[mattamos]

Hi all,

I'm trying to convert a mesh from our in-house format to Foam format, but I keep having problems failing the "upper triangular order" mesh check. I've had a look for what "upper triangular order" entails other than the obvious, but I can't find a definition anywhere.

Any help appreciated,

Matt

[mattijs]

Simply said upper-triangular order is that the order of faces corresponds to the order of the cells they connect.
- take all (higher numbered) cells connected to a cell.
- sort them according to their cell label
- the faces connecting to those cells should now also be ordered.

renumberMesh will do this for you.

[assert]

Simply said upper-triangular order is that the order of faces corresponds to the order of the cells they connect.
- take all (higher numbered) cells connected to a cell.
- sort them according to their cell label
- the faces connecting to those cells should now also be ordered.

Although this answer appeared clear to me, when I implement it, checkMesh keeps giving me the error 'Faces not in upper triangular order'.

Trying to following the advice, I:

• partitioned the faces within their boundary type
• ordered these faces (within their boundary type) by the index of the Cell that owns them

upperTriangularFace indicates that face 0 is incorrect, where it is the only face in its boundary. How can this be incorrectly ordered?

All files and output (and future solution) can be found at
https://github.com/richelbilderbeek/...eek/issues/181 , yet I also put the files here.

Trace of the faces used, the name of their boundary type and the index of the cell that owns the face:

#Face index - Boundary type - Index of Cell owning the Face
TRACE 's.str()' line 174 in file '..\..\Classes\CppTriangleMesh\trianglemeshbuilder.cpp': '0: inside: 1'
TRACE 's.str()' line 174 in file '..\..\Classes\CppTriangleMesh\trianglemeshbuilder.cpp': '1: top: 0'
TRACE 's.str()' line 174 in file '..\..\Classes\CppTriangleMesh\trianglemeshbuilder.cpp': '2: top: 1'
TRACE 's.str()' line 174 in file '..\..\Classes\CppTriangleMesh\trianglemeshbuilder.cpp': '3: right: 0'
TRACE 's.str()' line 174 in file '..\..\Classes\CppTriangleMesh\trianglemeshbuilder.cpp': '4: left: 0'
TRACE 's.str()' line 174 in file '..\..\Classes\CppTriangleMesh\trianglemeshbuilder.cpp': '5: front: 1'
TRACE 's.str()' line 174 in file '..\..\Classes\CppTriangleMesh\trianglemeshbuilder.cpp': '6: bottom: 0'
TRACE 's.str()' line 174 in file '..\..\Classes\CppTriangleMesh\trianglemeshbuilder.cpp': '7: bottom: 1'
TRACE 's.str()' line 174 in file '..\..\Classes\CppTriangleMesh\trianglemeshbuilder.cpp': '8: back: 1'

checkMesh output:

/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.1                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
/*   Windows 32 and 64 bit porting by blueCAPE: http://www.bluecape.com.pt   *\
|  Based on Windows porting (2.0.x v4) by Symscape: http://www.symscape.com   |
\*---------------------------------------------------------------------------*/
Build  : 2.1-88b2f2ae3a0b
Exec   : checkMesh
Date   : Apr 15 2014
Time   : 13:41:22
Host   : "AIRBEAR-W7-I5"
PID    : 5668
Case   : D:/Projects/Tools/build-ToolTestTriangleMeshConsole-Desktop_Qt_5_1_1_MinGW_32bit-Debug
nProcs : 1
SigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster
allowSystemOperations : Allowing user-supplied system call operations

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

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:           8
    internal points:  0
    faces:            9
    internal faces:   1
    cells:            2
    boundary patches: 6
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     0
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:     2

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
 ***Faces not in upper triangular order.
  <<Writing 1 unordered faces to set upperTriangularFace
    Face vertices OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces ...
    Patch               Faces    Points   Surface topology
    top                 2        4        ok (non-closed singly connected)
    right               1        4        ok (non-closed singly connected)
    left                1        4        ok (non-closed singly connected)
    front               1        4        ok (non-closed singly connected)
    bottom              2        4        ok (non-closed singly connected)
    back                1        4        ok (non-closed singly connected)

Checking geometry...
    Overall domain bounding box (-0.92388 -0.92388 1) (0.92388 0.92388 2)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (0 1.14967e-017 0) OK.
 ***Open cells found, max cell openness: 1, number of open cells 2
  <<Writing 2 non closed cells to set nonClosedCells
    Minimum face area = 1. Maximum face area = 2.  Face area magnitudes OK.
    Min volume = 0.777778. Max volume = 0.777778.  Total volume = 1.55556.  Cell volumes OK.
    Mesh non-orthogonality Max: 180 average: 180
 ***Number of non-orthogonality errors: 1.
  <<Writing 1 non-orthogonal faces to set nonOrthoFaces
 ***Error in face pyramids: 2 faces are incorrectly oriented.
  <<Writing 1 faces with incorrect orientation to set wrongOrientedFaces
    Max skewness = 0.404762 OK.
    Coupled point location match (average 0) OK.

Failed 4 mesh checks.

End

upperTriangularFace:

FoamFile
{
    version     2.0;
    format      ascii;
    class       faceSet;
    location    "constant/polyMesh/sets";
    object      upperTriangularFace;
}

1
(
0 
)

points:

FoamFile
{   version 2.0;
    format  ascii;
    class   vectorField;
    location    "constant/polyMesh";
    object  points;
}

8
(
(-0.92388000000000003 -0.382683 1)
(-0.92388000000000003 -0.382683 2)
(-0.382683 0.92388000000000003 1)
(-0.382683 0.92388000000000003 2)
(0.382683 -0.92388000000000003 1)
(0.382683 -0.92388000000000003 2)
(0.92388000000000003 0.382683 1)
(0.92388000000000003 0.382683 2)
)

faces:

FoamFile
{   version 2.0;
    format  ascii;
    class   faceList;
    location    "constant/polyMesh";
    object  faces;
}

9
(
4(2 4 5 3)
3(5 7 3)
3(3 1 5)
4(2 3 7 6)
4(4 6 7 5)
4(0 4 5 1)
3(2 6 4)
3(4 0 2)
4(0 1 3 2)
)

boundary:

FoamFile
{
  version  2.0;
  format   ascii;
  class    polyBoundaryMesh;
  location "constant\polyMesh";
  object   boundary;
}


6
(
  top
  {
    type zeroGradient;
    nFaces 2;
    startFace 1;
  }

  right
  {
    type zeroGradient;
    nFaces 1;
    startFace 3;
  }

  left
  {
    type zeroGradient;
    nFaces 1;
    startFace 4;
  }

  front
  {
    type zeroGradient;
    nFaces 1;
    startFace 5;
  }

  bottom
  {
    type zeroGradient;
    nFaces 2;
    startFace 6;
  }

  back
  {
    type zeroGradient;
    nFaces 1;
    startFace 8;
  }

)

owner:

FoamFile
{   version 2.0;
    format  ascii;
    class   labelList;
    note    "nPoints: 8 nCells: 2 nFaces: 9";
    location    "constant/polyMesh";
    object  owner;
}

9
(
1
0
1
0
0
1
0
1
1
)

neighbour:

FoamFile
{   version 2.0;
    format  ascii;
    class   labelList;
    note    "nPoints: 8 nCells: 2 nFaces: 9";
    location    "constant/polyMesh";
    object  neighbour;
}

9
(
0
-1
-1
-1
-1
-1
-1
-1
-1
)

[assert]

The algorithm to assign indices to a cell is as follows:

* Partition faces (yes, faces) in boundaries
* Maintain a cell index counter, start it at zero.
* Go through all these faces: find the face its owner (i.e. the cell that owns that face). If that cell has not been assigned a cell index yet, assign it a cell index. Increase that cell index counter.

[Bob Tipton]

While the final consequence of misordered face, owner and neighbour files RESULTS in a matrix which is not upper triangular, this message is misleading.

If the reorderMesh app were run automatically, this would not be an issue and the matrix would be correct.


The issue is, what order do the faces need to be in the "faces" file to produce such the desired matrix.


The answer can be seen by viewing the faces, owner and neighbour data in parallel, as follows.


The first column is the vertex indices as ordered in the faces file.
The second column are the owner [cell] indices - which must be in ascending order
The third column are the neighbour [cell] indices - which must also be in ascending order - within that cell.


If the files meet these conditions, they will create an upper triangular matrix when read. Mesh files written in this way, with good cells and faces, pass checkMesh.


How this is assured is up to the author.


(6, 7, 5, 4) 0 1
(2, 3, 7, 6) 0 2
(5, 7, 3, 1) 0 4
(6, 7, 11, 9) 1 3
(10, 11, 7, 5) 1 5
(11, 10, 8, 9) 1 8
(54, 55, 7, 6) 2 3
(3, 7, 55, 53) 2 6
(55, 54, 52, 53) 2 48
(61, 55, 7, 11) 3 7
(11, 9, 60, 61) 3 10
(55, 61, 60, 54) 3 49
(5, 7, 280, 279) 4 5
(278, 280, 7, 3) 4 6
(280, 278, 277, 279) 4 204
(11, 7, 280, 286) 5 7
(11, 286, 285, 10) 5 12
(280, 279, 285, 286) 5 205
(280, 7, 55, 330) 6 7
(55, 53, 329, 330) 6 52
(280, 330, 329, 278) 6 206"