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-   -   blockMesh & negative volume error (http://www.cfd-online.com/Forums/openfoam/116508-blockmesh-negative-volume-error.html)

sasanghomi April 21, 2013 06:28

blockMesh & negative volume error
 
4 Attachment(s)
Hi Dear foamers,

I created the mesh by using blockMesh and after checkMesh I had a negative volume error..
Can anyone explain how can I solve this problem ?
Code:

/*---------------------------------------------------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM Extend Project: Open source CFD        |
|  \\    /  O peration    | Version:  1.6-ext                              |
|  \\  /    A nd          | Web:      www.extend-project.de                |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
Build  : 1.6-ext-959ec266ba5c
Exec  : checkMesh
Date  : Apr 21 2013
Time  : 14:54:37
Host  : sasan-Inspiron-N5110
PID    : 15795
Case  : /home/sasan/Desktop/engine-blockMesh
nProcs : 1
SigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).

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

Create polyMesh for time = 0

Time = 0

Mesh stats
    all points:          172769
    live points:          172769
    all faces:            484260
    live faces:            484260
    internal faces:  451740
    cells:            156000
    boundary patches: 22
    point zones:      2
    face zones:      13
    cell zones:      0

Overall number of cells of each type:
    hexahedra:    156000
    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: 5
    The mesh has multiple regions which are not connected by any face.
  <<Writing region information to "0/cellToRegion"

Checking patch topology for multiply connected surfaces ...
    Patch              Faces    Points  Surface topology                 
    presin              800      861      ok (non-closed singly connected) 
    presout            800      861      ok (non-closed singly connected) 
    symmetry            6600    7147    ok (non-closed singly connected) 
    cylinderHead        2400    2521    ok (non-closed singly connected) 
    intakePort          1800    1886    ok (non-closed singly connected) 
    exhaustPort        1800    1886    ok (non-closed singly connected) 
    liner              800      891      ok (non-closed singly connected) 
    valveStem1          1680    1763    ok (non-closed singly connected) 
    valveStem2          1680    1763    ok (non-closed singly connected) 
    piston              5600    5843    ok (non-closed singly connected) 
    valve1              1000    1066    ok (non-closed singly connected) 
    valve2              1600    1661    ok (non-closed singly connected) 
    valve3              1000    1066    ok (non-closed singly connected) 
    valve4              1600    1661    ok (non-closed singly connected) 
    valveCurtainCyl1    400      451      ok (non-closed singly connected) 
    valveCurtainPort1  1280    1404    ok (non-closed singly connected) 
    valveCurtainCyl2    400      451      ok (non-closed singly connected) 
    valveCurtainPort2  1280    1404    ok (non-closed singly connected) 
    valveDetachCyl1    0        0        ok (empty)                       
    valveDetachPort1    0        0        ok (empty)                       
    valveDetachCyl2    0        0        ok (empty)                       
    valveDetachPort2    0        0        ok (empty)                       

Checking geometry...
    This is a 3-D mesh
    Overall domain bounding box (-0.05 0 -0.00712619) (0.05 0.05 0.0219694)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Mesh (non-empty, non-wedge) dimensions 3
    Boundary openness (-2.63084e-18 -8.37796e-15 2.66712e-16) Threshold = 1e-06 OK.
 ***High aspect ratio cells found, Max aspect ratio: 16856.8, number of cells 156000 Threshold = 1000
  Writing 156000 cells with high aspect ratio to set highAspectRatioCells
    Minumum face area = 3.52505e-08. Maximum face area = 1.99753e-06.  Face area magnitudes OK.
***Zero or negative cell volume detected.  Minimum negative volume: -1.42348e-09, Number of negative volume cells: 156000
  Writing 156000 zero volume cells to set zeroVolumeCells
Floating point exception (core dumped)

I attached several pictures of the mesh.
I appreciate your help.
Thanks and best regards.
Sasan.

nimasam April 21, 2013 09:59

it returns to the ordering of block, you can see negative volume ;) as you create your mesh by blockMesh, it shows negative volume as warnings

sasanghomi April 22, 2013 03:22

Hi Dr.sam,

thanks for your reply.
Can you say how can I overcome this error?
I should modify the vertices? Or I should change the ordering of points in construction of blocks??

I appreciate your help.
Thanks and best regards,
Sasan

nimasam April 22, 2013 04:22

Hi Dear sasan
in some simple cases when i see this warning in blockMesh i change the order of vertices, but maybe there are other ways to solve it


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