| stefano.garbin |
March 9, 2022 04:45 |
SHM not snapping to edge features after adding layers
2 Attachment(s)
Dear all,
I am trying to mesh a bike wheel with tyre using SHM.
STL file has a very good quality and is watertight (it's around 70Mb)
Here are the steps I am following:
-generate edge feature with surfaceFeatureExtract and verify them with paraview --> OK
-generate background mesh with blockMesh --> OK
-generate castellated mesh with SHM --> OK
-snap castellated mesh to STL surfaces and to explicit feature edges --> OK
-add 10 layers with 1st layer thickness of absolute size (relativeSizes false) -->???
In the last step I notices that inflated mesh looses snapping to some of the edge features, as in the attached pictures.
This is weird for me, and I don't understand what I am missing...
Any hint to get a good mesh (external aero)
Thanks
Stefano
I enclose snappyHexMeshDict and meshQualityDict
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v2012 |
| \\ / A nd | Website: 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
{
rim.stl
{
type triSurfaceMesh;
name rim;
}
hub.stl
{
type triSurfaceMesh;
name hub;
}
//cil { type cylinder; point1 (0 0 -0.1); point2 (0 0 0.1); radius 0.5; }
//cone {type searchableCone; point1 (0 0 -0.1); radius1 0.45; innerRadius1 0.2; point2 (0 0 0.1); radius2 0.45; innerRadius2 0.2; }
refinementBox
{
type box;
min (-3.0 -0.35 -0.8);
max ( 0.5 0.8 0.2);
}
}
// Settings for the castellatedMesh generation.
castellatedMeshControls
{
maxLocalCells 1000000;
maxGlobalCells 50000000;
minRefinementCells 100; //10;
maxLoadUnbalance 0.10;
// Number of buffer layers between different levels.
// 1 means normal 2:1 refinement restriction, larger means slower
// refinement.
nCellsBetweenLevels 3;
// 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 "hub.eMesh";
level 8;
}
{
file "rim.eMesh";
level 8;
}
);
// 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
{
rim
{
// Surface-wise min and max refinement level
//level (3 3);
level (8 8);
patchInfo
{
type wall;
}
}
hub
{
// Surface-wise min and max refinement level
//level (3 3);
level (8 8);
patchInfo
{
type wall;
}
}
}
// Resolve sharp angles
resolveFeatureAngle 15;
// 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
{
refinementBox
{
mode inside;
//levels ((1E15 3));
levels ((1E15 4));
gapLevel (3 0 8);
gapMode mixed;
}
//wheel_rim
"rim.*"
{
mode distance;
levels
(
//(0.025 5)
//(0.1 4)
(0.05 5)
);
}
"hub.*"
{
mode distance;
levels
(
//(0.025 5)
//(0.1 4)
(0.05 5)
);
}
}
// Mesh selection
// ~~~~~~~~~~~~~~
locationInMesh (-4.99 0.01 0.01);
allowFreeStandingZoneFaces false; //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 2.0;
//- Number of mesh displacement relaxation iterations.
nSolveIter 30;
//- Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 5;
// 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; //true;
//- Use castellatedMeshControls::features (default = true)
explicitFeatureSnap true;
//- Detect points on multiple surfaces (only for explicitFeatureSnap)
multiRegionFeatureSnap false;
// Attract points only to the surface they originate from.
// This can improve snapping of intersecting surfaces. Default is false.
//strictRegionSnap 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 true; //false;
relativeSizes false;
thicknessModel firstAndRelativeFinal;
//thicknessModel firstAndOverall;
//thicknessModel firstAndExpansion;
meshShrinker displacementMotionSolver;
solver displacementLaplacian;
displacementLaplacianCoeffs
{
diffusivity quadratic inverseDistance 1(wall);
}
// Per final patch (so not geometry!) the layer information
layers
{
//"wheel_rim.*"
"rim.*"
{
nSurfaceLayers 10;
}
"hub.*"
{
nSurfaceLayers 10;
}
}
// Expansion factor for layer mesh
//expansionRatio 1.1; ////da usare con thicknessModel firstAndExpansion;
// 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.
firstLayerThickness 0.01e-3;
finalLayerThickness 0.3; //0.7; //70% delle celle vicine //da usare con thicknessModel firstAndRelativeFinal;
//thickness 0.2e-3; //da usare con thicknessModel firstAndOverall;
// 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 0.002e-3; //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 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 190; //330; //170; //30; //60;
// At non-patched sides allow mesh to slip if extrusion direction makes
// angle larger than slipFeatureAngle.
slipFeatureAngle 30; //10;
// Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 5; //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 1.7.x! 90 degrees corresponds to 130
// in 1.7.x.
minMedialAxisAngle 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 30;
}
// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
#include "meshQualityDict"
}
// Advanced
// Write flags
writeFlags
(
scalarLevels
layerSets
layerFields // write volScalarField for layer coverage
);
// Debug flags
/*
debugFlags
(
layerInfo
);
*/
// Merge tolerance. Is fraction of overall bounding box of initial mesh.
// Note: the write tolerance needs to be higher than this.
mergeTolerance 1e-6;
// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1912 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object meshQualityDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
//- 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 180; //100; //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
//mettere valore negativo e' l'unico modo di fare estrudere i layers
minTetQuality -1e30; //1e-15;
//- 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 0.02;
//- 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 0.1;
// Advanced
//- Number of error distribution iterations
nSmoothScale 4;
//- Amount to scale back displacement at error points
errorReduction 0.75;
// ************************************************************************* //
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