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[snappyHexMesh] Surface triangulation using snappyHexMesh |
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April 20, 2018, 10:05 |
Surface triangulation using snappyHexMesh
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#1 |
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Shailesh BG
Join Date: Aug 2017
Location: Bangalore
Posts: 39
Rep Power: 9 |
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 ( ); // ************************************************************************* // 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; // ************************************************************************* // 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 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 $gland_radius$; } }; 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.
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Regards, Shailesh |
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April 21, 2018, 14:14 |
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#2 |
Member
Shailesh BG
Join Date: Aug 2017
Location: Bangalore
Posts: 39
Rep Power: 9 |
Please help
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Regards, Shailesh |
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April 23, 2018, 08:10 |
Wireframe
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#3 |
Member
Shailesh BG
Join Date: Aug 2017
Location: Bangalore
Posts: 39
Rep Power: 9 |
Hello,
This is basically the problem that I am facing. As you can see in the attached wireframe image of the surface, there are patches that are meshed as a flat surface area, surrounding which are concentric rings of unstructured mesh. I have basically copied the snappyHexMesh settings from the igloo tutorial. My geometry is 5mm thick, maybe that is the reason. Please, any help would be highly appreciated.
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Regards, Shailesh |
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October 10, 2019, 04:50 |
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#4 |
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Andrew
Join Date: Mar 2018
Posts: 82
Rep Power: 8 |
Hi shaileshbg, i am facing with the same problem but on a different geometry.
In the end do you managed to solve the problem? Astan |
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October 17, 2019, 04:42 |
TopoSet to define different regions
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#5 |
Member
Shailesh BG
Join Date: Aug 2017
Location: Bangalore
Posts: 39
Rep Power: 9 |
Hi Andrew,
We needed multiple regions to be created, generating an unstructured mesh inside a small region of 5mm was creating the problem. The workaround we found was to use topoSet to define different regions inside a bigger mesh.
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Regards, Shailesh |
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bad boundary mesh, snappyhexmesh 3d, temperature distribution |
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