Bond-graph Modeling in Modelica

This paper discusses a bond–graph model library implemented in Modelica. Modelica is a new language for physical systems modeling with main objective to facilitate exchange of models and simulation specifications. Bond graphs are a domain–independent way of modeling the dynamics of physical systems. Besides the presentation of the Modelica basic bond– graph library, also an application example is discussed, to test the usefulness of the library in practice. The translation of existing bond–graph models to Mode-lica was a straightforward process, indicating that Mode-lica has the proper features for bond–graph modeling. However, the implicitly generated sum–to–zero connection equations are not useful for bond–graph modeling and in fact can obscure model specification in Modelica. Our future aim is to build a Modelica import / export facility for our bond–graph / block–diagram modeling and simulation software 20-SIM. 1 INTRODUCTION The currently available modeling and simulation tools have their own proprietary model description languages, which complicate exchange of models between different tools. Having a real expressive and standardized model-ing language, exchange of models is really possible without losing non-trivial language constructs of the proprietary language from which the porting process starts. Modelica™ is a new language for physical systems mod-eling being developed in an international effort (Mode-lica, 1997; Mattsson et al., 1997). The main objective of this development is to facilitate the exchange of models, model libraries and simulation specifications. The Modelica design group covers a wide range of application domains, thus ensuring that the versatility of Mode-lica will be taken care of (Otter et al. Bond graphs are a domain-independent notion of physical systems modeling, where the physical processes are directly represented as vertices in a directed graph and the edges represent the ideal exchange of energy between the vertices. This domain independence makes bond graphs especially attractive in a multi-domain context. Furthermore , the equations associated with bond–graph elements can be automatically converted into simulation code, thus releasing the modeler of writing computable code as a simulation model. The contribution of this paper is the implementation of a library of bond–graph elements in Modelica. This work serves as a test on the versatility of the language. First, a brief overview of Modelica is given (section 2), and then the Modelica model library of bond–graph elements is presented (section 3). Section 4 presents an application example consisting of a computer–controlled physical system. In section 5, we draw conclusions. 2 MODELICA Modelica is a …