Object-Oriented Modeling of Multibody Systems
with a Symbolic Language and Simulation of a Jeep

Abstract

In this report, a new technique to model multibody systems is shown. An object-oriented multibody systems library based on a recursive algorithm is developed for the purpose of vehicle simulations. Objects can be plugged together according to their geometric position in space. The library is based on energy flow between objects, a concept borrowed from bond graphs, supporting the modeling process and providing an alternate point of view. Special attention was placed on an object-oriented implementation of vehicle-specific elements such as the tire object, the steering mechanism, the ground models, and the aerodynamic resistances. The closed loops of the suspension system were broken with a technique called tearing. Use of the symbolic modeling language Dymola made it possible to create efficient simulation code for the direct dynamics problem by taking advantage of its symbolic formulae manipulation capabilities. The new mixed symbolic and numeric inline integration approach was used, which includes numerical information already on the modeling level, leading to a significant speedup of CPU-time. A practical example of a M151-A2 1/4 ton truck demonstrates the capabilities of the library and the correctness of the results.