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Simulation error (delta T is decreasing while the iterations are being carried out)
Title
Question

Courant Number mean: 0.0163613 max: 1.00448
Interface Courant Number mean: 0.00015773 max: 0.241142
deltaT = 0.000254916
Time = 0.00156593

PIMPLE: iteration 1
smoothSolver: Solving for alpha.liquid, Initial residual = 0.00160927, Final residual = 2.5586e-10, No Iterations 2
Phase-1 volume fraction = 0.0170806 Min(alpha.liquid) = -3.07529e-07 Max(alpha.liquid) = 0.999998
MULES: Correcting alpha.liquid
MULES: Correcting alpha.liquid
Phase-1 volume fraction = 0.0170806 Min(alpha.liquid) = -9.82735e-06 Max(alpha.liquid) = 0.999998
DILUPBiCG: Solving for Ux, Initial residual = 0.0904852, Final residual = 4.99181e-06, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.0925329, Final residual = 3.61106e-06, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.0942319, Final residual = 3.21896e-06, No Iterations 1
GAMG: Solving for p_rgh, Initial residual = 0.0101787, Final residual = 6.88573e-05, No Iterations 3
time step continuity errors : sum local = 1.45928e-06, global = 5.03199e-07, cumulative = -5.27753e-05
GAMG: Solving for p_rgh, Initial residual = 0.00605928, Final residual = 6.59131e-09, No Iterations 13
time step continuity errors : sum local = 1.35045e-10, global = 3.61413e-11, cumulative = -5.27753e-05
ExecutionTime = 4.69 s ClockTime = 5 s

Courant Number mean: 0.0161746 max: 2.52635
Interface Courant Number mean: 0.000154353 max: 0.657568
deltaT = 0.000100695
Time = 0.00166663
PIMPLE: iteration 1
smoothSolver: Solving for alpha.liquid, Initial residual = 1.21772e-06, Final residual = 6.95791e-10, No Iterations 2
Phase-1 volume fraction = 0.0169872 Min(alpha.liquid) = -1.56426e-07 Max(alpha.liquid) = 0.999998
MULES: Correcting alpha.liquid
MULES: Correcting alpha.liquid
Phase-1 volume fraction = 0.0169872 Min(alpha.liquid) = -1.56426e-07 Max(alpha.liquid) = 0.999998
#0 Foam::error::printStack(Foam::Ostream&) at ??:?
#1 Foam::sigFpe::sigHandler(int) at ??:?
#2 ? in "/home/kvk/OpenFOAM/OpenFOAM-3.0.1/platforms/linuxGccDPInt32Opt/lib/libOpenFOAM.so"
#3 Foam::PBiCG::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const at ??:?
#4 ? at ??:?
#5 ? at ??:?
#6 ? at ??:?
#7 ? at ??:?
#8 __libc_start_main in "/lib/i386-linux-gnu/libc.so.6"
#9 ? at ??:?



/*--------------------------------*- C++ -*----------------------------------*\\
| ========= | |
| \\\\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\\\ / O peration | Version: 2.3.0 |
| \\\\ / A nd | Web: www.OpenFOAM.org |
| \\\\/ M anipulation | |
\\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
"alpha.liquid.*"
{
nAlphaCorr 2;
nAlphaSubCycles 1;
cAlpha 1;

MULESCorr yes;
nLimiterIter 3;

solver smoothSolver;
smoother symGaussSeidel;
tolerance 1e-8;
relTol 0;
}

pcorr
{
solver PCG;
preconditioner DIC;
tolerance 1e-5;
relTol 0;
}

p_rgh
{
solver GAMG;
tolerance 1e-8;
relTol 0.01;

smoother GaussSeidel;

cacheAgglomeration true;
nCellsInCoarsestLevel 10;
agglomerator faceAreaPair;
mergeLevels 1;
}

p_rghFinal
{
$p_rgh;
relTol 0;
}

"(U|k|epsilon).*"
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-5;
relTol 0;
}
}

PIMPLE
{
momentumPredictor yes;
nOuterCorrectors 1;
nCorrectors 2;
nNonOrthogonalCorrectors 0;
}

relaxationFactors
{
equations
{
".*" 1;
}
}

// ************************************************************************* //




OpenFOAM 13-03-16, 12:42 a.m. KVK

Answers:

0

Hi KVK,

Your deltaT is decreasing / changing because of implementation of adjustable Runtime in controlDict file which must have been kept on. Also please check your initial dT since your max Courant number ( Co = U*dT / dX ) is exceeding the limit value of 1.
Most of the times the solution diverges because of the Courant number exceeding 1 in such explicit solvers.
Try decreasing the initial time step (dT).

Regards,

Rahul Joshi

13-03-16, 8:29 a.m. rahuljoshi

FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application interFoam;

startFrom latestTime;

startTime 0;

stopAt endTime;

endTime 1;

deltaT 0.01;

writeControl adjustableRunTime;

writeInterval 0.05;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression uncompressed;

timeFormat general;

timePrecision 6;

runTimeModifiable yes;

adjustTimeStep on;

maxCo 1;
maxAlphaCo 1;

maxDeltaT 1;


// ************************************************************************* //


13-03-16, 10:44 a.m. KVK

can you tell me which one to change as i am a new bee to Open Foam . Thanks in advance


13-03-16, 10:46 a.m. KVK

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0

Hi KVK,


Keep the adjust time step - off

In case you keep it on, keep the deltaT as 0.001 and then try running your simulation.

13-03-16, 11:40 a.m. rahuljoshi

I have kept adjust time step -off but the error still exists as shown below

PIMPLE: iteration 1
#0 Foam::error::printStack(Foam::Ostream&) at ??:?
#1 Foam::sigFpe::sigHandler(int) at ??:?
#2 ? in "/home/kvk/OpenFOAM/OpenFOAM-3.0.1/platforms/linuxGccDPInt32Opt/lib/libOpenFOAM.so"
#3 Foam::symGaussSeidelSmoother::smooth(Foam::word const&, Foam::Field<double>&, Foam::lduMatrix const&, Foam::Field<double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&, unsigned char, int) at ??:?
#4 Foam::symGaussSeidelSmoother::smooth(Foam::Field<double>&, Foam::Field<double> const&, unsigned char, int) const at ??:?
#5 Foam::smoothSolver::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const at ??:?
#6 Foam::fvMatrix<double>::solveSegregated(Foam::dictionary const&) at ??:?
#7 Foam::fvMatrix<double>::solve(Foam::dictionary const&) at ??:?
#8 Foam::fvMatrix<double>::solve() at ??:?
#9 ? at ??:?
#10 __libc_start_main in "/lib/i386-linux-gnu/libc.so.6"
#11 ? at ??:?
Floating point exception (core dumped)
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application interFoam;

startFrom latestTime;

startTime 0;

stopAt endTime;

endTime 1;

deltaT 0.01;

writeControl adjustableRunTime;

writeInterval 0.05;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression uncompressed;

timeFormat general;

timePrecision 6;

runTimeModifiable yes;

adjustTimeStep off;

maxCo 1;
maxAlphaCo 1;

maxDeltaT 1;


// ************************************************************************* //



13-03-16, 11:51 a.m. KVK

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0

Hi KVK,


Try couple things

1. Keep deltaT as e-5

2. Check for any variables if they are tending to zero. Floating point exception error can occur because of it.



13-03-16, 11:59 a.m. rahuljoshi


0

Floating point error is nothing but some quantity being divided by zero and hence the solution with not proceed.

13-03-16, 12:03 p.m. rahuljoshi

application interFoam;

startFrom latestTime;

startTime 0;

stopAt endTime;

endTime 1;

deltaT 1e-5;

writeControl adjustableRunTime;

writeInterval 0.05;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression uncompressed;

timeFormat general;

timePrecision 6;

runTimeModifiable yes;

adjustTimeStep off;

maxCo 1;
maxAlphaCo 1;

maxDeltaT 1;


// ************************************************************************* //
solvers
{
"alpha.liquid.*"
{
nAlphaCorr 2;
nAlphaSubCycles 1;
cAlpha 1;

MULESCorr yes;
nLimiterIter 3;

solver smoothSolver;
smoother symGaussSeidel;
tolerance 1e-8;
relTol 0;
}

pcorr
{
solver PCG;
preconditioner DIC;
tolerance 1e-5;
relTol 0;
}

p_rgh
{
solver GAMG;
tolerance 1e-8;
relTol 0.01;

smoother GaussSeidel;

cacheAgglomeration true;
nCellsInCoarsestLevel 10;
agglomerator faceAreaPair;
mergeLevels 1;
}

p_rghFinal
{
$p_rgh;
relTol 0;
}

"(U|k|epsilon).*"
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-5;
relTol 0;
}
}

PIMPLE
{
momentumPredictor yes;
nOuterCorrectors 1;
nCorrectors 2;
nNonOrthogonalCorrectors 1;
}

relaxationFactors
{
equations
{
".*" 1;
}
}

// ************************************************************************* //


the above two are my control dict and fvsolution files. The simulation is ending abruptly at some time in middle as below

PIMPLE: iteration 1
smoothSolver: Solving for alpha.liquid, Initial residual = 0.999986, Final residual = 9.2483e-09, No Iterations 138
Phase-1 volume fraction = -12.544 Min(alpha.liquid) = -29744.2 Max(alpha.liquid) = 12901
MULES: Correcting alpha.liquid
MULES: Correcting alpha.liquid
Phase-1 volume fraction = 3.36842e+08 Min(alpha.liquid) = -7.83255e+23 Max(alpha.liquid) = 5.35775e+23
DILUPBiCG: Solving for Ux, Initial residual = 0.990449, Final residual = 3.42602e-06, No Iterations 17
DILUPBiCG: Solving for Uy, Initial residual = 0.59579, Final residual = 7.36343e-06, No Iterations 30
DILUPBiCG: Solving for Uz, Initial residual = 0.559222, Final residual = 9.83663e-06, No Iterations 26
GAMG: Solving for p_rgh, Initial residual = 0.937128, Final residual = 0.00885738, No Iterations 12
GAMG: Solving for p_rgh, Initial residual = 1.88765e-13, Final residual = 1.88765e-13, No Iterations 0
time step continuity errors : sum local = 6.226e+14, global = 6.33828e+07, cumulative = 6.33828e+07
GAMG: Solving for p_rgh, Initial residual = 2.0819e-13, Final residual = 2.0819e-13, No Iterations 0
GAMG: Solving for p_rgh, Initial residual = 2.0819e-13, Final residual = 2.0819e-13, No Iterations 0
time step continuity errors : sum local = 6.86671e+14, global = 6.33828e+07, cumulative = 1.26766e+08
ExecutionTime = 42.35 s ClockTime = 42 s

Courant Number mean: 4.02428e+14 max: 1.20117e+19
Interface Courant Number mean: 7.47408e+10 max: 1.88614e+15
Time = 0.22

PIMPLE: iteration 1
smoothSolver: Solving for alpha.liquid, Initial residual = 1.4338e-05, Final residual = 6.50799e-09, No Iterations 4
Phase-1 volume fraction = -2.49431e+25 Min(alpha.liquid) = -1.64242e+30 Max(alpha.liquid) = 5.05257e+27
MULES: Correcting alpha.liquid
MULES: Correcting alpha.liquid
Phase-1 volume fraction = -5.16478e+68 Min(alpha.liquid) = -2.12968e+91 Max(alpha.liquid) = 2.27409e+91
DILUPBiCG: Solving for Ux, Initial residual = 0.920589, Final residual = 1.25686e+06, No Iterations 1001
DILUPBiCG: Solving for Uy, Initial residual = 0.447941, Final residual = 2.59224, No Iterations 1001
DILUPBiCG: Solving for Uz, Initial residual = 0.905685, Final residual = 548.417, No Iterations 1001
GAMG: Solving for p_rgh, Initial residual = 1, Final residual = 0.00768092, No Iterations 1
GAMG: Solving for p_rgh, Initial residual = 2.86325e-31, Final residual = 2.86325e-31, No Iterations 0
time step continuity errors : sum local = 6.73556e+81, global = 1.09815e+65, cumulative = 1.09815e+65
GAMG: Solving for p_rgh, Initial residual = 2.86412e-31, Final residual = 2.86412e-31, No Iterations 0
GAMG: Solving for p_rgh, Initial residual = 2.86412e-31, Final residual = 2.86412e-31, No Iterations 0
time step continuity errors : sum local = 6.7376e+81, global = 1.09761e+65, cumulative = 2.19576e+65
ExecutionTime = 64.39 s ClockTime = 64 s

Courant Number mean: 3.36975e+81 max: 3.57268e+86
Interface Courant Number mean: 3.63838e+71 max: 3.74641e+76
Time = 0.23

PIMPLE: iteration 1
smoothSolver: Solving for alpha.liquid, Initial residual = 3.64905e-48, Final residual = 3.64905e-48, No Iterations 0
Phase-1 volume fraction = -5.16478e+68 Min(alpha.liquid) = -2.12968e+91 Max(alpha.liquid) = 2.27409e+91
MULES: Correcting alpha.liquid
#0 Foam::error::printStack(Foam::Ostream&) at ??:?
#1 Foam::sigFpe::sigHandler(int) at ??:?
#2 ? in "/home/kvk/OpenFOAM/OpenFOAM-3.0.1/platforms/linuxGccDPInt32Opt/lib/libOpenFOAM.so"
#3 Foam::multiply(Foam::Field<double>&, Foam::UList<double> const&, Foam::UList<double> const&) at ??:?
#4 void Foam::multiply<Foam::fvsPatchField, Foam::surfaceMesh>(Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh>&, Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh> const&, Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh> const&) at ??:?
#5 Foam::tmp<Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh> > Foam::operator*<Foam::fvsPatchField, Foam::surfaceMesh>(Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh> const&, Foam::tmp<Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh> > const&) at ??:?
#6 Foam::fv::gaussConvectionScheme<double>::flux(Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh> const&, Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&) const at ??:?
#7 ? at ??:?
#8 ? at ??:?
#9 __libc_start_main in "/lib/i386-linux-gnu/libc.so.6"
#10 ? at ??:?
Floating point exception (core dumped)




13-03-16, 12:29 p.m. KVK

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0

Your courant number exceeds 1.


Can you mail us your case file on this mail I'd.

contact_cfd@fossee.in

I will get back to you tomorrow.

13-03-16, 12:39 p.m. rahuljoshi

okay .


13-03-16, 12:42 p.m. KVK

Hello,


I am facing the same problem and I couldn't find a solution

this is my control dictionary

application interFoam;

startFrom startTime;

startTime 0;

stopAt endTime;

endTime 2;

deltaT 0.0001;

writeControl adjustableRunTime;

writeInterval 0.05;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression uncompressed;

timeFormat general;

timePrecision 6;

runTimeModifiable yes;

adjustTimeStep on;

maxCo 0.8;
maxAlphaCo 1;

maxDeltaT 0.01;

Any help please ???


12-10-16, 10:07 p.m. islem

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