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Old   August 6, 2012, 05:48
Default bouyantBoussinesqSimpleFoam continuity error
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Mojtaba Amiraslanpour
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Quote:
SIMPLE: convergence criteria
field p_rgh tolerance 0.01
field U tolerance 0.0001
field T tolerance 0.01
field "(k|epsilon|omega)" tolerance 0.001


Starting time loop

Time = 1

DILUPBiCG: Solving for Ux, Initial residual = 1, Final residual = 0.0169481, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 1, Final residual = 0.0186144, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 1, Final residual = 0.0176119, No Iterations 1
DILUPBiCG: Solving for T, Initial residual = 1, Final residual = 0.0291332, No Iterations 1


--> FOAM FATAL ERROR:
Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux : 2.05531
Specified mass inflow : 0.529467
Specified mass outflow : 0
Adjustable mass outflow : 1.82776e-17


From function adjustPhi(surfaceScalarField& phi, const volVectorField& U,const volScalarField& p
in file cfdTools/general/adjustPhi/adjustPhi.C at line 116.

FOAM exiting
p
Quote:
dimensions [0 2 -2 0 0 0 0];

internalField uniform 0;

boundaryField
{
wall
{
type zeroGradient;
}

air-inlet
{
type zeroGradient;
}

out_flow
{
type fixedValue;
value uniform 0.9;
}
}
U
Quote:
internalField uniform (0 0 0);

boundaryField
{
wall
{
type fixedValue;
value uniform (0 0 0);
}

air-inlet
{
type fixedValue;
value uniform (0 -1 0);
}

out_flow
{
type zeroGradient;
}
}
What is the problem?
Regards

Last edited by Mojtaba.a; August 6, 2012 at 06:11.
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Old   August 6, 2012, 06:15
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I just solved the problem. I hadn't worked with potentialFoam.
I know it was a stupid question. But for those who are beginner in openFOAM like me:
1) make a copy of your current case
2) use potentialFoam to run the case. in this step you initialize your values.
3) copy 0/U file into your own case.
4) start solving.

best ~
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Old   April 20, 2013, 01:23
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hi everybody,

I have the same problem. first, I ran potentialFoam and it says that no continuity error exists. then I changed the solver to buoyantBoussinesqSimpleFoam and ran it. but the following error appeared agian:

Code:
[1] --> FOAM FATAL ERROR: 
[1] Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux              : 0.0582779
Specified mass inflow   : 1.08721e-09
Specified mass outflow  : 0
Adjustable mass outflow : 0
[1] 
[1] 
[1]     From function adjustPhi(surfaceScalarField& phi, const volVectorField& U,const volScalarField& p
[1]     in file cfdTools/general/adjustPhi/adjustPhi.C at line 118.
[1] 
FOAM parallel run exiting
[1]

my U bcs:
Code:
dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
    fixedWalls
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    openW
    {
        type            zeroGradient;
    }
    hot
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    fb
    {
        type            empty;
    }
}

my p bcs:
Code:
dimensions      [0 2 -2 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    hot
    {
        type            fixedValue;
        value           uniform 0;
    }

    openW
    {
        type            fixedValue;
        value           uniform 0;
    }

    fixedWalls
    {
        type            fixedValue;
        value           uniform 0;
    }
    fb
    {
        type            empty;
    }
}
anybody knows what should I do?

thanks a lot
Mostafa
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Old   April 20, 2013, 01:57
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hi again,
it seems my problem was solved!!!!
I changed my zeroGradient velocity BC to fixedValue and waited to openFoam solved it in some iterations, then I changed it to zeroGradient again. there is no continuity error

I think the reason is when a model is solved by BCs different from the original BCs, actually the results are used as the initialize values for the next run. do I right????
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Old   April 20, 2013, 11:12
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NO, It didn't work. this way fixed my BC as fixedValue.

when I ran the potentialFoam the following results appeared:
Code:
Create time

Create mesh for time = 0

Reading field p

Reading field U


Calculating potential flow
DICPCG:  Solving for p, Initial residual = 0, Final residual = 0, No Iterations 0
DICPCG:  Solving for p, Initial residual = 0, Final residual = 0, No Iterations 0
continuity error = 0
Interpolated U error = 0
ExecutionTime = 5.27 s  ClockTime = 5 s

End
I think there is a problem, it added the phi but it didn't change my BCs.

please help me
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Old   April 20, 2013, 12:25
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Quote:
Originally Posted by adambarfi View Post
hi everybody,

I have the same problem. first, I ran potentialFoam and it says that no continuity error exists. then I changed the solver to buoyantBoussinesqSimpleFoam and ran it. but the following error appeared agian:
.
.
.

thanks a lot
Mostafa
Dear Mostafa,
You do not have any velocity inlet or pressure inlet in order to make your case work.
after defining a velocity inlet, I prefer to use zeroGradient BC for walls and inflow, and a fixed Value 0 BC for outflow in pressure dictionary.
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Old   April 20, 2013, 12:56
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thank you, Mojtaba

I have solved this case before, with this difference that the recent geometry is longer than later geometry. I increased grid number but the error was appeared, but when I decrease it, it worked. already I'm running it. I hope it return correct results.
but I don't understand why this error appears?????

thanks again.
Mostafa
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Old   April 20, 2013, 13:01
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Quote:
Originally Posted by adambarfi View Post
with this difference that the recent geometry is longer than later geometry
What do you mean by this?
You mean by decreasing number of grids you are able to run the case, but increasing it, causes the error?
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Old   April 20, 2013, 14:59
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yes, I think when I increase the grids the cumulative continuity error increases, while the grids are decreased this error decrease also.
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