CFD Online Discussion Forums - [blockMesh] Unable to change mesh density in blocks

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- - [blockMesh] Unable to change mesh density in blocks (https://www.cfd-online.com/Forums/openfoam-meshing/219164-unable-change-mesh-density-blocks.html)

Unable to change mesh density in blocks

I'm attaching a simplified mesh code that utilizes 5 block regions. Each block starts with a very simple mesh density of (1 1 1).

My goal is to change the x-direction mesh density. Let's take the middle block "BLOCK III". I can change the mesh density to (10 1 1) and the the blockMesh command works without a problem.

Now let's say I want to change the mesh density in both "BLOCK 0" and "BLOCK IV" to (20 1 1). Now I get an error message that says:

Code:

--> FOAM FATAL ERROR:

Inconsistent number of faces between block pair 0 and 4



    From function void Foam::blockMesh::calcMergeInfo()

    in file blockMesh/blockMeshMerge.C at line 221.

I don't understand why this is a problem since the blocks have the exact same x-dimensions. Can anyone help explain the problem? My code is below.

Many thanks,

~ Joseph

Code:

FoamFile 

{

    version    2.0;

    format     ascii;

    class      dictionary;

    object     blockMeshDict;

}



scale   0.001;



vertices

(

    (0 0 0)

    (100 0 0)

    (100 5 0)

    (105 5 0)

    (105 0 0)

    (205 0 0)

    (205 5 0)

    (205 50 0)

    (105 50 0)

    (100 50 0)

    (0 50 0)

    (0 5 0)



    (0 0 7)

    (100 0 7)

    (100 5 7)

    (105 5 7)

    (105 0 7)

    (205 0 7)

    (205 5 7)

    (205 50 7)

    (105 50 7)

    (100 50 7)

    (0 50 7)

    (0 5 7)

);



blocks

(

    // BLOCK 0

    hex (0 1 2 11 12 13 14 23)

    (1 1 1)

    simpleGrading (1 1 1)



    // BLOCK 1

    hex (3 4 5 6 15 16 17 18)

    (1 1 1)

    simpleGrading (1 1 1)



    // BLOCK 2

    hex (3 6 7 8 15 18 19 20)

    (1 1 1)

    simpleGrading (1 1 1)



    // BLOCK 3

    hex (2 3 8 9 14 15 20 21)

    (1 1 1)

    simpleGrading (1 1 1)



    // BLOCK 4

    hex (2 9 10 11 14 21 22 23)

    (1 1 1)

    simpleGrading (1 1 1)



);



edges

(

);



boundary

(

    inlet

    {

        type patch;

        faces

        (

            (10 11 23 22)

            (11 0 12 23)

        );

    }



    outlet

    {

        type patch;

        faces

        (

            (6 7 19 18)

            (5 6 18 17)

        );

    }



    upperWall

    {

        type wall;

        faces

        (

            (7 8 20 19)

            (8 9 21 20)

            (9 10 22 21)

        );

    }



    lowerWall

    {

        type wall;

        faces

        (

            (0 1 13 12)

            (1 2 14 13)

            (2 3 15 14)

            (3 4 16 15)

            (4 5 17 16)

        );

    }



    front

    {

        type empty;

        faces

        (

            (13 14 23 12)

            (14 21 22 23)

            (14 15 20 21)

            (15 18 19 20)

            (15 16 17 18)

        );

    }



    back

    {

        type empty;

        faces

        (

            (11 2 1 0)

            (3 6 5 4)

            (8 7 6 3)

            (9 8 3 2)

            (10 9 2 11)

        );

    }



);



mergePatchPairs

(



);

asfdasdf

You can not mesh two connected blocks with different mesh density.

In the image attached, you see two blocks, with a green and a red mesh. The face the two blocks are connected, the grid lines don't match. This is why OpenFOAM aborts with an error.

You have two options

Use matching mesh densities
Don't connect the blocks; create the mesh; connect the meshes using AMI

Gerhard,

Thanks so much for the reply. The thumbnail you showed does not match what I am trying to do. I am not changing the y-direction mesh density. BLOCK 0 and BLOCK IV are on the left of my domain and on top of each other.

Code:

|--------------|---|----------------|

|   Block IV   |III|     Block II   |

|              |   |                |

|--------------|---|----------------|

|   Block 0    |   |     Block I    |

|--------------|   |----------------|

I am just trying to change the x-direction mesh density, e.g.

Code:

    // BLOCK 0

    hex (0 1 2 11 12 13 14 23)

    (10 1 1)

    simpleGrading (1 1 1)  



    // BLOCK 4

    hex (2 9 10 11 14 21 22 23)

    (10 1 1)

    simpleGrading (1 1 1)

I feel like this is too simple of a problem to be a bug in the software but I cannot understand why this is not possible.

Thanks so much for your help! ~ Joseph

Your local coordinates are messed up.

Code:

blocks

(

    // BLOCK 0

    hex (0 1 2 11 12 13 14 23)

    (1 1 1)

    simpleGrading (1 1 1)



    // BLOCK 4

    hex (2 9 10 11 14 21 22 23)

    (1 1 1)

    simpleGrading (1 1 1)

);

While the local x-direction of block 0 coincides with the global x-direction, the local x-direction of block 4 doesn't.

Gerhard,

Thanks so much for helping me isolate my error. I knew that blocks had to be defined in a CCW manner but did not realize the first vertex sets the origin.

Best,

~ Joseph