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-   -   Scaling and SnappyHexMesh (http://www.cfd-online.com/Forums/openfoam-pre-processing/120792-scaling-snappyhexmesh.html)

kingmaker July 15, 2013 05:27

Scaling and SnappyHexMesh
 
Hello

I am trying to do a blower simulation. I have a working simulation. But while checking throught the log files I found that I have "did not succesfully snap mesh. Giving up" statement at the end of snappyHexMesh. So I searched some thing and some one suggested that we have to scale the mesh to correct units before doing snappyHexMesh.
I did it.

Now the problem is when I scale the mesh before snappyHexMesh, Some of the patches which should have faces on them are shown as empty and are removed by "createPatch" utility.

I am confused what I am doing wrong. Do I also have to change the base mesh. ?? :confused:

Here is the outline of the sequence of operations I perform before solving :

PHP Code:

1.surfaceFeatureExtract
2.BlockMesh
3.Decomposepar
4.transformPoint
(scaling)
5.snappyHexmesh
6.reconstructParMesh
7.toposet
8.decomposePar
9.MRFSimpleFoam 

(I am running a parallel simulation)

or is there any other reason for getting this "did not succesfully snap mesh. Giving up" problem...??

Thanks in advance

colinB July 15, 2013 06:21

Dear kingmaker,

Quote:

1.surfaceFeatureExtract
2.BlockMesh
3.Decomposepar
4.transformPoint
(scaling)
5.snappyHexmesh
6.reconstructParMesh
7.toposet
8.decomposePar
9.MRFSimpleFoam

in order to have get snappyHexMesh to do the meshing right
both the background mesh from blockMesh as well as the
stl file have to have the same scale.

So in order to do so you should scale the mesh before the domain
and stl file are decomposed, so the correct order of your workflow
should look like follows:

Quote:

1.surfaceFeatureExtract
2.BlockMesh
3.
transformPoint(scaling)
4.decomposePar

5.snappyHexmesh
6.reconstructParMesh
7.toposet
8.decomposePar
9.MRFSimpleFoam

one more question why do you use topoSet?
It looks to me like you are trying to refine the mesh in certain
regions, but are missing the refineMesh command, am I right?

I hope I could contribute
regards

kingmaker July 15, 2013 07:40

Hello colinB

Thank you for your reply. I will try this and post the result. Also about topoSet, I just do some patch merges and invertions in topoSet to make things easy. I am not doing any refinement there. So is it also necessary to do "refineMesh" command after that.. ??

colinB July 15, 2013 09:05

Hi

concerning topoSet:

I understand topoSet as a selection tool to pick certain cells in a region
and therefore I would expect a manipulation command right afterwards
like the refineMesh command (this is what I use it for).
So if you don't want to refine anything you don't have to use the command
here of course.

However I don't have a clue how to perform mesh merges and inversions
so I can not tell you whether the command is placed properly here and
whether it is maybe the source of your error message.

regards


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