Abstract
This study describes the low damped carbody oscillations of the HEMU-430X, a high-speed electric-multiple-unit experimental train of Korea. The HEMU-430X had already undergone a kind of hunting problem in the test period, but it was effectively suppressed through several measures and the test was finished successfully. However, recently, the HEMU-430X again experienced the similar but slightly different problem after its wheel profile was changed to XP55, which is widely used in high-speed trains in Korea. In this paper, the eigenbehavior and system damping ratio are analyzed using a linearized vehicle model to more systematically investigate the cause of the carbody oscillation of the HEMU-430X. The results show that the bogie lateral movement coupled with carbody upper sway has the least damping ratio in the case of the HEMU-430X and the magnitude of yaw directional constraints of the bogie plays an important role in causing the carbody oscillation. Parametric studies for suspension, equivalent conicity and creep coefficients are carried out. A solution is suggested and it is validated using field tests.
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