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May 5, 2017, 18:12 |
Edge Refinement
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#1 |
New Member
Franco
Join Date: Sep 2015
Location: Montreal
Posts: 26
Rep Power: 11 |
Hi foamers,
I'm having hard times with SHM and extrudeMess, since I'm trying to create a 2D mesh from SHM with extrudeMesh. The mesh is fine (I don't get any error with checkMesh), however, the refinement seems not to work on the edges. As you can see from the images, there are some very sharp edges at the four corner of the mash. I improved the feature level, but I can't get rid of the problem. I'm quite sure that there is a problem with the introduction of the viscous layers (when the layers are not added, I don't get this error), however, I can't understand which parameter I should change in addLayersControls (I tried with featureAngle, without success). Could you please help me? Thanks a lot!! Franco Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 4.1 | | \\ / 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 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 { Air.stl { type triSurfaceMesh; name Air; } Base1.stl { type triSurfaceMesh; name Base1; } Base2.stl { type triSurfaceMesh; name Base2; } Base3.stl { type triSurfaceMesh; name Base3; } Base4.stl { type triSurfaceMesh; name Base4; } Base5.stl { type triSurfaceMesh; name Base5; } Bottom.stl { type triSurfaceMesh; name Bottom; } Left.stl { type triSurfaceMesh; name Left; } Outlet.stl { type triSurfaceMesh; name Outlet; } RCF1.stl { type triSurfaceMesh; name RCF1; } RCF2.stl { type triSurfaceMesh; name RCF2; } RCF3.stl { type triSurfaceMesh; name RCF3; } RCF4.stl { type triSurfaceMesh; name RCF4; } Right.stl { type triSurfaceMesh; name Right; } Top.stl { type triSurfaceMesh; name Top; } refinementBox { type searchableBox; min (0.05 0 0); max (0.64 0.15 0.01); } }; // 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 1; //maxLoadUnbalance 0.10; // 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 "Base1.eMesh"; level 5;} {file "Base2.eMesh"; level 5;} {file "Base3.eMesh"; level 5;} {file "Base4.eMesh"; level 5;} {file "Base5.eMesh"; level 5;} {file "Bottom.eMesh"; level 5;} {file "Left.eMesh"; level 5;} {file "Outlet.eMesh"; level 5;} {file "RCF1.eMesh"; level 5;} {file "RCF2.eMesh"; level 5;} {file "RCF3.eMesh"; level 5;} {file "RCF4.eMesh"; level 5;} {file "Right.eMesh"; level 5;} {file "Top.eMesh"; level 5;} ); // 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 { Base1 { // Surface-wise min and max refinement level level (4 5); } Base2 { // Surface-wise min and max refinement level level (4 5); } Base3 { // Surface-wise min and max refinement level level (4 5); } Base4 { // Surface-wise min and max refinement level level (4 5); } Base5 { // Surface-wise min and max refinement level level (4 5); } Bottom { // Surface-wise min and max refinement level level (4 5); } Outlet { // Surface-wise min and max refinement level level (4 5); } Top { // Surface-wise min and max refinement level level (4 5); } Left { // Surface-wise min and max refinement level level (5 5); } Right { // Surface-wise min and max refinement level level (5 5); } RCF1 { // Surface-wise min and max refinement level level (5 6); } RCF2 { // Surface-wise min and max refinement level level (5 6); } RCF3 { // Surface-wise min and max refinement level level (5 6); } RCF4 { // Surface-wise min and max refinement level level (5 6); } } // Resolve sharp angles on fridges resolveFeatureAngle 30; //was 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 { Air { mode inside; levels ((1e15 5)); } /*refinementBox //Air { mode inside; levels ((1e15 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 (0.1 0.1 0.005); // 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 2.0; //- Number of mesh displacement relaxation iterations. nSolveIter 300; //- Maximum number of snapping relaxation iterations. Should stop // before upon reaching a correct mesh. nRelaxIter 5; nFeatureSnapIter 15; // default is 10 } // 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 { Left { nSurfaceLayers 3; } Right { nSurfaceLayers 3; } Base1 { nSurfaceLayers 3; } Base2 { nSurfaceLayers 3; } Base3 { nSurfaceLayers 3; } Base4 { nSurfaceLayers 3; } Base5 { nSurfaceLayers 3; } } // Expansion factor for layer mesh expansionRatio 1.15; // 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 0.4; // 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 0.2; // 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 30; // was 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 80; //was 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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May 6, 2017, 18:18 |
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#2 |
New Member
Franco
Join Date: Sep 2015
Location: Montreal
Posts: 26
Rep Power: 11 |
The problemhas been quickly solved by changing the factors in the snapcontroldict.
BTW, the introduction of the viscous layers does not affect the sharp edges shown in the figures (when addlayers is false, the sharp edges do not go way). |
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December 2, 2017, 08:07 |
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#3 |
Senior Member
Deep
Join Date: Oct 2017
Posts: 180
Rep Power: 9 |
This looks interesting. I am facing the exact same problem with SHM. Could you discuss more about what factors you changed? Perhaps, share your new shm dict ?
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December 2, 2017, 14:30 |
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#4 |
New Member
Franco
Join Date: Sep 2015
Location: Montreal
Posts: 26
Rep Power: 11 |
Dear Deep,
Unfortunately I'm not working anymore on this case and I do not remember which of the four factors I changed: I think it was tolerance or nSolveIter, but its a guess. If that does not work, I would consider changing the size of the blocks in the blockMeshDict file (I would decrease their size and defining a low level of refinement for the surfaces, edges...). Hope It helps, Franco |
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Tags |
extrude mesh, extrude2dmesh 2d mesh, snapphhexmesh |
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