Design of rail vehicles with passive and active suspensions using multidisciplinary optimization, multibody dynamics, and genetic algorithms

A methodology for the design optimization of rail vehicles with passive and active suspensions is presented. The methodology has the following features: (1) multibody dynamics is used for modelling and simulating complex realistic vehicle systems; (2) multidisciplinary optimization (MDO) methods are introduced to make coupled vehicle models and additional control systems a synergistic whole; (3) with genetic algorithms (GAs) and other effective search algorithms, the mechanical and control design variables can be optimized simultaneously; (4) with the scalarization technique, a vector optimization problem is converted into a scalar optimization problem. The proposed methodology is applied to several design optimization problems. First, a rail vehicle is optimized with respect to lateral stability. Second, the rail vehicle is designed so that ride quality is the sole design criterion. Third, the design variables are searched in the feasible design space so as to make the rail vehicle have optimal curving performance. Then, the rail vehicle is optimally designed for obtaining trade-off solutions among conflicting requirements from lateral stability, ride quality, and curving performance. Finally, the methodology is used to optimize the combined mechanical and control systems for vehicles with active suspensions. Of the results obtained, several of them contribute to the fields of rail vehicle dynamics and design, mechatronic systems, and numerical optimization.; For automatically identifying the “critical speed” (above which a rail vehicle's response becomes unstable), a new approach combining sequential quadratic programming (SQP) with the Dynamic Mode Tracking (DMT) technique is proposed and developed. The new approach is compared with that using SQP alone. It is found that without DMT, several more SQP runs are often needed to find the critical speed because the relationship between mode damping and speed deviate from their actual shapes. In the process of optimizing the lateral stability of a rail vehicle model, the existence of sharply-discontinuous “cliffs” in the plots of critical speed versus suspension stiffness is identified and originally interpreted. In recognition of the cliff phenomenon, the definition of critical speed is generalized to make it a more practical measure of lateral stability. In the design optimization of a rail vehicle with respect to the lateral stability, vertical ride quality, and curving performance, the resulting Edgeworth-Pareto (EP) optimal sets clearly demonstrated the trade-off relation between lateral stability and curving performance. Moreover, the resulting EP-optimal sets visualize a well-known fact that a relatively weak coupling exists between the vertical and lateral motions of a rail vehicle. (Abstract shortened by UMI.)...