"Mesher log" apparently incoherent with "mesh operation event log"


#1

Hi, using the snnappyhex mesher I ran into the following doubt.
In the “mesh operation event log” I got a warning regarding mesh quality check is not passed, but in the mesher detailed log I see in the final step that there is no bad cells,
which one is true?

2015-10-23 14:51Run finished.
2015-10-23 14:53Mesh check finished.
2015-10-23 14:53Number of nodes: 8182124
2015-10-23 14:53Number of faces: 22171920
2015-10-23 14:53Number of volumes: 7022492
2015-10-23 14:53Number of tetrahedra: 1
2015-10-23 14:53Number of hexahedra: 6208712
2015-10-23 14:53Number of prisms: 260128
2015-10-23 14:53Number of pyramids: 0
2015-10-23 14:53Number of polyhedra: 551032
2015-10-23 14:53Mesh quality check failed. The mesh is not OK. 2015-10-23 14:55Mesh import started.
2015-10-23 14:56Mesh bounding box diagonal length: 1.50671

Meshing log final steps:

Undo iteration 2----------------
Checking faces in error :
non-orthogonality > 65 degrees : 515
faces with face pyramid volume < 1e-13 : 0
faces with concavity > 80 degrees : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0…1) < 0.02 : 0
faces with volume ratio of neighbour cells < 0.01 : 13
faces with face twist < 0.01 : 4
faces on cells with determinant < 0.001 : 0
Detected 0 error faces on boundaries that have been merged.
These will be restored to their original faces.Detected 532 error faces in mesh. Restoring neighbours of faces in error.
Edge intersection testing:
Number of edges : 22171920
Number of edges to retest : 13922
Number of intersected edges : 1143854
Snapped mesh : cells:7022492 faces:22171920 points:8182124
Cells per refinement level:
0 14467
1 72628
2 772952
3 3400760
4 858331
5 1903354

Writing mesh to time constantWrote mesh in = 39.2 s.Mesh snapped in = 654.5 s.

Checking final mesh …Checking faces in error :
non-orthogonality > 65 degrees : 0
faces with face pyramid volume < 1e-13 : 0
faces with concavity > 80 degrees : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0…1) < 0.02 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.01 : 0
faces on cells with determinant < 0.001 : 0
Finished meshing without any errors
Finished meshing in = 1319.88 s.
End
Finalising parallel run


#2

Hi,

there are a lot of different criteria for mesh quality assessment. However this criteria are not absolute and in the end it is a question of interpretation.

The mesh check procedure which is used in the detailed log file is checking some basic mesh criteria. In contrast to this the mesh check procedure in the ‘mesh operation log’ is checking additional criteria which are not very important for 99% of CFD jobs. Your mesh should therefore be fine!

Cheers,
Milad


#3

Hi @jpola
I wanted to add that 2 different criteria are used here: the ones by snappyHexMesh (which report 0 errors in your case) and checkMesh which is another tool to assess meshes. The latter is stricter than snappyHexMesh so it is not unusual that the mesher reports no errors but checkMesh does. Nothing to be worried about, it means that the mesh quality is on the verge but probably still fine.
Happy simulating, Hannes