Frequency domain model for railway wheel squeal resulting from unsteady longitudinal creepage

Abstract

Railway wheel squeal is an unresolved noise pandemic facing the railway industry. Wheel squeal results from frictional self-excited vibration occurring in the wheel-rail contact. Solving the problem of squeal requires researchers to work towards a squeal model that can predict squeal wholly and in every situation. This will allow for squeal to be resolved during the design stages. The current research presents a frequency domain model for the excitation of squeal due to longitudinal creepage with rising, constant and falling friction. In this model the time varying part of the longitudinal creep force is modelled as a feedback loop and tested for stability with the Nyquist criterion. Crucial to the instability is modelling the dynamics of a wheel taking into consideration the moving load nature of the rotating wheel. If wheel rotation is accounted for in the model, modes in a doublet can become unstable through mode-coupling in the presence of large longitudinal creepage. The results of the model provide good agreement with that of squeal occurring on-track. Positive flow of energy for the modelled case of squeal results from the dynamic friction and normal forces being in phase with one another as well as the friction force causing normal displacement at the wheel-rail contact that is in phase with the normal displacement that caused the normal force in the first place. This closed phase loop causes positive interference of the normal vibration in the wheel-rail contact and allows the vibration amplitude to grow. Extending the model to include lateral creepage shows that the vibration of the wheel-rail contact can be unstable due to unsteady longitudinal creepage for more directions of the resulting creep force compared to unsteady lateral creepage in a case with constant friction.