Design and Implementation of Object-Oriented Model Libraries using Modelica
Sammanfattning: This thesis describes basic models for thermo-fluid systems and the implementation of the models using a flexible object-oriented structure in the ThermoFluid library. Model libraries provide an excellent way to package engineering knowledge of systems to be reused by non-experts. Many commercial simulation packages provide good model libraries, but they are usually domain specific and closed. Modelica(TM) is an open standard of an object-oriented modeling language for heterogeneous, multi-domain dynamic systems. Modelica combines the expressive power of equation based modeling with advanced object-oriented structuring features. A unique feature of Modelica are class parameters which allow a high-level parameterization of physical phenomena. The models are based on first principles. Control volumes contain the thermodynamic balance equations in lumped or one-dimensional discretized form. The library is built to be flexible: fluid property models in the control volume can be exchanged, single- or multi-component fluids are supported and the momentum balance submodel can be static or dynamic. Chemical reactions can be added to the model separately from other phenomena. Thermodynamic Jacobians are used to transform the dynamic equations into an efficient form. Low order moving boundary models for two phase flows are another result of the thesis. They make use of a novel approach for approximating the mean void fraction in the two phase region. The experiences from designing an object-oriented, reusable model library are summarized using design patterns. Design patterns are an attempt to describe "good practice" in modeling in a semi-formal way. The library has been used successfully for a broad range of industrial applications, among others modeling of micro gas turbine systems, carbon-dioxide based refrigeration systems, fuel cells, power plants and steam networks. The applications are briefly described in the thesis.
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