Considering the coupling vibration of a flexible carbody and the underneath suspended equipment, a vertical coupled vibration model of a high-speed train was constructed. A roller test rig was conducted to validate the theoretical model. To reduce carbody elastic vibration, the semi-active vibration reduction models based on the Sky-hook and the linear quadratic regulator control strategies were proposed. The semi-active suspension system was installed between the carbody and the suspended equipment, and the influence of the semi-active suspension on carbody vibration reduction was analyzed. The results show that the semi-active suspension can significantly reduce carbody vibration, especially at high operating speeds. The higher the elastic vibration of carbody, the better the vibration reduction effect of the semi-active suspension. Compared with the passive suspension and the semi-active suspension, the semi-active suspension of the Sky-hook control has a relatively wider vibration control range, and has an obvious effect on carbody rigid and elastic vibration reduction. Although the semi-active suspension of the linear quadratic regulator control had little influence on the rigid carbody vibration, it could reduce most of the elastic carbody vibration.

The effect of dynamic unbalance of the underframe suspended rotational equipment on the flexible vibrations of the carbody has become a major concern for high-speed trains. It is known from the field tests that the dynamic unbalance has a significant influence on carbody vibrations, especially the local flexible vibration, which leads to a decrease in the passenger ride comfort and may even cause structural damage to the carbody. A vertical mathematic model considering the carbody flexibility and the underframe suspended equipment is first set up, and then a three-dimensional dynamic model for a rigid–flexible coupled vehicle system is established. The effect mechanism of the dynamic unbalance on carbody flexible vibration is extensively studied, and the efficient measures to reduce the carbody flexible vibrations are proposed. The theoretical and simulation models are verified by comparing with a field test conducted on a newly designed high-speed railway. The results show that decreasing the unbalanced mass of the rotational equipment can reduce the carbody vibrations. Moreover, the use of elastic suspension for the underframe equipment can isolate the vibration transmission to the carbody. Both the theory of dynamic vibration absorber and dynamic unbalance should be considered to optimize reasonable suspension parameters, especially the suspension location and the suspension frequency.

Low-frequency carbody swaying on China’s high-speed trains is not only an impediment to ride comfort but it may also be an operational risk under some extreme situations. To study the mechanism and mitigate the carbody swaying problem for high-speed trains, a multibody dynamics model was established based on both linear and nonlinear analyses. Whilst it is generally assumed that carbody swaying is predominantly caused by carbody hunting motion, the results in this paper has shown that, under certain boundary conditions, bogie-hunting motion can also lead to low-frequency carbody swaying. This low-frequency swaying phenomenon was also found to be caused by the excessively low wheel-rail contact or mismatched suspension parameters. Parametric optimization analysis was accordingly conducted from the perspective of the wheel-rail contact relationship and the suspension system. The analysis indicated that although optimizing the suspension parameters can meet the requirement of vehicle stability, bogie's vibration worsen when the wheel profiles wear over time. Overall, while rail reprofiling was found to be one of the fundamental solutions to mitigate carbody swaying, it is cost prohibitive for most routine operational applications. Thus, for economic considerations and the fact that low wheel-rail contact conicity is also a contributing factor to carbody swaying, vehicles with worn wheels can also be operated on the rail line, which was successfully verified by the field data presented in this paper.