[snappyHexMesh] Local refinements

Kalabagh · September 1, 2021, 14:09

Hey there,

I'm in a 3D case with a complex geometry that implies complex meshing process. By now, I have reached a good mesh, but in some zones a local refinement is necessary.

The fact is that the type of local refinement I want to do is "edge refinement" as surfaces and regions nearby are ok and I don't want to overcharge more the mesh.

My question is how can I manage this with my snappyHexMeshDict??

I tried to create an .stl file with only the lines in their perfect position, but my software "Inventor" does not seem to agree with saving something that is just "lines", either in .stl.

Then I thought I would be able to call this file on the featureRefinement and assign refinement levels as normal.

Thanks.

Yann · September 2, 2021, 03:19

Hi,

You can use the surfaceFeatureExtract utility to extract the feature lines from your STL file. It will create a .eMesh file you can then use for featureRefinement in snappyHexMesh.

The surfaceFeatureExtract utility has been replaced by surfaceFeatures a while ago in the foundation branch so depending on the version you are running you need to use surfaceFeatureExtract or surfaceFeatures.

ESI-OpenCFD: https://develop.openfoam.com/Develop...ureExtractDict
OpenFOAM foundation: https://github.com/OpenFOAM/OpenFOAM...ceFeaturesDict

Cheers,
Yann

Kalabagh · September 23, 2021, 13:07

Hi Yann,

Thank you for your information. The fact is that I have learned a little bit more about surfaceFeatureExtract since your post. I've seen that you can adjust the amount of edges from stl file that will be included in the eMesh file. And also that with some adjustements you can made it so locally. But still, I don't see any possibility to select THAT specific edge I want. There is the "plane" option which all lines coplanar to the plane will get included. But if the geometry is a little complex, that plane will intersect also other zones of the mesh.

Is there any option to select specific edges and convert them into an eMesh file and use it in snappyHexMesh as another edge refinement?

Question: How to manage with the interference between the edge refinement coming from the general eMesh file and the local refinement that is using few but same edges??

Thanks

Yann · September 24, 2021, 03:36

Hi,

You can create a specific STL file containing only the surfaces around the edge you want to select and then use it with surfaceFeatureExtract. (Since you can use as many STL as you wish with surfaceFeatureExtract, and as many eMesh files as you wish with snappyHexMesh)

About your last question: you can control the refinement levels on edges, surfaces and volumes and snappy always keeps the finest level. So if you want a finer mesh on specific edges you just have to get an eMesh for these edges and define the refinement level you need. No matter if the surface refinement is coarser.

Cheers,
Yann

AtoHM · September 24, 2021, 05:06

Regarding your problem of exporting a line as stl: If you take a closer look at an stl in PV, or in the ascii file really, you will notice that the files consists of a list of triangles. There is no way to save a line as a triangle.

I am looking at an eMesh file of mine (I have never done before) and it seems, the file needs only some points and edges with point start and endindex. Would you be able to create the eMesh for your surface, identify the relevant edges you need to refine and delete the rest in the eMesh-file?

September 1, 2021, 14:09	Local refinements	#1
Kalabagh New Member Santi Parera Join Date: Jul 2019 Location: BARCELONA Posts: 25 Rep Power: 6	Hey there, I'm in a 3D case with a complex geometry that implies complex meshing process. By now, I have reached a good mesh, but in some zones a local refinement is necessary. The fact is that the type of local refinement I want to do is "edge refinement" as surfaces and regions nearby are ok and I don't want to overcharge more the mesh. My question is how can I manage this with my snappyHexMeshDict?? I tried to create an .stl file with only the lines in their perfect position, but my software "Inventor" does not seem to agree with saving something that is just "lines", either in .stl. Then I thought I would be able to call this file on the featureRefinement and assign refinement levels as normal. Thanks.

September 2, 2021, 03:19		#2
Yann Senior Member Yann Join Date: Apr 2012 Location: France Posts: 1,053 Rep Power: 26	Hi, You can use the surfaceFeatureExtract utility to extract the feature lines from your STL file. It will create a .eMesh file you can then use for featureRefinement in snappyHexMesh. The surfaceFeatureExtract utility has been replaced by surfaceFeatures a while ago in the foundation branch so depending on the version you are running you need to use surfaceFeatureExtract or surfaceFeatures. ESI-OpenCFD: https://develop.openfoam.com/Develop...ureExtractDict OpenFOAM foundation: https://github.com/OpenFOAM/OpenFOAM...ceFeaturesDict Cheers, Yann

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September 23, 2021, 13:07		#3
Kalabagh New Member Santi Parera Join Date: Jul 2019 Location: BARCELONA Posts: 25 Rep Power: 6	Hi Yann, Thank you for your information. The fact is that I have learned a little bit more about surfaceFeatureExtract since your post. I've seen that you can adjust the amount of edges from stl file that will be included in the eMesh file. And also that with some adjustements you can made it so locally. But still, I don't see any possibility to select THAT specific edge I want. There is the "plane" option which all lines coplanar to the plane will get included. But if the geometry is a little complex, that plane will intersect also other zones of the mesh. Is there any option to select specific edges and convert them into an eMesh file and use it in snappyHexMesh as another edge refinement? Question: How to manage with the interference between the edge refinement coming from the general eMesh file and the local refinement that is using few but same edges?? Thanks

September 24, 2021, 03:36		#4
Yann Senior Member Yann Join Date: Apr 2012 Location: France Posts: 1,053 Rep Power: 26	Hi, You can create a specific STL file containing only the surfaces around the edge you want to select and then use it with surfaceFeatureExtract. (Since you can use as many STL as you wish with surfaceFeatureExtract, and as many eMesh files as you wish with snappyHexMesh) About your last question: you can control the refinement levels on edges, surfaces and volumes and snappy always keeps the finest level. So if you want a finer mesh on specific edges you just have to get an eMesh for these edges and define the refinement level you need. No matter if the surface refinement is coarser. Cheers, Yann

September 24, 2021, 05:06		#5
AtoHM Senior Member M Join Date: Dec 2017 Posts: 642 Rep Power: 12	Regarding your problem of exporting a line as stl: If you take a closer look at an stl in PV, or in the ascii file really, you will notice that the files consists of a list of triangles. There is no way to save a line as a triangle. I am looking at an eMesh file of mine (I have never done before) and it seems, the file needs only some points and edges with point start and endindex. Would you be able to create the eMesh for your surface, identify the relevant edges you need to refine and delete the rest in the eMesh-file?