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#1 |
New Member
Luca
Join Date: Nov 2016
Posts: 21
Rep Power: 10 ![]() |
Hello everyone,
I've just made a mesh with the snappyHexMesh utility and the output of the checkMesh is the following: Code:
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // Create time Create polyMesh for time = 0 Time = 0 Mesh stats points: 49664748 faces: 133416406 internal faces: 127022521 cells: 42064644 faces per cell: 6.191397 boundary patches: 23 point zones: 0 face zones: 0 cell zones: 0 Overall number of cells of each type: hexahedra: 36623411 prisms: 1224431 wedges: 6661 pyramids: 0 tet wedges: 20942 tetrahedra: 215 polyhedra: 4188984 Breakdown of polyhedra by number of faces: faces number of cells 4 271482 5 258530 6 894296 7 372570 8 106010 9 1559249 10 2548 11 7004 12 558432 13 343 14 1728 15 145469 16 38 17 181 18 11072 21 32 Checking topology... Boundary definition OK. Cell to face addressing OK. Point usage OK. Upper triangular ordering OK. Face vertices OK. Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces... Patch Faces Points Surface topology front 12750 13206 ok (non-closed singly connected) back 12750 13206 ok (non-closed singly connected) inlet 2321 2576 ok (non-closed singly connected) outlet 2321 2576 ok (non-closed singly connected) bottom 80866 94536 ok (non-closed singly connected) top 21250 21726 ok (non-closed singly connected) pantograph_collector1 111478 112550 ok (non-closed singly connected) pantograph_collector2 109412 110426 ok (non-closed singly connected) pantograph_horizontality_bar 53231 55391 ok (non-closed singly connected) pantograph_derivation_arm 55987 70452 ok (non-closed singly connected) pantograph_rear_arm 72340 89511 ok (non-closed singly connected) pantograph_isolator_derivation 128785 143302 ok (non-closed singly connected) pantograph_spring 118509 134362 ok (non-closed singly connected) pantograph_lower_frame 429274 501838 ok (non-closed singly connected) pantograph_upper_frame 442465 505007 ok (non-closed singly connected) pantograph_frame 882573 916077 ok (non-closed singly connected) pantograph_head_susp 240285 246731 ok (non-closed singly connected) train_body_housing_3kV_NS 85689 96921 ok (non-closed singly connected) train_body_housing_3kV_S 280224 328994 ok (non-closed singly connected) train_body_housing_25kV 426226 466225 multiply connected (shared edge) train_body_train 1220269 1252982 ok (non-closed singly connected) ballast 1101600 1108563 ok (non-closed singly connected) panto_3kV_NS 503280 545602 multiply connected (shared edge) <<Writing 18 conflicting points to set nonManifoldPoints Checking geometry... Overall domain bounding box (-170 -20 -2.591712) (170 20 21.40829) Mesh (non-empty, non-wedge) directions (1 1 1) Mesh (non-empty) directions (1 1 1) Boundary openness (-1.34538e-16 -1.608956e-16 -3.225915e-13) OK. Max cell openness = 7.602287e-16 OK. Max aspect ratio = 53.00486 OK. Minimum face area = 8.801279e-09. Maximum face area = 0.6418475. Face area magnitudes OK. Min volume = 1.523543e-11. Max volume = 0.5135115. Total volume = 322056.3. Cell volumes OK. Mesh non-orthogonality Max: 74.98705 average: 9.127611 *Number of severely non-orthogonal (> 70 degrees) faces: 11. Non-orthogonality check OK. <<Writing 11 non-orthogonal faces to set nonOrthoFaces Face pyramids OK. ***Max skewness = 4.009831, 1 highly skew faces detected which may impair the quality of the results <<Writing 1 skew faces to set skewFaces Coupled point location match (average 0) OK. Failed 1 mesh checks. End // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // Reading the above output I had the following doubts: 1) It says "Failed 1 mesh checks" : is it referred to the high value of skewness detected? If so, does it mean that the critical errors, which can affect the quality of results (failed mesh checks), are indicated by three stars on the left (***) while the errors which are not affecting the quality of results are indicated with just one star*? If the above is right deleting the cell with high skewness I would get a checkMesh with zero critical error (saying Mesh OK at the end), right? 2) Amongst the faulty sets I got also wrongFaces: what exactly make a face, by definition, a "wrong" one? I can't find any documentation about it... Thanks a lot to everyone who will dedicate some of his/her time to help me. Cheers, Luca |
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#2 | |
Senior Member
Join Date: Nov 2010
Location: USA
Posts: 1,232
Rep Power: 25 ![]() |
Quote:
Do not do this. The correct response to having a bad quality mesh is to fix the problem, not to just delete everything that's bad. That being said 42M cells is relatively big. If I had 1 skew face I wouldn't bother fixing it. If you're careful with your discretizations and your initial conditions are done well it won't matter. |
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#3 |
New Member
Luca
Join Date: Nov 2016
Posts: 21
Rep Power: 10 ![]() |
Hi me3840,
thanks for your reply! I absolutely agree with your reasoning. Since I am continuing a work by a student who graduated before me, I inherited all his files and he did this strange thing, so I tried to follow his path but it doesn't make sense effectively. Since you already helped me, can I ask you if my understanding of the legend of the checkMesh output is correct? (See question 1 ) Thanks again for your help, Luca |
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#4 |
Senior Member
Join Date: Nov 2010
Location: USA
Posts: 1,232
Rep Power: 25 ![]() |
All of the mesh quality metrics affect the results. The question is how severe, which is up to the engineer to determine. Find out where the bad face is and see if it's important. If it's in a corner somewhere it's probably safe to just ignore, but if it's in a critical location probably not. It may cause you convergence problems, it may not, only way to know is to run it. Obviously if it's there because of a setting mistake then get rid of it and remesh.
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#5 |
Member
Hector
Join Date: Jul 2010
Location: Barcelona
Posts: 30
Rep Power: 16 ![]() |
wrongFaces is related to minTetQuality quality metric. For example, in one mesh generated with snappyhexmesh I got:
faces with face-decomposition tet quality < 1e-15 : 340 and wrongFaces set cotains 340 faces. |
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Tags |
checkmesh, wrongfaces |
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