Rotor Dynamics and Irregular Wear of Elastic Wheelsets

Abstract

High-speed trains in Germany often suffer from vibrations of the car body in the so-called medium-frequency range (30-300 Hz), also known as 100 Hz droning noise. The reason of this unpleasant phenomenon is the development of out-of-round wheels. This paper will discuss the influence of initial out-of-roundness of wheels as well as the influence of wheelset unbalances at high speeds on this wear process. Using a modular approach the model of the wheelset based on the method of flexible multibody systems is coupled to the rail with a complex wheel-rail contact module. In order to account for the long-term wear effects on the wheels the mechanical model is extended by a long-term wear model using a wear-feedback loop in a different time scale. The presented results of wear simulations are subsequently used to discuss the influence of initial out-of-roundness and wheelset unbalances at high speeds on the order and magnitude of developing wear patterns. 1 Motivation The introduction of the high speed train Intercity Express (ICE) in Germany (1991) has led to new and sometimes only poorly understood problems due to high speed. One of these new problems was easily noticed by passengers due to its loud and disturbing droning noise. The responsible structural vibrations of the car body were excited by out-of-round wheels, which obviously lost their original round shape under the influence of irregular wear. Consequently the changing wheel profiles were causing accelerated wear such that the wheels had to be reprofiled after reaching a critical limit. The characteristic frequency for the excited vibrations of the car body was in the range of 70-100 Hz, which is in the so-called medium frequency range (30-300 Hz). In order to analyse the rotor dynamics and possible mechanisms for the wear development, an appropriate approach to model flexible bodies in the medium-frequency range has to be selected. Combining the advantages of rigid multi body systems and finite element systems a suitable method is available to account for the first eigenmodes of the wheelset in the questionable frequency range. 2 Flexible Multibody Systems The method of multi body systems using a minimum set of generalized coordinates has proven to be a very suitable and successful method for the analysis K. Popp et al. (eds.), System Dynamics and Long-Term Behaviour of Railway Vehicles, Track and Subgrade