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Multiobjective Optimization for Safety and Reliability Trade-off: Applications on Early Phases of Aircraft Systems Design
Linköping University, Department of Management and Engineering, Machine Design. Linköping University, Faculty of Science & Engineering.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A strategic issue for any industrial company is to conceive safe and reliable systems while performing all systems’ intended functions at a minimum cost. System safety and reliability are fundamental to system design and involve a quantitative assessment prior to system development. Aircraft design is a multifaceted process that involves several different disciplines, system safety and reliability among them, to obtain o holistic approach of a complex product. During the last decades, the idea of trade-off between safety or reliability goals against other characteristics has become more prominent. Furthermore, while predictions of system performance can be made in early design phases with credible precision, within reasonable tolerances, reliability and system safety are seldom predicted with high accuracy and confidence. Making the right design decisions in the early design phase is vital to the success of a project. Nowadays, it is essential within the design of new products, to increase awareness (knowledge) early in the design phases and keep the design decisions (freedom) open as long as possible, and with that also keep down the allocated costs.

This thesis presents MOSART (Multiobjective Optimization for Safety and Reliability Trade-off), a method promoting a systematic approach regarding trade-offs between system safety and reliability goals against other contradictory targets, such as weight and cost, in early design phases.

A theoretical framework and context are presented in the first part of the thesis, including system safety and reliability methods and optimization techniques. The second and third parts are dedicated to contributions and papers, where seven papers are included. These papers approach different aspects of MOSART, from the basic idea to the implementation and usage of the method in the conceptual phase of aircraft systems design. Several aspects regarding the choice of system safety and reliability methods in early design phases are also included in the papers, e.g. evaluation of applicability of reliability methods in early design phases, considerations around the usage of these methods within the MOSART framework and a proposal of a guideline for how to choose the right reliability method. All the examples used in the papers are chosen from basic aircraft sub-systems.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. , 89 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1833
National Category
Production Engineering, Human Work Science and Ergonomics Embedded Systems Other Engineering and Technologies not elsewhere specified Computer Systems Design
Identifiers
URN: urn:nbn:se:liu:diva-134592ISBN: 9789176855768 (print)OAI: oai:DiVA.org:liu-134592DiVA: diva2:1075469
Public defence
2017-03-23, C3, C-huset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Funder
VINNOVA
Note

The research project has been financed by the researchprogrammes NFFP5 2009-01316 and NFFP6 2013-01223 funded by Saab Aeronautics and theNational Aviation Engineering Research Program (NFFP), jointly driven by the Swedish ArmedForces, the Swedish Defence Materiel Administration (FMV),

Available from: 2017-02-20 Created: 2017-02-20 Last updated: 2017-02-20Bibliographically approved
List of papers
1. On the Usage of Reliability Methods in Early Design Phases
Open this publication in new window or tab >>On the Usage of Reliability Methods in Early Design Phases
2012 (English)In: Proceedings of the 11th International Probabilistic Safety Assessment and Management Conference and the Annual European Safety and Reliability Conference 2012 (PSAM11 ESREL 2012), Curran Associates, Inc., 2012, 769-778 p.Conference paper (Refereed)
Abstract [en]

One important challenge in the early phases of product development is to apply reliability methods for estimating the safety and reliability of the system when information about the chosen equipment and components is limited. For systems consisting of units with several degraded states, and not only “up” and “down”, the results from reliability and system safety analysis are often difficult to interpret and use. The main contribution of this paper is to evaluate the applicability of different reliability methods for analyzing an overall system concept in early development stages. Furthermore, the paper constitutes the first step of a methodology intended to address the issues outlined above from a practical point of view. In the paper, two static methods, Reliability Block Diagram and Fault Tree Analysis, and one dynamic method, Markov Analysis, have been applied to conceptual design of an aircraft electrical system. These three methods have been evaluated regarding usefulness, modeling possibilities and applicability in the conceptual design. Each method is, from a practical point of view, dependent on the limitations of the software that is used. In order to overcome this issue the calculations and partly the modeling have been performed in three different software tools.

Two iterations have been performed for Markov Analysis, and the results are used to evaluate the method regarding applicability and possibilities of modeling the system and to find out what results can be gained by extending the model.

Place, publisher, year, edition, pages
Curran Associates, Inc., 2012
Keyword
System Reliability, Markov Analysis, Reliability Block Diagram, Fault Tree
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-94350 (URN)978-1-62276-436-5 (ISBN)
Conference
11th International Probabilistic Safety Assessment and Management Conference and the Annual European Safety and Reliability Conference 2012 (PSAM11 ESREL 2012), 25-29 June, Helsinki, Finland
Available from: 2013-06-25 Created: 2013-06-25 Last updated: 2017-02-20Bibliographically approved
2. Choosing the reliability approach: A guideline for selecting the appropriate reliability method in the design process
Open this publication in new window or tab >>Choosing the reliability approach: A guideline for selecting the appropriate reliability method in the design process
2013 (English)In: Proceedings of the 20th Advances in Risk and Reliability Technology Symposium 21–23 May 2013 / [ed] Lisa Jackson and John Andrews, Loughborough: Loughborough University, UK , 2013, 366-378 p.Conference paper (Other academic)
Abstract [en]

The main objective of a reliability study should always be to provide information as a basis for decisions, e.g. concept choice, design requirements, investment, choice of suppliers, design changes or guaranty claims. The choice of reliability method depends on the time allocated for the reliability study, the design stage, the problem at hand and the competence and resources available.

During a reliability study the engineer focuses on providing a graphical means of evaluating the relationships between different parts of the system, gathering or assessing the reliability data for the components and interpreting the results of the analyses. Even though the commercial software tools available claim to provide answers to most reliability questions, choosing which method is best suited is not an easy task. Often several methods can be applied and none of them will fit the purpose perfectly.

This paper presents a guideline for choosing the best suited reliability method in early design phases from two aspects: objective and system characteristics. The methods studied are the most common methods available in commercial software tools: Reliability Block Diagram (RBD), Fault Tree (FT), Event Tree (ET), Markov Analysis (MA) and Stochastic Petri Network (SPN). The guideline considers two aspects: the characteristics of the system studied and the scope of the analysis. The applicability of each of the five chosen methods is assessed for all possible combinations of system characteristics and objective. A study has been made at Saab Aeronautics to evaluate the practical use of the analysed methods and how this guideline can improve the selection of appropriate reliability methods in early design phases.

Place, publisher, year, edition, pages
Loughborough: Loughborough University, UK, 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-94352 (URN)9781907382611 (ISBN)
Conference
The 20th Advances in Risk and Reliability Technology Symposium, 21st – 23rd May 2013, Burleigh Court Conference Centre, Loughborough, Leicestershire, UK
Available from: 2013-06-25 Created: 2013-06-25 Last updated: 2017-02-20Bibliographically approved
3. Cost optimization with focus on reliability and system safety
Open this publication in new window or tab >>Cost optimization with focus on reliability and system safety
2013 (English)In: Safety, Reliability and Risk AnalysisBeyond the Horizon / [ed] R. D. J. M. Steenbergen , P. H. A. J. M. van Gelder , S. Miraglia and A. C. W. M. Ton. Vrouwenvelder, CRC Press, 2013, 2723-2730 p.Conference paper (Refereed)
Abstract [en]

When developing a safety critical system, there are many aspects that need to be balanced against each other in order to reach an optimal design such as safety requirements, reliability goal, performance specifications and budget constraints. In an early design stage, it is vital to be able to screen the design space for a set of promising design alternatives for further studies. This paper proposes an approach capable of investigating the trade-offs described above, combining the techniques for system safety and reliability analysis with optimization methods. Markov analysis is employed for modeling the system safety and reliability characteristics and a Genetic Algorithm is used for optimization. The proposed method is applied to the design of an electric supply system for an aircraft, involving selection of components from different suppliers. First a model is built for each objective, i.e. cost, safety, and reliability. The models are validated and optimization is performed. The obtained result is the selection of suppliers for each component in the system in order to achieve a balance between system safety, reliability, and other design objectives.

Place, publisher, year, edition, pages
CRC Press, 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-94353 (URN)10.1201/b15938-413 (DOI)9781138001237 (ISBN)9781315815596 (ISBN)
Conference
ESREL2013, 29 Sep-02 October, Amsterdam, Holland
Available from: 2013-06-25 Created: 2013-06-25 Last updated: 2017-02-20Bibliographically approved
4. An Industrial Implementation of an Optimization Based Method for Balancing Safety, Reliability and Weight of Aircraft Systems
Open this publication in new window or tab >>An Industrial Implementation of an Optimization Based Method for Balancing Safety, Reliability and Weight of Aircraft Systems
Show others...
2016 (English)In: Risk, Reliability and Safety: Innovating Theory and Practice: Proceedings of ESREL 2016 (Glasgow, Scotland, 25-29 September 2016) / [ed] Lesley Walls, Matthew Revie and Tim Bedford, CRC Press, 2016, 1707-1713 p.Conference paper (Refereed)
Abstract [en]

The aim of this paper is to show how a method able of trade-offs such as system safety, reliability, weight and cost can be practically implemented in industry (SAAB Aeronautics). The scope is to facilitate the decision-making on the optimal design in early design phases. The method consists of several steps guiding the user to model each objective, verify and validate the models, perform optimization and finally visualize and select the results. Within the practical implementation of this method, several challenges are addressed and solved. For example, one challenge is to implement the trade-off method using the existing programs. Another challenge is the user friendliness of the implementation. In order to solve these challenges, the analysis is started and performed in Matlab. A Graphical User Interface guides the user to select the analysis to perform, budgets/requirements for each objective and parameters with influence on end-result. Data regarding the safety and reliability objectives, exported from Reliability Workbench program to Excel, is imported to Matlab, where the analysis is performed. The results are extracted into an Excel file, where the user can work further on visualization and selection. Two small examples are used to demonstrate this practical implementation of the trade-off method. Lessons learned are presented, strengths, limitations and development potential.

Place, publisher, year, edition, pages
CRC Press, 2016
National Category
Computer Systems Embedded Systems Software Engineering
Identifiers
urn:nbn:se:liu:diva-134590 (URN)9781138029972 (ISBN)9781315374987 (ISBN)
Conference
ESREL 2016, Glasgow, Scotland, 25-29 September 2016
Available from: 2017-02-20 Created: 2017-02-20 Last updated: 2017-02-20Bibliographically approved
5. How to use an Optimization-based Method Capable of Balancing Safety, Reliability, and Weight in an Aircraft Design Process
Open this publication in new window or tab >>How to use an Optimization-based Method Capable of Balancing Safety, Reliability, and Weight in an Aircraft Design Process
2017 (English)In: Nuclear engineering and technology : an international journal of the Korean Nuclear Society, ISSN 1738-5733, E-ISSN 2234-358XArticle in journal (Refereed) Epub ahead of print
Abstract [en]

In order to help decision-makers in the early design phase to improve and make more cost-efficient system safety and reliability baselines of aircraft design concepts, a method (Multi-objective Optimization for Safety and Reliability Trade-off) that is able to handle trade-offs such as system safety, system reliability, and other characteristics, for instance weight and cost, is used. Multi-objective Optimization for Safety and Reliability Trade-off has been developed and implemented at SAAB Aeronautics. The aim of this paper is to demonstrate how the implemented method might work to aid the selection of optimal design alternatives. The method is a three-step method: step 1 involves the modelling of each considered target, step 2 is optimization, and step 3 is the visualization and selection of results (results processing). The analysis is performed within Architecture Design and Preliminary Design steps, according to the company’s Product Development Process. The lessons learned regarding the use of the implemented trade-off method in the three cases are presented. The results are a handful of solutions, a basis to aid in the selection of a design alternative. While the implementation of the trade-off method is performed for companies, there is nothing to prevent adapting this method, with minimal modifications, for use in other industrial applications.

Keyword
Aircraft Design, Early Design Phases, MOSART, Safety, Reliability, Trade-off
National Category
Production Engineering, Human Work Science and Ergonomics Embedded Systems Computer Science Computer Systems Reliability and Maintenance
Identifiers
urn:nbn:se:liu:diva-134591 (URN)10.1016/j.net.2017.01.006 (DOI)
Available from: 2017-02-20 Created: 2017-02-20 Last updated: 2017-03-12Bibliographically approved

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Output format
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