Abstract

Equation-based object-oriented modelling tools are often used to model hydraulic actuation systems, where the dynamics of a pressurized fluid, normally oil, is coupled to the mechanical dynamics of valves, actuators, and mechanical loads. A truly object-oriented approach requires that system components can be connected in an arbitrary fashion, as long as this makes physical sense, without leading to ill-posed or ill-conditioned numerical problems. Using a simple paradigmatic model, this paper shows that it is advisable to always consider both the fluid compressibility and the mechanical inertia of the moving parts at the fluid boundary into account, even though this may lead to very stiff dynamics, in order to avoid numerical issues that are cause by the variable index of the differential-algebraic equations of the system. The results obtained in the paper are corroborated by the actual experience of the authors on realistic, full scale industrial application models.