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Improving the quality of the polyhedral cells
  • lhcamilo September 2012
    Dear all,


    I am sorry to bother you with this, but recently I have been using engrid to generate a hex-polyhedra mesh hybrid grid for a pipe geometry to be run in OpenFOAM. The hexahedra mesh compose the boundary layer near the wall and the polyhedra compose the bulk region of the pipe. The tutorials have been quite helpful and thus far I have been quite successful. I was really pleased with the way the transition between hex/polyhedra was handled by Engrid.

    However as the following picture suggests,(https://docs.google.com/open?id=0B2Jogq8TtHDtbjk0Y19qMk1QNE0 ), there is still room for improvement. I have market out the type of cells that I want to avoid.

    Basically, I would like to humbly request some tips on how to create a more smooth polyhedral mesh in the bulk region and avoid such irregular cells. I am not sure exactly how to tackle this problem, I am clearly out of my depth here but I am eager to learn. Are there any particular settings that could help me? Should I try to improve the improve the surface mesh to produce more isometric triangles (and if so how would I go about doing that?)?

    Thanks in advance for the help.

    Leo
  • Oliver September 2012
    Leo,

    it looks like you used the old version of the polyhedral export. Try to compile the branch "release-1.4" from the GIT repository and the problem should be gone.

    Cheers,
    Oliver

  • lhcamilo September 2012
    Dear Oliver,


    Thank you very much for the speedy reply. I am really glad that the solution to my problem is simpler than I anticipated.

    Nevertheless, I might need to ask you to bear with me for a little longer. As you suggested, I did end up cloning the release branch from the github repo (git clone -b release-1.4 ), changed the necessary files to accommodated ubuntu 12.04 (namely build.bash and /src/scripts/setup_pathes.bash) and everything seemed to work well enough. I then launched Engrid and by checking the menu I could indeed verify that this was no longer v1.3.

    My problems started when I tried to export the polyhedra using the openfoam export tool, as it turns out the option was greyed out. So I went to settings and verified that the enable experimental features box was already ticked. So I unticked it, restarted Engrid, ticked it again, and restarted Engrid one more time. Sadly the export tool was still greyed out.

    Is there maybe another way of activating the openfoam polyhedral export tool?


    Thanks again for your help.

    cheers,

    Leo
  • Oliver September 2012
    Leo,

    shame on me: I removed the function from the experimental features and forgot to activate it in the main window ...

    Anyway, it should be working now!

    Cheers,
    Oliver
  • lhcamilo September 2012
    That did it, the concave cells are gone.


    Thank you very much for your help. Now I am going to try an tweak the mesh to see if I can improve it a little.


    Cheers,

    Leo
  • phsieh2005 November 2012
    Hi, Leo,

    Could you please tell how to generate and export polyhedral cells for openFoam cases?

    Thanks!

    Peiying
  • lhcamilo November 2012
    Hi there,

    In principle yes, I could make a report/tutorial of the steps I have taken,This would be for a pipe profile that I end up extruding with openFOAM' s extrudeMesh. The cells are then extruded polyhedrals.
    Unfortunately I am bit busy at the moment, I may be able to do that over the weekend but I am not making any promises, I will give it a shot.

    Regards,

    Leo
  • Oliver November 2012
    Hello Peiying,

    you can simply choose Export -> OpenFOAM -> polyhedral and the grid will be exported as polyhedral grid.

    Cheers,
    Oliver