[blockMesh] Face reduced to less than 3 points (simple cubic blocks)

mikeR · April 16, 2014, 10:22

I'm trying to create a structure but receive the posted error message

Quote:

Face xyz reduced to less than 3 point

I can merge 2 of my interfaces just fine, just one keeps acting up and I dont really know why this one gives me errors

my blockMeshDict file consists of 8 blocks out of which I'd like to create some kind of structure. Here is the code (interface 3 and 4 raise an error):

Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 1;

vertices
(
//1
    (0 0 0)
    (1 0 0)
    (1 0.5 0)
    (0 0.5 0)
    (0 0 0.5)
    (1 0 0.5)
    (1 0.5 0.5)
    (0 0.5 0.5)
//2
    (1 0 0)
    (1.5 0 0)
    (1.5 0.5 0)
    (1 0.5 0)
    (1 0 0.5)
    (1.5 0 0.5)
    (1.5 0.5 0.5)
    (1 0.5 0.5)
//3
    (0 0 -0.8)
    (1 0 -0.8)
    (1 0.5 -0.8)
    (0 0.5 -0.8)
    (0 0 0)
    (1 0 0)
    (1 0.5 0)
    (0 0.5 0)
//4
    (1 0 -0.8)
    (1.5 0 -0.8)
    (1.5 0.5 -0.8)
    (1 0.5 -0.8)
    (1 0 0)
    (1.5 0 0)
    (1.5 0.5 0)
    (1 0.5 0)
//5
    (0 0.5 0)
    (1 0.5 0)
    (1 1 0)
    (0 1 0)
    (0 0.5 0.5)
    (1 0.5 0.5)
    (1 1 0.5)
    (0 1 0.5)
//6
    (1 0.5 0) //40
    (1.5 0.5 0)
    (1.5 1 0)
    (1 1 0)
    (1 0.5 0.5)
    (1.5 0.5 0.5)
    (1.5 1 0.5)
    (1 1 0.5)
//7
    (0 0.5 -0.8)
    (1 0.5 -0.8)
    (1 1 -0.8)
    (0 1 -0.8)
    (0 0.5 0)
    (1 0.5 0)
    (1 1 0)
    (0 1 0)
//8
    (1 0.5 -0.8)
    (1.5 0.5 -0.8)
    (1.5 1 -0.8)
    (1 1 -0.8)
    (1 0.5 0)
    (1.5 0.5 0)
    (1.5 1 0)
    (1 1 0)
);

blocks
(
    hex (0 1 2 3 4 5 6 7) (10 10 10) simpleGrading (1 1 1)  //1
    hex (8 9 10 11 12 13 14 15) (10 10 10) simpleGrading (1 1 1)//2
    hex (16 17 18 19 20 21 22 23) (10 10 10) simpleGrading (1 1 1)//3
    hex (24 25 26 27 28 29 30 31) (10 10 10) simpleGrading (1 1 1)//4
    hex (32 33 34 35 36 37 38 39) (10 10 10) simpleGrading (1 1 1)//5
    hex (40 41 42 43 44 45 46 47) (10 10 10) simpleGrading (1 1 1)//6
    hex (48 49 50 51 52 53 54 55) (10 10 10) simpleGrading (1 1 1)//7
    hex (56 57 58 59 60 61 62 63) (10 10 10) simpleGrading (1 1 1)//8
);

edges
(
);
patches
(
patch inlet
(
    (0 4 7 3)
)
patch inlet2
(
    (43 47 46 42)
    (59 63 62 58)
)
patch outlet
( 
    (9 10 14 13)
)

patch wallBack
(
    (3 2 1 0)
    (8 11 10 9)
    (56 60 61 57)
    (56 59 58 57)
    (58 62 61 57)
    (42 46 45 41)
)
patch wallFront
(
    (6 7 4 5)
    (14 15 12 13)
    (44 45 46 47)
)
patch walltop
(
    (2 3 7 6)
    (33 37 38 34)
    (49 53 54 50)
)
patch wallbottom
(
    (0 1 5 4)
    (8 9 13 12)
)
patch interface1
(
    (2 6 5 1)
)
patch interface2
(
    (11 8 12 15)
)
patch interface3
(
    (10 11 15 14)
)
patch interface4
(
    (40 41 45 44)
)
patch interface5
(
    (41 40 43 42)
)
patch interface6
(
    (60 61 62 63)
)
);
boundary
(
);

mergePatchPairs
(
    (interface1 interface2)
    (interface5 interface6)
    (interface4 interface3)
);

// ************************************************************************* //

any ideas why just interface 4 and 3 give an error? They overlap quite well afaik and I checked the Structure with pyFoamDisplayBlockMesh but couldnt find an error

mikeR · April 16, 2014, 12:27

Here is another try but still the same error

Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 1;

vertices
(
//1
    (0 0 0)
    (1 0 0)
    (1 0.5 0)
    (0 0.5 0)
    (0 0 0.5)
    (1 0 0.5)
    (1 0.5 0.5)
    (0 0.5 0.5)
//2
    (1 0 0)
    (1.5 0 0)
    (1.5 0.5 0)
    (1 0.5 0)
    (1 0 0.5)
    (1.5 0 0.5)
    (1.5 0.5 0.5)
    (1 0.5 0.5)
//3
    (0 0 -0.8)
    (1 0 -0.8)
    (1 0.5 -0.8)
    (0 0.5 -0.8)
    (0 0 0)
    (1 0 0)
    (1 0.5 0)
    (0 0.5 0)
//4
    (1 0 -0.8)
    (1.5 0 -0.8)
    (1.5 0.5 -0.8)
    (1 0.5 -0.8)
    (1 0 0)
    (1.5 0 0)
    (1.5 0.5 0)
    (1 0.5 0)
//5
    (0 0.5 0)
    (1 0.5 0)
    (1 1 0)
    (0 1 0)
    (0 0.5 0.5)
    (1 0.5 0.5)
    (1 1 0.5)
    (0 1 0.5)
//6
    (1 0.5 0) //40
    (1.5 0.5 0)
    (1.5 1 0)
    (1 1 0)
    (1 0.5 0.5)
    (1.5 0.5 0.5)
    (1.5 1 0.5)
    (1 1 0.5)
//7
    (0 0.5 -0.8)
    (1 0.5 -0.8)
    (1 1 -0.8)
    (0 1 -0.8)
    (0 0.5 0)
    (1 0.5 0)
    (1 1 0)
    (0 1 0)
//8
    (1 0.5 -0.8)
    (1.5 0.5 -0.8)
    (1.5 1 -0.8)
    (1 1 -0.8)
    (1 0.5 0)
    (1.5 0.5 0)
    (1.5 1 0)
    (1 1 0)
);

blocks
(
    hex (0 1 2 3 4 5 6 7) (10 10 10) simpleGrading (1 1 1)  //1
    hex (8 9 10 11 12 13 14 15) (10 10 10) simpleGrading (1 1 1)//2
    hex (16 17 18 19 20 21 22 23) (10 10 10) simpleGrading (1 1 1)//3
    hex (24 25 26 27 28 29 30 31) (10 10 10) simpleGrading (1 1 1)//4
    hex (32 33 34 35 36 37 38 39) (10 10 10) simpleGrading (1 1 1)//5
    hex (40 41 42 43 44 45 46 47) (10 10 10) simpleGrading (1 1 1)//6
    hex (48 49 50 51 52 53 54 55) (10 10 10) simpleGrading (1 1 1)//7
    hex (56 57 58 59 60 61 62 63) (10 10 10) simpleGrading (1 1 1)//8
);

edges
(
);
patches
(
patch inlet
(
    (43 47 46 42)
    (59 63 62 58)
)
patch outlet
(
    (0 4 7 3)
)
patch wall
(
    (6 7 4 5)
    (14 15 12 13)
    (46 47 44 45)
    (10 14 13 9)
   // (26 30 29 25)
    (42 46 45 41)
    (58 62 61 57)
    (56 57 61 60)
    (57 56 59 58)
    (59 56 60 63)
    (9 8 11 10)
    (1 0 3 2)
    (2 3 7 6)
    (0 1 5 4)
    (8 9 13 12)
    (40 44 47 43)
)
patch interface1
(
    (10 11 15 14)
)
patch interface2
(
    (40 41 45 44)
)
patch interface3
(
    (1 2 6 5)
)
patch interface4
(
    (8 12 15 11)
)
patch interface5
(
    (40 43 42 41)
)
patch interface6
(
    (60 61 62 63)
)
);
boundary
(
);

mergePatchPairs
(
    (interface1 interface2)
    (interface4 interface3)
    (interface5 interface6)
);

// ************************************************************************* //

wyldckat · April 19, 2014, 09:47

Greetings mikeR,

From what I can see by using:

Code:

paraFoam -block

it looks like you're repeating points in the "vertices" list. That can lead to serious issues, as blockMesh might be getting confused with what exactly you're trying to do.

edit: I've updated the wiki page considerably, so feel free to check it out! http://openfoamwiki.net/index.php/BlockMesh

Best regards,
Bruno

mikeR · April 21, 2014, 15:21

Hey wyldckat,
thanks for the reply. From what I've figured out with try and error the problem seems to be with the mergePatchPairs. I guess it is not allowed use the same point for merging more than one patch. Is this correct?
I thought it was required to actually use repeating points in the vertices list and was wondered why there was no automatic face matching. I got the problem resolved by removing all the double entries.
Thank you for your comment!

wyldckat · April 21, 2014, 17:43

Hi mikeR,

Quote:

Originally Posted by mikeR

From what I've figured out with try and error the problem seems to be with the mergePatchPairs. I guess it is not allowed use the same point for merging more than one patch. Is this correct?

I'm not sure I understand your question. But it reminds me of a problem that occurs with stitchMesh... have a look at this post: http://www.cfd-online.com/Forums/ope...tml#post433137 post #10 - it's a long description, but the idea is that when we try to stitch 4 perpendicular duplicate patches, the last 2 pairs won't be stitch-able due to this reported issue:

Code:

Face * reduced to less than 3 points.  Topological/cutting error B.

My guess is that you triggered something very similar when using blockMesh.

Best regards,
Bruno

Perschr · February 19, 2017, 13:38

Hey everbody,

I have the same problem and as it hasn't been solved I thought to push up.

Here is my blockmeshdict:

Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.0                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 1;

vertices
(
    (    0    -0.005   -0.02)
    (  0.1    -0.005   -0.02)
    (  0.1     0.005   -0.02)
    (   0      0.005   -0.02)
    (    0    -0.005    0)
    (  0.1    -0.005    0)
    (  0.1     0.005    0)
    (   0      0.005    0)
    
//Zweite Box oben
    (  0.1    -0.005   -0.02)
    (  0.2    -0.005   -0.02)
    (  0.2     0.005   -0.02)
    (  0.1     0.005   -0.02)
    (  0.1    -0.005    0)
    (  0.2    -0.005    0)
    (  0.2     0.005    0)
    (  0.1     0.005    0)

//Zweite Box unten
    (  0.1    -0.005   -0.04)
    (  0.2    -0.005   -0.04)
    (  0.2     0.005   -0.04)
    (  0.1     0.005   -0.04)
    (  0.1    -0.005   -0.02)
    (  0.2    -0.005   -0.02)
    (  0.2     0.005   -0.02)
    (  0.1     0.005   -0.02)


//Dritte Box oben
    (  0.2    -0.005   -0.02)
    (  0.3    -0.005   -0.02)
    (  0.3     0.005   -0.02)
    (  0.2     0.005   -0.02)
    (  0.2    -0.005   0)
    (  0.3    -0.005   0)
    (  0.3     0.005   0)
    (  0.2     0.005   0)

//Dritte Box Mitte
    (  0.2    -0.005   -0.04)
    (  0.3    -0.005   -0.04)
    (  0.3     0.005   -0.04)
    (  0.2     0.005   -0.04)
    (  0.2    -0.005   -0.02)
    (  0.3    -0.005   -0.02)
    (  0.3     0.005   -0.02)
    (  0.2     0.005   -0.02)

//Dritte Box unten
    (  0.2    -0.005   -0.1)
    (  0.3    -0.005   -0.1)
    (  0.3     0.005   -0.1)
    (  0.2     0.005   -0.1)
    (  0.2    -0.005   -0.04)
    (  0.3    -0.005   -0.04)
    (  0.3     0.005   -0.04)
    (  0.2     0.005   -0.04)


//Box Düse
    (  0.3    -0.005   -0.02)
    (  0.4    -0.005   -0.005)
    (  0.4     0.005   -0.005)
    (  0.3     0.005   -0.02)
    (  0.3    -0.005   0)
    (  0.4    -0.005   0)
    (  0.4     0.005   0)
    (  0.3     0.005   0)

//Vierte Box Mitte
    (  0.3    -0.005   -0.04)
    (  0.6    -0.005   -0.04)
    (  0.6     0.005   -0.04)
    (  0.3     0.005   -0.04)
    (  0.3    -0.005   -0.02)
    (  0.6    -0.005   -0.02)
    (  0.6     0.005   -0.02)
    (  0.3     0.005   -0.02)

//Vierte Box unten
    (  0.3    -0.005   -0.1)
    (  0.6    -0.005   -0.1)
    (  0.6     0.005   -0.1)
    (  0.3     0.005   -0.1)
    (  0.3    -0.005   -0.04)
    (  0.6    -0.005   -0.04)
    (  0.6     0.005   -0.04)
    (  0.3     0.005   -0.04)


);

blocks
(
    hex (0 1 2 3 4 5 6 7) (75 1 15) simpleGrading (2 1 4)
    hex (8 9 10 11 12 13 14 15) (60 1 15) simpleGrading (1 1 4)
    hex (16 17 18 19 20 21 22 23) (60 1 30) simpleGrading (1 1 1)
    hex (24 25 26 27 28 29 30 31) (60 1 15) simpleGrading (1 1 4)
    hex (32 33 34 35 36 37 38 39) (60 1 30) simpleGrading (1 1 1)
    hex (40 41 42 43 44 45 46 47) (60 1 30) simpleGrading (1 1 0.15)
    hex (48 49 50 51 52 53 54 55) (60 1 15) simpleGrading (1 1 4)

//Vierte Box Mitte
    hex (56 57 58 59 60 61 62 63) (180 1 30) simpleGrading (1 1 1)
//Vierte Box unten
    hex (64 65 66 67 68 69 70 71) (180 1 30) simpleGrading (1 1 0.15)


);

edges
(
);

boundary
(
    inlet
    {
        type patch;
        faces
        (
            (0 4 7 3)
     );
    }
    outlet
    {
        type patch;
        faces
        (
            (65 66 70 69)
        (57 58 62 61)
        );
    }    
    symmetryplane
    {
        type symmetryPlane;
        faces
        (
            (4 5 6 7)
            (12 13 14 15)
            (28 29 30 31)
        (52 53 54 55)
        
        );
    }
    Wall
    {
        type wall;
        faces
        (
            (0 3 2 1)
            (16 20 23 19)
            (16 19 18 17)
            (40 44 47 43)
        (40 43 42 41)
        (51 50 49 48)
        (49 50 54 53)
        (60 61 62 63)
        (64 67 66 65)
    );
    }
    frontAndBack
    {
        type empty;
        faces
        (
            (0 1 5 4)
        (8 9 13 12)
        (16 17 21 20)
        (24 25 29 28)
        (48 49 53 52)
        (32 33 37 36)
        (56 57 61 60)
        (40 41 45 44)
        (64 65 69 68)
        (7 6 2 3)
        (15 14 10 11)
        (31 30 26 27)
        (55 54 50 51)
        (23 22 18 19)
        (39 38 34 35)
        (63 62 58 59)
        (47 46 42 43) 
        (71 70 66 67)
        );
    }
    interface1
    {
        type patch;
        faces
        (
            (1 2 6 5)
    );
    }
    interface2
    {
        type patch;
        faces
        (
            (8 12 15 11)
    );
    }
    interface3
    {
        type patch;
        faces
        (
            (9 10 13 14)
    );
    }
    interface4
    {
        type patch;
        faces
        (
            (24 28 31 27)
    );
    }
    interface5
    {
        type patch;
        faces
        (
            (25 26 30 29)
    );
    }
    interface6
    {
        type patch;
        faces
        (
            (48 52 55 51)
    );
    }
    interface7
    {
        type patch;
        faces
        (
            (17 18 22 21)
    );
    }
    interface8
    {
        type patch;
        faces
        (
            (32 36 39 35)
    );
    }
    interface9
    {
        type patch;
        faces
        (
            (33 34 38 37)
    );
    }
    interface10
    {
        type patch;
        faces
        (
            (56 60 63 59)
    );
    }
    interface11
    {
        type patch;
        faces
        (
            (41 42 45 46)
    );
    }
    interface12
    {
        type patch;
        faces
        (
            (64 68 71 67)
    );
    }
    interface13
    {
        type patch;
        faces
        (
            (11 10 9 8)
        );
    }
    interface14
    {
        type patch;
        faces
        (
            (20 21 22 23)
        );
    }
//    interface15
//    {
//        type patch;
//        faces
//        (
//            (24 27 26 25)
//        );
//    }
//    interface16
//    {
//        type patch;
//        faces
//        (
//            (36 37 38 39)
//        );
//    }
//   interface17
//    {
//        type patch;
//        faces
//        (
//            (32 35 34 33)
//        );
//    }
//    interface18
//    {
//        type patch;
//        faces
//        (
//            (44 45 46 47)
//        );
//    }
//    interface19
//    {
//        type patch;
//        faces
//        (
//            (56 59 58 57)
//        );
//    }
//    interface20
//    {
//        type patch;
//        faces
//        (
//            (68 69 70 71)
//        );
//    }
//
);

mergePatchPairs
(
    (interface1 interface2)
    (interface3 interface4)
    (interface5 interface6)
    (interface7 interface8)
    (interface9 interface10)
    (interface11 interface12)
    (interface13 interface14)
   // (interface15 interface16)
   // (interface17 interface18)
   // (interface19 interface20)

);

The last interfaces do not merge. What's the matter?

fredicenci · March 12, 2017, 14:34

Did you guys solve it? I have the same problem...

thanks

dasith0001 · July 20, 2023, 20:27

Hi,

I know this is a very old thread but just to update how to avoid this, as previously mentioned, avoid repeating the same nodes.

However, there are some instances that you have to repeat the same nodes to get different resolutions (and if you don't want to use refineMesh) of the mesh. And that leads to mergingPatches.

As it is correctly said, blockMesh do not allowed to share a node for merging more than one face with an another.

The work around I found for this is using '' stitchMesh -overwrite masterC51 slaveC62 ''

This does not give any errors in the mesh but please let me know if any other elegant ways of doing this.

Thank you.
Dasith

ashish1995 · July 17, 2024, 07:35

Just to add to dasith0001's solution, I had to add the -perfect flag to stitchMesh, to make it work. (My unmerged faces/patches matched perfectly, but without the flag, stitchMesh produced error.)

Code:

stitchMesh -overwrite -perfect master slave

After stitching succesfully, the master & slave patches remain in the boundary file with zero faces each. They can be removed manually, or using a createPatchDict having just the FoamFile header and the line

Code:

patches ();

April 19, 2014, 09:47		#3
wyldckat Retired Super Moderator Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 10,982 Blog Entries: 45 Rep Power: 128	Greetings mikeR, From what I can see by using: Code: paraFoam -block it looks like you're repeating points in the "vertices" list. That can lead to serious issues, as blockMesh might be getting confused with what exactly you're trying to do. edit: I've updated the wiki page considerably, so feel free to check it out! http://openfoamwiki.net/index.php/BlockMesh Best regards, Bruno __________________ OpenFOAM: FAQ \| Getting started Forum: How to get help, to post code/output and forum guide Read this before sending me PM Last edited by wyldckat; April 19, 2014 at 11:43. Reason: see "edit:"

July 20, 2023, 20:27		#8
dasith0001 Senior Member Desh Join Date: Mar 2021 Location: Sydney Posts: 118 Rep Power: 5	Hi, I know this is a very old thread but just to update how to avoid this, as previously mentioned, avoid repeating the same nodes. However, there are some instances that you have to repeat the same nodes to get different resolutions (and if you don't want to use refineMesh) of the mesh. And that leads to mergingPatches. As it is correctly said, blockMesh do not allowed to share a node for merging more than one face with an another. The work around I found for this is using '' stitchMesh -overwrite masterC51 slaveC62 '' This does not give any errors in the mesh but please let me know if any other elegant ways of doing this. Thank you. Dasith ashish1995 likes this. Last edited by dasith0001; July 20, 2023 at 22:37.

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[blockMesh] BlockMeshmergePatchPairs	hjasak	OpenFOAM Meshing & Mesh Conversion	11	August 15, 2008 08:36

April 21, 2014, 15:21		#4
mikeR New Member anonymous Join Date: Apr 2014 Posts: 8 Rep Power: 12	Hey wyldckat, thanks for the reply. From what I've figured out with try and error the problem seems to be with the mergePatchPairs. I guess it is not allowed use the same point for merging more than one patch. Is this correct? I thought it was required to actually use repeating points in the vertices list and was wondered why there was no automatic face matching. I got the problem resolved by removing all the double entries. Thank you for your comment!

March 12, 2017, 14:34		#7
fredicenci Member Fredi Cenci Join Date: Dec 2016 Posts: 38 Rep Power: 9	Did you guys solve it? I have the same problem... thanks

July 17, 2024, 07:35		#9
ashish1995 New Member Ashish Singh Join Date: Feb 2020 Posts: 1 Rep Power: 0	Just to add to dasith0001's solution, I had to add the -perfect flag to stitchMesh, to make it work. (My unmerged faces/patches matched perfectly, but without the flag, stitchMesh produced error.) Code: stitchMesh -overwrite -perfect master slave After stitching succesfully, the master & slave patches remain in the boundary file with zero faces each. They can be removed manually, or using a createPatchDict having just the FoamFile header and the line Code: patches ();