[sasanghomi]

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 ?

/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  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]

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]

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]

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

[viraj20feb]

Hello Mr. Nima,

I imported my mesh from Gmsh (http://www.cfd-online.com/Forums/ope...ecks-fail.html)

still I am facing the problem of Zero or negative volume. Can you please tell me how to solve it?

Thank you

[nimasam]

it is due to wrong face orientation in the grid. so you should change it. consider either clockwise or counter clock wise for the faces.