Evaluation of the dynamic behaviour of heavy-haul trains considering brake pipe pressure gradient under cyclic braking

The brake pipe pressure gradient has a significant impact on the dynamic performance of heavy-haul trains (HHTs). In this study, a pneumatic braking model was developed that considers the influence of the pressure gradient. This model employs a 1D isothermal assumption to simulate the pressure and flow along the brake pipe. Furthermore, a HHT longitudinal-vertical coupling dynamics model was established to evaluate the resulting coupler forces and vibration responses. This model incorporates key components, including locomotives, wagons, and couplers. The simulated brake cylinder pressure was dynamically converted into braking force acting on the wheels. Based on these integrated models, a systematic analysis was conducted to investigate the effects of different pressure gradients on the longitudinal impulse and vibration response characteristics of the HHT. The results show that the pressure gradient leads to a nonlinear reduction in brake pipe pressure along the train length. This reduction significantly lowers the steady-state brake cylinder pressure at the rear wagons and alters the coupler force characteristics during the release process. Moreover, the pressure gradient intensifies the longitudinal and pitch vibrations of the car body and wheelset during the release process, primarily due to the compression stage of the coupler.