It computes buckling under a axial compressive displacement load.

Just like in cosserat-continuum.cc, there is now a Python class
that implements the initial iterate and the Dirichlet boundary values
at the same time.

Rather than hardcoding a straight reference configuration

This is more flexible, and more consistent with what
cosserat-continuum.cc does.

That is simply more flexible than the old parametertree format.

Instead, use LocalIntegralEnergy and the newly introduced densities
for bulk models or planar shell models.

While doing so, give an error message when non-trivial volume loads
are requested.  I have no example file that actually uses them
at the moment, and just by looking at the code I find it hard to believe
that they actually worked.  Getting them to work will mean having
introduce a density for volume loads, which don't want to do
until I need them.

Since this is the last use of the CosseratEnergyLocalStiffness class,
this patch remove the entire class as well.

That way, we can also set the initial microrotation -- previously
it was hard-wired to the identity matrix.

Being able to explicitly choose the initial microrotation allows
to start, in particular, from a twisted strip.

That way, a single Python file is enough to describe the entire
boundary value problem.

Rather than as our homegrown .parset.  That way, after more changes
this will allow to have the entire problem description in a single
file, including the boundary data.

AlexanderMueller authored 3 years ago and Sander, Oliver committed 3 years ago

This commit adds the energy implementat for the nonlinear Reissner-Mindlin
shell model known as the Simo and Fox shell model.

Details may be found in

  "A consistent finite element formulation of the geometrically
   non-linear Reissner-Mindlin shell model [Müller, Bischoff]"

With this, the preparatory stretching experiment for film-on-substrate can be done using dune-gfe.
The vertices for adaptive refinement can now be selected without specifying a shell area.

Change the keywords for switching between the solvers to trustRegion and proximalNewton also in film-on-substrate

So far, the Cosserat rod energy implementation hat a first-order
finite element space hardcoded.  This patch removes that restriction.
As for the other models in this Dune module, the finite element basis
is now a template parameter of the model energy, and can be set to
any reasonable basis.

This is currently the faster solver

This is where they actually belong, create an own file for identity-dirichlet-values;
before we 'abused' a copy of the file cantilever-dirichlet-values.py

Good to measure whether there is locking, and whether the code works
at all.

So far: 2d only

This will be used in the paper with Hanne, Philipp and Markus
on projection-based FE.