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[snappyHexMesh] SHM doesn't snap the boundary between two surfaces on same plane |
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#1 |
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Join Date: Aug 2020
Posts: 16
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Hi everyone,
I have found out that some other people experienced the same issue years ago but there weren't any proper answers in the forum so I open this thread. As you can see in my mesh (see pic), there are two circular faces on the same plane. I see that the boundary between them is not snapped well and the result lookes like a stair ![]() Here is my snappyHexMeshDict. The outer circular surface is "wall_weir" and the inner is "outlet_liquid". Code:
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 { outletLiquidMeters.stl { type triSurfaceMesh; name outlet_liquid; } outletConusMeters.stl { type triSurfaceMesh; name outlet_conus; } inletSlurryMeters.stl { type triSurfaceMesh; name inlet_slurry; } bowlCylinderMeters.stl { type triSurfaceMesh; name wall_bowlCylinder; } bowlConusMeters.stl { type triSurfaceMesh; name wall_bowlConus; } weirMeters.stl { type triSurfaceMesh; name wall_weir; } screwBodyModifiedMeters.stl { type triSurfaceMesh; name wall_screwBody; } screwFlightsModifiedMeters.stl { type triSurfaceMesh; name wall_screwFlights; } }; // 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 1000000; // 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 10000000; // 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) Zero means no bad cells are // allowd during refinement stages minRefinementCells 10; //wieder auf null stellen! //maxLoadUnbalance 0.10; // Number of buffer layers between different levels. // 1 means normal 2:1 refinement restriction, larger means slower // refinement. In Summary, this paramter controls the transition // between cell refinement cells 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. // The file is automatically created when you use the utility // surfaceFeatures. features ( {file "outletLiquidMeters.eMesh"; level 2;} {file "outletConusMeters.eMesh"; level 0;} {file "weirMeters.eMesh"; level 0;} {file "bowlConusMeters.eMesh"; level 1;} {file "bowlCylinderMeters.eMesh"; level 1;} {file "screwBodyModifiedMeters.eMesh"; level 1;} {file "screwFlightsModifiedMeters.eMesh"; level 1;} {file "inletSlurryMeters.eMesh"; level 0;} ); // 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. The surfaces were defined in the // geometry section. refinementSurfaces { //cellZone fluid //cellZoneInside inside outlet_liquid { patchInfo { type patch; } level (1 1); } outlet_conus { patchInfo { type patch; } level (1 1); } wall_screwBody { patchInfo { type wall; } level (1 1); } wall_screwFlights { patchInfo { type wall; } level (1 1); } wall_bowlCylinder { patchInfo { type wall; } level (1 1); } wall_bowlConus { patchInfo { type wall; } level (1 1); } inlet_slurry { patchInfo { type patch; } level (1 1); } wall_weir { patchInfo { type wall; } level (1 1); } } // Cells that 'see' multiple intersections where the intersections make an // angle > resolveFeatureAngle get refined up to the maximum level. // The resolvedFeatureAngel controls the local curvature refinement. The // higher the value, the less features it captures. For example if you use // 100, it will not add refinement in high curvature areas. It also controls // edge feature snapping, high values will not resolve sharp angles in // surface intersections. resolveFeatureAngle 5; // Default 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 { /*box { mode inside; levels ((2 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 (0.128 0.032 0); // to decide which side of mesh to keep // 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: The higher the value // the better the body fitted mesh. The default value is 30. If you are // having problems with the mesh quality (related to the snapping step), // try to increase this value to 300. Have in mind that this will increase // the meshing time. nSolveIter 100; //- Maximum number of snapping relaxation iterations. Should stop // before upon reaching a correct mesh. Increase this value to // improve the quality of the body fitted mesh. nRelaxIter 5; // Feature snapping //- Number of feature edge snapping iterations. // Leave out altogether to disable. Increase this // value to improve the quality of the edge features. nFeatureSnapIter 10; //- Detect (geometric) features by sampling the surface // (default = false) implicitFeatureSnap false; //- Use castellatedMeshControls::features // (default = true) explicitFeatureSnap true; //- Detect features between multiple surfaces // (only for explicitFeatureSnap, default = false) multiRegionFeatureSnap 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 false; // Per final patch (so not geometry!) the layer information. // In this section we select the patches where we want to add // the layers. We can add multiple patches (if they exist). layers { // This patches were created in the geometry section. inlet_slurry {nSurfaceLayers 3;} outlet_liquid {nSurfaceLayers 3;} outlet_liquidConus {nSurfaceLayers 3;} wall_screw{nSurfaceLayers 3;} wall_bowl{nSurfaceLayers 3;} } // 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. // 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. nGrow 0; // Advanced settings // When not to extrude surface. 0 is flat surface, 90 is when two faces // are perpendicular featureAngle 30; // 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 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; // Max number of iterations after which relaxed meshQuality controls // get used. Up to nRelaxIter it uses the settings in meshQualityControls, // after nRelaxIter it uses the values in meshQualityControls::relaxed. nRelaxedIter 20; } // Generic mesh quality settings. At any undoable phase these determine // where to undo. meshQualityControls { maxNonOrtho 65; maxBoundarySkewness 20; maxInternalSkewness 4; maxConcave 80; minVol 1.00E-13; minTetQuality 1e-9; //minTetQuality -1e30; minArea -1; minTwist 0.02; minDeterminant 0.001; minFaceWeight 0.02; minVolRatio 0.01; minTriangleTwist -1; minFlatness 0.5; nSmoothScale 4; errorReduction 0.75; /*// 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 // 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; // ************************************************************************* // |
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#2 | |
Senior Member
Charles
Join Date: Aug 2016
Location: Vancouver, Canada
Posts: 138
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In the followings, which defines the boundary line between the two faces? Can you increase its level of resolution?
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Charles L. |
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#3 |
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Join Date: Aug 2020
Posts: 16
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Thank you for your reply Charles! I tried to increase the level of the edge features. It results in smaller rectangles along the intersection line but the rectangles don't disappear. For this I increased the level of "outletLiquidMeters" which defines the edges of the inner surface. Hmm but I didn't try to increase the edge level of both surfaces, I will give it a try now.
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#4 | |
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#5 |
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Join Date: Aug 2020
Posts: 16
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Hi!
I solved the issue! I hope that it will other people because I have never thought changing this setting before. Code:
multiRegionFeatureSnap false |
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Tags |
meshing, snapedge, snapping, snappyhexmesh |
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