//----------------------------------------------------//
//- sigma explicit large strain explicit terms
//----------------------------------------------------//
if(divDSigmaLargeStrainExpMethod == "standard")
{
    divDSigmaLargeStrainExp =
        fvc::div
        (
            mu*(gradDU & gradDU.T())
          + 0.5*lambda*(gradDU && gradDU)*I //- equivalent to 0.5*lambda*(I*tr(gradDU & gradDU.T()))
          + ((sigma + DSigma) & DF.T()),
            "div(sigma)"
       );
}
else if(divDSigmaLargeStrainExpMethod == "surface")
{
    divDSigmaLargeStrainExp =
        fvc::div
        (
            muf * (mesh.Sf() & fvc::interpolate(gradDU & gradDU.T()))
          + 0.5*lambdaf * (mesh.Sf() & (fvc::interpolate(gradDU && gradDU)*I))
          + (mesh.Sf() & fvc::interpolate( sigma & DF.T() ))
          + (mesh.Sf() & fvc::interpolate(DSigma & DF.T() ))
        );
}
else
{
    FatalError
        << "divDSigmaLargeStrainExp not found!"
        << exit(FatalError);
}

//- relax large strain component
divDSigmaLargeStrainExp.relax();