[JKP]

Dear all,


I am fairly new to OpenFoam and kind of teaching myself here.

At the moment I have a specific problem I am trying to solve of exhaust gas flow (supposedly) being laminarised by perforated plates.

I was able to build and run the case without any obstacles in the construction which worked fine.


Now I added the perforated plates in the stl files (Blender) and am trying to mesh it but I am struggling to get a valid mesh for my simulation.

After BlockMesh it is still fine and the castellation seems to be fine as well then the wheels seem to come off in the snapping phase I think. I do not have enough experience with snappyHexMesh to decide where to go from here in order to reduce checkMesh errors.
Here is the checkMesh result:

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Topological cell zip-up check OK.
    Face-face connectivity OK.
  <<Writing 8 cells with two non-boundary faces to set twoInternalFacesCells
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
                   Patch    Faces   Points                  Surface topology Bounding box
                   inlet    14381    15070  ok (non-closed singly connected) (3.46945 29.8359 -1.49903) (5.92666 31.5565 1.49903)
                   walls   909073  1032337  ok (non-closed singly connected) (-4.00381 -14.5776 -4.00378) (5.92666 31.5565 4.0038)
                     hp1   162374   169347      ok (closed singly connected) (-2.83194 12.277 -2.84054) (2.81408 12.3229 2.80655)
                     hp2   272382   283339      ok (closed singly connected) (-3.66778 9.82214 -3.63524) (3.70164 9.87094 3.69692)
                  outlet    29312    29805  ok (non-closed singly connected) (-2.02366 -14.5776 -2.02366) (2.02366 -14.5775 2.02366)

Checking geometry...
    Overall domain bounding box (-4.00381 -14.5776 -4.00378) (5.92666 31.5565 4.0038)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (2.85443e-16 -6.7258e-16 -1.09876e-14) OK.
    Max cell openness = 6.3046e-16 OK.
    Max aspect ratio = 37.8632 OK.
    Minimum face area = 2.47539e-06. Maximum face area = 0.0650258.  Face area magnitudes OK.
    Min volume = 3.35581e-08. Max volume = 0.0160424.  Total volume = 1408.94.  Cell volumes OK.
    Mesh non-orthogonality Max: 65.2569 average: 11.3054
    Non-orthogonality check OK.
    Face pyramids OK.
 ***Max skewness = 6.84115, 7 highly skew faces detected which may impair the quality of the results
  <<Writing 7 skew faces to set skewFaces
    Coupled point location match (average 0) OK.
 ***Error in face tets: 209 faces with low quality or negative volume decomposition tets.
  <<Writing 209 faces with low quality or negative volume decomposition tets to set lowQualityTetFaces
    Min/max edge length = 0.000278067 0.256505 OK.
   *There are 25676 faces with concave angles between consecutive edges. Max concave angle = 87.0458 degrees.
  <<Writing 25676 faces with concave angles to set concaveFaces
    Face flatness (1 = flat, 0 = butterfly) : min = 0.331368  average = 0.999085
   *There are 153 faces with ratio between projected and actual area < 0.8
    Minimum ratio (minimum flatness, maximum warpage) = 0.331368
  <<Writing 153 warped faces to set warpedFaces
    Cell determinant (wellposedness) : minimum: 0 average: 13.449
 ***Cells with small determinant (< 0.001) found, number of cells: 33
  <<Writing 33 under-determined cells to set underdeterminedCells
 ***Concave cells (using face planes) found, number of cells: 521150
  <<Writing 521150 concave cells to set concaveCells
    Face interpolation weight : minimum: 0.0220622 average: 0.450148
 ***Faces with small interpolation weight (< 0.05) found, number of faces: 12129
  <<Writing 12129 faces with low interpolation weights to set lowWeightFaces
    Face volume ratio : minimum: 0.0105608 average: 0.773804
    Face volume ratio check OK.

Failed 5 mesh checks.

And here is my snappyHexMeshDict:

// Settings for the castellatedMesh generation.
castellatedMeshControls
{

    // Refinement parameters
    // ~~~~~~~~~~~~~~~~~~~~~

    // If local number of cells is >= maxLocalCells on any processor
    // switches from from refinement followed by balancing
    // (current method) to (weighted) balancing before refinement.
    maxLocalCells 200000;

    // Overall cell limit (approximately). Refinement will stop immediately
    // upon reaching this number so a refinement level might not complete.
    // Note that this is the number of cells before removing the part which
    // is not 'visible' from the keepPoint. The final number of cells might
    // actually be a lot less.
    maxGlobalCells 5000000;

    // The surface refinement loop might spend lots of iterations refining just a
    // few cells. This setting will cause refinement to stop if <= minimumRefine
    // are selected for refinement. Note: it will at least do one iteration
    // (unless the number of cells to refine is 0)
    minRefinementCells 10;

    // Allow a certain level of imbalance during refining
    // (since balancing is quite expensive)
    // Expressed as fraction of perfect balance (= overall number of cells /
    // nProcs). 0=balance always.
    maxLoadUnbalance 0.10;


    // Number of buffer layers between different levels.
    // 1 means normal 2:1 refinement restriction, larger means slower
    // refinement.
    nCellsBetweenLevels 2;



    // Explicit feature edge refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    // Specifies a level for any cell intersected by its edges.
    // This is a featureEdgeMesh, read from constant/triSurface for now.
    features
    (
        { file "vdk.eMesh"; level 4; }
    );



    // Surface based refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~

    // Specifies two levels for every surface. The first is the minimum level,
    // every cell intersecting a surface gets refined up to the minimum level.
    // The second level is the maximum level. Cells that 'see' multiple
    // intersections where the intersections make an
    // angle > resolveFeatureAngle get refined up to the maximum level.

    refinementSurfaces
    {
        vdk
    {
        //Global surface refinement level
        level (0 0);

        //Local (per region) refinement level
        regions
        {
            inlet
        { level (1 1); patchInfo { type patch; } }

            pp1
        { level (5 5); patchInfo { type wall; } }

            pp2
        { level (5 5); patchInfo { type wall; } }

            walls
        { level (2 2); patchInfo { type wall; } }

            outlet
        { level (1 1); patchInfo { type patch; } }
        }
    }
    }

    // Resolve sharp angles
    resolveFeatureAngle 30;


    // Region-wise refinement
    // ~~~~~~~~~~~~~~~~~~~~~~

    // Specifies refinement level for cells in relation to a surface. One of
    // three modes
    // - distance. 'levels' specifies per distance to the surface the
    //   wanted refinement level. The distances need to be specified in
    //   descending order.
    // - inside. 'levels' is only one entry and only the level is used. All
    //   cells inside the surface get refined up to the level. The surface
    //   needs to be closed for this to be possible.
    // - outside. Same but cells outside.

    refinementRegions
    {
        vdk
    {
        mode distance;    //distance, inside, outside
        levels 
        (
        (1e-3 4)
        (1e-2 3)
        (1 1)
        );
    }
    }


    // Mesh selection
    // ~~~~~~~~~~~~~~

    // After refinement patches get added for all refinementSurfaces and
    // all cells intersecting the surfaces get put into these patches. The
    // section reachable from the locationInMesh is kept.
    // NOTE: This point should never be on a face, always inside a cell, even
    // after refinement.
    locationInMesh (0 0 0);


    // Whether any faceZones (as specified in the refinementSurfaces)
    // are only on the boundary of corresponding cellZones or also allow
    // free-standing zone faces. Not used if there are no faceZones.
    allowFreeStandingZoneFaces true;
}



// Settings for the snapping.
snapControls
{
    //- Number of patch smoothing iterations before finding correspondence
    //  to surface
    nSmoothPatch 8;

    //- Relative distance for points to be attracted by surface feature point
    //  or edge. True distance is this factor times local
    //  maximum edge length.
    tolerance 2.0;

    //- Number of mesh displacement relaxation iterations.
    nSolveIter 300;

    //- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    nRelaxIter 8;

    // Feature snapping

        //- Number of feature edge snapping iterations.
        //  Leave out altogether to disable.
        nFeatureSnapIter 10;

        //- Detect (geometric only) features by sampling the surface
        //  (default=false).
        implicitFeatureSnap false;

        //- Use castellatedMeshControls::features (default = true)
        explicitFeatureSnap true;

        //- Detect points on multiple surfaces (only for explicitFeatureSnap)
        multiRegionFeatureSnap false;
}



// Settings for the layer addition.
addLayersControls
{
    // Are the thickness parameters below relative to the undistorted
    // size of the refined cell outside layer (true) or absolute sizes (false).
    relativeSizes true;

    // Per final patch (so not geometry!) the layer information
    layers
    {
         pp1 { nSurfaceLayers 3; }       
         pp2 { nSurfaceLayers 3; }       
         walls { nSurfaceLayers 3; }       
    }

    // Expansion factor for layer mesh
    expansionRatio 1.0;

    // Wanted thickness of final added cell layer. If multiple layers
    // is the thickness of the layer furthest away from the wall.
    // Relative to undistorted size of cell outside layer.
    // See relativeSizes parameter.
    finalLayerThickness 0.3;

    // Minimum thickness of cell layer. If for any reason layer
    // cannot be above minThickness do not add layer.
    // Relative to undistorted size of cell outside layer.
    minThickness 0.1;

    // If points get not extruded do nGrow layers of connected faces that are
    // also not grown. This helps convergence of the layer addition process
    // close to features.
    // Note: changed(corrected) w.r.t 17x! (didn't do anything in 17x)
    nGrow 0;

    // Advanced settings

    // When not to extrude surface. 0 is flat surface, 90 is when two faces
    // are perpendicular
    featureAngle 60;

    // At non-patched sides allow mesh to slip if extrusion direction makes
    // angle larger than slipFeatureAngle.
    slipFeatureAngle 30;

    // Maximum number of snapping relaxation iterations. Should stop
    // before upon reaching a correct mesh.
    nRelaxIter 3;

    // Number of smoothing iterations of surface normals
    nSmoothSurfaceNormals 1;

    // Number of smoothing iterations of interior mesh movement direction
    nSmoothNormals 3;

    // Smooth layer thickness over surface patches
    nSmoothThickness 10;

    // Stop layer growth on highly warped cells
    maxFaceThicknessRatio 0.5;

    // Reduce layer growth where ratio thickness to medial
    // distance is large
    maxThicknessToMedialRatio 0.3;

    // Angle used to pick up medial axis points
    // Note: changed(corrected) w.r.t 17x! 90 degrees corresponds to 130 in 17x.
    minMedianAxisAngle 90;


    // Create buffer region for new layer terminations
    nBufferCellsNoExtrude 0;


    // Overall max number of layer addition iterations. The mesher will exit
    // if it reaches this number of iterations; possibly with an illegal
    // mesh.
    nLayerIter 50;
}

I am adding a picture and hope that will help to show the problem.



Can someone point me into the right direction of what to try next to avoid skewed and distorted cells?


Kind regards
Jan

[JKP]

OK


So I did a little testing but I was not able to improve the mesh so far.

I have concentrated on the snappy dict file and tried with higher and lower tolerance in the snapping step and then with lower and higher amount of refinement.



I still get the same errors apart from the interpolation weight problem.


So far finer Mesh seems to be the way to go as it at least lowered the amounts of the problems whereas a higher tolerance didn't help.



I am still in over my head here and would be glad for some ideas. Is Snappy even the right place to look? is it the stl? should I work on the blender model?



Any brainstorm to reduce my trial runs is appreciated as meshing this takes some time.


Here is the result after increasing the refinement area around the mesh. And I switched off the layers for the perforated plates for now until I get the snapping under control.

Enabling all (cell, face, edge, point) topology checks.

Enabling all geometry checks.

Time = 2

Mesh stats
    points:           6871617
    faces:            17318462
    internal faces:   15931314
    cells:            5281067
    faces per cell:   6.29603
    boundary patches: 11
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     4131864
    prisms:        273681
    wedges:        0
    pyramids:      0
    tet wedges:    444
    tetrahedra:    0
    polyhedra:     875078
    Breakdown of polyhedra by number of faces:
        faces   number of cells
            4   119509
            5   99453
            6   173822
            7   368
            8   332
            9   302110
           10   235
           11   215
           12   119948
           13   100
           14   35
           15   53680
           17   12
           18   5256
           21   3

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Topological cell zip-up check OK.
    Face-face connectivity OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
                   Patch    Faces   Points                  Surface topology Bounding box
                      p0        0        0                        ok (empty)
                      p1        0        0                        ok (empty)
                      p2        0        0                        ok (empty)
                      p3        0        0                        ok (empty)
                      p4        0        0                        ok (empty)
                      p5        0        0                        ok (empty)
                   inlet    13678    14406  ok (non-closed singly connected) (3.46945 29.8359 -1.49903) (5.92666 31.5565 1.49903)
                   walls   911496  1035496  ok (non-closed singly connected) (-4.00381 -14.5776 -4.00378) (5.92666 31.5565 4.0038)
                     pp1   162494   169460      ok (closed singly connected) (-2.83194 12.277 -2.84054) (2.81408 12.3229 2.80655)
                     pp2   272484   283434      ok (closed singly connected) (-3.66778 9.82214 -3.63524) (3.70164 9.87094 3.69692)
                  outlet    26996    27489  ok (non-closed singly connected) (-2.02366 -14.5776 -2.02366) (2.02366 -14.5776 2.02366)

Checking geometry...
    Overall domain bounding box (-4.00381 -14.5776 -4.00378) (5.92666 31.5565 4.0038)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (3.28904e-16 -1.36471e-16 -1.07457e-14) OK.
    Max cell openness = 4.41915e-16 OK.
    Max aspect ratio = 9.91648 OK.
    Minimum face area = 7.41772e-06. Maximum face area = 0.0644253.  Face area magnitudes OK.
    Min volume = 2.13284e-07. Max volume = 0.0161741.  Total volume = 1408.94.  Cell volumes OK.
    Mesh non-orthogonality Max: 65.2569 average: 13.0087
    Non-orthogonality check OK.
    Face pyramids OK.
 ***Max skewness = 4.63672, 2 highly skew faces detected which may impair the quality of the results
  <<Writing 2 skew faces to set skewFaces
    Coupled point location match (average 0) OK.
 ***Error in face tets: 208 faces with low quality or negative volume decomposition tets.
  <<Writing 208 faces with low quality or negative volume decomposition tets to set lowQualityTetFaces
    Min/max edge length = 0.000278067 0.25508 OK.
   *There are 8080 faces with concave angles between consecutive edges. Max concave angle = 87.0458 degrees.
  <<Writing 8080 faces with concave angles to set concaveFaces
    Face flatness (1 = flat, 0 = butterfly) : min = 0.331368  average = 0.998599
   *There are 236 faces with ratio between projected and actual area < 0.8
    Minimum ratio (minimum flatness, maximum warpage) = 0.331368
  <<Writing 236 warped faces to set warpedFaces
    Cell determinant (wellposedness) : minimum: 7.50771e-06 average: 19.1688
 ***Cells with small determinant (< 0.001) found, number of cells: 4
  <<Writing 4 under-determined cells to set underdeterminedCells
 ***Concave cells (using face planes) found, number of cells: 368683
  <<Writing 368683 concave cells to set concaveCells
    Face interpolation weight : minimum: 0.0786499 average: 0.452607
    Face interpolation weight check OK.
    Face volume ratio : minimum: 0.0177011 average: 0.754259
    Face volume ratio check OK.

Failed 4 mesh checks.

End

Anything?
Kind regards
Jan

[JKP]

After several more attempts I have lowered my failures in the mesh. Still not gone though and I am still interested in getting this to work.


My trials have been to work with searchable box regions to increase detail around the perforated plates.



My last run:

Preparing the case for meshing in parallel...


*****
running snappyHexMesh without overwrite to analyse the single steps...


real    30m25,395s
user    227m50,777s
sys    7m57,937s

*****
Merging the mesh parts back together...


*****
Deleting the processor folders...

*****
checking castellation phase in mesh generation...


real    2m9,101s
user    2m6,601s
sys    0m2,496s
Failed 1 mesh checks.
----------------
 ***Concave cells (using face planes) found, number of cells: 215861
----------------

Mesh stats:
    cells:            3993337
**
checking snapping phase in mesh generation...
        

real    2m16,446s
user    2m13,854s
sys    0m2,588s
Failed 3 mesh checks.
----------------
 ***Max skewness = 6.5216, 38 highly skew faces detected which may impair the quality of the results
 ***Error in face tets: 221 faces with low quality or negative volume decomposition tets.
 ***Concave cells (using face planes) found, number of cells: 159440
----------------

and this is the corresponding hexmeshdict:

// Which of the steps to run
castellatedMesh true;
snap            true;
addLayers       false;


// Geometry. Definition of all surfaces. All surfaces are of class
// searchableSurface.
// Surfaces are used
// - to specify refinement for any mesh cell intersecting it
// - to specify refinement for any mesh cell inside/outside/near
// - to 'snap' the mesh boundary to the surface
geometry
{
    vdk
    {
        type triSurfaceMesh;
        file "vdk.stl";
    
    regions
    {  
        inlet {name inlet;}
        holeplate1 {name pp1;}
        holeplate2 {name pp2;}
        walls {name walls;}
        outlet {name outlet;}
    }
    }

    pp1Box            //USER DEFINED REGION NAME
    {
        type searchableBox; 
        min (-3.0  12.2  -3.0);
        max ( 3.0  12.4  2.9);
    }

    pp2Box            //USER DEFINED REGION NAME
    {
        type searchableBox; 
        min (-3.8  9.75  -3.8);
        max ( 3.8  9.95  3.8);
    }

};



// Settings for the castellatedMesh generation.
castellatedMeshControls
{

    // Refinement parameters
    // ~~~~~~~~~~~~~~~~~~~~~

    // If local number of cells is >= maxLocalCells on any processor
    // switches from from refinement followed by balancing
    // (current method) to (weighted) balancing before refinement.
    maxLocalCells 200000;

    // Overall cell limit (approximately). Refinement will stop immediately
    // upon reaching this number so a refinement level might not complete.
    // Note that this is the number of cells before removing the part which
    // is not 'visible' from the keepPoint. The final number of cells might
    // actually be a lot less.
    maxGlobalCells 16000000;

    // The surface refinement loop might spend lots of iterations refining just a
    // few cells. This setting will cause refinement to stop if <= minimumRefine
    // are selected for refinement. Note: it will at least do one iteration
    // (unless the number of cells to refine is 0)
    minRefinementCells 10;

    // Allow a certain level of imbalance during refining
    // (since balancing is quite expensive)
    // Expressed as fraction of perfect balance (= overall number of cells /
    // nProcs). 0=balance always.
    maxLoadUnbalance 0.10;


    // Number of buffer layers between different levels.
    // 1 means normal 2:1 refinement restriction, larger means slower
    // refinement.
    nCellsBetweenLevels 2;



    // Explicit feature edge refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    // Specifies a level for any cell intersected by its edges.
    // This is a featureEdgeMesh, read from constant/triSurface for now.
    features
    (
        { file "vdk.eMesh"; level 2; }
    );



    // Surface based refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~

    // Specifies two levels for every surface. The first is the minimum level,
    // every cell intersecting a surface gets refined up to the minimum level.
    // The second level is the maximum level. Cells that 'see' multiple
    // intersections where the intersections make an
    // angle > resolveFeatureAngle get refined up to the maximum level.

    refinementSurfaces
    {
        vdk
    {
        //Global surface refinement level
        level (0 0);

        //Local (per region) refinement level
        regions
        {
            inlet
        { level (1 1); patchInfo { type patch; } }

            pp1
        { level (3 3); patchInfo { type wall; } }

            pp2
        { level (3 3); patchInfo { type wall; } }

            walls
        { level (2 2); patchInfo { type wall; } }

            outlet
        { level (1 1); patchInfo { type patch; } }
        }
    }
    }

    // Resolve sharp angles
    resolveFeatureAngle 30;


    // Region-wise refinement
    // ~~~~~~~~~~~~~~~~~~~~~~

    // Specifies refinement level for cells in relation to a surface. One of
    // three modes
    // - distance. 'levels' specifies per distance to the surface the
    //   wanted refinement level. The distances need to be specified in
    //   descending order.
    // - inside. 'levels' is only one entry and only the level is used. All
    //   cells inside the surface get refined up to the level. The surface
    //   needs to be closed for this to be possible.
    // - outside. Same but cells outside.

    refinementRegions
    {

        pp1Box
    {
        mode inside;    //distance, inside, outside
        levels 
        ((1.0 5));
    }
        pp2Box
    {
        mode inside;    //distance, inside, outside
        levels 
        ((1.0 5));
    }

//    vdk
//    {
//        mode distance;    //distance, inside, outside
//        levels 
//        (
//        (1e-3 5)
//        (1e-2 0)
//        (0.3 0)
//        );
//    }

    }


    // Mesh selection
    // ~~~~~~~~~~~~~~

    // After refinement patches get added for all refinementSurfaces and
    // all cells intersecting the surfaces get put into these patches. The
    // section reachable from the locationInMesh is kept.
    // NOTE: This point should never be on a face, always inside a cell, even
    // after refinement.
    locationInMesh (0 0 0);


    // Whether any faceZones (as specified in the refinementSurfaces)
    // are only on the boundary of corresponding cellZones or also allow
    // free-standing zone faces. Not used if there are no faceZones.
    allowFreeStandingZoneFaces true;
}



// Settings for the snapping.
snapControls
{
    //- Number of patch smoothing iterations before finding correspondence
    //  to surface
    nSmoothPatch 10;

    //- Relative distance for points to be attracted by surface feature point
    //  or edge. True distance is this factor times local
    //  maximum edge length.
    tolerance 1.0;

    //- Number of mesh displacement relaxation iterations.
    nSolveIter 300;

    //- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    nRelaxIter 10;

    // Feature snapping

        //- Number of feature edge snapping iterations.
        //  Leave out altogether to disable.
        nFeatureSnapIter 10;

        //- Detect (geometric only) features by sampling the surface
        //  (default=false).
        implicitFeatureSnap false;

        //- Use castellatedMeshControls::features (default = true)
        explicitFeatureSnap true;

        //- Detect points on multiple surfaces (only for explicitFeatureSnap)
        multiRegionFeatureSnap true;
}

I am sure there are a lot of people here that know more about this than I do. If I am doing something wrong asking questions then please tell me as I am really new to this business. Below I will add two more pictures of the mesh created.



I get skewed and weird faces connected to the edges of the holes in the plates lowering or increasing snapping tolerance does not seam to change this.


When i lower the refinement I get less skewed faces but the mesh is then not clean and the perforated plates show mistakes.



I hope someone will have a suggestion as to what I could try.


Kind regards
Jan

[JKP]

Maybe someone at least can recommend another forum or something?

[virengos]

Hello Jan,
can you share the geometry? I could perform a short test with Salome.
Best,
Damian

[JKP]

Of course I will Damian,



thanks for the offer:


https://drive.google.com/open?id=1OW...qjTGsRAqov-j2L


I have added the blender file and the stl exports to the folder so you should have access to that. If you need anything else please let me know, I appreciate the help.


Kind regards

[virengos]

Hi Jan,
I've checked your meshing case and I think you should rework your basis geometry.
- the STL objects should be watertight (use the forum SEARCH function for this), means connected on the vertices
- the are also some gaps between the holeplates and the wall due to the geometry inaccuracy
- can you avoid the trimmed holes directly on the wall ?

- is the original CAD geometry available in STEP or IGES format ? this would be perfect.

My favorite approach would be as follows:
- negative model creation based on STEP model in Salome
- groups definitions for edge refinement on the holeplates
- combined hexa / tetra mesh with the Netgen algorithms

Other meshing tools you could check:
- cfMesh
- GMSH
- (Hexpress/Hybrid from Numeca)
best,
Damian

[JKP]

Thanks a lot Damian,


will look for the watertight approach.
Unfortunately I only had pdf versions of the drawings which I used as background image in Blender in order to draw the model.

They are actually cut like that, I mean through the holes, maybe I can avoid that just to make the geometry and meshing easier.



They actually have a gap of about 200mm to the outer walls and are suspended on three steel beams which I did not include as I thought that they would just make it messy and not add particularly to the result of the simulation.


much appreciated Damian
regards

[JKP]

Just as an update I ran some of the corrections in Blender and rechecked the mesh of the plates which reduced the non manifolds, well I don't have those faces in the plates and the overlapping faces. I also recalculated all the normals. This left me with just 8 skewed faces which I will try to tweak manually.
Still have 220 face tets problems which are related to the very angle of the perforations/holes. Here it seams to snap verteces to the edge that in turn twist the block (see picture in the first post).
I've got the unprofessional feeling that this might be a tolerance issue?

[H2O_Fiddle]

Hi JKP,


i am furious about "skew faces"-problems with snappyHexMesh and haven't found a solution for it until now, too. My case is a complex and nested structure with a lot of thin elements, similar to your perforated plate. I could achieve some improvements by variing some meshing-parameters, which are suggested in:


Floating Point Exception - Mesh Related??


But still having problems, interested in any further ideas or work-arounds.