Bond graph modeling from an object oriented modeling point of view

Along with an ever increasing model complexity, a so-called object oriented approach to physical systems modeling has become more and more popular throughout the last few years. Frequently used keywords are multi-domain modeling, model reuse, and non-causal equations. On the other hand the physical systems modeling methodology based on bond graphs has been in use worldwide since Paynter devised bond graphs more than 35 years ago. It seems that due to different roots and a different terminology, aspects of one of the two approaches are not fully appreciated by those who adhere to the other modeling paradigm. By relating features of object-oriented modeling (OOM) to corresponding ones of the older bond graph methodology, it is pointed out what both modeling approaches have in common and what is different. As a working modeling language, Modelica is used since it seems that this object oriented modeling language is going to receive an increasing attention as a neutral exchange format between proprietary modeling tools. As an application example that combines the electrical, the hydraulic and the mechanical energy domain in a single system, a hydraulic drive with a controlled displacement pump is considered.