Modelica - A Language for Equation-Based Physical Modeling and High Performance Simulation

摘要

A new language called Modelica for hierarchical physical modeling is developed through an international effort. Modelica 1.0 [http:// www.Dynasim.se/Modelica] was announced in September 1997. It is an object-oriented language for modeling of physical systems for the purpose of efficient simulation. The language unifies and generalizes previous object-oriented modeling languages and techniques.rnCompared to the widespread simulation languages available today this language offers two important advances: 1) non-causal modeling based on differential and algebraic equations; 2) multidomain modeling capability, i.e. it is possible to combine electrical, mechanical, thermodynamic, hydraulic etc. model components within the same application model.rnA class in Modelica may contain variables (i.e. instances of other classes), equations and local class definitions. The multi-domain capability is partly based on a notion of connectors, which are classes just like any other entity in Modelica.rnSimulation models can be developed using a graphical editor for connection diagrams. Connections are established just by drawing lines between objects picked from a class library. The Modelica model is translated into a set of constants, variables and equations. Equations are sorted and converted to assignment statements when possible. Strongly connected sets of equations are solved by calling a symbolic and/or numeric solver. The C/C++ code generated from Modelica models is quite efficient.rnHigh performance parallel simulation code can be obtained either at the coarse-grained level by identifying fairly independent submodels which are simulated in parallel, or at the fine-grained level by parallelizing on clustered expression nodes in the equation graph. Preliminary results using the coarsegrained approach have been obtained in an application on simulating an autonomous aircraft watching car traffic.