Mesh quality improvement

anon_a · February 14, 2012, 06:29

Hello Foamers

I have a simple mesh generated by blockMesh, which however contains some "bad" cells. I generate sets for these cells with "checkMesh -allTopology -allGeometry" and can visualize them in paraView after isolating them with "setSet -batch makeCellSets.setSet" and "subsetMesh badCells". However, I have not been able to fix them.

Is there a non-manual (scriptable) way of using the foam mesh manipulation utilities in which I could fix the "bad" cells? I am looking for a combination of the mesh manipulation tools that can improve the quality of my mesh, mostly in terms of simulation stability.

Sorry if the question is rather vague or this information has been posted elsewhere but I have not been able to find it.

anon_a · February 20, 2012, 09:19

Bump. I would appreciate an answer, even if it's negative.
I wonder what I am doing so wrong and no one answers my posts

wyldckat · February 20, 2012, 10:04

Greetings anon_a,

AFAIK, no, there is no utility in OpenFOAM that fixes bad cells. The standard is to do things right the first time around.

Nonetheless, there are a few things that might come in handy in some situations:

"applications/utilities/mesh/advanced/removeFaces" - should be able to remove excess faces that are between cells.
"applications/utilities/mesh/advanced/modifyMesh" - can do limited mesh manipulation, such as collapsing edges, which might be useful for taking out skew faces.

But, if the problem you are getting is with blockMesh, then it's you who is doing things wrong

Try:

Code:

paraFoam -block

This can help you visualize and diagnose what you might be wrongly defining on "blockMeshDict"

Best regards,
Bruno

anon_a · February 20, 2012, 11:47

Ok, I was sure I was the one doing it wrong :-D
My geometry is slightly more complicated than I can handle with blockMesh anymore, so I guess I will try something else.

I was asking because I would prefer to adapt the mesh to the changes in the flow along with time. For example, create the blockMesh in the beginning, run the simulation for 1ms, refine/remove cells, correct the "bad" cells, resume the simulation for 1 ms and so on. I am sure someone must have done something similar, right?

Thanks a lot for the answer Bruno!

wyldckat · February 20, 2012, 12:59

Ah, then that's a whole other ball game...
See the tutorials that use dynamic meshes, because there are several that use point displacement. But I've yet to understand how they work

anon_a · February 20, 2012, 13:08

I was afraid you were going to say that...
So the keyword here is point displacement, I will look for that.
Thanks :-)

February 14, 2012, 06:29	Mesh quality improvement	#1
anon_a Disabled Join Date: Mar 2011 Posts: 174 Rep Power: 15	Hello Foamers I have a simple mesh generated by blockMesh, which however contains some "bad" cells. I generate sets for these cells with "checkMesh -allTopology -allGeometry" and can visualize them in paraView after isolating them with "setSet -batch makeCellSets.setSet" and "subsetMesh badCells". However, I have not been able to fix them. Is there a non-manual (scriptable) way of using the foam mesh manipulation utilities in which I could fix the "bad" cells? I am looking for a combination of the mesh manipulation tools that can improve the quality of my mesh, mostly in terms of simulation stability. Sorry if the question is rather vague or this information has been posted elsewhere but I have not been able to find it.

February 20, 2012, 10:04		#3
wyldckat Retired Super Moderator Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 10,982 Blog Entries: 45 Rep Power: 128	Greetings anon_a, AFAIK, no, there is no utility in OpenFOAM that fixes bad cells. The standard is to do things right the first time around. Nonetheless, there are a few things that might come in handy in some situations: "applications/utilities/mesh/advanced/removeFaces" - should be able to remove excess faces that are between cells. "applications/utilities/mesh/advanced/modifyMesh" - can do limited mesh manipulation, such as collapsing edges, which might be useful for taking out skew faces. But, if the problem you are getting is with blockMesh, then it's you who is doing things wrong Try: Code: paraFoam -block This can help you visualize and diagnose what you might be wrongly defining on "blockMeshDict" Best regards, Bruno __________________ OpenFOAM: FAQ \| Getting started Forum: How to get help, to post code/output and forum guide Read this before sending me PM

February 20, 2012, 12:59		#5
wyldckat Retired Super Moderator Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 10,982 Blog Entries: 45 Rep Power: 128	Ah, then that's a whole other ball game... See the tutorials that use dynamic meshes, because there are several that use point displacement. But I've yet to understand how they work __________________ OpenFOAM: FAQ \| Getting started Forum: How to get help, to post code/output and forum guide Read this before sending me PM

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February 20, 2012, 09:19		#2
anon_a Disabled Join Date: Mar 2011 Posts: 174 Rep Power: 15	Bump. I would appreciate an answer, even if it's negative. I wonder what I am doing so wrong and no one answers my posts

February 20, 2012, 11:47		#4
anon_a Disabled Join Date: Mar 2011 Posts: 174 Rep Power: 15	Ok, I was sure I was the one doing it wrong :-D My geometry is slightly more complicated than I can handle with blockMesh anymore, so I guess I will try something else. I was asking because I would prefer to adapt the mesh to the changes in the flow along with time. For example, create the blockMesh in the beginning, run the simulation for 1ms, refine/remove cells, correct the "bad" cells, resume the simulation for 1 ms and so on. I am sure someone must have done something similar, right? Thanks a lot for the answer Bruno!

February 20, 2012, 13:08		#6
anon_a Disabled Join Date: Mar 2011 Posts: 174 Rep Power: 15	I was afraid you were going to say that... So the keyword here is point displacement, I will look for that. Thanks :-)