An Open-Source Framework for Efficient Co-simulation of Fluid Power Systems

Simulation of fluid power systems typically requires models from multiple disciplines. Achieving accurate load dynamics for a system with complex geometry, for example, may require both a 1D model of the hydraulic circuit and a 3D multi-body model. However, most simulation tools are limited to a single discipline. A solution to these kinds of problems is co-simulation, where different tools are coupled and simulated together. Co-simulation can provide increased accuracy, improved modularity and facilitated collaboration between different organizations. Unfortunately, tool coupling typically requires tedious and error-prone manual work. It may also introduce numerical problems. For these reasons, co-simulation is often avoided as long as possible. These problems have been addressed by the development of an open-source framework for asynchronous co-simulation. Simulation tools can be interconnected through a stand-alone master simulation tool. An extensive range of tools is also supported via the Functional Mockup Interface standard. A graphical user interface has been implemented in the OpenModelica Connection Editor. System models can be created and edited from both a schematic view and a 3D view. Numerical robustness is enforced by the use of transmission line modelling. A minimalistic programming interface consisting of only two functions is used. An example model consisting of a hydraulic crane with two arms, two actuators and a hanging load is used to verify the framework. The composite model consists of nine multi-body models, one hydraulic system model and a controller. It is shown that models from various simulation tools can be replaced with a minimal amount of user input.