Analysis on abnormal low-frequency vertical vibration of medium–low-speed maglev vehicle.

A newly-developed medium–low-speed maglev test vehicle was used to obtain the vertical dynamic response signals of the vehicle-line coupled system when the test vehicle was standing still on four different types of lines through field tests. It was found that abnormal low-frequency vertical vibration occurred on the car body, so that an excellent ride index of the test vehicle cannot be ensured. As the stability of the vehicle at standstill is the prerequisite to the stability of the vehicle running at a certain speed, it is necessary to investigate the causes underlying the abnormal vibration and propose corrective measures through theoretical studies in combination with the measured results. Therefore, this paper established a coupled vehicle-track system dynamics model considering active feedback control, and investigated the stability and bifurcation behavior of the coupled system through nonlinear dynamics theory and numerical simulation. Field test results show that: the vertical ride index of the test vehicle was rated as "Unqualified" when it was standing still; the vertical vibration eigenfrequency of the car body is basically the same (between 2.10 and 2.20 Hz) when the test vehicle was standing still on the four different lines, indicating that the abnormal vibration was basically independent of the line type; the vertical dynamic response of each measurement point on the electromagnet, F-rail and bridge was normal. The theoretical and simulation studies show that: the numerical simulation of the theoretical model can effectively reproduce the abnormal vibration; the malfunction in the nonlinear characteristics of the air spring vertical damping (i.e. the damping malfunction) is the main reason for this vibration, and the abnormal vibration corresponded to the supercritical Hopf bifurcation dynamics behavior in nonlinear dynamics; after the air spring was restored to normal, the equilibrium point of the coupled system was stable under the influence of different initial disturbances. This study may provide an important reference for reducing the abnormal low-frequency vertical vibration of the test vehicle at standstill. [ABSTRACT FROM AUTHOR]