High-speed tracked vehicle model order reduction for static and dynamic simulations

In this paper, a model order reduction strategy is adopted for the static and dynamic behaviour simulation of a high-speed tracked vehicle. The total number of degree of freedom of the structure is condensed through a selection of interface degrees of freedom and significant global mode shapes, for an approximated description of vehicle dynamic behaviour. The methodology is implemented in a customised open-source software to reduce the computational efforts. The modelled tracked vehicle includes the sprung mass, the unsprung masses, connected by means of torsional bars, and all the track assemblies, composing the track chain. The proposed research activity presents a comprehensive investigation of the influence of the track chain, combined with longitudinal vehicle speed, on statics and vehicle dynamics, focusing on vertical dynamics. The vehicle response has been investigated both in frequency and time domain. In this last case road-wheel displacements are assumed as inputs for the model, under different working conditions, hence considering several road profiles with different amplitudes and characteristic excitation frequencies. Simulation results have proven a high fidelity in model order reduction approach and a significant contribution of the track chain in the global dynamic behaviour of the tracked vehicle.

Influence and Control Strategy for Local Settlement for High-Speed Railway Infrastructure

This paper discusses the main impact factors of the local settlement and differential settlement of high- speed railway lines. The analysis results show that groundwater exploitation is the direct cause of differ- ential settlement. Based on the study of ballastless track additional load and of vehicle, track, and bridge dynamic responses under different differential settlements, a control standard of differential settlement during operation is proposed preliminarily.

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.