Moving finite elements and dynamic vehicle interaction

Elastic “shock” waves emanating from the wheel-rail interface of a train running at a speed close to one of the propagation velocities of the soil may cause great amounts of nuisances to the population. An integrated rigid body – FEM model has been created in order to advance the understanding of these effects and predict the effects of different countermeasures. Usage of a fixed mesh includes more elements than necessary for an accurate solution and limits the analysis to a rather short distance.This paper replaces a large fixed mesh with a smaller mobile grid. A special algorithm has been developed to ensure that the nodes are translated with the same speed as the passing vehicle. The values of fields are updated through an interpolation procedure.Results indicate that a size of about 15 m in front of and behind the wheel-rail interfaces is enough to ensure the same results as the fixed mesh in a fraction of the time. The initial transient phase is followed by a relatively constant wave pattern being transported underneath the train. Waves are shown to be greatly magnified if the speed of the system exceeds the Rayleigh velocity of the top layer of crust.