| MohdShaeq |
February 27, 2024 00:53 |
Unable to generate the desired mesh
4 Attachment(s)
Hello,
I have been trying very hard to generate a hexahedral mesh for a relatively simple geometry with snappyHexMesh. Even though I have now gained a fair bit of experience in working with the utility, however, I have not been able to generate the desired mesh as not all the features/surfaces are correctly recognised. I have tried several values of level under the features and refinementSurfaces sub-dictionaries, unfortunately to no avail.
Attached herewith are the images of the STL-surfaces and the generated mesh. The snappyHexMeshDict is as follows:-
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 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
{
Geometrie // STL filename
{
type triSurfaceMesh;
file "Geometrie.stl";
regions
{
Brennkammer
{
name Brennkammer;
}
Einlass
{
name Einlass;
}
Kanal_aussen
{
name Kanal_aussen;
}
Kanal_innen
{
name Kanal_innen;
}
}
}
Verfeinerungszylinder1
{
type searchableCylinder;
point1 (0 0 -0.03);
point2 (0 0 0.07);
radius 0.001652;
}
Verfeinerungszylinder2
{
type searchableCylinder;
point1 (0 0 0);
point2 (0 0 -0.02);
radius 0.043;
}
};
// Settings for the castellatedMesh generation.
castellatedMeshControls //sub-dictionary of controls for castellated mesh.
{
// 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 300000; //100000;
// 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 30000000; //1000000;
// 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; //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 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 "Geometrie.eMesh";
level 5; //4; //5; //6
}
);
// 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
{
Geometrie
{
level (1 1); // default (min max) refinement for whole surface
regions
{
Brennkammer
{
level (0 0);
patchInfo
{
type wall; // Optional specification of patch type (default is wall). No constraint types (cyclic, symmetry) etc. are allowed.
}
}
Einlass
{
level (6 6);
patchInfo
{
type patch; // Optional specification of patch type (default is wall). No constraint types (cyclic, symmetry) etc. are allowed.
}
}
Kanal_aussen
{
level (3 3);
patchInfo
{
type wall; // Optional specification of patch type (default is wall). No constraint types (cyclic, symmetry) etc. are allowed.
}
}
Kanal_innen
{
level (3 3);
patchInfo
{
type wall; // Optional specification of patch type (default is wall). No constraint types (cyclic, symmetry) etc. are allowed.
}
}
}
}
}
// 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
{
Geometrie
{
mode distance;
levels ((0.005 3));
}
Verfeinerungszylinder1
{
mode inside;
levels ((1E15 3));
}
Verfeinerungszylinder2
{
mode distance;
levels ((0.02 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 -0.02);
// 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;
//- 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 ;
// - Use castellatedMeshControls :: features ( default = true )
explicitFeatureSnap true ;
// - Detect points on multiple surfaces ( only for explicitFeatureSnap )
multiRegionFeatureSnap true ;
}
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
{
Geometrie
{
nSurfaceLayers 2;
}
}
// 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 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 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 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 50;
}
// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
#include "meshQualityDict"
maxNonOrtho 65;
maxBoundarySkewness 20;
maxInternalSkewness 4;
maxConcave 80;
minVol 1e-13;
minTetQuality 1e-13;
minArea -1;
minTwist 0.05;
minDeterminant 0.001;
minFaceWeight 0.05;
minVolRatio 0.01;
minTriangleTwist -1;
/*
// 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
//- Number of error distribution iterations
nSmoothScale 4;
//- Amount to scale back displacement at error points
errorReduction 0.75;
*/
// Advanced
nSmoothScale 4;
errorReduction 0.75;
relaxed
{
maxNonOrtho 55;
}
//- Number of error distribution iterations
nSmoothScale 4;
//- Amount to scale back displacement at error points
errorReduction 0.75;
}
// Write flags
writeFlags
(
scalarLevels // write volScalarField with cellLevel for postprocessing
layerSets // write cellSets, faceSets of faces in layer
layerFields // write volScalarField for layer coverage
);
// Merge tolerance. Is fraction of overall bounding box of initial mesh.
// Note: the write tolerance needs to be higher than this.
mergeTolerance 1e-6;
// ************************************************************************* //
I kindly entreat those reading this thread to provide me with suggestions and/or improvements. I would be highly thankful to you all.
Kind regards,
Mohd Shaeq |
