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How to set and read time-dependent source terms

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Old   September 16, 2012, 13:19
Default How to set and read time-dependent source terms
  #1
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Dean Meyer
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Dear Foamers,

I would like to read a time-dependent source term, which can be defined by a function in a file in the case directory and read from the solver itself.
So far I managed to set the source term using funkySetFields, but only as initial condition. My approach is the following: In createFields.H the field of the mass source is defined as follows:
Code:
       
        volScalarField massSource
        (
        IOobject
        (
            "massSource",
            runTime.timeName(),
            mesh,
            IOobject::MUST_READ_IF_MODIFIED,
            IOobject::NO_WRITE
        ),
        mesh
        );
The equation to solve looks like
Code:
    fvScalarMatrix rhoEqn
    (
      fvm::ddt(rho) 
    + some terms
    == massSource
    );
    rhoEqn.solve();
Finally the user should be able to define "massSource" with a mathematical expression as function of time and space in a file in the case directory. I tried to do it with funkySetFields, it works well for time 0, but I need it for all times. Example:
Code:
    massSource
    {
        field massS;
        expression    "sin(pi*time())*(pos().x+pos().y"; //arbitrary function 
        //condition    "...";
    }
In conclusion: How can I define and read time-dependent source terms from the case directory?
Thank you for any ideas.
D.
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Old   September 18, 2012, 05:33
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shakil ahmmed
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you can use the source term as a boundary condition, in that case you can easily use groovyBC.Or if you can access to the 'internalField' when creating source object, you might be able to do this.
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Old   September 20, 2012, 11:14
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David Gaden
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You could also use the equationReader extension. I'm working on a paper that will demonstrate this exact idea using it.
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Old   September 24, 2012, 17:37
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Bernhard Gschaider
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Quote:
Originally Posted by DeanM View Post
Dear Foamers,

I would like to read a time-dependent source term, which can be defined by a function in a file in the case directory and read from the solver itself.
So far I managed to set the source term using funkySetFields, but only as initial condition. My approach is the following: In createFields.H the field of the mass source is defined as follows:
Code:
       
        volScalarField massSource
        (
        IOobject
        (
            "massSource",
            runTime.timeName(),
            mesh,
            IOobject::MUST_READ_IF_MODIFIED,
            IOobject::NO_WRITE
        ),
        mesh
        );
The equation to solve looks like
Code:
    fvScalarMatrix rhoEqn
    (
      fvm::ddt(rho) 
    + some terms
    == massSource
    );
    rhoEqn.solve();
Finally the user should be able to define "massSource" with a mathematical expression as function of time and space in a file in the case directory. I tried to do it with funkySetFields, it works well for time 0, but I need it for all times. Example:
Code:
    massSource
    {
        field massS;
        expression    "sin(pi*time())*(pos().x+pos().y"; //arbitrary function 
        //condition    "...";
    }
In conclusion: How can I define and read time-dependent source terms from the case directory?
Thank you for any ideas.
D.
In addition to the two other solutions given (equationReader and groovyBC) you can search the forum for expressionSource which comes with swak4Foam and does what you want (I've explained the usage in one of those threads ... you'll find it)
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