If you'd like to compute the gradient for post-processing purposes, you
need to set up a separate variational problem which would return the
gradient. Dealing with the gradient of a vector is a little tricky since
FFC and DOLFIN are not yet equipped to deal with tensor functions. Below
is an example FFC input file which would be useful for post-processing.
I'll add it to src/demo/pde/elasticity shortly. If you want to compute a
stress tensor from the strain, you'd probably want to make the elementE
"Discontinuous vector Lagrange".
Garth
# Compute normal strain components
#
elementE = FiniteElement("Vector Lagrange", "triangle", 1, 3)
elementU = FiniteElement("Vector Lagrange", "triangle", 2)
v = BasisFunction(elementE) # test function
e = BasisFunction(elementE) # strain (to be computed)
u = Function(elementU) # displacement
def normal_strain(u): # eps_xx eps_yy gam_xy
return [u[0].dx(0), u[1].dx(1), (u[0].dx(1) + u[1].dx(0))]
a = dot(v, e)*dx
L = dot(v, normal_strain(u))*dx
On Fri, 2006-02-17 at 10:03 +0000, Alexander Jarosch wrote:
Hello everybody,
I am new to this mailing list and also new to the dolfin project. I
started to play around with the Stokes solver and have to say dolfin is
really neat to use, great job.
I have a question, is there already a function to calculate the gradient
of the velocity field?
regards,
Alex.
_______________________________________________
DOLFIN-dev mailing list
DOLFIN-dev@xxxxxxxxxx
http://www.fenics.org/cgi-bin/mailman/listinfo/dolfin-dev
