There are two different means to simulate a Modelica model in JModelica.org: either as a Functional Mock-Up Unit (FMU) or as a JModelica.org Model Unit (JMU). In the former case, the model is converted into an Ordinary Differential Equation (ODE), whereas in the latter case, the model is simulated as a Differential Algebraic Equation (DAE). The default, and recommended, means to simulate models is to use FMUs, since this approach provides better performance, a more robust initialization mechanism, and significantly better support for hybrid systems. Simulation of JMUs may still be useful, however, in some optimization applications where simulation of the model as a DAE/JMU, is an important prerequisite for optimization by means of the collocation algorithms.
This chapter demonstrates how to initialize and simulate a model which has been compiled to a JMU. To read about simulation of FMUs, see Chapter 5, Simulation of FMUs.