//--------------------------------------------------//
//- rotate fields
//--------------------------------------------------//
{
  Info << "Rotating fields" << endl;

  F = I + DF;

  U += DU;

  epsilon += DEpsilon;

  sigma += DSigma;

  volTensorField Finv = inv(F);

  J = det(F);

  rho = rho/J;

  epsilon = symm(Finv.T() & epsilon & Finv);

  sigma  = 1/J * symm(F & sigma & F.T());
}