Preprocessing unstructured grids (tetrahedral mesh)

rakshith · January 18, 2010, 14:38

Hi,

I have recently started writing a 3D finite volume code. I am currently stuck in preprocessing the grids.

I would like to know the algorithm to construct the face neighbours (i.e. left cell and right cell to a face).

rakshith

zmester · January 18, 2010, 19:59

hi

Do you mean you have the grid in a certain format from an external software and you want to do the calculation with your own solver? I recommend you to use Gambit, Icem, etc for meshing and export the mesh in .msh format. This file contains the information about the left and right cell of a face.

rakshith · January 18, 2010, 23:41

Thanks a lot for the info. But I do not have access to any of the licensed grid generators. Hence I am using free softwares. Therefore I need to do all the preprocessing before it is fed into my solver.

julien.decharentenay · January 19, 2010, 00:37

Which software are you using?

For Gmsh, you probably need to match the nodes number to find the neighbours. And depending on your selected surface orientation, you will find the left and right.

If you are using open-source software, you may want to find another open-source software that reads the specific mesh format to see how they go about it.

Good luck
Julien

aspho_nour · May 15, 2010, 14:43

hi and i hope that's you are in good health.
i've downloaded and running gmsh 2.4.2 , when i've opened the file karman.geo this message appear:

Info : -------------------------------------------------------
Info : Gmsh version : 2.4.2
Info : Build OS : Windows
Info : Build options : Ann Blas Chaco DIntegration FlTree Fltk FltkJpeg FltkPng FltkZlib Gmm Lapack MathEx Med Metis NativeFileChooser Netgen NoSocklenT OpenCascade OpenGL Tetgen
Info : Build date : 20090921
Info : Build host : christop-e38ece
Info : Packager : Administrator
Info : Home directory : C:\DOCUME~1\HBNS\LOCALS~1\Temp/
Info : Launch date : Sat May 15 17:34:44 2010
Info : Command line : C:\Documents and Settings\HBNS\Bureau\gmsh.exe
Info : -------------------------------------------------------
Info : Reading 'D:/1_1_REDACTION_THESE/gmsh-2.4.2-Windows/tutorial/karman.geo'
Warning : Only automatic transfinite surface specifications can be copied
Warning : Only automatic transfinite surface specifications can be copied
Warning : Only automatic transfinite surface specifications can be copied
Warning : Only automatic transfinite surface specifications can be copied
Warning : Only automatic transfinite surface specifications can be copied
Warning : Only automatic transfinite surface specifications can be copied
Warning : Only automatic transfinite surface specifications can be copied
Warning : Only automatic transfinite surface specifications can be copied
Info : Read 'D:/1_1_REDACTION_THESE/gmsh-2.4.2-Windows/tutorial/karman.geo'

is there a solution for this error , does this error have an impact fot continue the work with it.

January 18, 2010, 14:38	Preprocessing unstructured grids (tetrahedral mesh)	#1
rakshith New Member rakshith Join Date: Jan 2010 Posts: 3 Rep Power: 16	Hi, I have recently started writing a 3D finite volume code. I am currently stuck in preprocessing the grids. I would like to know the algorithm to construct the face neighbours (i.e. left cell and right cell to a face). rakshith

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January 18, 2010, 19:59		#2
zmester New Member Zoltán Hercz Join Date: Sep 2009 Posts: 17 Rep Power: 17	hi Do you mean you have the grid in a certain format from an external software and you want to do the calculation with your own solver? I recommend you to use Gambit, Icem, etc for meshing and export the mesh in .msh format. This file contains the information about the left and right cell of a face.

January 18, 2010, 23:41		#3
rakshith New Member rakshith Join Date: Jan 2010 Posts: 3 Rep Power: 16	Thanks a lot for the info. But I do not have access to any of the licensed grid generators. Hence I am using free softwares. Therefore I need to do all the preprocessing before it is fed into my solver.

January 19, 2010, 00:37		#4
julien.decharentenay Senior Member Julien de Charentenay Join Date: Jun 2009 Location: Australia Posts: 231 Rep Power: 18	Which software are you using? For Gmsh, you probably need to match the nodes number to find the neighbours. And depending on your selected surface orientation, you will find the left and right. If you are using open-source software, you may want to find another open-source software that reads the specific mesh format to see how they go about it. Good luck Julien

May 15, 2010, 14:43		#5
aspho_nour New Member noureddine Join Date: May 2009 Posts: 4 Rep Power: 17	hi and i hope that's you are in good health. i've downloaded and running gmsh 2.4.2 , when i've opened the file karman.geo this message appear: Info : ------------------------------------------------------- Info : Gmsh version : 2.4.2 Info : Build OS : Windows Info : Build options : Ann Blas Chaco DIntegration FlTree Fltk FltkJpeg FltkPng FltkZlib Gmm Lapack MathEx Med Metis NativeFileChooser Netgen NoSocklenT OpenCascade OpenGL Tetgen Info : Build date : 20090921 Info : Build host : christop-e38ece Info : Packager : Administrator Info : Home directory : C:\DOCUME~1\HBNS\LOCALS~1\Temp/ Info : Launch date : Sat May 15 17:34:44 2010 Info : Command line : C:\Documents and Settings\HBNS\Bureau\gmsh.exe Info : ------------------------------------------------------- Info : Reading 'D:/1_1_REDACTION_THESE/gmsh-2.4.2-Windows/tutorial/karman.geo' Warning : Only automatic transfinite surface specifications can be copied Warning : Only automatic transfinite surface specifications can be copied Warning : Only automatic transfinite surface specifications can be copied Warning : Only automatic transfinite surface specifications can be copied Warning : Only automatic transfinite surface specifications can be copied Warning : Only automatic transfinite surface specifications can be copied Warning : Only automatic transfinite surface specifications can be copied Warning : Only automatic transfinite surface specifications can be copied Info : Read 'D:/1_1_REDACTION_THESE/gmsh-2.4.2-Windows/tutorial/karman.geo' is there a solution for this error , does this error have an impact fot continue the work with it.