[deepbandivadekar]

Hello,

Can someone please help me with the time step continuity error I'm getting?

I'm using simpleFoam and this is what I get when I run the case

#0  Foam::error::printStack(Foam::Ostream&) at ??:?
#1  Foam::sigFpe::sigHandler(int) at ??:?
#2  ? in "/lib/x86_64-linux-gnu/libc.so.6"
#3  Foam::divide(Foam::Field<double>&, double const&, Foam::UList<double> const&) at ??:?
#4  Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > Foam::operator/<Foam::fvPatchField, Foam::volMesh>(Foam::dimensioned<double> const&, Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > const&) at ??:?
#5  ? at ??:?
#6  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#7  ? at ??:?

In the log file the last entries are like this:

Time = 8

DILUPBiCG:  Solving for Ux, Initial residual = 0.954901, Final residual = 0.072332, No Iterations 71
DILUPBiCG:  Solving for Uy, Initial residual = 0.94901, Final residual = 0.0562591, No Iterations 68
DICPCG:  Solving for p, Initial residual = 0.999999, Final residual = 0.0958529, No Iterations 293
time step continuity errors : sum local = 3.77895e+12, global = -1.04947e+10, cumulative = -1.04947e+10
ExecutionTime = 0.53 s  ClockTime = 1 s

Time = 9

DILUPBiCG:  Solving for Ux, Initial residual = 1, Final residual = 0.0892879, No Iterations 261
DILUPBiCG:  Solving for Uy, Initial residual = 1, Final residual = 0.0170661, No Iterations 132
DICPCG:  Solving for p, Initial residual = 1, Final residual = 0.0934216, No Iterations 192
time step continuity errors : sum local = 6.39919e+21, global = 5.204e+20, cumulative = 5.204e+20
ExecutionTime = 0.79 s  ClockTime = 1 s

Time = 10

DILUPBiCG:  Solving for Ux, Initial residual = 1, Final residual = 0.0895149, No Iterations 116
DILUPBiCG:  Solving for Uy, Initial residual = 1, Final residual = 0.0685429, No Iterations 109

The time step continuity errors are very large as you can see. I have been through the threads related to this topic and I haven't understood yet what is causing these errors.
I toyed around the relTol as mentioned in threads like this:
Time step continuity
But these are errors are very small in magnitude, whereas mine are on the other end of the spectrum.

What should be the source of these errors?

[deepbandivadekar]

This is my choice of p and U solvers in the fvSolutions

solvers
{
    p
    {
        solver          PCG;
    preconditioner    DIC;
        tolerance       1e-07;
        relTol          0.1;
//        smoother        GaussSeidel;
    }

    U
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance       1e-07;
        relTol          0.1;
    }
}

SIMPLE
{
//    nUCorrectors    2;
    nNonOrthogonalCorrectors 0;
    
    residualControl
    {
      p    1e-6;
      U 1e-6;
    }

    pRefCell 0;
    pRefValue 0;
}

relaxationFactors
{
    fields
    {
        p               0.2;
        U               0.9;
//        k               0.9;
//        epsilon         0.9;
    }
}

This is a 2D (quasi 3D) case of flow through porous medium.

Is the error related to any of these parameters ?

[deepbandivadekar]

Update: Decreasing relaxation factors did not help as per this thread here: simpleFoam time step continuity errors


I changed it to 0.5 for U and same (0.2) for p in fvsolution

The boundary conditions seem to be okay for this case. Nothing has changed in the output.

I don't see how this error can be resolved. Can anyone please help?

[deepbandivadekar]

Anyone at all ? Still stuck here..

[kera]

Hallo!

There are still other stuff which may lead to this error:

1) Have you checked the quality of your mesh?
2) The boundary conditions at the inlet and outlet for U and p?

Regards,
Ricky

Originally Posted by deepbandivadekar

Update: Decreasing relaxation factors did not help as per this thread here: simpleFoam time step continuity errors


I changed it to 0.5 for U and same (0.2) for p in fvsolution

The boundary conditions seem to be okay for this case. Nothing has changed in the output.

I don't see how this error can be resolved. Can anyone please help?

[deepbandivadekar]

Originally Posted by kera

Hallo!

There are still other stuff which may lead to this error:

1) Have you checked the quality of your mesh?
2) The boundary conditions at the inlet and outlet for U and p?

Regards,
Ricky

Thanks kera for responding.

1) Yes, with checkMesh. Also visually in paraview. Mesh is fine.
2) As suggested in the tutorial (image attached)

[jaydeep]

Originally Posted by deepbandivadekar

Thanks kera for responding.

1) Yes, with checkMesh. Also visually in paraview. Mesh is fine.
2) As suggested in the tutorial (image attached)

There was one time I had similar error, in my case I had forgotten to scale my mesh (inch to m). Did you have any scaling operation?

Please post your case for more details

[deepbandivadekar]

I did. But I don't see how that should cause something like this. At max it would need more number of iterations to converge. Am I right?

[deepbandivadekar]

Inch to metre..hmm maybe. Those are inconsistent units.