//--------------------------------------------------//
//- rotate fields
{
Info << "Rotating fields" << endl;
F = I + gradDU;
U += DU;
epsilon += DEpsilon;
sigma += DSigma;
volTensorField Finv = inv(F);
J = det(F);
rho = rho/J;
epsilon = symm(Finv & epsilon & Finv.T());
sigma = 1/J * symm(F.T() & sigma & F);
}