Time-domain modelling of curve squeal: a fast model for one- and two-point wheel/rail contact

Doktorsavhandling, 2017

Curve squeal is a type of railway noise that may arise when a railway vehicle negotiates a relatively tight curve. A single frequency, corresponding to a wheel mode, dominates the radiated sound, which makes squeal a very tonal noise. The high number of tight curves in cities and urban areas, its tonal nature and high noise levels make squeal a significant source of noise pollution. The rising awareness of the impact of noise on public health increases the need to address the squeal problem. Consequently, there is an increased need for practical simulation tools. In this thesis, a computationally fast squeal model formulated in the time domain is proposed. The computational efficiency is achieved by modelling the tangential contact with a point-contact model, which considers the contact variables globally. The friction model and the contact compliance are defined in a rigorous manner using Kalker's variational theory. Validation results show that the contact model is valid up to at least 5 kHz. The proposed model is further extended to include the effects of spin creepage, contact angle and two-point wheel/rail contact. Spin creepage is treated as a contact property with its influence included in the friction model. Additionally, the model is also extended with an existing model for sound radiation from the railway wheel. Parameter studies show a strong influence of parameters that influence the dynamics coupling responsible for squeal: the contact angle, friction and the wheel/rail contact position. These parameters influence both squeal occurrence, amplitudes and frequency. Spin, however, influences only squeal amplitudes. With the wheel being a significant factor in curve squeal, the influence of the wheel modal damping is also investigated. To mitigate squeal in a specific case, all modes that are susceptible to squeal in that case have to be damped. Otherwise, squeal may shift to another mode and develop even higher amplitudes. The amount of modal damping required to prevent squeal is relatively low. Finally, a two-point wheel/rail contact case is analysed. Results show that squeal can occur on curve-outer wheels. The two-point-contact case is relatively complicated: squeal is the result of a combination of the dynamic interplay of the two contact points and the presence of two closely spaced wheel modes.