CoSimulation

Cosimulation is a simulation approach in which a complex system is represented by multiple submodels, each executed by its own solver. Submodels may come from different domains, such as mechanical dynamics, electrical circuits, software controllers, or fluid processes, and are often implemented in distinct simulation tools. The submodels exchange boundary data at defined synchronization points to produce an integrated view of system behavior.

In a cosimulation design, a master algorithm coordinates the execution. At each synchronization step, the boundary values are transferred between simulators, and the submodels advance to the next time point. Coupling can be loose, with longer time steps and occasional data exchange, or tight, with frequent exchanges and iterative refinement to improve accuracy and stability. The approach requires careful handling of units, causality, and initialization.

A commonly used standard for cosimulation is the Functional Mock-up Interface (FMI), which defines how models are packaged as Functional Mock-up Units (FMUs) and how simulators exchange data. FMI supports two modes: model exchange and cosimulation, the latter including its own solver steps. Other toolchains may implement custom wrappers or middleware to enable integration.

Cosimulation enables reuse of domain-specific solvers, rapid prototyping, and the study of complex cyber-physical systems. It is widely used in automotive development, aerospace, power systems, robotics, and process control. Challenges include numerical stability, synchronization errors, data loss, deadlock risk, and the need for compatible units and interfaces across tools. Despite these challenges, cosimulation remains a practical method for modeling heterogeneous systems where single tools cannot capture all dynamics efficiently.