Conference article

Redundancies in Multibody Systems and Automatic Coupling of CATIA and Modelica

Hilding Elmqvist
Dassault Systèmes, Lund, Sweden

Sven Erik Matsson
Dassault Systèmes, Lund, Sweden

Christophe Chapuis
Dassault Systèmes, Velizy Villacoublay, France

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Published in: Proceedings of the 7th International Modelica Conference; Como; Italy; 20-22 September 2009

Linköping Electronic Conference Proceedings 43:63, s. 551-560

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Published: 2009-12-29

ISBN: 978-91-7393-513-5

ISSN: 1650-3686 (print), 1650-3740 (online)


Traditionally; multibody systems have been defined in Modelica by connecting bodies and joints in a model diagram. Additionally the user must enter values for parameters defining masses; inertias and three dimensional vectors of positions and orientations. More convenient definition of multibody systems can be made using a 3D editor available; for example; in CATIA from Dassault Systèmes with immediate 3D viewing.

A tool has been developed that translates a CATIA model to Modelica by traversing the internal CATIA structure to get information about parts and joints and how they are related. This information is then used to generate a corresponding Modelica model. The traversal provides information about the reference coordinate system; the center of mass in the local coordinate system; the mass; the inertia; the shape and color of the body exported in VRML format for animation purposes and the icon exported as a PNG file to be used in the Modelica diagrams.

The Modelica diagram layout is automatically generated and is based on the spanning tree structure of the mechanism. Models obtained in this way often contain redundant constraints. A new method has been developed for Dymola to facilitate simulation of such models; i.e. the model reduction is performed automatically.

An important property of the translated model is the possibility to use Modelica extends (inheritance) for adding controllers and other features of the model for dynamic simulation. For instance; the engine model can be extended by introducing models of the gas forces of the combustion acting on the cylindrical joints of the pistons. In that way; the translated model is separated and can be changed independently of the added models.


MultiBody systems; Modelica; CATIA


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