Development of high and low fidelity models for multibody railroad vehicle systems

Accurate numerical modeling of railroad vehicle systems is vital to increasing railroad safety and efficiency. The formulations of both flexible and rigid multibody dynamics are particularly well-suited to the studying of railroad vehicle dynamics. In this thesis, three topics in the modeling of computational multibody railroad system dynamics are presented.;The first topic is an investigation which reveals that there is significant coupling between the structural flexibility of a tank car's tank and the location of the wheel/rail contact as well as the contact forces. The coupling between the deformation of the car body and the contact geometry is demonstrated through the comparison of computer simulations of a railroad tank car modeled with a flexible tank and a rigid tank. The simulations are performed using the methods of multibody dynamics utilizing a nonlinear multibody framework and an elastic three-dimensional wheel/rail contact methodology. The flexible tank is modeled using the floating frame of reference formulation, which is a nonlinear finite element formulation for modeling bodies that experience small deformations.;The second topic is the development of a new nonlinear flexible rail formulation for use with multibody railroad vehicle system dynamics. This formulation is simpler and more general than contemporary methods proposed recently in the literature. The rail is modeled using the floating frame of reference formulation, but allows for the rail surface to have C2 or C3 continuity, or higher if desired, with respect to the parameters by which the surface is described. The method also allows for the nonlinear coupling of rail deformation and wheel/rail contact forces.;The third topic is a new low-fidelity formulation with low computational cost for the numerical modeling of the gross dynamics of long trains. The formulation creates simple and efficient method to constrain bodies to follow the track. It also presents a set of force formulations to model such railroad-specific components as propulsive and braking, resistance, and inter-car coupling forces.