Analysis of abnormal low-frequency lateral carbody sway in metro vehicles induced by alternating side wear of rails

Low-frequency carbody sway in the range of 2–3 Hz is a recurrent abnormal vibration phenomenon in metro systems, degrading ride comfort and operational stability. Field observations indicate that this vibration is concentrated in specific line sections and is closely associated with deterministic geometric excitation caused by alternating side wear of rails, hereafter termed rail alternate side wear, in which lateral wear alternates periodically between the left and right rails. The excitation mechanism of wear-induced low-frequency carbody sway is investigated through an integrated approach combining field measurements, wheel and rail profile inspection, vehicle–track coupled multibody dynamics simulation, and wear-evolution analysis. Measurements show that the abnormal vibration is dominated by a coupled lateral-roll motion of the carbody with a nearly constant dominant frequency of approximately 2.5 Hz. A mileage-dependent generalised lateral irregularity is reconstructed from the measured wheel and rail profiles to quantify the equivalent periodic geometric excitation induced by rail alternate side wear. Numerical simulations incorporating mileage-dependent wheel–rail contact conditions reasonably reproduce the dominant vibration characteristics observed in the field tests and demonstrate that low equivalent conicity and insufficient secondary lateral damping significantly promote frequency locking and response amplification. By linking the measured wear morphology, mileage-dependent wheel–rail contact geometry, vehicle modal response, and iterative wear evolution, the results clarify the feedback interaction between rail alternate side wear and low-frequency carbody sway, and indicate that coordinated control of rail wear and vehicle suspension parameters can mitigate this abnormal response.