Learning Forum

[Tolga]

Hello everyone,

I am trying to simulate sloshing effects on a baffle by using 2-Way FSI simulation. I coupled Transient Structural and Fluent for this purpose. Solution starts without any problem but once it reaches the t=0.68 s an error occurs. And it says that;

"Error at Node 4: alloc_thread_sv: storage already exists for SV_WALL_FACE_FORCE on thread 6, domain 2

999999: mpt_accept: warning: connection timed out after 120 secondsMPI Application rank 0 exited before MPI_Finalize() with status 2"

Also another thing that I realize is, convergence rate is too small and it has order of 1e-14. Is it because the motion is too slow?

[Stephen Orlando]

HiArray,nThere are a few things that can be done to investigate further. 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. For CFX, look at the .out file. Also, look at the System Coupling log file, .scl. It's also good to rerun the case, but stop it just before the known failure and then examine the results. This might give some clues as to what happened. What is the convergence target for the data transfers? It looks like the data transfers are converging, but either Fluent or Mechanical isn't converging in each coupling step.nI 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.htmlnSystem Coupling Tutorials \\ Tutorials with Workbench-Setup Workflows \\ Tutorials with Workbench Setup and Execution \\ Oscillating Plate FSI with Fluent and MechanicalnnYou can also look at the following for a similar tutorial but run with the System Coupling GUI outside of Workbench. The new System Coupling GUI (run outside of Workbench) is available by searching for System Coupling 2019R3 (or newer) in the Windows Start menu.https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v211/en/sysc_tut/sysc_tut_reedvalve_fluent.htmlnnFSI 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.htmlnSystem Coupling User's Guide \\ System Coupling Data Transfers \\ Supplemental Processing Algorithms \\ Quasi-Newton Stabilization AlgorithmnnIt 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/v211/en/sysc_ug/sysc_bestpractices_fsi.htmlnSystem Coupling User's Guide \\ Best Practices for System Coupling \\ Best Practices for Coupled Fluid-Structure Interaction (FSI)n