[Other] how to remove or join bad/tiny cells

cutter · December 15, 2014, 10:15

Hi everybody,

from time to time I have severe problems with meshes that contain bad shaped or very small cells in areas with high fluid velocities or gradients. The cells usually result from the refinement and snapping process of snappyHexMesh or cartesianMesh (cfMesh). Due to these bad cells the simulations either run extremely slow (Courant adaption) or even crash (numeric problems).

Please let me know if you know a tool that allows to join small/bad cells with neighboring cells in order to weaken the CFL conditions or improve the mesh quality!

I already know I can remove some of the bad cells by using checkMesh and setSet (see https://openfoamwiki.net/index.php/SetSet). I also know that it's much better to obtain a better mesh in the first place, but that's not possible for some really complicated geometries.

Thanks!
Cutter

chriss85 · December 18, 2014, 04:11

I'm also interested in this. You can use the Co utility to generate a field containing the CFL values, and then filter it with topoSet I think. But I don't know how to go on from there. How to join specific cells with neighbours?

December 15, 2014, 10:15	how to remove or join bad/tiny cells	#1
cutter Senior Member Join Date: Mar 2010 Location: Germany Posts: 154 Rep Power: 16	Hi everybody, from time to time I have severe problems with meshes that contain bad shaped or very small cells in areas with high fluid velocities or gradients. The cells usually result from the refinement and snapping process of snappyHexMesh or cartesianMesh (cfMesh). Due to these bad cells the simulations either run extremely slow (Courant adaption) or even crash (numeric problems). Please let me know if you know a tool that allows to join small/bad cells with neighboring cells in order to weaken the CFL conditions or improve the mesh quality! I already know I can remove some of the bad cells by using checkMesh and setSet (see https://openfoamwiki.net/index.php/SetSet). I also know that it's much better to obtain a better mesh in the first place, but that's not possible for some really complicated geometries. Thanks! Cutter

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December 18, 2014, 04:11		#2
chriss85 Senior Member Join Date: Oct 2013 Posts: 397 Rep Power: 19	I'm also interested in this. You can use the Co utility to generate a field containing the CFL values, and then filter it with topoSet I think. But I don't know how to go on from there. How to join specific cells with neighbours?