shaileshbg |
April 20, 2018 10:05 |
Surface triangulation using snappyHexMesh
3 Attachment(s)
Hello,
My geometry is very similar to the iglooWithFridges tutorial, I have a hemispherical dome of 5mm thickness (inner_radius = 0.067m and outer_radius = 0.072m)
In snappyHexMeshDict I have used "searchableSphere", to define my hemispheres as in the tutorial. But the surface temperature pattern of the converged solution (h tolerance 1*e-8) has a lot of concentric circles and irregular patterns on it.
When I see the surface mesh structure it is very bad and the temperature pattern seems to be mimicking the underlying mesh arrangement. Please find below:
1) blockMeshDict
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 5 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
convertToMeters 1;
vertices
(
(-0.072 0 -0.072)
( 0.072 0 -0.072)
( 0.072 0.072 -0.072)
(-0.072 0.072 -0.072)
(-0.072 0 0.072)
( 0.072 0 0.072)
( 0.072 0.072 0.072)
(-0.072 0.072 0.072)
);
blocks
(
hex (0 1 2 3 4 5 6 7) (35 35 35) simpleGrading (1 1 1)
);
edges
(
);
boundary
(
top
{
type wall;
faces
(
(3 7 6 2)
);
}
left
{
type patch;
faces
(
(0 4 7 3)
);
}
right
{
type patch;
faces
(
(2 6 5 1)
);
}
adiabatic_wall
{
type wall;
faces
(
(1 5 4 0)
);
}
back
{
type wall;
faces
(
(0 3 2 1)
);
}
front
{
type wall;
faces
(
(4 5 6 7)
);
}
);
mergePatchPairs
(
);
// ************************************************************************* //
2) snappyHexMeshDict
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 5 |
| \\ / 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 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
{
skin
{
type searchableSphere;
centre (0 0 0);
radius 0.072;
}
gland_int
{
type searchableSphere;
centre (0 0 0);
radius 0.067;
}
};
// 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 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 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 10;
// Number of buffer layers between different levels.
// 1 means normal 2:1 refinement restriction, larger means slower
// refinement.
nCellsBetweenLevels 2;
// 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 "tissue.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
{
"skin.*"
{
// Surface-wise min and max refinement level
level (1 3);
// Optional specification of patch type (default is wall). No
// constraint types (cyclic, symmetry) etc. are allowed.
patchInfo
{
type wall;
}
}
"gland_int.*"
{
// Surface-wise min and max refinement level
level (1 3);
// Optional specification of patch type (default is wall). No
// constraint types (cyclic, symmetry) etc. are allowed.
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
{
}
// 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 0.07 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;
//- 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 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) features by sampling the surface (default=false)
implicitFeatureSnap true;
//- Use castellatedMeshControls::features (default = true)
explicitFeatureSnap 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 true;
// Per final patch (so not geometry!) the layer information
layers
{
}
// 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 0.5;
// 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
// are perpendicular
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; //-1; //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;
//- 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 -1e30;
//- 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 0.02;
//- minimum normalised cell determinant
//- 1 = hex, <= 0 = folded or flattened illegal cell
minDeterminant 0.001;
//- minFaceWeight (0 -> 0.5)
minFaceWeight 0.02;
//- 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;
// ************************************************************************* //
3) chechMesh with -constant -allGeometry and -allTopology enabled:
Code:
/*---------------------------------------------------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 5.x |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
Build : 5.x-197d9d3bf20a
Exec : checkMesh -constant -allGeometry -allTopology
Date : Apr 20 2018
Time : 18:38:43
Host : "shailesh-office"
PID : 15016
I/O : uncollated
Case : /home/shailesh/Niramai/Niramai_cases/with_subprocess/tissue
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster (fileModificationSkew 10)
allowSystemOperations : Allowing user-supplied system call operations
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time
Create polyMesh for time = constant
Enabling all (cell, face, edge, point) topology checks.
Enabling all geometry checks.
Time = constant
Mesh stats
points: 45828
faces: 114686
internal faces: 92036
cells: 36766
faces per cell: 5.62264
boundary patches: 3
point zones: 0
face zones: 0
cell zones: 0
Overall number of cells of each type:
hexahedra: 25550
prisms: 3462
wedges: 0
pyramids: 0
tet wedges: 49
tetrahedra: 0
polyhedra: 7705
Breakdown of polyhedra by number of faces:
faces number of cells
4 4413
5 2750
6 184
7 9
8 4
9 289
12 47
15 4
18 5
Checking topology...
Boundary definition OK.
Cell to face addressing OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Topological cell zip-up check OK.
Face-face connectivity OK.
Number of regions: 1 (OK).
Checking patch topology for multiply connected surfaces...
Patch Faces Points Surface topology Bounding box
adiabatic_wall 972 1202 ok (non-closed singly connected) (-0.07200057 0 -0.07200057) (0.07200922 0 0.0720023)
skin 11774 14388 ok (non-closed singly connected) (-0.07200057 0 -0.07200057) (0.07200922 0.072 0.0720023)
gland_int 9904 12103 ok (non-closed singly connected) (-0.0670025 0 -0.0670025) (0.06700874 0.067 0.06700874)
Checking geometry...
Overall domain bounding box (-0.07200057 0 -0.07200057) (0.07200922 0.072 0.0720023)
Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
Mesh has 3 solution (non-empty) directions (1 1 1)
Boundary openness (-3.212073e-16 1.233535e-15 -1.489339e-16) OK.
Max cell openness = 2.991617e-16 OK.
Max aspect ratio = 6.68332 OK.
Minimum face area = 4.107907e-08. Maximum face area = 8.233134e-06. Face area magnitudes OK.
Min volume = 1.066943e-11. Max volume = 8.01391e-09. Total volume = 0.0001517856. Cell volumes OK.
Mesh non-orthogonality Max: 59.97431 average: 13.79679
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 2.044807 OK.
Coupled point location match (average 0) OK.
Face tets OK.
Min/max edge length = 0.0001321193 0.003578196 OK.
*There are 95 faces with concave angles between consecutive edges. Max concave angle = 36.95977 degrees.
<<Writing 95 faces with concave angles to set concaveFaces
Face flatness (1 = flat, 0 = butterfly) : min = 0.8505382 average = 0.9918693
All face flatness OK.
Cell determinant (wellposedness) : minimum: 0.1125888 average: 3.694367
Cell determinant check OK.
***Concave cells (using face planes) found, number of cells: 240
<<Writing 240 concave cells to set concaveCells
Face interpolation weight : minimum: 0.1119196 average: 0.4449788
Face interpolation weight check OK.
Face volume ratio : minimum: 0.0262782 average: 0.7161729
Face volume ratio check OK.
Failed 1 mesh checks.
End
I read on the forum that concave cells error is more of a warning message and can be safely ignored.
This is a simplified version of my problem wherein which I am considering the internal field to be of a uniform temperature of 30c.
The surface is exposed to air with a constant temperature of 22c and h = 13.5W/mK and the 5mm thickness ring is adiabatic.
I have two heat sources defined in my fvOptions file.
One of the alternatives that I learned was to draw my own stl file in blender/salome and mesh it in salome keeping in mind surface triangulation, then import into snappyHexMesh and define different cellzones there. But I am working on parametric analysis and would want to vary my geometry, for that I am using pyFoamFromTemplate to parse the parameter files
Code:
$$ gland_radius = gr
$$ skin_radius = sr
geometry
{
skin
{
type searchableSphere;
centre (0 0 0);
radius $skin_radius$;
}
gland_int
{
type searchableSphere;
centre (0 0 0);
radius $gland_radius$;
}
};
As you can see this method is ideally suited for me. Since my surface mesh is so bad what I want maybe is surface triangulation equivalent in SHM.
Any help and suggestion would be very helpful to me as I am struggling and have no clue on how to move forward.
Please find attached:
1) Image of surface temperature distribution.
2) Surface temperature distribution mapped on a wireframe model.
3) C/S view of the mesh.
|