Keywords: high-speed electric multiple unit, swaying phenomenon, dynamic simulation.

This paper studies the small-amplitude and low-frequency swaying phenomenon of the high-speed electric multiple unit (EMU) in China. The intrinsic relationship of the swaying phenomenon on the line, is analysed in the paper. The swaying phenomenon is reproduced on the roller rig. The frequency of swaying is about 2 4Hz. On some trains, the car-body and the bogie have the same simultaneous, lateral, low-frequency harmonic vibration. However, some car-bodies are static while the bogie is hunting. The test results show that the running safety of the vehicle is not a problem.

The non-linear dynamic simulation model of both motor car and trailer car, were set up based on rigid multi-body system dynamics. The Maxwell model of yaw damper has been corrected by test results. The corrected model characterizes the dynamic properties of the yaw damper, with errors not exceeding 10%. The hunting bifurcations of simulated results and rig test results have been compared. The accuracy of the simulation model has been proven.

On the one hand, low-frequency hunting is advantageous, because severe hunting is less likely to occur under high speed or high equivalent conicity, so the operation safety is better. On the other hand, we should try to improve the speed of the swaying that occurs, or to minimize the swaying amplitude. The swaying occurs over a broad range of running speed, but the severe hunting does not appear when the speed is lower than 500km/h.

Simulation analysis shows that the impact on the ride index is not great, but the passengers are prone to feelings of motion sickness. The influence of the dynamic safety is also small. The wheelset lateral force and the derailment coefficient are far below the limit value, according to relative standards. The hunting frequency should be well designed to avoid severe swaying. For example, for the vehicle researched in this paper, the hunting frequency should be greater than 3Hz when the speed is higher than 250km/h.

The equivalent conicity, the primary longitudinal stiffness, and the parameters of the yaw damper, have a significant impact on the swaying phenomenon. It is important to establish an accurate dynamic model for yaw dampers in the numerical simulation, so that the simulation results will be more consistent with the experimental results.

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