Running safety assessment of special railway vehicles with a mobile launch system

Special railway vehicles with a mobile launch system can perform launch operations under mobile conditions. Nevertheless, severe transient impacts induced by launch pose significant challenges to running safety. In this study, a coupled multibody dynamics (MBD) model integrating the train, track, launch apparatus, and payload was established. Considering that conventional safety indicators are inadequate under intense transient wheel-rail impact and temporary separation conditions, this study proposes a staged multi-criteria safety assessment framework that combines wheel-rail force-based indices and geometric indicators to evaluate the running safety of the launch vehicle during launch-on-move operation. Under the proposed framework, the effects of operating speed, wheel-rail contact conditions, and track gradient were systematically evaluated, and the corresponding running safety domains were identified. The results show that running safety is jointly influenced by speed and track gradient: risks remain controllable at low speeds and small gradients, whereas high speeds combined with steep gradients (±30‰) tend to increase the risks of wheel jumping and derailment. Degraded wheel-rail contact conditions further contribute to derailment-related risks and wheel unloading. The highest safe speed decreases from 70 km/h under dry conditions to 30 km/h under wet conditions and 10 km/h under greasy conditions. These findings provide a basis for safety assessment and safety-oriented operation of rail vehicles subjected to instantaneous strong wheel-rail impact loads.