[panpanzhong]

Hi OpenFoam users, I am using snappyHexMesh in OF2.2.1 to generate a mesh of a duct. Everything is fine except the layers at the corner of the duct always shrink in thickness. I have tried changing the featureAngle in addlayers section and it does seem to help a bit. But the best result I have obtained from changing featureAngle still has corner layers shrinking a bit. Below is my snappyHexMesh code. Please also see the attached picture generated by this code. Thank you very much


/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.2.1 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ 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
{
nozzle.stl
{
type triSurfaceMesh;

//tolerance 1E-5; // optional:non-default tolerance on intersections
//maxTreeDepth 10; // optional:depth of octree. Decrease only in case
// of memory limitations.

// Per region the patchname. If not provided will be <name>_<region>.
regions
{
}
}
};

// 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 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 0;

// 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 5;


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

// Specifies a level for any cell intersected by explicitly provided
// edges.
// This is a featureEdgeMesh, read from constant/triSurface for now.
// Specify 'levels' in the same way as the 'distance' mode in the
// refinementRegions (see below). The old specification
// level 2;
// is equivalent to
// levels ((0 2));

features
(
/*
{
// file "nozzle.eMesh";
// level 1;
// levels ((0.0 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
{
nozzle.stl
{
// Surface-wise min and max refinement level
level (0 0);

//- Optional angle to detect small-large cell situation
// perpendicular to the surface. Is the angle of face w.r.t.
// the local surface normal. Use on flat(ish) surfaces only.
// Otherwise leave out or set to negative number.
//perpendicularAngle 10;

//- Optional faceZone and (for closed surface) cellZone with
// how to select the cells that are in the cellZone
// (inside / outside / specified insidePoint)
//faceZone sphere;
//cellZone sphere;
//cellZoneInside inside; //outside/insidePoint

//- Optional specification of what to do with faceZone faces:
// internal : keep them as internal faces (default)
// baffle : create baffles from them. This gives more
// freedom in mesh motion
// boundary : create free-standing boundary faces (baffles
// but without the shared points)
//faceType baffle;
}
}

// Feature angle:
// - used if min and max refinement level of a surface differ
// - used if feature snapping (see snapControls below) is used
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
// increasing 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
{
nozzle.stl
{
mode distance;
levels ((0.002 2) (0.004 1));
// levels ((1.0 5) (2.0 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 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 3;//3;

// Maximum relative distance for points to be attracted by surface.
// True distance is this factor times local maximum edge length.
// Note: changed(corrected) w.r.t 17x! (17x used 2* tolerance)
tolerance 1.0;//2.0;

// Number of mesh displacement relaxation iterations.
nSolveIter 50;//200;//30;

// Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 5;//5;

// Feature snapping

// Number of feature edge snapping iterations.
// Leave out altogether to disable.
nFeatureSnapIter 10;//50;

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

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

// Detect features between multiple surfaces
// (only for explicitFeatureSnap, default = false)
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;

// Layer thickness specification. This can be specified in one of four ways
// - expansionRatio and finalLayerThickness (cell nearest internal mesh)
// - expansionRatio and firstLayerThickness (cell on surface)
// - overall thickness and firstLayerThickness
// - overall thickness and finalLayerThickness

// Expansion factor for layer mesh
expansionRatio 1.2;

// Wanted thickness of the layer furthest away from the wall.
// If relativeSizes this is relative to undistorted size of cell
// outside layer.
//finalLayerThickness 0.3;

// Wanted thickness of the layer next to the wall.
// If relativeSizes this is relative to undistorted size of cell
// outside layer.
firstLayerThickness 0.000089;

// Wanted overall thickness of layers.
// If relativeSizes this is relative to undistorted size of cell
// outside layer.
//thickness 0.5


// Minimum overall thickness of total layers. If for any reason layer
// cannot be above minThickness do not add layer.
// If relativeSizes this is relative to undistorted size of cell
// outside layer..
minThickness 0.000089;//0.5;


// Per final patch (so not geometry!) the layer information
// Note: This behaviour changed after 21x. Any non-mentioned patches
// now slide unless:
// - nSurfaceLayers is explicitly mentioned to be 0.
// - angle to nearest surface < slipFeatureAngle (see below)
// Disable any mesh shrinking and layer addition on any point of
// a patch by setting nSurfaceLayers to 0
layers
{
nozzle.stl_Combustor_ASCII
{
nSurfaceLayers 9;
// Per patch layer data
// expansionRatio 1.3;
// finalLayerThickness 0.3;
// 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 360;

// At non-patched sides allow mesh to slip if extrusion direction makes
// angle larger than slipFeatureAngle.
slipFeatureAngle 20;//20;

// Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 5;

// Number of smoothing iterations of surface normals
nSmoothSurfaceNormals 5;//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 1000;

// Angle used to pick up medial axis points
// Note: changed(corrected) w.r.t 17x! 90 degrees corresponds to 130 in 17x.
minMedianAxisAngle 300;

// 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;

// Max number of iterations after which relaxed meshQuality controls
// get used. Up to nRelaxedIter it uses the settings in
// meshQualityControls,
// after nRelaxedIter it uses the values in
// meshQualityControls::relaxed.
nRelaxedIter 20;

// Additional reporting: if there are just a few faces where there
// are mesh errors (after adding the layers) print their face centres.
// This helps in tracking down problematic mesh areas.
additionalReporting true;
}

// 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;//65;

// Max skewness allowed. Set to <0 to disable.
maxBoundarySkewness 20;//20;
maxInternalSkewness 4;//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;//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. This has to be a positive number for tracking
// to work. Set to very negative number (e.g. -1E30) to
// disable.
// <0 = inside out tet,
// 0 = flat tet
// 1 = regular tet
minTetQuality 1e-9;

// 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;

//- if >0 : preserve single 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;

// Advanced

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

// Optional : some meshing phases allow usage of relaxed rules.
// See e.g. addLayersControls::nRelaxedIter.
relaxed
{
//- Maximum non-orthogonality allowed. Set to 180 to disable.
maxNonOrtho 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;

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

[wc34071209]

Hello,

have you finally solved the problem?

[cfdivan]

Hi,

Have you took a look at:
http://www.openfoam.org/mantisbt/view.php?id=1038

I am not sure that it help you.

Regards,

[bob91]

Hi everybody,
I have same problem
have you finally solved the problem? please help me !!!!!

[SailorLiu]

I have exactly the same problem as this one.
Does anyone have any ideas?

[Gary]

Hi


I followed your method i.e. using your snappyHexMeshDict, but still could not add the layers on walls.


I have been struggling with this problem for a long time and wonder if you could help me on this?

Please see the simple rectangle channel in stl format for your reference.


Sorry, could not upload the file, so see below the paste


solid channel_inlet
facet normal -1 0 0
outer loop
vertex 0 0.0005 -0.0005
vertex 0 -0.0005 -0.0005
vertex 0 -0.0005 0.0005
endloop
endfacet
facet normal -1 -0 -0
outer loop
vertex 0 -0.0005 0.0005
vertex 0 0.0005 0.0005
vertex 0 0.0005 -0.0005
endloop
endfacet
endsolid channel_inlet
solid channel_sides
facet normal 0 -1 0
outer loop
vertex 0.01 -0.0005 0.0005
vertex 0 -0.0005 0.0005
vertex 0 -0.0005 -0.0005
endloop
endfacet
facet normal 0 -1 0
outer loop
vertex 0 -0.0005 -0.0005
vertex 0.01 -0.0005 -0.0005
vertex 0.01 -0.0005 0.0005
endloop
endfacet
facet normal 0 0 -1
outer loop
vertex 0.01 -0.0005 -0.0005
vertex 0 -0.0005 -0.0005
vertex 0 0.0005 -0.0005
endloop
endfacet
facet normal -0 -0 -1
outer loop
vertex 0 0.0005 -0.0005
vertex 0.01 0.0005 -0.0005
vertex 0.01 -0.0005 -0.0005
endloop
endfacet
facet normal 0 1 0
outer loop
vertex 0.01 0.0005 -0.0005
vertex 0 0.0005 -0.0005
vertex 0 0.0005 0.0005
endloop
endfacet
facet normal 0 1 0
outer loop
vertex 0 0.0005 0.0005
vertex 0.01 0.0005 0.0005
vertex 0.01 0.0005 -0.0005
endloop
endfacet
facet normal -0 0 1
outer loop
vertex 0.01 0.0005 0.0005
vertex 0 0.0005 0.0005
vertex 0 -0.0005 0.0005
endloop
endfacet
facet normal 0 -0 1
outer loop
vertex 0 -0.0005 0.0005
vertex 0.01 -0.0005 0.0005
vertex 0.01 0.0005 0.0005
endloop
endfacet
endsolid channel_sides
solid channel_outlet
facet normal 1 0 0
outer loop
vertex 0.01 -0.0005 0.0005
vertex 0.01 -0.0005 -0.0005
vertex 0.01 0.0005 -0.0005
endloop
endfacet
facet normal 1 0 0
outer loop
vertex 0.01 0.0005 -0.0005
vertex 0.01 0.0005 0.0005
vertex 0.01 -0.0005 0.0005
endloop
endfacet
endsolid channel_outlet



Regards,