[lavdwall]

Hi everyone,

I am using the velocityLaplacianFvMotionSolver with motionDirectional diffusivity to move a cylindrical pipe wall (decreasing diameter) in a post-Processing utility. The results are quite good for a small displacement of the pipe wall, but for larger displacements non-orthogonal and wrongly oriented faces appear. I therefore looked into the source code of motionDirectional diffusivity and I found this:

void Foam::motionDirectionalDiffusivity::correct()
{
    static bool first = true;


    if (!first)
    {
        const volVectorField& cellMotionU =
            mesh().lookupObject<volVectorField>("cellMotionU");


        volVectorField D
        (
            IOobject
            (
                "D",
                mesh().time().timeName(),
                mesh()
            ),
            diffusivityVector_.y()*vector::one
          + (diffusivityVector_.x() - diffusivityVector_.y())*cellMotionU
           /(mag(cellMotionU) + dimensionedScalar("small", dimVelocity, SMALL)),
            zeroGradientFvPatchVectorField::typeName
        );
        D.correctBoundaryConditions();


        const surfaceVectorField n(mesh().Sf()/mesh().magSf());
        faceDiffusivity_ == (n & cmptMultiply(fvc::interpolate(D), n));
    }
    else
    {
        first = false;


        const velocityMotionSolver& mSolver =
            mesh().lookupObject<velocityMotionSolver>("dynamicMeshDict");


        const_cast<velocityMotionSolver&>(mSolver).solve();
        correct();
    }
}

Does anyone understand what happens exactly during the calculation of the faceDiffusivity? I read that the first two components of the diffusivity vector, i.e. and diffusivityVector_.x() and diffusivityVector_.y(), are the mean orthogonality and skewness but I cannot find any article about this...

Can anyone give me the theoretical background behind the calculation above?

Thank you very much!

Kind regards,
Laurien

[lavdwall]

Anyone?

I'm just looking for an article or document about this topic. Maybe the person who wrote this piece of code can help me...