CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Meshing & Mesh Conversion

[snappyHexMesh] Reading checkMesh output

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree1Likes
  • 1 Post By me3840

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 26, 2017, 13:32
Question Reading checkMesh output
  #1
New Member
 
Luca
Join Date: Nov 2016
Posts: 21
Rep Power: 6
streamline90 is on a distinguished road
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
streamline90 is offline   Reply With Quote

Old   December 3, 2017, 01:52
Default
  #2
Senior Member
 
Join Date: Nov 2010
Location: USA
Posts: 1,232
Rep Power: 21
me3840 is on a distinguished road
Quote:
Originally Posted by streamline90 View Post
Hello everyone,

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?

Luca

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.
me3840 is offline   Reply With Quote

Old   December 3, 2017, 12:24
Default
  #3
New Member
 
Luca
Join Date: Nov 2016
Posts: 21
Rep Power: 6
streamline90 is on a distinguished road
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
streamline90 is offline   Reply With Quote

Old   December 3, 2017, 12:27
Default
  #4
Senior Member
 
Join Date: Nov 2010
Location: USA
Posts: 1,232
Rep Power: 21
me3840 is on a distinguished road
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.
streamline90 likes this.
me3840 is offline   Reply With Quote

Old   October 28, 2019, 09:52
Default
  #5
Member
 
Hector
Join Date: Jul 2010
Location: Barcelona
Posts: 30
Rep Power: 13
hectorgabriel85 is on a distinguished road
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.
hectorgabriel85 is offline   Reply With Quote

Reply

Tags
checkmesh, wrongfaces

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
New Solver error Foam::error::printStack upuli OpenFOAM Running, Solving & CFD 4 May 11, 2018 01:43
bscw cgns wing kocjH SU2 3 May 16, 2017 02:56
''unknown radialModelType type Gidaspow'' PROBLEM WITH THE BED TUTORIAL AndoniBM OpenFOAM Running, Solving & CFD 2 March 25, 2015 18:44
Possible Bug in pimpleFoam (or createPatch) (or fluent3DMeshToFoam) cfdonline2mohsen OpenFOAM 3 October 21, 2013 09:28
Problem in running ICEM grid in Openfoam Tarak OpenFOAM 6 September 9, 2011 17:51


All times are GMT -4. The time now is 20:21.