On Mon, May 15, 2006 at 03:41:10PM +0000, Alexander Jarosch wrote:
Thanks for the input Anders, I will make further testing and post
results on the list.
Some other thing I mentioned earlier in a mail is that a vertex is
missing if one is converting a gmsh msh file with the dolfin-convert in
2d. here an example. The test.geo file would be:
Point(1) = {0,0,0,15};
Point(2) = {3000,0,0,15};
Point(3) = {3000,200,0,15};
Point(4) = {0,200,0,15};
Line(1) = {2,1};
Line(2) = {1,4};
Line(3) = {4,3};
Line(4) = {3,2};
Line Loop(5) = {3,4,1,2};
Plane Surface(6) = {5};
Physical Surface(7) = {6};
and if I mesh it with gmsh, ver. 1.64.0 like that
# gmsh test.geo -2 -clscale 1.0 -o test.msh
and than run
# dolfin-convert test.msh test.xml
the vertex with the corner points nr. 597, 1123 and 2045 is missing.
can anyone reproduce that problem?
cheers,
Alex
I don't get any triangle with vertices (597, 1123, 2045) in test.msh:
logg@gwaihir:~/tmp$ cat test.msh | grep 597 | grep 1123
logg@gwaihir:~/tmp$
I have gmsh 1.61.3.
Post your test.msh and I'll take a look when I get a chance.
/Anders
Anders Logg wrote:
On Fri, May 12, 2006 at 11:51:16AM +0000, Alexander Jarosch wrote:
Hello everybody,
I try to do a non linear viscous Stokes problem and I use this ffc form :
elementE = FiniteElement("Vector Lagrange", "triangle", 1, 3)
elementU = FiniteElement("Vector Lagrange", "triangle", 1)
v = TestFunction(elementE) # test function
e = TrialFunction(elementE) # strain (to be computed)
u = Function(elementU) # displacement
def normal_strain(u): # eps_xx eps_yy eps_xy
return [u[0].dx(0), u[1].dx(1), 0.5*(u[0].dx(1) + u[1].dx(0))]
a = dot(v, e)*dx
L = dot(v, normal_strain(u))*dx
to get my strain rates from the velocity field coming out of the stokes
problem. Than use these strain rates to calculate new viscosities and
iterate the stokes problem until I converge to a non linear fluid. But
somehow the approach is not stable and the strain rates seems to go
wrong already after the initial stokes solution.
Did anybody try something similar and maybe can give me some tips on how
to do a better approach?
Thanks for any suggestions,
Alex
There is a demo in src/demo/pde/elasticity/ for post-processing of
strain rates which computes both the normal and the shear strains.
Maybe you could compare with that demo to find out what goes wrong?
Your variational problem looks ok and should compute the projection of
[u[0].dx(0), u[1].dx(1), 0.5*(u[0].dx(1) + u[1].dx(0))].
Another thing you could experiment with is to project onto
discontinuous Lagrange. I think I remember I got unexpected results
when I experimented with something similar a while ago and projected
onto linears.
/Anders
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