Frequency veering of railway vehicle systems and its mapping to vibration characteristics

Abstract

Frequency veering is a phenomenon that occurs during the process of modal parameter changes, which is closely related to the response characteristics of the system. Firstly, take the system with simple DOFs as the research object, the variations of modal damping ratio and modal shape in the process of frequency veering are analyzed, and the criterion for identifying frequency veering is preliminarily proposed. Then, to explore the modal evolution of complex vehicle systems with multiple DOFs, an adaptive modal continuous tracking algorithm based on local search algorithm is proposed using the Euclidean closeness of complex modal shapes as an index. The frequency veering phenomenon is analyzed with the established vehicle system dynamics model (Model Ⅰ) and reproduced through the SIMPACK model for multi-body dynamics simulation (Model Ⅱ). The perturbation method is used to analyze the mechanism of the vehicle system eigenvectors being prone to mutations during frequency veering, and the abnormal changes of the modal shapes in the process of frequency veering are further verified. In addition, two quantitative indexes for identifying frequency veering are proposed based on the modal assurance criterion (MAC) and modal shape similarity (MSS). Finally, the mapping relationship between frequency veering and vehicle system response characteristics is explored. The results indicate that before and after frequency veering, the modal shapes interchange, and in the frequency veering zone, the damping-hopping phenomenon also occurs, resulting in a significant decrease in system stability. Corresponding to the phenomena of modal damping ratios and modal shapes, the motion morphology of the vehicle system is clearly observable, and the DOF response of the car body and bogie is obviously increased, which is also manifested in the increase of the vibration of the car body and the bogie and the deterioration of the vehicle ride quality.