Research on the full elastic coupling vibration characteristics of under-car equipment for railway freight wagons based on virtual operational transfer path analysis method

In order to investigate the synergistic effects of local modal characteristics and vibration path contributions in suspended components of freight railway vehicles, a C70 coal gondola was selected as the research subject. A full-degree-of-freedom elastic system dynamics model was first developed based on pseudo excitation, and vibration tests were conducted on the undercarriage air reservoir suspension using a full-scale vehicle vibration test rig to validate the model. The frequency-domain vibration characteristics of various vehicle components were analyzed to explore energy attenuation patterns. By defining characteristic vibration factors, the combined effects of random track irregularities and the progressive evolution of wheel polygonal wear on system dynamics were examined. A virtual operational transfer path analysis (VOTPA) method was proposed based on the full-degree-of-freedom elastic dynamics model, incorporating phase difference effects. Principal contribution analysis was employed to achieve hierarchical quantification of vibration path contributions. The results indicated that the vertical and lateral vibrations of the vehicle system were primarily concentrated below 200 Hz, with vibration energy progressively attenuating from the wheelset and side frame to the bolster and carbody. The vibration of the undercarriage air reservoir suspension exhibited an initial increase followed by a decrease with increasing speed, with pronounced local modal characteristics observed near specific frequencies. While higher-order polygonal wear dominated wheelset system vibrations, lower-order polygonal excitation was more likely to propagate through vibration paths to the carbody and suspended structures, inducing local modal resonance. The energy surge in air reservoir vibration was primarily attributed to local modal amplification effects caused by the vertical vibration of the side bearing at the No. 2 carbody end, rather than the direct contribution of primary vibration paths. These findings provide a theoretical basis for understanding the coupled vibration transmission mechanisms between undercarriage equipment and the vehicle system, supporting the optimization of their dynamic design and performance.