Keywords: vehicle-track interaction, flexible wheelset, flexible track, non-elliptic wheel-rail contact, structural dynamics, high-frequency behaviour, hunting.

Today, the modelling of railway vehicles as multi-body systems is the established standard method for the simulation of the running behaviour. In most cases, rigid bodies are used, but the modelling can be extended to a flexible multi-body system, taking the structural dynamics of certain bodies into account. Usually, the deformations are described by a modal synthesis, i.e. by a superposition of shape functions. While the extension of the multi-body method to flexible bodies is comparatively simple for the carbody or the bogie frame, the modelling of flexible wheelsets and flexible track structures is more difficult: Because the contact forces move around the wheels and the rails resulting from the overturning motion of the wheelset and its motion along the track, the shape functions used in the modal synthesis depend on time. Also, the large dimension of the track compared to the vehicle can be a problem.

To enable simpler handling of the modelling, semi-analytical solutions exploiting symmetries of the structures are used. The wheelset and the track can be considered as cyclic structures, therefore the shape functions describing their deformations can be expressed using trigonometric functions, avoiding piecewise interpolation. This also enables their integration into a commercially available multi-body simulation program.

Despite the enhanced methods, the integration of a flexible wheelset and a flexible track structure still requires greater effort than for the case of a flexible car body or bogie frame. Therefore, the question arises, which influences the flexibilities of the wheelset and the track affect the behaviour of the entire vehicle-track system.

Simulation results show that the structural dynamics of the wheelset and of the track have a distinct impact on the vehicle's running behaviour. Comparisons show that the flexibility of both elements influence the motions significantly. Therefore, an enhanced vehicle-track model should include flexible wheelsets as well as a flexible track. Together with a contact model, which calculates the pressure and tangential stresses in the wheel-rail contact, this forms a powerful tool for the investigation of phenomena related to higher frequencies such as noise and wear.

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