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-   -   Time Step Continuity (http://www.cfd-online.com/Forums/openfoam-solving/109764-time-step-continuity.html)

hiasl November 26, 2012 07:40

Time Step Continuity
 
Hi,

I am new to OpenFoam and I try to simulate a axisymmetric flow. My result doesn't look very useful in the paraviewer. By solving with the icoFoam-solver I get the following message (here the last time step):


Code:

Time = 0.6

Courant Number mean: 2.23e+34 max: 5.65961e+37
DILUPBiCG:  Solving for Ux, Initial residual = 0.998035, Final residual = 6.06503e+07, No Iterations 1001
DILUPBiCG:  Solving for Uy, Initial residual = 0.902429, Final residual = 8.16874, No Iterations 1001
DILUPBiCG:  Solving for Uz, Initial residual = 0.997655, Final residual = 2.25247, No Iterations 1001
DICPCG:  Solving for p, Initial residual = 1, Final residual = 18.6765, No Iterations 1001
time step continuity errors : sum local = 6.55952e+47, global = -8.33417e+31, cumulative = -8.33417e+31
DICPCG:  Solving for p, Initial residual = 0.998855, Final residual = 7.59938, No Iterations 1001
time step continuity errors : sum local = 4.59185e+51, global = -4.68485e+35, cumulative = -4.68568e+35
ExecutionTime = 38.21 s  ClockTime = 39 s

Can somebody help me?
Thank you!!

atmcfd November 27, 2012 04:48

Hi,

There is a serious problem in your case setup because the Courant number

Code:

Courant Number mean: 2.23e+34 max: 5.65961e+37
Can never , ever be so high. You are not implementing the right BCs.
What case are you trying to simulate?

Regards,

A.T.M

yzf1215 December 2, 2012 06:45

Please do checkMesh before calculation, probably there are some mesh problems. Also, reduce the time-step to see if there is any changes.

hiasl December 3, 2012 07:03

the blockMesh:

Code:

convertToMeters 0.001;

vertices
(
    (0 0 0)          // 0 Bottom
    (88 3.0730 0)    // 1 Bottom
    (88 3.0730 2)    // 2      Top
    (0 0 2)          // 3      Top
    (88 -3.0730 0)    // 4 Bottom
    (88 -3.0730 2)    // 5      Top
    (32.5 -1.134925 2)// 6      Top
    (32.5 1.134925 2) // 7      Top
    (32.5 1.134925 0) // 8 Bottom
    (32.5 -1.134925 0)// 9 Bottom
    (62.5 -2.1825 0)  //10 Bottom
    (62.5  2.1825 0)  //11 Bottom
    (0 0 1)          //12  Mid
    (32.5 1.134925 1) //13  Mid
    (32.5 -1.134925 1)//14  Mid
    (62.5 -2.1825 1)  //15  Mid
    (62.5 2.1825 1)  //16  Mid
    (88 -3.0730 1)    //17  Mid
    (88 3.0730 1)    //18  Mid
    (62.5 2.1825 2)  //19      Top
    (62.5 -2.1825 2)  //20      Top
);

blocks
(
  // hex (0 9 8 0 3 6 7 3) (20 20 20) simpleGrading (1 1 1)      //wedge
  // hex (8 9 4 1 7 6 5 2) (20 20 20) simpleGrading (1 1 1)      //wholeBlock

    hex (0 9 8 0 12 14 13 12) (50 50 50) simpleGrading (0.1 1 10)    //wedgeBottom      0
    hex (12 14 13 12 3 6 7 3) (50 50 50) simpleGrading (0.1 1 0.1)  //wedgeTop          1
    hex (9 10 11 8 14 15 16 13) (50 50 50) simpleGrading (10 1 10)    //  midBottom    2
    hex (14 15 16 13 6 20 19 7) (50 50 50) simpleGrading (10 1 0.1)  //  midTop                3
    hex (10 4 1 11 15 17 18 16) (50 50 50) simpleGrading (0.1 1 10)  //      outBottom  4
    hex (15 17 18 16 20 5 2 19) (50 50 50) simpleGrading (0.1 1 0.1)//      outTop      5
);

edges
(
);
boundary
(

front
    {
          type wedge;
          faces
          (
              (0 8 13 12)
              (12 13 7 3)
          );
      }

back
    {
          type wedge;
          faces
          (
              (0 12 14 9)
              (12 3 6 14)
          );
      }

tankWall
    {
          type wall;
          faces
          (
              (1 4 17 18)
              (18 17 5 2)
          );
      }

bottomWall
    {
          type wall;
          faces
          (
              (0 9 8 0)
              (8 9 10 11)
              (11 10 4 1)
          );
      }
rotatingPlate
    {
          type wall;
          faces
          (
              (3 7 6 3)
          );
      }

openFluid
    {
          type patch;
          faces
          (
              (7 19 20 6)
              (19 2 5 20)
              (9 14 15 10)
              (10 15 17 4)
              (14 6 20 15)
              (15 20 5 17)
              (11 1 18 16)
              (8 11 16 13)
              (16 18 2 19)
              (13 16 19 7)
          );
      }

axis
    {
          type empty;
          faces
          (
              (0 12 12 0)
              (12 3 3 12)
          );
      }
);


mergePatchPairs
(
);

checkMesh tells me this:

Code:

Build  : 2.1.1-221db2718bbb
Exec  : checkMesh
Date  : Dec 03 2012
Time  : 12:00:30
Host  : "lstma243"
PID    : 25757
Case  : /tmp/OpenFOAM/matthias-2.1.1/tutorials/incompressible/icoFoam/cavity
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMas                                                                                        ter
allowSystemOperations : Disallowing user-supplied system call operations

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

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:          772751
    faces:            2272500
    internal faces:  2222500
    cells:            750000
    boundary patches: 7
    point zones:      0
    face zones:      0
    cell zones:      0

Overall number of cells of each type:
    hexahedra:    745000
    prisms:        5000
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:    0

Checking topology...
    Boundary definition OK.
    Cell to face addressing 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
    front              5000    5151    ok (non-closed singly connected)
    back                5000    5151    ok (non-closed singly connected)
    tankWall            5000    5151    ok (non-closed singly connected)
    bottomWall          7500    7651    ok (non-closed singly connected)
    rotatingPlate      2500    2551    ok (non-closed singly connected)
    openFluid          25000    25351    ok (non-closed singly connected)
    axis                0        0        ok (empty)

Checking geometry...
    Overall domain bounding box (0 -0.003073 0) (0.088 0.003073 0.002)
    Mesh (non-empty, non-wedge) directions (1 0 1)
    Mesh (non-empty) directions (1 1 1)
    Wedge front with angle 2 degrees
    Wedge back with angle 2 degrees
 ***Number of edges not aligned with or perpendicular to non-empty directions: 7                                                                                        47400
  <<Writing 747703 points on non-aligned edges to set nonAlignedEdges
    Boundary openness (1.20325e-17 -9.40901e-17 3.47075e-15) OK.
    Max cell openness = 1.23591e-15 OK.
    Max aspect ratio = 296.346 OK.
    Minumum face area = 1.16905e-11. Maximum face area = 1.31286e-07.  Face area                                                                                        magnitudes OK.
    Min volume = 9.64031e-15. Max volume = 6.66225e-12.  Total volume = 5.40846e                                                                                        -07.  Cell volumes OK.
    Mesh non-orthogonality Max: 1.96008 average: 0.932908
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 0.333336 OK.
    Coupled point location match (average 0) OK.

Failed 1 mesh checks.

End

I tried several timesteps (until 2e-6) but the error always got too big...


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