[MaroneM]

Hi everyone!

I am wondering how can I save the "Initial residual" reported by the different OpenFOAM numerical solvers as a variable that then I can use for example to define the convergence criteria for a system of partial differential Eq. In particular I am now interested in the momentum equation (UEqn.H), which I am taking from OpenFOAM's native "buoyantBoussinesqSimpleFoam" implementation, which I present bellow:

    MRF.correctBoundaryVelocity(U);

    tmp<fvVectorMatrix> tUEqn
    (
        fvm::div(phi, U)
      + MRF.DDt(U)
      + turbulence->divDevReff(U)
     ==
        fvOptions(U)
    );
    fvVectorMatrix& UEqn = tUEqn.ref();

    UEqn.relax();

    fvOptions.constrain(UEqn);

    if (simple.momentumPredictor())
    {
        solve
        (
            UEqn
          ==
            fvc::reconstruct
            (
                (
                  - ghf*fvc::snGrad(rhok)
                  - fvc::snGrad(p_rgh)
                )*mesh.magSf()
            )
        );

        fvOptions.correct(U);
    }

I would like to do something more or less like the following:

scalar initResUx = yourSolutionHere;
scalar initResUy = yourSolutionHere;
scalar initResUz = yourSolutionHere;

scalar initResUEqn = initResUx+initResUy+initResUz;

Thank you in advance! ^^