Mathematical Simulation of Air Suspension Failure and Derailment

Air suspensions are a commonly used component of modern transit and passenger vehicle suspensions. New vehicle performance specifications usually require testing and analyses with the air suspension inflated and also deflated. However, the tests and analyses usually do not include the dynamic effects that may occur at the instant of deflation. Transportation Technology Center, Inc. (TTCI) recently investigated a revenue service flange climb derailment for a large North American transit system. The derailment occurred on the diverging route of a No. 10 turnout. Initial investigation by the transit system did not identify any track or equipment that showed significant deviations from their normal practices; no obvious cause for the derailment was identified, although the air suspension had been deflated after the derailment. To assist in determining potential contributing factors for the derailment, TTCI conducted NUCARS® simulations of the car negotiating the turnout, using these parameters: • Vehicle dynamic response to local track geometry conditions, including motions of the air suspension; • Sudden deflation of the air suspension; • Wheel and rail profiles. This paper presents the methods used to represent sudden component failures in the NUCARS simulations, including the air suspension deflation. The simulation results show how the sudden deflation of the air suspension combined with local track geometry and wheel/rail contact conditions could contribute to a flange climb derailment.