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SHM for CHT: it is meshing where it shouldnt be

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Old   April 30, 2016, 13:54
Default SHM for CHT: it is meshing where it shouldnt be
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Lisandro Maders
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Hi everybody,

I am trying to make a mesh for a CHT problem. The problem is show in Figure attached, this is a cut in the symmetry plane.

I want to have a fluid mesh between the internal blue surface and red one; and want to have a solid mesh between the red surface and the external blue one.

What is snappyHexMesh doing for now: it is meshing everything, including the bounding box created with blockMesh; or there are cases in which it does not mesh the internal blue, which is correct, but keep meshing the bounding box;

I believe it is not recognizing well the external surface. I am new in SHM so it is possible I am not using proper refine values.

My big doubts are: there is only one place to set the location point of the mesh in SHMdict. I have looked at the tutorial of CHT mesh and it is placed inside any of the domains (it seems that does not matter). So I think it is possible that it will create 3 regions of mesh, and I need to delete the most internal one (inside the internal blue surface, which i do not want). Is it right? If so, how to do so..

OBS: I have followed some instructions and hints of other threads here in the forum but it did not work for me..

Regards,

Lisandro Maders
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File Type: png snappyHexMesh_CHT_Problem.png (18.4 KB, 13 views)
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Old   April 30, 2016, 14:26
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I will put some pictures of what it is doing and also what it should do. I did mesh the regions separately to test the parameters, so the final mesh should be a sum of the 2..
Attached Images
File Type: png malha_fluido.png (111.7 KB, 13 views)
File Type: png malha_solido.png (82.6 KB, 11 views)
File Type: png regionMeshed.png (106.7 KB, 10 views)
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Old   April 30, 2016, 16:21
Default Improving a bit but still needing some help with SHM
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Here is where I am at the moment..

I was able to at least have separated regions for fluid and solid zones, that is what I want. However, I still have 2 extra domains which I do not want. They can be seen in Figure "internalMesh_BlueSurface", which is the yellow region meshed, inside the internal cylinder; and in the Figure "blockMesh_boundingBoxMesh". The latter I really do not understand, why is it meshing between the blockMesh bounding box and my external surface?

Any way, is it ok to delete the regions I do not want and rename the patches like fluidZone_to_domain3, for example?

Regards,

Lisandro Maders
Attached Images
File Type: png cfd_online1.png (55.9 KB, 9 views)
File Type: png fluidZone.png (184.4 KB, 10 views)
File Type: png solidZone.png (97.2 KB, 7 views)
File Type: png internalMesh_BlueSurface.png (41.9 KB, 8 views)
File Type: png blockMesh_boundingBoxMesh.png (142.7 KB, 9 views)
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Old   April 30, 2016, 19:01
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Trying and learning. I do not know if this is the correct way of doing so, but what worked for me was:

1. Specify the location point inside any place between any surfaces.
2. Specify locationInMesh parameter in snappyHexMeshDict for each cellZone you want (in my case, fluid and solid zones)
3. Then, it will generate 4 domains: fluid, solid (which I want), domainX (bounding box of blockMesh until external surface) and domainY (inside my internal cylinder, which I do not want a mesh).
4. Then, I did what is specified in Background Mesh in snappy with multi domain (CHT) , using setSet to specify the zones I want. I am not sure if this is really necessary, maybe I could jump to step 5.
5. Once in my constant/regionProperties it is said which cellZones are fluid and solid, it will only calculate such regions, so I believe the solver is blind for domainX and domainY regions..

If anyone with more experience could confirm it, it would be good.


Regards,

Lisandro Maders
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Old   May 10, 2016, 06:15
Default Not able to use STL regions for patches
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I have a STL file with multiple regions, like:

"solid region1
...
endsolid region1
solid region2
.....
endsolid region2"

But I am not being able to use them to create patches. I am specifying them as regions in snappyHexMeshDict like below. What am I doing wrong?

I have attached the entire snappyHexDict file as well.

Code:
   raiox.stl
   {
       type triSurfaceMesh;
       name raiox;
       regions
       {
           calor_emissao
           {
                name calor_emissao;
           }
           calor_fonte
           {
                name calor_fonte;
           }
           furos
           {
                name furos;
           }
           sup_raiox
           {
                name sup_raiox;
           }
           ventilador
           {
                name ventilador;
           }
       }
I am really struggling with this, if anyone could give me some hints, I would appreciate.

I think I can be setting something wrong in snappyHexMeshDict, but I do not know what it can be..


Looking forward for some answer. Cheers
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File Type: zip snappyHexMeshDict.zip (3.8 KB, 0 views)
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Old   May 10, 2016, 06:47
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Are you certain your STL is watertight?
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Old   May 10, 2016, 11:42
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Yes because it is meshing properly. I have the regions now in the way I want. The only thing is bothering me is that it creates 2 extra "domain" regions. But I read in some threads here that I can just ignore because in the regionProperties file I say which are the regions I really want to make the calculations.

So, if this "issue" of creating extra domains is not really an issue, my problem now is to use the separated stl regions as boundary conditions...
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