# Constrained optimization of rotor-bearing systems by evolutionary algorithms

Sammanfattning: In the design of mechanical components and systems, nature has often been the source of inspiration. It is easy to point out solutions in nature that are optimal in some sense. One example is the structure of the surface of a shark's skin. This is designed by nature to minimize the resistance when the shark swims in the water. Another example is the shape of an egg shell. This is an optimal load carrying structure that often is found in engineering design applications. An even more fascinating question is how nature has found these optimal solutions? The answer to this question is evolution. Instead of just analyzing and copy optimal structures invented by nature it seems reasonable to mimic the process how nature has come up with these solutions. Research on how these ideas can be interpreted and used in engineering design started in the early seventies and has now become a large field known as Evolutionary Algorithms (EAs). During the past decade these methods have emerged as potent tools for engineering design optimization. Some of these methods are especially suited for problems that involve multiple objectives such as almost all real engineering design problems. Just until recently, these methods have seldom been used in the area of rotordynamical design. This thesis deals with the question how these methods can be adapted and applied in order to improve the design and design process of large rotor-bearing system. A hypothesis for this work is that EAs are suitable to use in the late design process of these systems. The aim of this work is to evaluate this hypothesis by studying real applications found in industry. This thesis comprises an introductory part and four appended papers. The introductory part is divided into three different sections. In the first section the concept of engineering design optimization is introduced. In the second part Genetic Algorithms (GAs) is presented. Finally, the analysis and design of rotor-bearing systems is discussed in more general terms. The purpose with the introductory part is to introduce and prepare the reader to the concepts discussed in the papers. The introductory part may serve as a survey or start point for newcomers interested in these areas. This overview is also the most important contribution of the introductory part of the thesis. The appended papers cover selected problems of constrained rotor- bearing system optimizations. In the papers A the multiobjective optimization of a generator is presented and discussed. Paper B introduces a constraint handling technique based on concepts found in multiobjective GAs. In paper C and D this techniques is used for two different rotor-bearing system optimization problems where the actual geometry parameters of the bearings are used as design variables.

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