[Netgen] prismatic layer

vaina74 · January 20, 2011, 09:53

Hi, Netgen users.

is there a possibility to generate a prismatic layer or something similar in order to get closer to wall surfaces, avoiding too much large amount of cells?

philippose · January 22, 2011, 13:55

Hello there,

A Good Evening to you :-)! I hope its not too cold (like it is here) where ever you are located...!

Prismatic cells in Netgen.... well.... I had started on this about 8 to 10 months ago, and put together an extremely primitive functionality for creating prismatic cells specifically with the idea of "near-wall" meshes in mind.

You could try it out by going to the "special-> prismatic boundary layer" menu option after completing a full meshing (surface + volume) operation.

Once you select this option, in the console you are asked to provide a list of the face IDs (not the boundary condition IDs, but the actual face IDs which you can find in the console if you double click on a face after meshing) one after the other, till you provide an ID of "-1" which indicates the end of the list.

Then you can provide the height of the first layer (closest to the wall), followed by the number of layers, and a "growth / shrink" factor.

Once this is done, Netgen will attempt to create a set of layers consisting of prismatic cells.

Now.... this is highly experimental, and does not handle pyramid cells yet (required in some areas to interface between the layers and the rest of the volume mesh), and will fail in cases where the geometry is complicated.

Having said this much..... have you tried "Engrid"? Doesn't this software provide the capability to create boundary layers? I know that it uses the netgen meshing core for the volume meshing... but an in-house code for the boundary layers....

Have a nice day ahead!

Philippose

vaina74 · January 22, 2011, 14:35

Hi, Philippose.

Thanks for your detailed reply. I've just tried to apply your instructions but, after the prismatic layer menu option, nothing happens (all freezes). I think I have an old version (the last stable 4.9.13), maybe you refer to a 'dev' release. Anyway, it doesn't matter. You talked about a seriously primitive and experimental tool. I know and use enGrid and its prismatic layer function but it's a very, very, very slow process.
What about a tool for converting a tet into a polyhedral mesh? Are you working on this? It could be very interesting, even if OpenFOAM already gives the polyDualMesh application - but I've got some doubts about the meaning of the <angle> parameter.

Best regards.

January 20, 2011, 09:53	prismatic layer	#1
vaina74 Senior Member Join Date: Feb 2010 Posts: 213 Rep Power: 17	Hi, Netgen users. is there a possibility to generate a prismatic layer or something similar in order to get closer to wall surfaces, avoiding too much large amount of cells?

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January 22, 2011, 13:55		#2
philippose Senior Member Philippose Rajan Join Date: Mar 2009 Location: Germany Posts: 552 Rep Power: 25	Hello there, A Good Evening to you :-)! I hope its not too cold (like it is here) where ever you are located...! Prismatic cells in Netgen.... well.... I had started on this about 8 to 10 months ago, and put together an extremely primitive functionality for creating prismatic cells specifically with the idea of "near-wall" meshes in mind. You could try it out by going to the "special-> prismatic boundary layer" menu option after completing a full meshing (surface + volume) operation. Once you select this option, in the console you are asked to provide a list of the face IDs (not the boundary condition IDs, but the actual face IDs which you can find in the console if you double click on a face after meshing) one after the other, till you provide an ID of "-1" which indicates the end of the list. Then you can provide the height of the first layer (closest to the wall), followed by the number of layers, and a "growth / shrink" factor. Once this is done, Netgen will attempt to create a set of layers consisting of prismatic cells. Now.... this is highly experimental, and does not handle pyramid cells yet (required in some areas to interface between the layers and the rest of the volume mesh), and will fail in cases where the geometry is complicated. Having said this much..... have you tried "Engrid"? Doesn't this software provide the capability to create boundary layers? I know that it uses the netgen meshing core for the volume meshing... but an in-house code for the boundary layers.... Have a nice day ahead! Philippose

January 22, 2011, 14:35		#3
vaina74 Senior Member Join Date: Feb 2010 Posts: 213 Rep Power: 17	Hi, Philippose. Thanks for your detailed reply. I've just tried to apply your instructions but, after the prismatic layer menu option, nothing happens (all freezes). I think I have an old version (the last stable 4.9.13), maybe you refer to a 'dev' release. Anyway, it doesn't matter. You talked about a seriously primitive and experimental tool. I know and use enGrid and its prismatic layer function but it's a very, very, very slow process. What about a tool for converting a tet into a polyhedral mesh? Are you working on this? It could be very interesting, even if OpenFOAM already gives the polyDualMesh application - but I've got some doubts about the meaning of the <angle> parameter. Best regards.