Meshing problem

sancho78rus · November 27, 2021, 02:51

I'm trying to mesh race car.
Everything went ok before we added diffuser to the floor.
After that meshing time increased 3 times and I got errors after checking mesh and cannot do potentialFoam.
Please help.

Code:

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:           8311921
    faces:            22546314
    internal faces:   21680401
    cells:            7144048
    faces per cell:   6.19071
    boundary patches: 6
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     6305947
    prisms:        113448
    wedges:        2
    pyramids:      0
    tet wedges:    4703
    tetrahedra:    68
    polyhedra:     719880
    Breakdown of polyhedra by number of faces:
        faces   number of cells
            4   38309
            5   31075
            6   143250
            7   131096
            8   40681
            9   231452
           10   2317
           11   485
           12   79586
           13   74
           14   115
           15   20545
           16   2
           17   4
           18   885
           21   4

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
   *Number of regions: 141
    The mesh has multiple regions which are not connected by any face.
  <<Writing region information to "0/cellToRegion"
  <<Writing region 0 with 7143908 cells to cellSet region0
  <<Writing region 1 with 1 cells to cellSet region1
  <<Writing region 2 with 1 cells to cellSet region2
  <<Writing region 3 with 1 cells to cellSet region3
  <<Writing region 4 with 1 cells to cellSet region4
  <<Writing region 5 with 1 cells to cellSet region5
  <<Writing region 6 with 1 cells to cellSet region6
  <<Writing region 7 with 1 cells to cellSet region7
  <<Writing region 8 with 1 cells to cellSet region8
  <<Writing region 9 with 1 cells to cellSet region9
  <<Writing region 10 with 1 cells to cellSet region10
  <<Writing region 11 with 1 cells to cellSet region11
  <<Writing region 12 with 1 cells to cellSet region12
  <<Writing region 13 with 1 cells to cellSet region13
  <<Writing region 14 with 1 cells to cellSet region14
  <<Writing region 15 with 1 cells to cellSet region15
  <<Writing region 16 with 1 cells to cellSet region16
  <<Writing region 17 with 1 cells to cellSet region17
  <<Writing region 18 with 1 cells to cellSet region18
  <<Writing region 19 with 1 cells to cellSet region19
  <<Writing region 20 with 1 cells to cellSet region20
  <<Writing region 21 with 1 cells to cellSet region21
  <<Writing region 22 with 1 cells to cellSet region22
  <<Writing region 23 with 1 cells to cellSet region23
  <<Writing region 24 with 1 cells to cellSet region24
  <<Writing region 25 with 1 cells to cellSet region25
  <<Writing region 26 with 1 cells to cellSet region26
  <<Writing region 27 with 1 cells to cellSet region27
  <<Writing region 28 with 1 cells to cellSet region28
  <<Writing region 29 with 1 cells to cellSet region29
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  <<Writing region 60 with 1 cells to cellSet region60
  <<Writing region 61 with 1 cells to cellSet region61
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  <<Writing region 139 with 1 cells to cellSet region139
  <<Writing region 140 with 1 cells to cellSet region140

Checking patch topology for multiply connected surfaces...
                   Patch    Faces   Points                  Surface topology
            frontAndBack    28929    30391  ok (non-closed singly connected)
                   inlet      120      143  ok (non-closed singly connected)
                  outlet      120      143  ok (non-closed singly connected)
               lowerWall      622      699  ok (non-closed singly connected)
               upperWall      622      699  ok (non-closed singly connected)
               motorBike   835500   890235  ok (non-closed singly connected)

Checking geometry...
    Overall domain bounding box (-6 -0.69 -2.5) (14 4.31 2.5)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (6.74785e-17 4.0558e-16 2.29111e-16) OK.
    Max cell openness = 9.88519e-16 OK.
    Max aspect ratio = 45.4329 OK.
    Minimum face area = 2.31973e-09. Maximum face area = 0.277542.  Face area magnitudes OK.
    Min volume = 5.52173e-13. Max volume = 0.12513.  Total volume = 493.918.  Cell volumes OK.
    Mesh non-orthogonality Max: 64.9944 average: 8.8021
    Non-orthogonality check OK.
    Face pyramids OK.
 ***Max skewness = 7.45245, 5 highly skew faces detected which may impair the quality of the results
  <<Writing 5 skew faces to set skewFaces
    Coupled point location match (average 0) OK.

Failed 1 mesh checks.

End

sancho78rus · November 27, 2021, 14:49

If ignore it and run mpirun potentialFoam, I get this error:
cannot solve incomplete matrix, no diagonal or off-diagonal coefficient

geth03 · December 10, 2021, 06:19

hi,

could you post the checkMesh-result from the simulation that runs without a problem?

sancho78rus · December 10, 2021, 06:30

Quote:

Originally Posted by geth03

hi,

could you post the checkMesh-result from the simulation that runs without a problem?

Hi.
Here it is:

Code:

/*---------------------------------------------------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  9
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
Build  : 9-a0f1846504f2
Exec   : checkMesh
Date   : Dec 05 2021
Time   : 13:04:48
Host   : "openfoam-vm"
PID    : 6527
I/O    : uncollated
Case   : /home/anton/dif9
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster (fileModificationSkew 10)
allowSystemOperations : Allowing user-supplied system call operations

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:           6266492
    faces:            16854825
    internal faces:   16205092
    cells:            5317779
    faces per cell:   6.21687
    boundary patches: 6
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     4616017
    prisms:        86743
    wedges:        0
    pyramids:      0
    tet wedges:    5159
    tetrahedra:    28
    polyhedra:     609832
    Breakdown of polyhedra by number of faces:
        faces   number of cells
            4   27460
            5   23128
            6   133257
            7   112616
            8   40010
            9   184467
           10   3022
           11   1055
           12   66868
           13   117
           14   185
           15   16753
           16   6
           17   4
           18   880
           21   4

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
            frontAndBack     1640     1792  ok (non-closed singly connected)
                   inlet      120      143  ok (non-closed singly connected)
                  outlet      120      143  ok (non-closed singly connected)
               lowerWall    30740    32145  ok (non-closed singly connected)
               upperWall      400      451  ok (non-closed singly connected)
               motorBike   616713   665767  ok (non-closed singly connected)

Checking geometry...
    Overall domain bounding box (-6 -0.69 -2.5) (14 4.31 2.5)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (7.98522e-17 6.70506e-16 2.90347e-16) OK.
    Max cell openness = 7.42443e-16 OK.
    Max aspect ratio = 37.0962 OK.
    Minimum face area = 1.43585e-08. Maximum face area = 0.255204.  Face area magnitudes OK.
    Min volume = 3.02126e-10. Max volume = 0.125899.  Total volume = 493.879.  Cell volumes OK.
    Mesh non-orthogonality Max: 64.8274 average: 9.24804
    Non-orthogonality check OK.
    Face pyramids OK.
 ***Max skewness = 8.86648, 5 highly skew faces detected which may impair the quality of the results
  <<Writing 5 skew faces to set skewFaces
    Coupled point location match (average 0) OK.

Failed 1 mesh checks.

End

We solved the problem by deleting some holes in model.

geth03 · December 10, 2021, 06:36

when you compare those two checkMesh-results, you see for the case where the problem occurs the following terminal output:

The mesh has multiple regions which are not connected by any face.

i think that was the problem.

sancho78rus · December 10, 2021, 10:30

Quote:

Originally Posted by geth03

when you compare those two checkMesh-results, you see for the case where the problem occurs the following terminal output:

The mesh has multiple regions which are not connected by any face.

i think that was the problem.

I understand that. But how could I find these regions?

geth03 · December 14, 2021, 02:28

i think after executing checkmesh, a directory called "sets" will be created in the polymesh directory. according to your checkmesh result those regions are called region1, region2 etc.
if you want to visualize one region for example you can execute the following command in the terminal:
foamToVTK -cellSet region1
a VTK directory will be created in your case directory. you can use paraview now to view your result.

sancho78rus · December 14, 2021, 02:29

Quote:

Originally Posted by geth03

i think after executing checkmesh, a directory called "sets" will be created in the polymesh directory. according to your checkmesh result those regions are called region1, region2 etc.
if you want to visualize one region for example you can execute the following command in the terminal:
foamToVTK -cellSet region1
a VTK directory will be created in your case directory. you can use paraview now to view your result.

Thanks for reply.
Will try next time.

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November 27, 2021, 14:49		#2
sancho78rus New Member Anton Join Date: Nov 2021 Location: Saint-Petersburg Posts: 10 Rep Power: 4	If ignore it and run mpirun potentialFoam, I get this error: cannot solve incomplete matrix, no diagonal or off-diagonal coefficient

December 10, 2021, 06:19		#3
geth03 Senior Member Join Date: Dec 2019 Location: Cologne, Germany Posts: 365 Rep Power: 8	hi, could you post the checkMesh-result from the simulation that runs without a problem?

December 10, 2021, 06:36		#5
geth03 Senior Member Join Date: Dec 2019 Location: Cologne, Germany Posts: 365 Rep Power: 8	when you compare those two checkMesh-results, you see for the case where the problem occurs the following terminal output: The mesh has multiple regions which are not connected by any face. i think that was the problem.

December 14, 2021, 02:28		#7
geth03 Senior Member Join Date: Dec 2019 Location: Cologne, Germany Posts: 365 Rep Power: 8	i think after executing checkmesh, a directory called "sets" will be created in the polymesh directory. according to your checkmesh result those regions are called region1, region2 etc. if you want to visualize one region for example you can execute the following command in the terminal: foamToVTK -cellSet region1 a VTK directory will be created in your case directory. you can use paraview now to view your result.