Stability assessment of railway vehicles considering undefined nonlinearity in static force-velocity characteristics of hydraulic yaw dampers

Yaw dampers are usually tuned according to the nominal static force-velocity (F-V) characteristics specified by the vehicle manufacturer. However, in the low-speed region, the static F-V curve often varies significantly among damper suppliers due to a lack of standardised specifications. This variability underscores the necessity of accounting for nonlinearities in the analysis and understanding their relationship with the dynamic behaviour of yaw dampers and their impact on overall vehicle stability. To address these issues, we developed and validated a simplified physical damper model that incorporates these undefined nonlinearities through rig testing. Using this model, simulations were performed to investigate how these nonlinearities affect dynamic damper characteristics and vehicle stability. Our findings indicate that undefined nonlinearities in the low-speed region of the static F-V curve significantly influence the dynamic stiffness and damping of yaw dampers, particularly at small amplitudes and low frequencies. These effects have a pronounced impact on carbody stability in conditions with low wheel-rail conicity and significantly affect passenger's comfort. The insights gained from this study offer valuable implications for the design, optimisation and standardisation of yaw dampers in high-speed trains.