Multiobjective Optimization for Safety and Reliability Trade-off : Applications on Early Phases of Aircraft Systems Design

Sammanfattning: 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.