gradientamr's Introduction

GradientAMR

This project shows how to use the gradient of flow variables as a criteria to control Adaptive Mesh Refinement (AMR) for OpenFOAM simulations.

Getting Started

Run the prepare.sh to generate the mesh and setup the simulation.
Then run the case with pimpleFoam

How it works

The following coded function object in controlDict creates a field which, in each timestep, contains the magnitude of the velocity gradient (which is a tensor):

    calcGradient
    {
        libs        ("libutilityFunctionObjects.so");
        type        coded;
        name        computeVelocityGradientMag;
        executeControl      timeStep;
        executeInterval     1;
        writeControl        writeTime;
        writeInterval       1;

        codeExecute
        #{
            const volVectorField& U  =  mesh().lookupObject<volVectorField>("U");

            static autoPtr<volScalarField> velocityGradientMagPtr;
            if(!velocityGradientMagPtr.valid()) {
              Info << "Creating velocityGradientMag" << nl;

              velocityGradientMagPtr.set
              (
                  new volScalarField
                  (
                    IOobject
                    (
                        "velocityGradientMag",
                        time_.timeName(),
                        U.mesh(),
                        IOobject::NO_READ,
                        IOobject::AUTO_WRITE
                    ),
                    mag(fvc::grad(U))
                  )
              );
            }
            volScalarField &velocityGradientMag = velocityGradientMagPtr();
            velocityGradientMag.checkIn();
            velocityGradientMag = mag(fvc::grad(U));
            Info << " max velocityGradientMag " << max(velocityGradientMag) << nl;
        #};
    }

That field is defined as refinement criteria on dynamicMeshDict:

dynamicFvMesh   dynamicRefineFvMesh;

dynamicRefineFvMeshCoeffs
{
    // How often to refine
    refineInterval  2;

    // Field to be refinement on
    field           velocityGradientMag;

    // Refine field inbetween lower..upper
    lowerRefineLevel 30;
    upperRefineLevel 1e6;

    // If value < unrefineLevel unrefine
    unrefineLevel   10;

    // Refine cells only up to maxRefinement levels
    maxRefinement   2;

    ...
}

The mesh is dynamically refined when the magnitude of the velocity gradient exceeds 30 1/s, and is unrefined when it goes below 10 1/s.