Bachelor's thesis Sven Hinrichs


Automated documentation of complex simulation models using the example of an expansion valve model for refrigerant circuits

For sustainable model development of complex simulation models a complete documentation is necessary. In short development cycles, however, said documentation is usually given too little importance which is why the reusability is reduced. For this reason, within in this work a methodology for the automatic documentation of simulation models is to be created for the modelling language Modelica.

This methodology is to be based on UML / SysML and serves as a visualisation of the model structure as well as groundwork for further studies of new / other model developers. The advantages lie in the development of the modelling process which gives the modeler an overview of the current situation of the model at any given time. Especially for inexperienced developers, the presentation is suitable for a systematic introduction to model development. In addition, this should serve as an introduction to automatic model generation from the system modelling language SysML. As a demonstration example, the expansion valve of a refrigerant circuit is used. Based on this, the methodological development of the documentation will be discussed.

The expansion valve (EV) is an important component in the refrigerant circuit and serves as a mass flow control. This reduces the refrigerant’s high-pressure level to a lower pressure level and supplies the mass flow to the evaporator as a vapor / liquid mixture. Thus, it has two important functions: the regulation of the overheating on the evaporator and the thermodynamic state of the refrigerant mass flow at the compressor inlet, since droplet impact on the compressor is to be avoided. The EV is decisive for the service life and wear of the heat pump.

The relaxation of refrigerant in the EV is complex due to the overlapping of thermodynamic and fluid mechanisms. This makes a full description more difficult. Within the scope of this thesis, a simulation model will be developed in Modelica using different gray-box approaches and also dynamic boundary conditions will be mapped. The model of the expansion valve is based on Bernoulli's equation of energy with a flow coefficient as a correction factor. In addition, the throttling mechanism and metastability coefficient are considered. The modeling considers the normative standards according to DIN 9126 in order to ensure high software quality.

Later in this work, there will be a critical discussion about the interactive simulation of SysML models using Modelica models. It serves as groundwork for an automatic model generation. In this approach, the graphical system modelling language SysML should be able to generate modelling models and translate them into executable Modelica models.