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[snappyHexMesh] Failed 10 mesh checks after snappyHexMesh 

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June 11, 2016, 11:24 
Failed 10 mesh checks after snappyHexMesh

#1 
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Max Vorstadt
Join Date: May 2016
Posts: 28
Rep Power: 10 
Dear all, I'm running snappyHexMesh to generate a mesh around a plate and a cylinder, but I'm apparently obtaining a bad resulting mesh. After running blockMesh, checkMesh's report looks fine:
Code:
Checking geometry... Overall domain bounding box (0.225 0.35 0.125) (1.12 0.35 0.84) Mesh has 3 geometric (nonempty/wedge) directions (1 1 1) Mesh has 3 solution (nonempty) directions (1 1 1) Boundary openness (3.71949e18 6.24427e17 1.8895e17) OK. Max cell openness = 1.849e16 OK. Max aspect ratio = 1.07621 OK. Minimum face area = 0.0032691. Maximum face area = 0.00351823. Face area magnitudes OK. Min volume = 0.000197167. Max volume = 0.000197167. Total volume = 0.908547. Cell volumes OK. Mesh nonorthogonality Max: 0 average: 0 Nonorthogonality check OK. Face pyramids OK. Max skewness = 2.02586e14 OK. Coupled point location match (average 0) OK. Mesh OK. End Code:
Enabling all geometry checks. Time = 0 Mesh stats points: 26716253 faces: 73469248 internal faces: 70259631 cells: 23392159 faces per cell: 6.14432 boundary patches: 7 point zones: 0 face zones: 0 cell zones: 0 Overall number of cells of each type: hexahedra: 21925085 prisms: 164543 wedges: 0 pyramids: 0 tet wedges: 769 tetrahedra: 0 polyhedra: 1301762 Breakdown of polyhedra by number of faces: faces number of cells 4 2466 5 2193 6 163374 7 141807 8 6875 9 857584 10 314 11 136 12 108408 14 87 15 18158 18 360 Checking topology... Boundary definition OK. Cell to face addressing OK. Point usage OK. Upper triangular ordering OK. Face vertices OK. Topological cell zipup check OK. Faceface connectivity OK. Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces... Patch Faces Points Surface topology Bounding box inlet 22488 24182 ok (nonclosed singly connected) (0.225 0.35 0.125) (0.225 0.35 0.84) outlet 11398 12527 ok (nonclosed singly connected) (1.12 0.35 0.125) (1.12 0.35 0.84) lateralWall 255501 280238 ok (nonclosed singly connected) (0.225 0.35 0.125) (1.12 0.35 0.84) upperWall 288 325 ok (nonclosed singly connected) (0.225 0.35 0.84) (1.12 0.35 0.84) lowerWall 1152 1225 ok (nonclosed singly connected) (0.225 0.35 0.125) (1.12 0.35 0.125) Cylinder 280699 285958 ok (nonclosed singly connected) (0.0601417 0.0599639 3.35276e10) (0.0600005 0.0599639 0.24) Plate_round 2638091 2665903 ok (nonclosed singly connected) (0.223998 0.35 0.015) (1.12 0.35 0.000998369) Checking geometry... Overall domain bounding box (0.225 0.35 0.125) (1.12 0.35 0.84) Mesh has 3 geometric (nonempty/wedge) directions (1 1 1) Mesh has 3 solution (nonempty) directions (1 1 1) Boundary openness (5.87433e16 6.97082e17 1.48306e13) OK. ***High aspect ratio cells found, Max aspect ratio: 1.24904e+94, number of cells 35 <<Writing 35 cells with high aspect ratio to set highAspectRatioCells Minimum face area = 5.21919e10. Maximum face area = 0.00357495. Face area magnitudes OK. ***Zero or negative cell volume detected. Minimum negative volume: 6.5735e10, Number of negative volume cells: 35 <<Writing 35 zero volume cells to set zeroVolumeCells Mesh nonorthogonality Max: 179.989 average: 7.91616 *Number of severely nonorthogonal (> 70 degrees) faces: 115. ***Number of nonorthogonality errors: 109. <<Writing 224 nonorthogonal faces to set nonOrthoFaces ***Error in face pyramids: 240 faces are incorrectly oriented. <<Writing 183 faces with incorrect orientation to set wrongOrientedFaces ***Max skewness = 16.2622, 20 highly skew faces detected which may impair the quality of the results <<Writing 20 skew faces to set skewFaces Coupled point location match (average 0) OK. ***Error in face tets: 717 faces with low quality or negative volume decomposition tets. <<Writing 318 faces with low quality or negative volume decomposition tets to set lowQualityTetFaces Min/max edge length = 2.07766e05 0.0607762 OK. *There are 66069 faces with concave angles between consecutive edges. Max concave angle = 89.3598 degrees. <<Writing 66069 faces with concave angles to set concaveFaces Face flatness (1 = flat, 0 = butterfly) : min = 0.0400623 average = 0.999966 *There are 86 faces with ratio between projected and actual area < 0.8 Minimum ratio (minimum flatness, maximum warpage) = 0.0400623 <<Writing 86 warped faces to set warpedFaces Cell determinant (wellposedness) : minimum: 9.01638e05 average: 10.1297 ***Cells with small determinant (< 0.001) found, number of cells: 4 <<Writing 4 underdetermined cells to set underdeterminedCells ***Concave cells (using face planes) found, number of cells: 590857 <<Writing 590857 concave cells to set concaveCells Face interpolation weight : minimum: 0.01328 average: 0.478489 ***Faces with small interpolation weight (< 0.05) found, number of faces: 11 <<Writing 11 faces with low interpolation weights to set lowWeightFaces Face volume ratio : minimum: 10.9825 average: 0.902224 ***Faces with small volume ratio (< 0.01) found, number of faces: 142 <<Writing 142 faces with low volume ratio cells to set lowVolRatioFaces Failed 10 mesh checks. End PS: An UPDATE> I have tried separately the 3 steps and the errors just appear after the addLayers step, the others work well, hope that helps! Last edited by jet_engine; June 11, 2016 at 16:58. Reason: Found the step causing the problem but not the problem itself 

June 13, 2016, 02:13 

#2 
New Member
Marco Atzori
Join Date: Mar 2016
Posts: 22
Rep Power: 10 
Hi!
With the snappyHexMeshDict only I cannot reproduce the case, so I tryed to guess, but I cannot be sure. Anyway: Try for instance to increase the minThickness: minThickness 0.05; => minThickness 0.3; With the option relativeSizes true; you are asking to produce the first layer that is 0.05 of a cell, maybe "he" gives up. I don't know the size of the underlying blocks, but considering the refinment levels and nCellsBetweenLevels 3; my hypothesis is that the cells in the layers are simply too small. Best Regards! 

June 13, 2016, 14:00 

#3  
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Max Vorstadt
Join Date: May 2016
Posts: 28
Rep Power: 10 
Quote:
Thank you for your answer, I've proceded to try it and here is the output: Code:
Checking topology... Boundary definition OK. Cell to face addressing OK. Point usage OK. Upper triangular ordering OK. Face vertices OK. Topological cell zipup check OK. Faceface connectivity OK. Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces... Patch Faces Points Surface topology Bounding box inlet 22488 24182 ok (nonclosed singly connected) (0.225 0.35 0.125) (0.225 0.35 0.84) outlet 9294 10419 ok (nonclosed singly connected) (1.12 0.35 0.125) (1.12 0.35 0.84) lateralWall 210533 235262 ok (nonclosed singly connected) (0.225 0.35 0.125) (1.12 0.35 0.84) upperWall 288 325 ok (nonclosed singly connected) (0.225 0.35 0.84) (1.12 0.35 0.84) lowerWall 1152 1225 ok (nonclosed singly connected) (0.225 0.35 0.125) (1.12 0.35 0.125) Cylinder 280699 285958 ok (nonclosed singly connected) (0.0601417 0.0599639 3.35276e10) (0.0600005 0.0599639 0.24) Plate_round 2638091 2665903 ok (nonclosed singly connected) (0.223998 0.35 0.015) (1.12 0.35 0.000998369) Checking geometry... Overall domain bounding box (0.225 0.35 0.125) (1.12 0.35 0.84) Mesh has 3 geometric (nonempty/wedge) directions (1 1 1) Mesh has 3 solution (nonempty) directions (1 1 1) Boundary openness (6.15461e16 2.68982e15 7.85125e14) OK. ***High aspect ratio cells found, Max aspect ratio: 4.6537e+92, number of cells 2 <<Writing 2 cells with high aspect ratio to set highAspectRatioCells Minimum face area = 1.95889e09. Maximum face area = 0.00355656. Face area magnitudes OK. ***Zero or negative cell volume detected. Minimum negative volume: 6.44127e13, Number of negative volume cells: 2 <<Writing 2 zero volume cells to set zeroVolumeCells Mesh nonorthogonality Max: 169.126 average: 8.14453 *Number of severely nonorthogonal (> 70 degrees) faces: 16. ***Number of nonorthogonality errors: 32. <<Writing 48 nonorthogonal faces to set nonOrthoFaces ***Error in face pyramids: 64 faces are incorrectly oriented. <<Writing 40 faces with incorrect orientation to set wrongOrientedFaces ***Max skewness = 31.6768, 2 highly skew faces detected which may impair the quality of the results <<Writing 2 skew faces to set skewFaces Coupled point location match (average 0) OK. ***Error in face tets: 240 faces with low quality or negative volume decomposition tets. <<Writing 106 faces with low quality or negative volume decomposition tets to set lowQualityTetFaces Min/max edge length = 2.99844e05 0.0606271 OK. *There are 59376 faces with concave angles between consecutive edges. Max concave angle = 89.8234 degrees. <<Writing 59376 faces with concave angles to set concaveFaces Face flatness (1 = flat, 0 = butterfly) : min = 0.11079 average = 0.999975 *There are 85 faces with ratio between projected and actual area < 0.8 Minimum ratio (minimum flatness, maximum warpage) = 0.11079 <<Writing 85 warped faces to set warpedFaces Cell determinant (wellposedness) : minimum: 0.0342967 average: 10.9159 Cell determinant check OK. ***Concave cells (using face planes) found, number of cells: 574493 <<Writing 574493 concave cells to set concaveCells Face interpolation weight : minimum: 0.0329211 average: 0.477303 ***Faces with small interpolation weight (< 0.05) found, number of faces: 2 <<Writing 2 faces with low interpolation weights to set lowWeightFaces Face volume ratio : minimum: 1.3994 average: 0.894135 ***Faces with small volume ratio (< 0.01) found, number of faces: 16 <<Writing 16 faces with low volume ratio cells to set lowVolRatioFaces Failed 9 mesh checks. End Thanks again! 

June 13, 2016, 14:21 

#4 
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Marco Atzori
Join Date: Mar 2016
Posts: 22
Rep Power: 10 
Hi Max!
Let me to make a couple of questions to better understand: 1) Are you performing RANS/URANS, right? Are you using wallfunctions as well? 2) In that case, are you sure that so high refinement levels (=> number of cells) are needed? If not, try simply to change wildly nCellsBetweenLevels 3 => nCellsBetweenLevels 2, and consider if the mesh is still good enough or not. 3) If I understand, you obtain a good convergence without layers: so, why do you want to add them? Cheers! Marco 

June 15, 2016, 09:00 

#5  
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Max Vorstadt
Join Date: May 2016
Posts: 28
Rep Power: 10 
Quote:
Yes, I am using wall functions for the variables that need them. My simulation is a SpalartAllmaras DDES. There is no need for a perfect refinement, and therefore I have done the change you mentioned, but the output did not change very much: Code:
Checking geometry... Overall domain bounding box (0.225 0.35 0.125) (1.12 0.35 0.84) Mesh has 3 geometric (nonempty/wedge) directions (1 1 1) Mesh has 3 solution (nonempty) directions (1 1 1) Boundary openness (6.15461e16 2.68982e15 7.85125e14) OK. ***High aspect ratio cells found, Max aspect ratio: 4.6537e+92, number of cells 2 <<Writing 2 cells with high aspect ratio to set highAspectRatioCells Minimum face area = 1.95889e09. Maximum face area = 0.00355656. Face area magnitudes OK. ***Zero or negative cell volume detected. Minimum negative volume: 6.44127e13, Number of negative volume cells: 2 <<Writing 2 zero volume cells to set zeroVolumeCells Mesh nonorthogonality Max: 169.126 average: 8.14453 *Number of severely nonorthogonal (> 70 degrees) faces: 16. ***Number of nonorthogonality errors: 32. <<Writing 48 nonorthogonal faces to set nonOrthoFaces ***Error in face pyramids: 64 faces are incorrectly oriented. <<Writing 40 faces with incorrect orientation to set wrongOrientedFaces ***Max skewness = 31.6768, 2 highly skew faces detected which may impair the quality of the results <<Writing 2 skew faces to set skewFaces Coupled point location match (average 0) OK. ***Error in face tets: 240 faces with low quality or negative volume decomposition tets. <<Writing 106 faces with low quality or negative volume decomposition tets to set lowQualityTetFaces Min/max edge length = 2.99844e05 0.0606271 OK. *There are 59376 faces with concave angles between consecutive edges. Max concave angle = 89.8234 degrees. <<Writing 59376 faces with concave angles to set concaveFaces Face flatness (1 = flat, 0 = butterfly) : min = 0.11079 average = 0.999975 *There are 85 faces with ratio between projected and actual area < 0.8 Minimum ratio (minimum flatness, maximum warpage) = 0.11079 <<Writing 85 warped faces to set warpedFaces Cell determinant (wellposedness) : minimum: 0.0342967 average: 10.9159 Cell determinant check OK. ***Concave cells (using face planes) found, number of cells: 574493 <<Writing 574493 concave cells to set concaveCells Face interpolation weight : minimum: 0.0329211 average: 0.477303 ***Faces with small interpolation weight (< 0.05) found, number of faces: 2 <<Writing 2 faces with low interpolation weights to set lowWeightFaces Face volume ratio : minimum: 1.3994 average: 0.894135 ***Faces with small volume ratio (< 0.01) found, number of faces: 16 <<Writing 16 faces with low volume ratio cells to set lowVolRatioFaces Failed 9 mesh checks. Thank you again for your response. Best regards, Max. 

June 15, 2016, 09:50 

#6 
New Member
Marco Atzori
Join Date: Mar 2016
Posts: 22
Rep Power: 10 
Hi Max!
The world is small I’m using now a IDDES About the refinement: In my personal experience the refinement could have an influence, depending also on the Re and on what you are more interested in, and in my case layers are needed… I think that first of all is better to have a clue about the importance of the layers in this case. Please, could you check what is your yPlus, without layers? BTW, do you have a reference case that can be used to check your results? Sometime “good residuals” do not mean “good results” … About the dictionary: I’m surprise a bit that the change in nCellsBetweenLevels has apparently no effects on the mesh: what is the total number of cells now? It is reduced has it should? Cheers!! Marco Atzori 

November 19, 2016, 05:57 
Error checkmesh ofter run snappyhexmeshdict

#7 
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Mousa Hemmati
Join Date: Nov 2016
Location: Iran, Ilam
Posts: 8
Rep Power: 9 
Hi. l run snappyHexMeshDict overwrite then checkMesh, but similar error happend.
please help me. Best wishes 

November 20, 2016, 02:48 
Error checkmesh ofter run snappyhexmeshdict

#8 
New Member
Mousa Hemmati
Join Date: Nov 2016
Location: Iran, Ilam
Posts: 8
Rep Power: 9 
Hi Max.
Is stl files at the origin is drawn? 

November 20, 2016, 17:25 

#9 
New Member
Marco Atzori
Join Date: Mar 2016
Posts: 22
Rep Power: 10 
Dear Hemmati,
Could you please give us more info about your case? (In my experience the .stl is rarely the main source of the problems, more often they are caused by some parameters in the mesher dictionary but without precise info is impossible to give precise suggestions ) Best! Marco 

November 21, 2016, 13:37 

#10 
New Member
Mousa Hemmati
Join Date: Nov 2016
Location: Iran, Ilam
Posts: 8
Rep Power: 9 
Hi Marco.
I modelled the steeped spillway. I draw the basic geometry in SolidWorks. But my mistake was that I did not draw in the origin. If the initial geometry drawing in the origin, most likely, CheckMesh after snappyHexMesh will be ok. Best... 

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error, mesh, snappyhex, snappyhexmeshdict 
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