[yongxiang]

Hello OFers,


after try-and-error for quite a time and searching on the forum, I still can not get a satisfactory mesh with SHM. I am generating a mesh around a 3D cylindrical element. As shown in the figure, certain vertices are not sanped to the red edge line. Here below is the snappyHexMeshDict and meshQualityDict I used. If anyone have any suggestion?



Edge_Not_snaped.jpg


/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1906 |
| \\ / 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 false;
snap true;
addLayers false;

//castellatedMesh false;
//snap false;
//addLayers true;


// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
#include "meshQualityDict"

// Advanced

//- Number of error distribution iterations
nSmoothScale 4;
//- amount to scale back displacement at error points
errorReduction 0.75;
}

// 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
{
cylinder_right.stl
{
type triSurfaceMesh;
name cylinder_right;
patchInfo
{
type wall;
}
}


cylinder_left.stl
{
type triSurfaceMesh;
name cylinder_left;
patchInfo
{
type wall;
}
}

box_left
{
type searchableBox; // region defined by bounding box
min (-0.01 0 -0.04);
max (0.025 0.015 -0.017);
}

box_right
{
type searchableBox; // region defined by bounding box
min (-0.01 0 0.017);
max ( 0.025 0.015 0.04);
}

cylinderReg_left
{
type searchableCylinder;
point1 (0.0 0.0 -0.03);
point2 (0.0 0.013 -0.03);
radius 0.01;
}

cylinderReg_right
{
type searchableCylinder;
point1 (0.0 0.0 0.03);
point2 (0.0 0.013 0.03);
radius 0.01;
}
};


// 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 2000000;

// 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 10000000;

// 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;

// Number of buffer layers between different levels.
// 1 means normal 2:1 refinement restriction, larger means slower
// refinement.
nCellsBetweenLevels 20;



// 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 "cylinder_left_top.eMesh";
level 3;
}
{
file "cylinder_right.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
{
cylinder_right
{
// Surface-wise min and max refinement level
level (2 3);
// Additional refinement in tight gaps
//MEJ: only to trigger entering gap finding
//gapLevelIncrement 1;

//MEJ: from cell level 2 onwards start checking for opposite
// surfaces
//gapLevel (1 2 10);

//MEJ: from cell level 2 onwards start checking for opposite
// surfaces
// blockLevel 3;
patchInfo
{
type wall;
}
}

cylinder_left
{
level (0 0);
// blockLevel 3;

patchInfo
{
type wall;
}
}
}

// Resolve sharp angles
resolveFeatureAngle 80;


// 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
{

box_left
{
mode inside;

// Dummy base level
levels ((10000 1));
// If cells
// - have level 4..9
// - and are in a gap < 3 cell sizes across
// - with the gap on the inside ('inside'), outside ('outside')
// or both ('mixed') of the surface
// refine them
// gapLevel (100 100 100);
// gapMode inside;
}

box_right
{
mode inside;
levels ((10000 1));
// mode distance;
// levels ((0.005 3) (0.01 2));
}

cylinderReg_left
{
mode inside;
levels ((10000 2));
}
cylinderReg_right
{
mode inside;
levels ((1e15 2));
}

}


// 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 0.05 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 false;
}



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

nSmoothInternal 5; // $nSmoothPatch;
//- 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;

//- Number of mesh displacement relaxation iterations.
nSolveIter 40;

//- 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) 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 false;

// Per final patch (so not geometry!) the layer information
layers
{
cylinder_left
{
nSurfaceLayers 10;
}
cylinder_right
{
nSurfaceLayers 10;
}
}


// Expansion factor for layer mesh
expansionRatio 1.2;

// 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 0.00008;
// finalLayerThickness 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.
// See relativeSizes parameter.
minThickness 0.0000001;
// minThickness 0.05;

// 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 1.7.x! (didn't do anything in 1.7.x)
nGrow 0;


// Advanced settings

// When not to extrude surface. 0 is flat surface, 90 is when two faces
// are perpendicular
featureAngle 130;

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

// Number of smoothing iterations of surface normals
nSmoothSurfaceNormals 50;

// Number of smoothing iterations of interior mesh movement direction
nSmoothNormals 50;

// Smooth layer thickness over surface patches
nSmoothThickness 100;

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

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

// Angle used to pick up medial axis points
// Note: changed(corrected) w.r.t 16x! 90 degrees corresponds to 130 in 16x.
minMedialAxisAngle 145;

// 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;
}






// Advanced

// Merge tolerance. Is fraction of overall bounding box of initial mesh.
// Note: the write tolerance needs to be higher than this.
mergeTolerance 1e-10;


//// Debug flags
//debugFlags
//(
// mesh // write intermediate meshes
// attraction // write attraction as .obj files
//);
//
//// Write flags
//writeFlags
//(
// scalarLevels // write volScalarField with cellLevel for postprocessing
//);

// ************************************************** *********************** //


/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1906 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object meshQualityDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

//- Maximum non-orthogonality allowed. Set to 180 to disable. 65
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;

minFlatness 0.5;
//- 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-14;

//- 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-13;

//- Minimum face area. Set to <0 to disable.
minArea -1;

//- Minimum face twist. Set to <-1 to disable. dot product of face normal
// (itself the average of the triangle normals)
// and face centre triangles normal
minTwist 0.01;

//- Minimum normalised cell determinant. This is the determinant of all
// the areas of internal faces. It is a measure of how much of the
// outside area of the cell is to other cells. The idea is that if all
// outside faces of the cell are 'floating' (zeroGradient) the
// 'fixedness' of the cell is determined by the area of the internal faces.
// 1 = hex, <= 0 = folded or flattened illegal cell
minDeterminant 0.001;

//- Relative position of face in relation to cell centres (0.5 for orthogonal
// mesh) (0 -> 0.5)
minFaceWeight 0.05;

//- Volume ratio of neighbouring cells (0 -> 1)
minVolRatio 0.01;

//- Per triangle normal compared to that of preceding triangle. Must be >0
// for Fluent compatibility
minTriangleTwist -1;


//- If >0 : preserve cells with all points on the surface if the
// resulting volume after snapping (by approximation) is larger than
// minVolCollapseRatio times old volume (i.e. not collapsed to flat cell).
// If <0 : delete always.
minVolCollapseRatio 0.5;

relaxed
{
maxNonOrtho 75;
}
// ************************************************** *********************** //

[annan]

Dear Yongxiang,

try these settings :

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1906 |
| \\ / 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 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
{
cylinder_right.stl
{
type triSurfaceMesh;
name cylinder_right;
patchInfo
{
type wall;
}
}


cylinder_left.stl
{
type triSurfaceMesh;
name cylinder_left;
patchInfo
{
type wall;
}
}

box_left
{
type searchableBox; // region defined by bounding box
min (-0.01 0 -0.04);
max (0.025 0.015 -0.017);
}

box_right
{
type searchableBox; // region defined by bounding box
min (-0.01 0 0.017);
max ( 0.025 0.015 0.04);
}

cylinderReg_left
{
type searchableCylinder;
point1 (0.0 0.0 -0.03);
point2 (0.0 0.013 -0.03);
radius 0.01;
}

cylinderReg_right
{
type searchableCylinder;
point1 (0.0 0.0 0.03);
point2 (0.0 0.013 0.03);
radius 0.01;
}
};


// 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 2000000;

// 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 10000000;

// 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 0;

// 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 "cylinder_left_top.extendedFeatureEdgeMesh";
level 0;
}
{
file "cylinder_right.extendedFeatureEdgeMesh";
level 0;
}
);

// 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
{
cylinder_right
{
// Surface-wise min and max refinement level
level (2 2);
patchInfo
{
type wall;
}
}

cylinder_left
{
level (2 2);

patchInfo
{
type wall;
}
}
}

// 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
{

box_left
{
mode inside;
levels ((1E15 3));
}

box_right
{
mode inside;
levels ((1E15 3));
}

cylinderReg_left
{
mode inside;
levels ((1E15 3));
}
cylinderReg_right
{
mode inside;
levels ((1e15 3));
}

}


// 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 0.05 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 false;
}



// Settings for the snapping.
snapControls
{
//- Number of patch smoothing iterations before finding correspondence
// to surface
nSmoothPatch 3;

nSmoothInternal 5; // $nSmoothPatch;
//- 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 5;

// Feature snapping

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

//- Detect (geometric) 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;


}



// 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 false;

// Per final patch (so not geometry!) the layer information
layers
{
cylinder_left
{
nSurfaceLayers 10;
}
cylinder_right
{
nSurfaceLayers 10;
}
}


// Expansion factor for layer mesh
expansionRatio 1.2;

// 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 0.00008;
// finalLayerThickness 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.
// See relativeSizes parameter.
minThickness 0.0000001;
// minThickness 0.05;

// 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 1.7.x! (didn't do anything in 1.7.x)
nGrow 0;


// Advanced settings

// When not to extrude surface. 0 is flat surface, 90 is when two faces
// are perpendicular
featureAngle 130;

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

// Number of smoothing iterations of surface normals
nSmoothSurfaceNormals 50;

// Number of smoothing iterations of interior mesh movement direction
nSmoothNormals 50;

// Smooth layer thickness over surface patches
nSmoothThickness 100;

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

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

// Angle used to pick up medial axis points
// Note: changed(corrected) w.r.t 16x! 90 degrees corresponds to 130 in 16x.
minMedialAxisAngle 145;

// 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
{
#include "meshQualityDict"

// Advanced

//- Number of error distribution iterations
nSmoothScale 4;
//- amount to scale back displacement at error points
errorReduction 0.75;
}

// Advanced

// Merge tolerance. Is fraction of overall bounding box of initial mesh.
// Note: the write tolerance needs to be higher than this.
mergeTolerance 1e-10;

[yongxiang]

Hello Anna,
thanks for your reply. I tried your suggestion. But the edge vertices are still not fully snapped to the edge. Do you think it is related to the mesh quality criteria?


regards