Object-oriented formulation of thermal fluid streams often yields large non-linear equation systems whose numerical solution is difficult to achieve. This paper revisits the fundamental equations for thermal fluid streams and introduces a new term: the steady mass flow pressure $\hat{p}$. Using this term, the equations can be brought into a form where all non-linear computations are explicit. This enables a robust and object-oriented formulation of even complex architectures. The modelling of aircraft environmental control systems is presented as one possible application example.

This paper introduces the DLR Thermofluid Stream Library: a free open-source library for the robust modeling of complex thermofluid architectures. Designed to be easy to use, easy to adapt, and enriched by a number of examples, this library contains the fundamental components for many different applications, such as thermal management of electric cars, power plants, or building physics. Different from many previous software implementations, the library exploits a new computational concept on the basis of the fluid inertance that derives the mass flow balance in such a manner that large non-linear equations systems in implicit form can be avoided. Hence, there is a reliable and efficient computational scheme for simulation and initialization. Although this scheme is explained in detail in previous publications, this paper focuses on the implementational aspects of the library, explaining its structure, the underlying equations of key components and providing basic examples. In addition to the practical value of the library, we also aim to display the underlying thought driving the design of the software.

Many modern models contain changes that affect the structure of their underlying equation system, e.g. the breaking of mechanical devices or the switching of ideal diodes. The modeling and simulation of such systems in current equation-based languages frequently poses serious difficulties. In order to improve the handling of variable-structure systems, a new modeling language has been designed for research purposes. It is called Sol and it caters to the special demands of variable-structure systems while still representing a general modeling language. This language is processed by a new translation scheme that handles the differential-algebraic equations in a highly dynamic fashion. In this way, almost arbitrary structural changes can be processed. In order to minimize the computational effort, each change is processed as locally as possible, preserving the existing computational structure as much as possible. Given this methodology, truly object-oriented modeling and simulation of variable-structure systems is made possible. The corresponding process of modeling and simulation is illustrated by two examples from different domains.

Here is information on how to publish, spread your research, and search for your publications. Most of LiU's research publications are directly imported into DiVA from the Web of Science. Before registering a publication, always check if the publication is already in DiVA!

Here is information on how to publish, spread your research, and search for your publications. Most of LiU's research publications are directly imported into DiVA from the Web of Science. Before registering a publication, always check if the publication is already in DiVA!

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