Fluid Structure Interaction: System Coupler RMS Diverging

    • varunkalai


      I am running a 2-way fluid structure interaction in the carotid artery. My time step size is set to 0.001 in system coupler with a maximum of 200 coupling iterations set. I am having issues with convergence in system coupler, specifically with 1G Fluent data transfer. The RMS does not converge, I have attached an image for reference.

      So far I have tried these methods to mitigate the problem:

      1.) Adjust under relaxation factors in FLUENT

      2.) Reduce time step size in system coupler

      3.) Adjust under relaxation for data transfer in system coupler

      Any suggestions on how to mitigate this problem would be appreciated, thank you!

    • Stephen Orlando
      Ansys Employee
      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/v211/en/sysc_ug/sysc_gen_scservice_dt_supplemental_iqnils.html
      System Coupling User's Guide \\ System Coupling Data Transfers \\ Supplemental Processing Algorithms \\ Quasi-Newton Stabilization Algorithm
      The instructions for how to move a Workbench System Coupling case into the new System Coupling GUI are found in this tutorial: Oscillating Plate FSI Co-Simulation with Partial Setup Export from Workbench (CFX-Mechanical) (ansys.com). This tutorial is for Mechanical and CFX, but the instructions for exporting the System Coupling setup from Workbench are the same for Mechanical and Fluent case (specifically the instructions found here: Export the Partial Co-Simulation Setup (ansys.com)).
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