Gradient of Hydrstatic Stress becomes Zero

Question

I have calculated Stress and Hydrostatic stress again while calculating gradient of Hydrostatic stress It becomes Zero, Can anyone point out my mistake,

def h_term(c_old,u_old):
term1 =  0.5*(grad(u_old) + grad(u_old).T) - Omega*c_old*Identity(2)
sigma = (E*term1)/(3*(1-2*nu))
sigma_h = (tr(sigma) + nu*tr(sigma))/3
h_term = grad(sigma_h)    
return h_term

here c_old and u_old is the previous time step solution and I am solving Plane strain problem.

Thanks in advance

what is the order of the function space that are you using for the displacements? — hernan_mella, Nov 17, 2016

LeoCosta · Answer 1 · Feb 21, 2017

Best answer

Hi Hirshikesh

you forgot to project result to get the grad

def h_term(c_old,u_old, mesh):
    d = u_old.geometric_dimension()
    term1 =  0.5*(grad(u_old) + grad(u_old).T) - Omega*c_old*Identity(d)
    sigma = (E*term1)/(3*(1-2*nu))
    sigma_h = (tr(sigma) + nu*tr(sigma))/3
    V1 = FunctionSpace(mesh, 'P', 1)
    sigma_h = project(sigma_h, V1)
    h_term = grad(sigma_h)    
    return h_term

answered Feb 21, 2017 by LeoCosta FEniCS User (1,190 points)
selected Feb 21, 2017 by hirshikesh

Thank you so much

commented Feb 21, 2017 by hirshikesh FEniCS User (1,890 points)

hirshikesh · Answer 2 · Nov 17, 2016

I am using 2 order (VectorFunctionSpace(meshn,'CG',2))

answered Nov 17, 2016 by hirshikesh FEniCS User (1,890 points)

Could you do a more detailed question? a minimal non working example of your code is a good start point.

commented Nov 18, 2016 by hernan_mella FEniCS Expert (19,460 points)

Thanks for your reply, I have got the answer. Actually I was not updating my solution

commented Nov 18, 2016 by hirshikesh FEniCS User (1,890 points)

Gradient of Hydrstatic Stress becomes Zero

2 Answers