| Summary: | A time domain wheel/rail interaction model in the vertical direction is developed taking account of surface defects. This model consists of a wheel moving over a finite element track model with a detailed non-Hertzian contact model. This numerical non-Hertzian contact model is either used for roughness pre-processing or is directly applied in combination with dynamic interaction calculations at each time step as the wheel moves along the rail. A non-reflecting boundary condition for the finite length track model is developed using a damped tapered tip. It is shown that the modal size of the track model is reduced by applying this damped tapered tip compared to traditional boundary conditions. The time domain wheel/rail interaction model is validated against field measurements from SNCF, in terms of rolling and impact noise predictions. Detailed roughness profiles are considered as the excitation by employing the non-Hertzian contact model. A big improvement is achieved at high frequencies in terms of rail vibration prediction, compared to a Hertzian contact model in combination with pre-processed roughness, by directly applying the non-Hertzian contact model for a wheelflat impact. The characteristics of the impact vibration due to a wheel flat are studied using a simple mass-spring representation of the track system. The frequency domain characteristics of the coupled system, assuming a linear contact spring, are found to be well related to the features of time domain simulations with a nonlinear spring due to the fact that a wheel flat irregularity has a relatively flat spectrum of the roughness. It is shown that the rail acts as a dynamic absorber during impact and the peak impact force is at its minimum when the rail absorbing effect is maximised. The predictions of rolling vibration are in deviations from the measurements. The possible errors are studied and suggesting these might be due to operational error of rail roughness measurements.
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