Frequency veering between car body and under-chassis equipment of railway vehicles in vertical bending mode

Abstract

The coupled system of the car body and the under-chassis equipment is a significant part of the railway vehicle and directly influences the vehicle dynamics. A continuous modal parameter tracking method is proposed to analyse the frequency veering phenomenon occurring between a car body and under-chassis equipment. Veering determination methods based on the modal assurance criterion, mode shape similarity and phase difference were proposed. Results show that altering the natural frequency of the under-chassis equipment causes frequency veering between the first-order vertical bending of the car body and vertical motion of the under-chassis equipment. For the car body with a single under-chassis equipment, frequency veering occurs when the natural frequency of the under-chassis equipment approach the frequency of the first-order vertical bending mode of the car body without under-chassis equipment, and the modal damping of the veering modes changes significantly in the veering zone and intersect at the veering point. The proportions of the car body bending vector magnitudes associated with the natural frequency of the equipment on each veering mode before veering are interchanged during the veering. Furthermore, when the natural frequency of the under-chassis equipment is equal to that at the veering point, the vibration transmissibility near the car body first-order bending motion is the lowest. For the car body with multiple under-chassis equipment, a frequency locus may veer more than once due to different types of modal coupling between the car body vertical bending and the under-chassis equipment vertical vibrations. When the natural frequency of the under-chassis equipment is equal to that of the modal damping intersection point, the vibration transmissibility near the car body first-order bending motion is minimal.