Modelica is an object-oriented language for modeling of large, complex and heterogeneous physical systems. It is suited for multi-domain modeling, for example for modeling of mechatronics including cars, aircrafts and industrial robots which typically consist of mechanical, electrical and hydraulic subsystems as well as control systems. General equations are used for modeling of the physical phenomena. No particular variable needs to be solved for manually. A Modelica tool will have enough information to do that automatically. The language has been designed to allow tools to generate efficient code automatically. The modeling effort is thus reduced considerably since model components can be reused and tedious and error-prone manual manipulations are not needed. The principles of objectoriented modeling and the details of the Modelica language as well as several examples are presented. 1.

Modeling and simulation have become central to all disciplines of engineering and science. In a comprehensive modeling and simulation environment, it is desirable to integrate models specified in different modeling formalisms and to extend modeling language constructs to support multi-domain and multi-formalism modeling integrated with powerful visualization capabilities. This paper is concerned with the design of a complete integrated environment that combines the powerful mechanical model design of various CAD packages with the structuring mechanisms of object oriented modeling languages including a mathematical and logical behavior representation. We present an integrated environment for simulation of multi-domain models which has been implemented using Modelica as a standard model representation. The user can work with mechanical models designed with AutoDesk's Mechanical Desktop, extend the corresponding Modelica model in various ways, and analyze the simulation results in a high performance interactive visualization environment.