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

Frequency veering is a phenomenon that occurs during modal parameter changes and is closely related to the response characteristics of the system. First, by taking a system with simple DOFs as the research object, the variations in the modal damping ratio and mode shape in the process of frequency veering are analysed, and a criterion for identifying this phenomenon is preliminarily proposed. Then, to explore the modal changes in complex vehicle systems with multiple DOFs, an adaptive modal continuous tracking algorithm based on a local search algorithm is proposed that takes the Euclidean closeness between complex mode shapes as an index. Frequency veering is analysed with the established vehicle system dynamics model (Model I) and reproduced through the SIMPACK model (Model II) for multibody dynamics simulation. The perturbation method is used to analyse the mechanism by which the vehicle system eigenvectors are prone to mutations during frequency veering, and the abnormal changes in the mode shapes during this process are further verified. In addition, two quantitative indices for identifying frequency veering phenomena are proposed based on the modal assurance criterion and mode shape similarity. Finally, the mapping relationship between the frequency veering and vehicle system response is explored. The results indicate that before and after frequency veering, the mode shapes interchange, and in the frequency veering zone, the damping-hopping phenomenon occurs, resulting in a significant decrease in system stability. Corresponding to the phenomena of modal damping ratios and mode shapes, the motion morphology of the vehicle system is clearly observable. Moreover, the response at the DOFs of the car body and bogie are obviously enhanced; these responses are also manifested in the increasing vibrations of the car body and bogie and the deterioration of the vehicle ride quality.