Dynamic performance of heavy-haul combined train applying emergency braking on straight line

A heavy-haul train-track coupled model is developed. Taking the emergency braking of the 2×104 t combined train as example, the train longitudinal impulse, the coupler dynamic behaviors and wheel-rail interactions of vehicles distributing in the different positions are analyzed. The results indicate that under the coupler compressing forces, the couplers of middle locomotives may tilt to the free swing limits, which induces the unidirectional tilt of their connected wagon couplers. Consequently, the coupler longitudinal forces produce the lateral components, and then affect the wheel-rail dynamic interaction. The performance of the middle locomotive and their neighboring freight wagons deteriorate significantly, becoming the most dangerous parts in the combined train. The wagons disconnecting with the locomotives can basically keep their couplers to stabilize in the centering positions, even though the maximum coupler longitudinal force acts on it. And its corresponding running safety also has little changes.

Vibration response analysis of floating slab track supported by nonlinear quasi-zero-stiffness vibration isolators

To improve the low-frequency vibration reduction effect of a steel spring floating slab track(FST),nonlinear quasizero-stiffness(QZS)vibration isolators composed of positive stiffness elements(PSEs)and negative stiffness elements(NSEs)were used to support the FST.First,considering the mechanical characteristics of the nonlinear QZS vibration isolators and the dynamic displacement limit(3 mm)of the FST,the feasible parameter groups were studied with the nonlinear stiffness variation range and bearing capacity as evaluation indices.A vertical vehicle quasi-zero-stiffness floating slab track(QZS-FST)coupled dynamic model was then established.To obtain a reasonable nonlinear stiffness within a few millimeters,the original length of the NSEs must be analyzed first,because it chiefly determines the stiffness nonlinearity level.The compression length of the NSEs at the equilibrium position must be determined to obtain the low stiffness of the floating slab without vehicle load.Meanwhile,to meet the dynamic displacement limit of the FST,the PSE stiffness must be increased to obtain a higher stiffness at the critical dynamic displacement.Various stiffness groups for the PSEs and NSEs can provide the same dynamic bearing capacity and yet have a significantly different vibration reduction effect.Excessive stiffness nonlinearity levels cannot effectively improve the vibration reduction effect at the natural frequency.Furthermore,they also significantly amplify the vibrations above the natural frequency.In this paper,the vertical vibration acceleration level(VAL)of the floating slab and the supporting force of the FST can be decreased by 6.9 dB and 55%,respectively,at the resonance frequency.