System Coupling shows that simulation is running but no progress is being made
I am running a two way FSI in workbench. When I start the simulation it runs without any errors. I do get the warnings in the screenshot below. The simulation will run for about two hours, making progress, then it just stops. It looks like it is running but no progress is made. I've left it running for hours and it won't make progress. I have tried lowering the number of iterations and and simplifying the mesh but it still gets stuck. In the second screenshot below you can see that it is stuck at 68%. It took about 2 hours to get to 68%. Then after 2.5 hours it is still on 68%. Thanks for your help!
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When running System Coupling and it stops running, the first thing to do is examine the output files for each solver to look for clues to what happened. For Fluent, look at the transcript .trn file. For Mechanical, look at the .out file. Also, look at the System Coupling log file, .scl.
I recommend going over this tutorial in the Ansys documentation that shows a 2-way FSI simulation with Fluent and Mechanical. https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v202/en/sysc_tut/sysc_tut_oscplate_wb_fluent.html
You can also look at the following for the same tutorial but run with the System Coupling GUI or Command Line Interface that is run outside of Workbench: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v202/en/sysc_tut/sysc_tut_oscplate_cli_fluent.html
FSI simulations with very soft materials or membranes are prone to numerical instabilities. In 2020R1 we have introduced a stabilization method in System Coupling called the Quasi-Newton Stabilization Algorithm. Note that this has to be used with the new System Coupling GUI or Command Line Interface that is run outside of Workbench. More information here: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v202/en/sysc_ug/sysc_gen_scservice_dt_supplemental_iqnils.html
It is very important to build up the FSI simulation in stages as opposed to setting up the 2-way FSI right at the start. This document "Best Practices for Coupled Fluid-Structure Interaction (FSI)" describes this process and is available here: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v202/en/sysc_ug/sysc_bestpractices_fsi.html