A new concept is presented on how to set up the equations of complex fluid networks. This concept avoids the creation of large non-linear equation systems and hence leads to a very robust modeling approach while still being competitive in levels of performance. The concept has been implemented in Modelica and tested for the rapid pre-design of aircraft environmental control systems.
The air in aircraft cabins is controlled for pressure, temperature and humidity. The number of temperature zones is generally kept low, for reasons of necessary ducting space. We devise a new ducting concept, which enables a large number of temperature zones. Controllability of the system is however predicted to be a potential obstacle. For a quick resolution of this question, a Modelica model is created. Model creation is focused on a short development time as well as usefulness for controller synthesis. A workflow is presented that enables a quick iteration time between controller synthesis in Matlab and controller testing in a Modelica environment. Finally, the impact of this new concept on the energy consumption of the air generation unit is discussed.
Psychological aspects of equation-based modelling languages like Modelica are under-represented in literature. This does not reflect the growth of the corresponding userbase. In this paper we try to close this gap by tackling the problem from three sides: we conduct expert interviews, we conduct an experiment based on self-reported timings to analyse the effects of inheritance on understandability, and we conduct an online experiment to analyse the effects of model representations on the performance at modelling tasks. The expert interviews suggest that experienced modelling experts tend to develop their models from the top-down, while novices do the opposite. Results from the second experiment indicate that the effect of inheritance on the time to understand a model is both significant and large. The results of the last experiment imply that graphical representations outperform block-diagrams for several metrics. These results open a broad research field on the theory ofgoodmodelling practice.
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