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-   -   How to modify icoFoam.C to include source term (http://www.cfd-online.com/Forums/openfoam-solving/99228-how-modify-icofoam-c-include-source-term.html)

erncyc March 29, 2012 00:53

How to modify icoFoam.C to include source term
 
Hi,

I am a novice in the use of OpenFOAM. I was wondering if anyone might be willing to help me modify icoFoam.C so that I can include a source term f, which has the form:

f = (eta)*(u_n+1 - u_n) / dt

u_n+1 and u_n are the current and previous velocities. eta is a variable defined in setFields and created in create.H. I tried the code below but I don't seem to get good results. Indeed if i choose smaller time steps, the solver crashes.

fvVectorMatrix UEqn
(
fvm::ddt(U)
+ fvm::div(phi, U)
- fvm::laplacian(nu, U)

);

solve(UEqn == -fvc::grad(p)-eta*(fvm::ddt(U)));




Please help, thank you.

nimasam March 29, 2012 04:06

Quote:

Originally Posted by erncyc (Post 352073)
Hi,

I am a novice in the use of OpenFOAM. I was wondering if anyone might be willing to help me modify icoFoam.C so that I can include a source term f, which has the form:

f = (eta)*(u_n+1 - u_n) / dt

u_n+1 and u_n are the current and previous velocities. eta is a variable defined in setFields and created in create.H. I tried the code below but I don't seem to get good results. Indeed if i choose smaller time steps, the solver crashes.

fvVectorMatrix UEqn
(
fvm::ddt(U)
+ fvm::div(phi, U)
- fvm::laplacian(nu, U)

);

solve(UEqn == -fvc::grad(p)-eta*(fvm::ddt(U)));




Please help, thank you.

try this:
Code:

fvVectorMatrix UEqn
        (
            (1+eta)*fvm::ddt(U)
          + fvm::div(phi, U)
          - fvm::laplacian(nu, U)
         
        );

        solve(UEqn == -fvc::grad(p));


erncyc March 29, 2012 04:32

How to modify icoFoam.C to include source term
 
Hi Nima,

Thank you for your prompt reply. I have tried that option but the result i get is really weird...the solver seems to get 'stuck' as can be seen below








Courant Number mean: 0.00944072 max: 0.0228351
DILUmyPBiCG: Solving for Ux, Initial residual = 4.94675e-05, Final residual = 2.71278e-105, No Iterations 22
DILUmyPBiCG: Solving for Uy, Initial residual = 7.4114e-05, Final residual = 5.49146e-105, No Iterations 22
DICPCG: Solving for p, Initial residual = 4.46202e-05, Final residual = 8.4033e-17, No Iterations 97
time step continuity errors : sum local = 7.31098e-19, global = -2.32262e-21, cumulative = 1.11216e-17
DICPCG: Solving for p, Initial residual = 1.64486e-06, Final residual = 9.034e-17, No Iterations 92
time step continuity errors : sum local = 7.20432e-19, global = -1.28127e-21, cumulative = 1.11203e-17
ExecutionTime = 19.94 s ClockTime = 35 s

Time = 0.6035

Courant Number mean: 0.00944072 max: 0.0228347
DILUmyPBiCG: Solving for Ux, Initial residual = 4.94634e-05, Final residual = 2.7106e-105, No Iterations 22
DILUmyPBiCG: Solving for Uy, Initial residual = 7.40934e-05, Final residual = 5.84491e-105, No Iterations 22
DICPCG: Solving for p, Initial residual = 4.46209e-05, Final residual = 8.40861e-17, No Iterations 97
time step continuity errors : sum local = 7.16085e-19, global = 4.24348e-21, cumulative = 1.11246e-17
DICPCG: Solving for p, Initial residual = 1.64556e-06, Final residual = 9.18026e-17, No Iterations 92
time step continuity errors : sum local = 7.14218e-19, global = 3.90334e-21, cumulative = 1.11285e-17
ExecutionTime = 19.96 s ClockTime = 35 s

nimasam March 29, 2012 05:22

Quote:

Originally Posted by erncyc (Post 352109)
but the result i get is really weird...the solver seems to get 'stuck'

whats wrong with the result? do u mean high iteration numbers?

erncyc March 29, 2012 05:28

yes i get very low residuals as soon as the iterations begin and they do not reduce significantly

nimasam March 29, 2012 05:36

i have no idea! i dont think it is a cause of error

tfuwa February 18, 2013 10:59

Hi,

I am modifying the icoFoam solver to include a momentum source in y direction.

Code:

        fvVectorMatrix UEqn
        (
            fvm::ddt(U)
          + fvm::div(phi, U)
          - fvm::laplacian(nu, U)
                + Source 
        );

        solve(UEqn == -fvc::grad(p));

where, the Source is defined as,

Code:

        volVectorField Source
    (
        IOobject
        (
            "Source",
            runTime.timeName(),
            mesh,
            IOobject::NO_READ,
            IOobject::NO_WRITE
        ),
        mesh,
        dimensionedVector("Source", dimensionSet(0,1,-2,0,0,0,0),vector(0, 100, 0) )
    );

This is ok. No error during the compile.

However, when I tried to make the Source time dependent as follows,

Code:

        volVectorField Source
    (
        IOobject
        (
            "Source",
            runTime.timeName(),
            mesh,
            IOobject::NO_READ,
            IOobject::NO_WRITE
        ),
        mesh,
        dimensionedVector("Source", dimensionSet(0,1,-2,0,0,0,0),vector(0, cos(runTime.time().value()), 0) )
    );

The compiler complains that:

Code:

createFields.H: In function ‘int main(int, char**)’:
createFields.H:62:102: error: call of overloaded ‘cos(const double&)’ is ambiguous
createFields.H:62:102: note: candidates are:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:64:1: note: double cos(double)
/opt/openfoam171/src/OpenFOAM/lnInclude/dimensionedScalar.H:76:19: note: Foam::dimensionedScalar Foam::cos(const dimensionedScalar&)
/opt/openfoam171/src/OpenFOAM/lnInclude/Scalar.H:238:1: note: Foam::doubleScalar Foam::cos(Foam::doubleScalar)
/opt/openfoam171/src/OpenFOAM/lnInclude/Scalar.H:238:1: note: Foam::floatScalar Foam::cos(Foam::floatScalar)
/opt/openfoam171/src/finiteVolume/lnInclude/readPISOControls.H:8:10: warning: unused variable ‘momentumPredictor’ [-Wunused-variable]
/opt/openfoam171/src/finiteVolume/lnInclude/readPISOControls.H:11:10: warning: unused variable ‘transonic’ [-Wunused-variable]
/opt/openfoam171/src/finiteVolume/lnInclude/readPISOControls.H:14:9: warning: unused variable ‘nOuterCorr’ [-Wunused-variable]
make: *** [Make/linux64GccDPOpt/icoScalarSFoam.o] Error 1

Could anyone let me know the reason? Thanks.

nimasam February 18, 2013 11:10

as function "cos" is defined in math.h too!, so you should define which one, you want to use, so it would be solve with following structure:
Quote:

Foam::cos (........)

tfuwa February 18, 2013 11:38

Hi Nima,

Many thanks for your quick reply. The problem is solved.

Now, I would like to see the Source term only exists at a specific area.

if (x y z) in zone (x1 to x2, y1 to y2, z1 to z2)
Source = (0, a, 0)
else
Source = (0, 0, 0)
endif

Can you please enlighten me on how to realize this?

nimasam February 18, 2013 13:38

there are two options:
1- define it from Dictionary, for example look at interFoam (dambreak test case) to see how to define a non-uniform internalField

2- you can write a pieces of code, you can use mesh.C() which returns position vector
then you can check it whether your cell is set up in specific area or not

houwy April 22, 2014 09:00

Quote:

Originally Posted by tfuwa (Post 408476)
Hi Nima,

Many thanks for your quick reply. The problem is solved.

Now, I would like to see the Source term only exists at a specific area.

if (x y z) in zone (x1 to x2, y1 to y2, z1 to z2)
Source = (0, a, 0)
else
Source = (0, 0, 0)
endif

Can you please enlighten me on how to realize this?

Have you solved your problem? I want to do something like yours. I need some help!


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