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.
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Last modified: June 5, 2005 -- © François Cellier