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[snappyHexMesh] Problems when changing mesh levels |
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June 1, 2022, 07:36 |
Problems when changing mesh levels
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#1 |
Member
Ilan
Join Date: Dec 2018
Posts: 52
Rep Power: 7 |
Hello Foamers !
I need some advice for on of the mesh I am doing. With snappyHexMesh, I have to define 3 refinement areas : 2 circles (one inside and one distance mode) and one box. Here is my problem : With coarse mesh, snappyHexMesh is working well. I have this kind of results : Attachment 90095 Attachment 90094 But when I increase the level of the box and the "inside mode" circle, I lose my LV5 on the "distant mode" circle. Does anyone has a idea about how to solve this problem ? Attachment 90096 Attachment 90097 I tried to increase the nCellsBetweenLevels to 8 but it won't change a thing. When I have lv 4 for the box and the "inside mode" circle, snappy just ignore the "distant mode" circle... Thank you ! Have a great day ! Magistrane PS : Complete code : Code:
/*--------------------------------*- C++ -*----------------------------------*\ ========= | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox \\ / O peration | Website: https://openfoam.org \\ / A nd | Version: 9 \\/ M anipulation | \*---------------------------------------------------------------------------*/ FoamFile { 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 { refinementBox // User defined region name { type searchableBox; // region defined by bounding box min (0 -0.13 -0.05); max (1 0.13 0.05); } refinementCylinder2 { type searchableCylinder; point1 (0 0 -0.05); point2 (0 0 0.05); radius 0.098; } refinementCylinder { type searchableCylinder; point1 (0 0 -0.05); point2 (0 0 0.05); radius 0.13; } }; // 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 100; // Number of buffer layers between different levels. // 1 means normal 2:1 refinement restriction, larger means slower // refinement. nCellsBetweenLevels 8; // 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 (); // 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 { /*refinementCylinder { // Surface-wise min and max refinement level level (1 2); }*/ } // Resolve sharp angles on fridges 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 { refinementBox { mode inside; levels ((1e15 3)); } refinementCylinder { mode inside; levels ((1e15 3)); } refinementCylinder2 { mode distance; levels ((0.01 5)); } } // 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 0.2 0.004); // 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 4.0; //- Number of mesh displacement relaxation iterations. nSolveIter 30; //- Maximum number of snapping relaxation iterations. Should stop // before upon reaching a correct mesh. nRelaxIter 5; } // 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 { /* refinementCylinder { nSurfaceLayers 1; }*/ } // Expansion factor for layer mesh expansionRatio 1.3; // 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 0.7; // 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; //- 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; //- 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 minTetQuality 1e-30; //- 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; // Advanced //- Number of error distribution iterations nSmoothScale 4; //- Amount to scale back displacement at error points errorReduction 0.75; } // Advanced // Merge tolerance. Is fraction of overall bounding box of initial mesh. // Note: the write tolerance needs to be higher than this. mergeTolerance 1e-6; // ************************************************************************* // |
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June 1, 2022, 08:10 |
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#2 |
Senior Member
Yann
Join Date: Apr 2012
Location: France
Posts: 1,083
Rep Power: 26 |
Hi Magistrane,
First thing coming to my mind: are you sure you are not hitting the maximum cells limit defined by parameters maxLocalCells and maxGlobalCells ? You can check your log file, snappy should warn you if it does reach the limit. Regards, Yann |
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June 1, 2022, 08:40 |
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#3 |
Member
Ilan
Join Date: Dec 2018
Posts: 52
Rep Power: 7 |
Hey Yann,
It was the case. I saw it 20 min ago just before you answered and tried to push globallcellmax to 100 000 000. And it worked. Thanks, you was right again. Thus, I have another question now before closing the thread : Is it possible to forbid snappy to cut cells in one specific direction to limit the meshing computational time ? I work in 2D and it's painful to have a 100 M points 3D mesh to get a 1M points 2D one. I would like to forbid it to cut in the z-direction. Bonne journée ! |
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June 1, 2022, 08:57 |
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#4 |
Senior Member
Yann
Join Date: Apr 2012
Location: France
Posts: 1,083
Rep Power: 26 |
You are welcome!
Unfortunately for your last question: as far as I know there is no way to force snappy to refine cells only in 2D Bonne journée à toi aussi ! Yann |
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