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[snappyHexMesh] Resolving High Concave Cells After SnappyHexMesh and Question about checkMesh |
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August 12, 2024, 09:04 |
Resolving High Concave Cells After SnappyHexMesh and Question about checkMesh
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#1 |
New Member
Join Date: Jul 2024
Posts: 16
Rep Power: 2 |
Hello Foamers,
I have the following problem with my mesh after using snappyHexMesh. The code gives me as last line: Code:
Writing mesh to time constant Wrote mesh in = 122.927 s. Mesh snapped in = 8220.96 s. Checking final mesh ... Checking faces in error : non-orthogonality > 65 degrees : 0 faces with face pyramid volume < 1e-13 : 0 faces with face-decomposition tet quality < 1e-15 : 0 faces with concavity > 80 degrees : 8 faces with skewness > 4 (internal) or 20 (boundary) : 0 faces with interpolation weights (0..1) < 0.05 : 0 faces with volume ratio of neighbour cells < 0.01 : 0 faces with face twist < 0.02 : 0 faces on cells with determinant < 0.001 : 0 Finished meshing with 8 illegal faces (concave, zero area or negative cell pyramid volume) Finished meshing in = 10389.5 s. End I thought 8 cells is not so bad but to be on the safe side I run checkMesh -allGeometry -allTopology, here I get the following message: Code:
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // Create time Create polyMesh for time = 0 Enabling all (cell, face, edge, point) topology checks. Enabling all geometry checks. Time = 0s Mesh stats points: 5843473 faces: 14176371 internal faces: 12508532 cells: 4213063 faces per cell: 6.33385 boundary patches: 27 point zones: 0 face zones: 1 cell zones: 1 Overall number of cells of each type: hexahedra: 3380166 prisms: 191350 wedges: 0 pyramids: 0 tet wedges: 5540 tetrahedra: 0 polyhedra: 636007 Breakdown of polyhedra by number of faces: faces number of cells 4 4208 5 35807 6 170363 7 21992 8 1028 9 293064 10 3729 11 580 12 74129 13 135 14 113 15 28269 17 2 18 2588 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. <<Writing 5 cells with two non-boundary faces to set twoInternalFacesCells Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces... Patch Faces Points Surface topology Bounding box frontWall 69024 80320 ok (non-closed singly connected) (-0.09615 -0.09615 0.029) (0.09615 0.09615 0.029) backWall 69024 80320 ok (non-closed singly connected) (-0.09615 -0.09615 -0.029) (0.09615 0.09615 -0.029) innerGap 49141 61077 ok (non-closed singly connected) (-0.0705896 -0.0705895 -0.0201288) (0.0705896 0.0705914 0.0200236) outerGap 61387 73589 ok (non-closed singly connected) (-0.0961502 -0.0961502 -0.0200004) (0.0961502 0.0961502 0.0200004) middleGap 58933 69921 ok (non-closed singly connected) (-0.083599 -0.083599 -0.0200014) (0.083599 0.083599 0.0200014) innerRing 262903 286859 ok (non-closed singly connected) (-0.0701587 -0.0701534 -0.029) (0.0701555 0.0701596 0.029) outerRing 244359 267563 ok (non-closed singly connected) (-0.0961587 -0.0961587 -0.029) (0.0961687 0.0961687 0.029) roller01 41893 46165 ok (non-closed singly connected) (-0.0130047 0.0701492 -0.0204491) (0.0130046 0.0956182 0.0204491) roller02 43252 47563 ok (non-closed singly connected) (0.0126893 0.0660956 -0.0204491) (0.038693 0.0920837 0.0204491) roller03 43261 47723 ok (non-closed singly connected) (0.0358861 0.0542839 -0.0204491) (0.0618779 0.0802708 0.0204491) roller04 42780 47085 ok (non-closed singly connected) (0.0542843 0.0358858 -0.0204491) (0.0802722 0.0618784 0.0204491) roller05 42733 47091 ok (non-closed singly connected) (0.0660951 0.0126893 -0.0204491) (0.0920939 0.038693 0.0204491) roller06 41456 45729 ok (non-closed singly connected) (0.0701473 -0.0130047 -0.0204491) (0.0956182 0.0130047 0.0204491) roller07 42405 46646 ok (non-closed singly connected) (0.0660956 -0.038693 -0.0204491) (0.0920944 -0.0126893 0.0204491) roller08 43786 48146 ok (non-closed singly connected) (0.0542836 -0.0618784 -0.0204491) (0.0802722 -0.0358861 0.0204491) roller09 42890 47216 ok (non-closed singly connected) (0.0358858 -0.0802722 -0.0204491) (0.0618784 -0.0542843 0.0204491) roller10 42241 46483 ok (non-closed singly connected) (0.0126893 -0.092094 -0.0204491) (0.038693 -0.0660951 0.0204491) roller11 41553 45815 ok (non-closed singly connected) (-0.0130047 -0.0956182 -0.0204491) (0.0130047 -0.070148 0.0204491) roller12 42401 46641 ok (non-closed singly connected) (-0.038693 -0.0920944 -0.0204491) (-0.0126893 -0.0660956 0.0204491) roller13 43782 48143 ok (non-closed singly connected) (-0.0618784 -0.0802722 -0.0204491) (-0.0358861 -0.0542836 0.0204491) roller14 42893 47221 ok (non-closed singly connected) (-0.0802722 -0.0618784 -0.0204491) (-0.0542843 -0.0358858 0.0204491) roller15 42302 46544 ok (non-closed singly connected) (-0.0920844 -0.038693 -0.0204491) (-0.0660951 -0.0126893 0.0204491) roller16 41552 45814 ok (non-closed singly connected) (-0.0956182 -0.0130047 -0.0204491) (-0.0701494 0.0130047 0.0204491) roller17 43548 47776 ok (non-closed singly connected) (-0.0920941 0.0126893 -0.0204491) (-0.0660956 0.038693 0.0204491) roller18 42755 47094 ok (non-closed singly connected) (-0.0802722 0.0358861 -0.0204491) (-0.0542836 0.0618784 0.0204491) roller19 42780 47083 ok (non-closed singly connected) (-0.0618784 0.0542843 -0.0204491) (-0.0358858 0.0802722 0.0204491) roller20 42805 47161 ok (non-closed singly connected) (-0.038693 0.0660951 -0.0204491) (-0.0126893 0.0920843 0.0204491) Checking geometry... Overall domain bounding box (-0.0961587 -0.0961587 -0.029) (0.0961687 0.0961687 0.029) Mesh has 3 geometric (non-empty/wedge) directions (1 1 1) Mesh has 3 solution (non-empty) directions (1 1 1) Boundary openness (6.41921e-17 -3.93575e-16 1.51684e-15) OK. Max cell openness = 4.35747e-16 OK. Max aspect ratio = 14.6072 OK. Minimum face area = 4.27779e-10. Maximum face area = 1.43632e-06. Face area magnitudes OK. Min volume = 1.33505e-13. Max volume = 1.06963e-09. Total volume = 0.000353475. Cell volumes OK. Mesh non-orthogonality Max: 65.011 average: 14.5431 Non-orthogonality check OK. Face pyramids OK. ***Max skewness = 12.3099, 159 highly skew faces detected which may impair the quality of the results <<Writing 159 skew faces to set skewFaces Coupled point location match (average 0) OK. ***Error in face tets: 83 faces with low quality or negative volume decomposition tets. <<Writing 79 faces with low quality or negative volume decomposition tets to set lowQualityTetFaces *Edges too small, min/max edge length = 0 0.00150081, number too small: 6 <<Writing 6 points on short edges to set shortEdges *There are 42787 faces with concave angles between consecutive edges. Max concave angle = 83.8282 degrees. <<Writing 42787 faces with concave angles to set concaveFaces Face flatness (1 = flat, 0 = butterfly) : min = 0.252789 average = 0.999112 *There are 8484 faces with ratio between projected and actual area < 0.8 Minimum ratio (minimum flatness, maximum warpage) = 0.252789 <<Writing 8484 warped faces to set warpedFaces Cell determinant (wellposedness) : minimum: 9.11575e-20 average: 11.0895 ***Cells with small determinant (< 0.001) found, number of cells: 5 <<Writing 5 under-determined cells to set underdeterminedCells ***Concave cells (using face planes) found, number of cells: 323424 <<Writing 323424 concave cells to set concaveCells Face interpolation weight : minimum: 0.0840176 average: 0.454772 Face interpolation weight check OK. Face volume ratio : minimum: 0.0161983 average: 0.776495 Face volume ratio check OK. Failed 4 mesh checks. End What I don't understand at all is why my code tells me that I only have 8 illegal cells and then there is such a big difference. I am also wondering why I only get an error with the normal checkMesh command? I think my biggest problem is the huge amount of concave cells. I have looked in Paraview where these are located and then tried to give these affected bodies a higher refinement level in snappyhexMeshDict/castellatedMeshControls/refinementSurfaces. Unfortunately without success. Does anyone have any further ideas? |
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August 13, 2024, 06:16 |
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#2 |
Senior Member
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Hi,
There is a difference in the mesh quality parameters that are considered by snappyHexMesh and those by checkMesh. My very simplified experience: Usually, the output you get from normal checkMesh (so without -allTopology -allGeometry) are the ones to focus on. The additional output you get with -allTopology -allGeometry may be important for some specific solvers. For most single phase solvers they are not needed. You see that there are some skewed cells from checkMesh, those are probably the boundary skewness cells reported by snappyHexMesh as the worst result (~12) is between the 4 and 20 mentioned at the end of the log. My advice would be to run your solver with this mesh and if it fails, try to focus on the skewed cells, maybe tighten the boundary value in the meshQualityDict of snappy and rerun snappy. Regards, Tom |
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August 13, 2024, 07:38 |
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#3 | |
New Member
Join Date: Jul 2024
Posts: 16
Rep Power: 2 |
Quote:
Hi tomf, Thank you very much for your contribution, that explains a lot. Since you mention single-phase solvers, I am trying to run a two-phase simulation but always fail. Should I also focus on checkMesh -allGeometry -allTopology or not for now? |
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August 13, 2024, 08:53 |
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#4 |
Senior Member
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Hi,
From the past I have had some issues with particle solvers with meshes that have some of these errors, but I do not remember that being the case with VOF or Euler-Euler solvers. Of course it could depend on other settings, which may be depending on you mesh quality, but there is not enough information to tell this. Regards, Tom |
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August 13, 2024, 10:06 |
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#5 | |
New Member
Join Date: Jul 2024
Posts: 16
Rep Power: 2 |
Quote:
Hi tomf, That answers all your questions about the mesh. Thank you very much for your help! |
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Tags |
checkmesh error, snappy hex mesh |
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