On Thu, Oct 13, 2016 at 11:57 AM, Rossi, Simone <sro...@email.unc.edu>
wrote:

> Dear all,
> I’m playing around with the elasticity tests in the system of equations
> examples (more specifically Ex4 and Ex5).
> In particular I’m trying to set the poisson ratio to nu = 0.49995.
> With this choice the solution I get using second order lagrangian elements
> does not make any sense.
> For first order elements the solution looks more reasonable, but still
> different from what I get from FreeFEM++.
> Does it depend on the enforcement of the Dirichlet boundary conditions?
> Thanks,
> Simone
>


nu=0.49995 is almost incompressible. Normally people use special
formulations for that type of problem, e.g. a mixed method to enforce
almost incompressibility (similar to Stokes in fluids). That probably
explains why you get bad results by naively using the simple formulation
from ex4 and ex5.

David
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