Understanding and debugging a complex coupling scheme poses a great challenge for a user when a variety of schedulers and actions are involved. Rocman provides a visualization tool that displays the data flow of actions to help users comprehend and debug coupling schemes. When a coupling scheme is constructed, an output file is generated that describes the coupling scheme and its schedulers and actions in the Graph Description Language (GDL). The output file can then be visualized by tools such as AiSee [13].
As a concrete example, Figure 6 illustrates a simplified fluid and solid coupling scheme with subcycling of individual physics modules. In a ``system time step'', the tractions are first transferred from the fluids interface mesh onto the solids interface mesh (step 1), and a finite-element analysis of elasticity is then performed to compute the displacements of the interface (step 2). During the process, the solids module may perform multiple smaller time steps based on its stability limit, and obtain jump conditions (tractions) from Rocman, which performs interpolation in time. After the solids module reaches the designated system time step, Rocman transfers the displacements of the interface (step 3). The fluids module then solves for tractions by obtaining mesh motion and solids velocity as boundary conditions (step 4).
Figure 7 shows the visualization of this simplified coupling scheme. In the graph, each node represents an action or a scheduler (a container of actions), corresponding to the steps in the above description of the coupling scheme. Each edge represents the execution order of actions and is labeled with data passed between actions. This figure was generated automatically using the GDL output of Rocman, except for the circled numbers which were added manually. A scheduler node can be unfolded in AiSee graph viewer to reveal the details of the actions that the scheduler contains. This visualization capability helps development of new coupling schemes by allowing them to be debugged visually at a high level.
