dolfin team mailing list archive

[Alexander Jarosch <alexanj@xxxxx>]

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

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
>
> _______________________________________________
> DOLFIN-dev mailing list
> DOLFIN-dev@xxxxxxxxxx
> http://www.fenics.org/cgi-bin/mailman/listinfo/dolfin-dev
>
>  


--
Alexander H. Jarosch

Jarðvísindastofnun Háskólans
Institute of Earth Sciences, University of Iceland
Náttúrufræðahús, Askja
Building of Natural Sciences, Askja
Sturlugata 7
IS - 101 Reykjavík
Iceland

Tel.: +354 525 4906
http://raunvis.hi.is/~jarosch/