, August
26-28, 1998.
[IX] ANDERSSON J., KRUS P. AND NILSSON K., “Optimization as a Support for Selec-
tion and Design of Aircraft Actuation Systems”, in Proceedings of the Seventh
AIAA/USAF/NASA/ISSMO Symposium on Multidisciplinary Analysis and Opti-
mization, St. Louis, USA, September 2-4, 1998.
[X] SVENSON H., ANDERSSON J. AND RYDBERG K.-E., “Modelling of Losses and
Temperature Calculations in Fluid Power Systems”, in Proceedings of the Sixth
Scandinavian International Conference on Fluid Power, Tampere, Finland, May
26-28, 1999.
[XI] ANDERSSON J., KRUS P., NILSSON K. AND STORCK, K., “Modelling and Simula-
tion of Heat Generation in Electro-Hydrostatic Actuation Systems”, in Proceed-
ings of the 4:th JHPS International Symposium on Fluid Power, Tokyo, Japan,
November 15-17, 1999.
[XII] PERSSON P., KAMMERLIND P., BERGMAN B. AND ANDERSSON J., “A Methodol-
ogy for Multi-Characteristic System Improvement with Active Expert Involve-
ment”, Quality and Reliability Engineering International, vol. 16, 2000, pp. 405-
416.
[XIII] ANDERSSON J., “A Survey of Multiobjective Optimization in Engineering De-
sign”, Technical report LiTH-IKP-R-1097, Department of Mechanical Engi-
neering, Linköping University, Linköping, Sweden, 2000.
Description:crease. Therefore, the applications for numerical optimization have increased
dramati- cally. optimization techniques in engineering design. The first aim is
to
