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-   -   [blockMesh] Problem with Mesh Volume (https://www.cfd-online.com/Forums/openfoam-meshing/96676-problem-mesh-volume.html)

seboxx January 29, 2012 10:01
Problem with Mesh Volume
 
2 Attachment(s)
Dear Foamers,

I am struggling with a Problem for several weeks already and starting to get really desperate. I have posted it in the main forum already, but I figured posting a new thread here as I have narrowed the problem down to blockMesh, I guess so at least.

The Problem is I want to simulate a thin layer with a bump, I have modelled the bump with a blockMeshDict.
What is wrong here is that the volume is not recognized correctly. You can see in checkMesh the total volume of 1256.62. But this cannot be correct, since a flat disc with height one and radius 20 would have exactly that volume (Pi*r^2)

But the graphical output in paraview is correct. Whats wrong here? :(

Now when I do checkMesh, this is the output
Code:
/*---------------------------------------------------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.0.0                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.com                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
Build  : 2.0.0-a317a4e7cd55
Exec  : checkMesh
Date  : Jan 29 2012
Time  : 15:48:06
Host  : ernie
PID    : 7269
Case  : /home/boie/OpenFOAM/OpenFOAM-reloaded/boie-2.0.0/simulations/tests/justbump
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster
allowSystemOperations : Disallowing user-supplied system call operations

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

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:          80802
    internal points:  0
    faces:            160400
    internal faces:  79600
    cells:            40000
    boundary patches: 3
    point zones:      0
    face zones:      0
    cell zones:      0

Overall number of cells of each type:
    hexahedra:    40000
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:    0

Checking topology...
    Boundary definition 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                 
    frontWall          40000    40401    ok (non-closed singly connected) 
    backWall            40000    40401    ok (non-closed singly connected) 
    circular            800      1600    ok (non-closed singly connected) 

Checking geometry...
    Overall domain bounding box (-20 -20 -0.0312941) (20 20 21)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (8.25305e-21 7.15265e-20 -3.39808e-19) OK.
    Max cell openness = 2.24782e-16 OK.
    Max aspect ratio = 321.104 OK.
    Minumum face area = 0.000702619. Maximum face area = 0.283752.  Face area magnitudes OK.
    Min volume = 0.000692074. Max volume = 0.0803204.  Total volume = 1256.62.  Cell volumes OK.
    Mesh non-orthogonality Max: 87.5911 average: 38.3172
  *Number of severely non-orthogonal faces: 624.
    Non-orthogonality check OK.
  <<Writing 624 non-orthogonal faces to set nonOrthoFaces
    Face pyramids OK.
    Max skewness = 2.81207 OK.

Mesh OK.

End

bastil January 30, 2012 03:17
I don't see you problem. Your formula is right and I get:

3.14*20^2=3.14*400=1256.

So for me everything seems to be fine.

seboxx January 30, 2012 03:21
Hi bastil,

well the problem is the volume must be larger than this.
See the attached picture, its a bump and not a disc anymore. The Problem is similiar to taking a cube and a cube with a large dent in it but with the same length of the edges. The volume should be different

seboxx January 30, 2012 08:19
2 Attachment(s)
To illustrate my problem I have made 2 more screenshots. In the first picture you look from on top on the geometry.
In the second picture is the same geometry with a different angle of observation. checkMesh reports no errors and a total volume of:
Quote:
Total volume = 400.
But that is the volume like if i project the geometry into the xy-plane.
On the second picture you see the real geometry and clearly the volume must be larger...

I really have no idea what is going wrong here :(


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