volVectorField Ur = Ua - Ub;
    volScalarField magUr = mag(Ur);

    volScalarField Ka = draga->K(magUr);
    volScalarField K = Ka;

    if (dragPhase == "b")
    {
        volScalarField Kb = dragb->K(magUr);
        K = Kb;
    }
    else if (dragPhase == "blended")
    {
        volScalarField Kb = dragb->K(magUr);
        K = (beta*Ka + alpha*Kb);
    }

    volVectorField liftCoeff = Cl*(beta*rhob + alpha*rhoa)*(Ur ^ fvc::curl(U));