In this investigation, a nonlinear air suspension system model that accounts for the coupling between air springs, leveling valves, and differential pressure valves is developed and integrated into general-purpose multibody dynamics computer algorithms. It is demonstrated that the proposed model can capture highly nonlinear air suspension characteristics resulting from the coupling with leveling and differential pressure valves, and good agreements are obtained between the numerical and on-track test results. Furthermore, the effect of flow characteristics of leveling valves on the wheel load unbalance on spiral curve sections is discussed. The numerical results obtained by the proposed model clearly indicate the importance of modeling the nonlinear flow characteristics of the leveling and differential pressure valves for assessing the vehicle safety in low speed operations on a small radius curved track.

In this investigation, a flexible track model based on the moving track approach is generalized for use in the curve negotiation analysis of multibody railroad vehicles. The track model consists of discrete rail and sleeper bodies defined underneath the wheelset, and the equations of motion are formulated along the track and rail trajectories using the general track geometry description utilized in the railroad vehicle dynamics simulation. In the vehicle curve negotiation, the outer rail is subjected to the overturning moment caused by the flange contact force, thus the rail roll deflection and its effect on the location of contact point need to be carefully considered for an accurate prediction of the wheel/rail contact forces for the flexible track model. To this end, the multi-variable look-up tables that account for the change in roll angles of both rails are introduced in this study. The multiple look-up contact tables are prepared for various assumed rail roll angles by the contact geometry analysis prior to the dynamic analysis, and then they are interpolated as a function of roll angles of both rails, the modified wheel lateral displacement that accounts for the rail lateral displacement, and the angle of attack of the wheelset. By doing so, existing railroad vehicle dynamics simulation algorithms assuming rigid rails can be extended to account for the track flexibility without significant modifications of the code.

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