Use of Multibody System Techniques in the Analysis of Railroad Vehicle Stability and Derailment

The forces that govern the dynamics and stability of railroad vehicle systems must be understood in order to prevent derailment. These forces can change significantly based on the position, orientation, and contact configuration of a wheelset with respect to the track. Additionally, these forces can experience large changes in magnitude as the forward velocity of the vehicle increases. In this dissertation, the forces that govern wheelset motion during various derailment scenarios are examined, including gyroscopic, friction, and kinematic contributions. Multiple multibody system derailment models are used to provide the results, including a new fully nonlinear unconstrained multibody system wheel climb derailment model. These models characterize vehicle systems that operate at both high and low velocities, experiencing modes of derailment such as wheel lift and wheel climb. It is shown in this study that a proper investigation of railroad vehicle derailment requires a three-dimensional analysis that does not place simplifying constraints on the motion of the wheelset with respect to the track. The wheelset orientation with respect to the track must be taken into account when determining derailment criteria in kinematic processes, such as wheel climb. To this end, it is shown that derailment criteria, such Nadal’s derailment limit, are not conservative in all cases when the wheelset orientation is not taken into account. In the case of model components that are modeled as deformable bodies, the concept of reference conditions is revisited. A distinction is made between the reference conditions, which define the equations to be solved, and substructuring techniques, which allow for efficient model assembly and reduce model dimensionality. It is shown that, when the reference conditions are not applied at a preprocessing stage, substructuring techniques such as the Craig-Bampton method lead to the free modes of deformation. An extended slider-crank model is presented to demonstrate that the free modes cannot be used in all applications, highlighting the importance of the use of reference conditions to obtain an accurate solution.