Shimmy mechanics and nonlinear vibration characteristics of monorail vehicle

This study investigates the nonlinear vibration characteristics of a monorail vehicle equipped with tires. A 3-degree-of-freedom dynamic model of the monorail vehicle's bogie was first established. Numerical simulations identified a limit cycle in the system, manifesting as shimmy vibration in the bogie's yaw, coupled with roll motion. The trajectory equations of the limit cycle were derived, and its occurrence conditions and system equilibrium points were analyzed. The influence of key bogie parameters on the limit cycle was also examined to offer design guidance for its suppression. Additionally, the nonlinear vibration characteristics of the bogie, considering clearances between the guide wheel, stabilizing wheel, and track, revealed the presence of two limit cycles along with quasi-periodic and chaotic vibrations under boundary disturbances. Finally, it was shown that increasing yaw damping by increasing the longitudinal span of secondary lateral damper of bogie effectively suppresses self-excited vibrations and improves ride quality.