Combining Equation-based and Multibody Models

This article highlights the combination of equationbased modeling with multibody models. In other words, it combines the equation-based modeling language Modia and the multibody module Modia3D. The multibody system is defined in an object-oriented way and parts of it are defined by equations. Algebraic loops are treated that appear due to the connection of multibody and equation-based components. A new approach to variable structure systems are socalled predefined acausal components which consist of pre-compiled causal parts and acausal equations. To generalize the concepts for variable structure systems, the multibody module is defined as a predefined acausal component. As a result, the number of degrees of freedom of the multibody system can vary during simulation. This is demonstrated with a non-trivial example of a walking space robot from the MOSAR space project.