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Igloo tutorial: Mesh doesn't follow edges

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Old   October 5, 2012, 04:55
Question Igloo tutorial: Mesh doesn't follow edges
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Maxime Perelli
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Hello,
I am trying to start with snappyHexMesh, especially with igloo tutorial
Tutorial is successfull, and I wanted to do exactly the same stuff, BUT from an CAD import.
So I designed exactly the same geometry, and I exported it in STL
Then I generate the *.eMesh file with surfaceFeaturConvert
BlockMesh
snappyHexMesh
Everything is ok, since I checked the result in Paraview
I don't succeed to have aligned Mesh on edge.
I don't understand, because I have exactly the same blockMesh and snayppyHexMesh files, and I just adapted the last one (geometry)
geometry
{
igloo.stl
{
type triSurfaceMesh;
name igloo;
tolerance 1e-5;
maxTreeDepth 10;

regions
{
igloo;
}
}
};
Any idea?
Sans titre.jpg
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Old   October 5, 2012, 07:38
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Eloïse
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Hi!
Is your STL a sphere or a half-sphere?
Which version of OF do you use?
Regards,
Eloïse
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Old   October 5, 2012, 07:40
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Maxime Perelli
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hello,
geometry is exactly he same than the one in the tutorial: so this is a half-sphere
OF2.0.1
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Old   October 5, 2012, 07:46
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OF2.0 has a bug related to circular feature edges. For some reason, it does not snap to them. See the details about it on this post:
SnappyHexMesh refuses to refine certain edges
It has been solved for OF2.1 so if you can, I'd recommend you to upgrade to that version.

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Old   October 5, 2012, 09:57
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ok I am trying to install OF2.1.1.
But I have a pre-installed version of OF (caelinux) and sourcing gives me troubles...
So I will continue on Monday and will give you feedback
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Old   October 5, 2012, 10:21
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wyldckat is just really nicewyldckat is just really nicewyldckat is just really nicewyldckat is just really nice
Greetings to all!

Quote:
Originally Posted by -mAx- View Post
But I have a pre-installed version of OF (caelinux) and sourcing gives me troubles...
You can unset an OpenFOAM environment (since 2.0) by running either one of the following commands:
Code:
wmUNSET
#or
source $WM_PROJECT_DIR/etc/config/unset.sh
For more on this: Advanced tips for working with the OpenFOAM shell environment

Best regards,
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Old   October 8, 2012, 02:50
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ok, I installed OF2.1.1
But the issue remains
On the picture I draw also the edged from surfaceFeatureConvert *.eMesh (in red)
Again, I only changed lines in geometry and I updated name everywhere

geometry
{
igloo.stl
{
type triSurfaceMesh;
name igloo;
tolerance 1e-5;
maxTreeDepth 10;

regions
{
igloo;
}
}
};


Sans titre.png
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Old   October 8, 2012, 03:53
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Hi Max,
Can you post your entire snappyHexMeshDict?
Regards,
Eloïse
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Old   October 8, 2012, 04:02
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/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.0.1 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
// Which of the steps to run
castellatedMesh true;
snap true;
addLayers true;
 
// 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
{
igloo.stl
{
type triSurfaceMesh;
name igloo;
tolerance 1e-5;
maxTreeDepth 10;

regions
{
igloo;
}
}
};
 
 
// 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 1000000;
// 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 2000000;
// 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 100;
// Number of buffer layers between different levels.
// 1 means normal 2:1 refinement restriction, larger means slower
// refinement.
nCellsBetweenLevels 1;
 
 
// 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 "igloo.eMesh";
level 3;
}
);
 
 
// 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
{
igloo
{
// Surface-wise min and max refinement level
level (2 2);
regions
{
// Region-wise override
igloo
{
level (1 1);
}
}
}
}
// Resolve sharp angles on fridges
resolveFeatureAngle 60;
 
// 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
{
}
 
// 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 (3 0.28 0.43);
 
// 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 3;
//- Relative distance for points to be attracted by surface feature point
// or edge. True distance is this factor times local
// maximum edge length.
tolerance 4.0;
//- Number of mesh displacement relaxation iterations.
nSolveIter 30;
//- Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 5;
}
 
 
// 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
{
igloo
{
nSurfaceLayers 1;
}
}
// 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.
// is the thickness of the layer furthest away from the wall.
// See relativeSizes parameter.
finalLayerThickness 0.5;
//- 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.
// See relativeSizes parameter.
minThickness 0.25;
//- 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
// make straight angle.
featureAngle 60;
//- Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 5;
// 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 16x! 90 degrees corresponds to 130 in 16x.
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;
}
 
 
// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
//- Maximum non-orthogonality allowed. Set to 180 to disable.
maxNonOrtho 65;
//- Max skewness allowed. Set to <0 to disable.
maxBoundarySkewness 20;
maxInternalSkewness 4;
//- Max concaveness allowed. Is angle (in degrees) below which concavity
// is allowed. 0 is straight face, <0 would be convex face.
// Set to 180 to disable.
maxConcave 80;
//- Minimum pyramid volume. Is absolute volume of cell pyramid.
// Set to a sensible fraction of the smallest cell volume expected.
// Set to very negative number (e.g. -1E30) to disable.
minVol 1e-13;
//- Minimum quality of the tet formed by the face-centre
// and variable base point minimum decomposition triangles and
// the cell centre. Set to very negative number (e.g. -1E30) to
// disable.
// <0 = inside out tet,
// 0 = flat tet
// 1 = regular tet
minTetQuality 1e-30;
//- Minimum face area. Set to <0 to disable.
minArea -1;
//- Minimum face twist. Set to <-1 to disable. dot product of face normal
//- and face centre triangles normal
minTwist 0.05;
//- minimum normalised cell determinant
//- 1 = hex, <= 0 = folded or flattened illegal cell
minDeterminant 0.001;
//- minFaceWeight (0 -> 0.5)
minFaceWeight 0.05;
//- minVolRatio (0 -> 1)
minVolRatio 0.01;
//must be >0 for Fluent compatibility
minTriangleTwist -1;
 
// Advanced
//- Number of error distribution iterations
nSmoothScale 4;
//- amount to scale back displacement at error points
errorReduction 0.75;
}
 
// Advanced
// Flags for optional output
// 0 : only write final meshes
// 1 : write intermediate meshes
// 2 : write volScalarField with cellLevel for postprocessing
// 4 : write current intersections as .obj files
debug 0;
 
// Merge tolerance. Is fraction of overall bounding box of initial mesh.
// Note: the write tolerance needs to be higher than this.
mergeTolerance 1e-6;
 
// ************************************************** *********************** //
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Old   October 8, 2012, 09:21
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Eloïse
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I'm sorry but I can't figure out what's wrong... I'm actually not using V2.1 myself yet so I can't test your snappyHexMeshDict, but I taught it would do the trick!
Maybe someone else has an idea?
Regards,
Eloïse
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Old   October 8, 2012, 09:30
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Maxime Perelli
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Ok thanks anyway
I post the blockMesh File, and I also attach the stl file (form igloo geometry) if it can help
igloo.zip

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.0.1 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
convertToMeters 1;
vertices
(
(-2.03 -2.0 0)
( 8.03 -2.0 0)
( 8.03 8.0 0)
(-2.03 8.0 0)
(-2.03 -2.0 5)
( 8.03 -2.0 5)
( 8.03 8.0 5)
(-2.03 8.0 5)
);
blocks
(
hex (0 1 2 3 4 5 6 7) (20 20 20) simpleGrading (1 1 1)
);
edges
(
);
boundary
(
maxY
{
type empty;
faces
(
(3 7 6 2)
);
}
minX
{
type empty;
faces
(
(0 4 7 3)
);
}
maxX
{
type empty;
faces
(
(2 6 5 1)
);
}
minY
{
type empty;
faces
(
(1 5 4 0)
);
}
ground
{
type wall;
faces
(
(0 3 2 1)
);
}
maxZ
{
type empty;
faces
(
(4 5 6 7)
);
}
);
mergePatchPairs
(
);
// ************************************************** *********************** //
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