Search

In conventional aircraft energy systems, self-regulating pneumatic valves (SRPVs) are used to control the pressure and mass flow of the bleed air. The dynamic behaviour of these valves is complex and dependent on several physical phenomena. In some cases, limit cycles can occur, deteriorating performance. This article presents a complex multi-physical model of SRPVs implemented in Modelica. First, the working principle is explained, and common challenges in control-system design-problems related to these valves are illustrated. Then, a Modelica-model is presented in detail, taking into account several physical domains. It is shown, how limit cycle oscillations occurring in aircraft energy systems can be reproduced with this model. The sensitivity of the model regarding both solver options and physical parameters is investigated. [ABSTRACT FROM AUTHOR]

The paper describes the derivation of finite-element models of one-dimensional fluid flows with heat transfer in pipes, using the Galerkin/least-squares approach. The models are first derived for one-phase flows, and then extended to homogeneous two-phase flows. The resulting equations have then been embedded in the context of object-oriented system modelling; this allows one to combine the fluid flow model with a model for other phenomena such as heat transfer, as well as with models of other discrete components such as pumps or valves, to obtain complex models of heat exchangers. The models are then validated by simulating a typical heat exchanger plant. [ABSTRACT FROM AUTHOR]

The paper discusses current approaches to the modelling and simulation of thermo-hydraulic processes, to be used as a tool for system studies in thermal power plant control. After reviewing the desirable features of simulation environments, an approach based on the Modelica language is presented and motivated. Finally, the general concepts presented above are exemplified by modelling a simple process based on a heat exchanger. [ABSTRACT FROM AUTHOR]