Multi-objective optimization of railway bogie suspension damping

Licentiate thesis, 2011

In this thesis multi-objective optimization is used to find Pareto fronts showing the set of optimized damping parameters of primary and secondary bogie suspensions. Special interests are put on requirements to enhance safety and comfort of a railway vehicle. A complete multibody system model of a railway vehicle as well as a reduced linearized model describing the bogie system are used for studying the dynamics. Objectives of performance for safety, ride quality and wear are introduced and utilized in the optimizations. The use of several objectives leads to the formulation of a multi-objective optimization problem. The optimization problem is solved using an evolutionary algorithm and the obtained solutions have been analyzed for several cases and considerations. The results are presented in terms of Pareto fronts (trade–off curves in the performance objective space) as well as Pareto sets (trade–off curves in the design parameter space). These trade–off curves are of importance for design of suspension damping functional components, in that they provide valuable information for choosing the optimal setting. The optimization results obtained are compared to and found to be in the neighborhood of parameters used in a vehicle in service. This illustrates the feasibility of the multi-objective optimizations done in this thesis. It is shown that the damping characteristics of bogie primary and secondary suspensions have significant impact on the dynamical behavior of the railway vehicle. Sensitivity analyzes show the dependency of the safety–comfort Pareto front with respect to forward speed, and that the quality of the wheel and the rail profiles has a large impact on the railway vehicle dynamics. Moreover, it is found that the use of conventional bogie suspensions with optimized damping parameters can allow for higher service speeds of railway vehicles. Further exploitation of the multi-objective optimization results involves applications of adaptive control strategies of bogie primary and secondary suspension dampings. Such strategies for switching damping parameters of the bogie suspension with respect to different ride conditions are outlined and discussed.