Hi,
I'm a (relatively) new user to the Fenics system and have a
question. I'm not sure if this is the correct place to send this,
but I couldn't find anything
in the repository or the manuals (perhaps there's a relevant example
somewhere I missed ... ?), so I ended up here.
I'm using Fenics to study the equations of linear elasticity (in a
mixed Stokes formulation), which allows me to directly compute a
displacement U and
pressure P. In addition to these two variables, I am interested in
the stress of the system. I have been able to obtain the stress by
defining a suitable
projection:
stresselement = VectorElement("Discontinuous Lagrange", "triangle",
1, 9)
S = TrialFunction(stresselement)
T = TestFunction(stresselement)
a = dot(S, T)*dx
# Sigma is the symmetric stress computed from the displacement, U
L = dot(Sigma, t)*dx
and then solving the resulting linear system for S. Next, I would
like to do some calculations with the stresses; for example,
integrate the stress along a boundary.
To do this, I need the stress vector, s = Sn, where n is the normal
on the boundary. However, I am unclear how to do this, as I have
defined the stress as a 9-component
vector instead of a 3x3 matrix (and n will be defined as a 3
component vector if I use the FacetNormal function).
Any suggestions on how to handle this? Thanks!
Katy
