# Growing Courant number in OpenFOAM FSI simulation

**URL:** <https://precice.discourse.group/t/growing-courant-number-in-openfoam-fsi-simulation/902>\
**Category:** Using preCICE\
**Tags:** openfoam, calculix, fsi\
**Created:** [February 9, 2022, 10:46am UTC](https://precice.discourse.group/t/growing-courant-number-in-openfoam-fsi-simulation/902 "2022-02-09T10:46:04Z")\
**Posts on this page:** 1\
**Showing post:** 4

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**Author:** ![Stan](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/stan/32/599_2.png) [@Stan](https://precice.discourse.group/u/Stan)\
**Post date:** [February 15, 2022, 2:34am UTC](https://precice.discourse.group/t/growing-courant-number-in-openfoam-fsi-simulation/902/4 "2022-02-15T02:34:17Z")

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Hi @Makis , I have the same issue while simulating a FSI case using OpenFOAM and our in-house solver with preCICE. Our solver converged well but the courant number became increasingly large at around 9s and then the OpenFOAM crashed at 9.26s. The log file of OpenFOAM solver and the configuration file are attached here. Since the log file is too large, I delete some content in it.  
[olaFlow\_part.zip](https://precice.discourse.group/uploads/short-url/wyKK2lvCQHk8uoBgfmkRHqPxUlQ.zip) (2.3 MB)  
[precice-config.xml](https://precice.discourse.group/uploads/short-url/uzp60w8fukRRstRzCnjUHNRPLzR.xml) (2.6 KB)  
Is it because the mesh deformation gets so large that the courant number rapidly increases and OpenFOAM crashes? Could you please share any hints on how to make the fluid mesh withstand larger deformation?

 ![InitialMesh](https://global.discourse-cdn.com/free1/uploads/precice/original/2X/8/8cf3746fac371e19c67829e711e2790ff3cda581.jpeg) Initial mesh ![FinalMesh](https://global.discourse-cdn.com/free1/uploads/precice/original/2X/1/1c28bdda958d03b6c7d284e0fbdf37d453c47699.jpeg) Final mesh

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