Hybrid Simulation of the Nonlinear Dynamics of High Speed Railway Vehicles

The computation of railway dynamics on an irregular track leads to strongly nonlinear equations, which are solved in the time domain by means of a hybrid computer Yet the modelling of a single wheel is very complex, due to the nonlinear shape of the profiles and due to nonlinear saturation effects of the creep forces in the contact area. Without developping new simulation techniques, the analog simulation of a whole vehicle (with eight wheels) would require an excessive amount of computing-components. This problem is successfully solved by modelling the characteristics of only one wheel on the analog computer, and using it for the dynamic simulation like a subroutine call in a digital program. Two bogies with a total of four independent wheelsets are simulated by using a multiplexing technique, based on the logical circuitry of the analog computer.A digital computer is interfaced to the analog machine in order to vary constructive parameters, to output the track irregularities, and to digitize forces and essential state variables during the process of simulation. These data are used for the evaluation of quality criteria (such as ride quality, lateral force level, wear characteristics) and as input for an optimization algorithm.