volScalarField sigmaEq(IOobject("sigmaEq", runTime.timeName(), mesh, IOobject::NO_READ, IOobject::AUTO_WRITE), sqrt((3.0/2.0) *magSqr(dev(sigma))))
volSymmTensorField sigma(IOobject("sigma", runTime.timeName(), mesh, IOobject::NO_READ, IOobject::AUTO_WRITE), rho *sigmaD)