Parametric and self-excited oscillation produced in railway wheelset due to mass imbalance and large wheel tread angle.

Railway vehicle wheelsets experience hunting motion when the running speed exceeds a critical value. While it is well known that hunting motion is a self-excited oscillation due to a nonconservative contact force acting between the rail and wheel, this study investigates another type of parametric resonance also caused by wheelset mass imbalance in cases of large tread angle. Because the critical speed of the self-excited oscillation decreases or large tread angles, it can be induced simultaneously with parametric resonance. Focusing on such situations, we theoretically and experimentally clarify the following wheelset nonlinear dynamics, which depend on the running speed. The wheelset is first destabilized through a pitchfork bifurcation and undergoes parametric resonance with a stable nontrivial steady-state amplitude. As the running speed increases, the stable steady-state amplitude is destabilized through a subcritical Hopf bifurcation by a nonconservative contact force effect related to the self-excitation. In addition to a constant amplitude oscillation, it is theoretically indicated that an oscillation with a beating amplitude can be produced in the neighborhood of the Hopf bifurcation point, depending on the disturbance magnitude. A simple apparatus with a roller rig has experimentally confirmed these nonlinear phenomena that depend on the running speed and the disturbance. [ABSTRACT FROM AUTHOR]