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  • MixSim 2.1 - meshing failure

  • When MixSim 2.1 fails to generate a mesh, several things can be done to help it.
    Meshing failures can look different:
    - A messagse appears telling that meshing failed for a certain object. It tells the user to look for more information in the main text console window, and it asks whether the Gambit database should be saved for manual investigation and repair.
    - Gambit fails without MixSim realising that. A series of unintelligible error message scrolls through the main text console window, and finally, the FLUENT client process crashes: On Windows, a separate message is brought up by the Operating System, telling about a serious problem in fl6220.exe. ("fl6220.exe has encountered a problem and needs to close. We are sorry for the inconvenience.") On Linux, error messages including a stack backtrace appear in the main text console window, telling about a segmentation violation. In the Gambit transcript, the last line may tell "ERROR: Defaults does not exist."
    - Another variant: Gambit succeeds, the mesh is exported by Gambit and read by MixSim's FLUENT component. But then, either a warning tells the user about bad mesh quality and to expect convergence troubles, or the FLUENT process fails at establishing the mesh topology ("Building grid...") and decides to clear the partially read grid from the memory. A series of error messages appears when MixSim attempts to set up the FLUENT case.
    If, during meshing, a dialog window pops up telling that meshing failed, and asking whether to save the Gambit database for manual investigation and repair, it is safe to answer yes. In this situation, check the transcript in the main text console window for additional information. If you can confirm that the problem occurred during volume meshing of a volume named "tank", the following is likely to help:

    Exit from MixSim in order to close its GAMBIT process.
    Load the GAMBIT database in GAMBIT -- consider using GAMBIT 2.3.16.
    Delete all volume meshes.
    Remesh all volumes, one by one (!!!), using the settings that appear in the appropriate panel when you pick the volume. Make sure you use "remove old mesh" AND "remove unused lower mesh"! Also please make sure the "tank" volume is the LAST one to be meshed.
    Export the mesh. Launch MixSim. Load the Model file (the last one ever saved immediately before the failing meshing run was started -- its modification date & time may even be identical or shortly after the creation date of the journal file itself!). Use "Grid -- Load Existing Grid File" to load the mesh. Proceed as usual.If the conditions mentioned in the first "Resolution" entry of this Solution don't apply, choose the following route:
    - Use "Grid -- Create Gambit Journal File".
    - Close MixSim. Delete any existing *.lok files.
    - Launch MixSim 2.2.30 (!!). If you haven't installed it, you can launch it from the .../Fluent.Inc/mixsim2.1.10 installation directory. Underneath that, you will find "bin/gambit" on Linux or "ntbinntx86gambit.exe" on Windows. (Make sure you haven't any environment variable "FLUENT_INC" set! On an lnamd64 machine, prepend "env FLUENT_ARCH=lnx86".
    - Run the Gambit journal created by MixSim.
    NOTE: Any parameter "Minimum Surface Mesh Size" will fail to have an effect this way. That means, if a short edge is found in the surface geometry, the automatically set meshing parameters may cause the mesher to produce an excessive number of small cells. In that case, check and improve the geometry, or increase the "Shortest Edge Multiplier" for that object!
    - After successful completion of the journal runin Gambit, export the mesh.
    - Launch MixSim; load the latest model file that was ever saved immediately before creating the journal file. (Its modification date & time may even be identical or shortly after the creation date of the journal file itself!) Use "Grid -- Load Existing Grid File" to load the mesh you've just created in GAMBIT 2.3. Proceed as usual.In cases where GAMBIT crashes without any message other than "ERROR: Defaults does not exist" in the transcript file, the following has been found to help:

    Apply the following patch to a personal copy of the file .../Fluent.Inc/mixsim2.1.10/Mixsim-Object-Library/CylindricalTank.mxo, place that file in a directory for your personal MixSim Object Definition files. In MixSim, before you create a new model, specify that directory as the "User Object Directory/Library Path". Make the specification permanent by using "File -- Save Defaults".
    This will affect subsequently generated models.

    To update/fix existing model files, you can apply the same patch to the existing model files!

    --- CylindricalTank.mxo 9 Oct 2006 15:46:28 -0000 1.70
    +++ CylindricalTank.mxo 2 Nov 2006 11:03:14 -0000
    @@ -628,9 +628,9 @@
    234 do param "$facCtotriate" init 1
    234 cond($facCtotriate .le. $facNtotriate)
    234 $factodo = $facstotriate[$facCtotriate]
    234 if cond(0 .eq. quality(q_essk, q_gt, -1, $factodo))
    - 234 default set "MESH.FACE.EXACT_MESH_EVALS" numeric 0
    + 232 default set "MESH.FACE.EXACT_MESH_EVALS" numeric 0
    234 face mesh $factodo triangle size $trianglesize
    234 if cond(0 .ne. opererr())
    234 $badfacet = 999999
    234 $midfacet = 999999
    @@ -646,8 +646,9 @@
    234 if cond(0 .lt. ($badfacet + $midfacet))
    234 default set "MESH.FACE.EXACT_MESH_EVALS" numeric 1
    234 face delete $factodo lowertopology onlymesh
    234 face mesh $factodo triangle size $trianglesize
    + 234 default set "MESH.FACE.EXACT_MESH_EVALS" numeric 0
    234 if cond(0 .ne. opererr())
    234 $badexact = 999999
    234 $midexact = 999999
    234 else
    @@ -665,9 +666,8 @@
    234 else
    234 $ifposredofacet = $midexact - $midfacet
    234 endif
    234 if cond($ifposredofacet .gt. 0)
    - 234 default set "MESH.FACE.EXACT_MESH_EVALS" numeric 0
    234 face delete $factodo lowertopology onlymesh
    234 face mesh $factodo triangle size $trianglesize
    234 endif
    234 endif



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