[Katl]

I need to add a source term in the time loop, which is calculated in one of my boundary conditions.

First I defined the following field in createFields.H:

 Info<< "Creating field sourceH\n" << endl;
    volScalarField sourceH
    (
        IOobject
        (
            "sourceH",
            runTime.timeName(),
            mesh,
            IOobject::READ_IF_PRESENT,
            IOobject::AUTO_WRITE
        ),
         Hclip/dim_s*0
    );

It is set to zero by "Hclip/dim_s*0" in the beginning and should be changed/updated in a specific boundary condition.

But how can I change the values of the field in the bc???

I tried the following:

scalarField sourceH = patch().lookupPatchField<volScalarField, scalar>("sourceH").patchInternalField();
scalar groundArea = 1.0; 
scalarField srcH = (HU.boundaryField()[patchNr]&n)/groundArea;
scalar cellSource = (gSum(srcH))/patch().size();
 for (int celli = 0; celli <= patch().size(); celli++) 
      {
       sourceH[celli]=cellSource;
      }

But "sourceH" is still zero...