This study addresses the critical need for computational tools to model complex nonlinear multibody dynamic systems in the presence of parametric and external uncertainty. Polynomial chaos has been used extensively to model uncertainties in structural mechanics and in fluids, but to our knowledge they have yet to be applied to multibody dynamic simulations. We show that the method can be applied to quantify uncertainties in time domain and frequency domain.
This work establishes a semi-empirical wheel-soil interaction model, developed in the framework of plasticity theory and equilibrium analysis, to be used in vehicle dynamics simulations. Vehicle-terrain interaction is a complex phenomena governed by soil mechanical behavior and tire deformation. The application of soil load bearing capacity theory is used in this study to determine the tangential and radial stresses on the soil-wheel interface. Using semi-empirical data, the tire deformation geometry is determined to establish the drawbar pull, tractive force, and wheel load. To illustrate the theory developed, two important case studies are presented: a rigid wheel and a flexible tire on deformable terrain; the differences between the two implementations are discussed. The outcome of this work shows promising results which indicate that the modeling methodology presented could form the basis of a three-dimensional off-road tire model. In an off-road three-dimensional tire model, the traction behavior should include shear forces arising from the surface shear with the soil as well as the bulldozing effect during turning maneuvers.
This paper presents an effort to use multi-body dynamics with unilateral contact to model the friction wedge interaction with the bolster and the side frame. The new friction wedge model is a 3D, dynamic, stand-alone model of a bolster-friction wedge-side frame assembly. It allows the wedge four degrees of freedom: vertical displacement, longitudinal (between the bolster and the side frame) displacement, toe-in and toe-out, and yaw (rotation about the vertical axis). The dedicated train modeling software NUCARS® has been used to run simulations with similar inputs and to compare — when possible — the results with those obtained from the new stand-alone MATLAB friction wedge model. The stand-alone model shows improvement in capturing the transient dynamics of the wedge better. Also, it can predict not only normal forces going into the frame and bolster, but also use the associated moments to enhance model behavior. Significant simulation results are presented and the main differences between the current NUCARS® model and the new stand-alone MATLAB models are highlighted.
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