CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Meshing & Mesh Conversion

[blockMesh] Strange non-hexahedral cells?

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 17, 2016, 09:35
Default Strange non-hexahedral cells?
  #1
New Member
 
Join Date: May 2016
Posts: 3
Rep Power: 10
maka15 is on a distinguished road
Hi,
I'm quite new to openfoam and I am seeing a strange behavior on a very simple blockMesh I want to use for snappyHexMesh..
It is just a cuboid with cube-cells, but when I view the Mesh with paraView, I see very strange cells, that I can't explain. I only see them in the middle of the block in the XZ-Plane. Attached you find an image of ParaView showing these strange cells, if you want to reconstruct using the Dicts below, create a slice in ParaView, click "Y normal" and don't move the plane...
Would be nice, if someone here has an idea, what I am doing wrong..

Thanks a lot for your help!

system/blockMeshDict
Code:
FoamFile
{
    version 2.0;
    format ascii;
    class dictionary;
    location system;
    object blockMeshDict;
}

    convertToMeters 1;
    vertices  
    (
      ( -0.02 -0.02 -0.032)
      ( 0.02 -0.02 -0.032)
      ( 0.02 0.02 -0.032)
      ( -0.02 0.02 -0.032)
      ( -0.02 -0.02 0.013)
      ( 0.02 -0.02 0.013)
      ( 0.02 0.02 0.013)
      ( -0.02 0.02 0.013)
    );
    blocks  
    ( 
      hex ( 0 1 2 3 4 5 6 7) ( 80 80 90)
      simpleGrading ( 1 1 1)
    );
    edges  
    (
    );
    patches  
    (
    );
    mergePatchPairs  
    (
    );
system/controlDict
Code:
FoamFile
{
    version 2.0;
    format ascii;
    class dictionary;
    location system;
    object controlDict;
}

    startFrom startTime;
    startTime 0;
    stopAt endTime;
    endTime 1000.0;
    deltaT 1.0;
    writeControl timeStep;
    writeInterval 1000.0;
    purgeWrite 0;
    writeFormat ascii;
    writePrecision 100;
    writeCompression uncompressed;
    timeFormat general;
    timePrecision 6;
    graphFormat raw;
    runTimeModifiable yes;
system/fvSchemes (only so paraFoam does not warn about missing files..)
Code:
FoamFile
{
    version 2.0;
    format ascii;
    class dictionary;
    location system;
    object fvSchemes;
}

    divSchemes
    {
    }

    gradSchemes
    {
    }

    laplacianSchemes
    {
    }
system/fvSolution (only so paraFoam does not warn about missing files..)
Code:
FoamFile
{
    version 2.0;
    format ascii;
    class dictionary;
    location system;
    object fvSolution;
}

    solvers
    {
    }
Attached Images
File Type: jpg block_mesh_strange_cells.jpg (196.5 KB, 27 views)
maka15 is offline   Reply With Quote

Old   May 17, 2016, 10:16
Default
  #2
Senior Member
 
Join Date: Aug 2013
Posts: 407
Rep Power: 16
Antimony is on a distinguished road
Hi,

Do a checkMesh and see the type of cells that it reports. My guess is that it will still be hexes.

The reason you see the weird cells is because Paraview decomposes polyhedral cells automatically and when you take a slice, it triangulates the slice. Uncheck both options and you will see that they are regular hexes only.

Cheers,
Antimony
Antimony is offline   Reply With Quote

Old   May 17, 2016, 11:17
Default
  #3
New Member
 
Join Date: May 2016
Posts: 3
Rep Power: 10
maka15 is on a distinguished road
Hi,

thanks for your help, Antimony!

checkMesh reports only hexes, you are right.

If I uncheck decomposing and triangulating, it does look better, but still weird, see attached image.

@Mods: It seems, this is more likely a problem with paraView than with blockMesh, could you please move the thread to the right subforum?
Attached Images
File Type: jpg block_mesh_strange_cells_2.jpg (201.8 KB, 18 views)
maka15 is offline   Reply With Quote

Old   May 19, 2016, 09:56
Default
  #4
Senior Member
 
Mikko
Join Date: Jul 2014
Location: The Hague, The Netherlands
Posts: 243
Rep Power: 13
Flowkersma is on a distinguished road
Hi,

Try using ExtractCellsByRegion filter when you want to visualize the mesh. If you want slice like behavior check Extract only intersected and Extract intersected marks. If you compare the results from ExtractCellsByRegion filter to the results of Slice filter, maybe you can find a reason for the "strange" behavior.

Regards,
Mikko
Flowkersma is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
[snappyHexMesh] SHM Layer Addition Phase dickcruz OpenFOAM Meshing & Mesh Conversion 4 November 1, 2018 08:05
Strange cells in Trimmed mesh yatsh94 Siemens 0 February 28, 2017 18:40
[snappyHexMesh] snappyHexMesh Segmentation Fault avd28 OpenFOAM Meshing & Mesh Conversion 11 May 11, 2015 21:32
[snappyHexMesh] snappyHexMesh aborting Tobi OpenFOAM Meshing & Mesh Conversion 0 November 10, 2010 04:23
7 Node Hexahedral Cells Mark FLUENT 0 February 5, 2007 12:10


All times are GMT -4. The time now is 05:35.