dolfin team mailing list archive

[Alexander Jarosch <alexanj@xxxxx>]

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

--
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/