Hi Robert,
your fix seems to solve the problem (the single-field formulation gives the expected displacements) and the other examples work as well.
Thank you!

On 27 Mar 2017 15:22, "Robert Cimrman" <cimr...@ntc.zcu.cz> wrote:
Hi Jan,

it is a bug. Can you try [1]? Also verify, please, that your example mentioned in [2] still works - this is related.


[1] https://github.com/rc/sfepy/tree/fix-variable-state-data-sharing
[2] https://groups.google.com/forum/?_escaped_fragment_=topic/sfepy-devel/DOaxK9CTK2c#!topic/sfepy-devel/DOaxK9CTK2c

On 27.3.2017 13:09, Jan Heczko wrote:
Hi, everyone!

I'm trying to implement an example with hypoelastic material, i.e. a
material whose stress-strain relationship is given in rate-form:
d_stress = E : d_strain
The linear elastic material is a subset of this, but one can obtain
different types of behavior with non-constant E.

I tried two approaches (enclosed), both contain the balance equation in
rate-form. The equation consists of a single `dw_lin_elastic_iso` term in
both cases.

When displacements are prescribed, the problem is not solved as expected:
the solution is zero everywhere except where the EBCs are prescribed.
The approach with two fields (displacement and velocity) works with
boundary conditions prescribed for velocities. Actually, the second field
(displacements) is present only to directly output displacements, since I
am not interested in velocities.

My questions:
- Is the above described behavior correct in Sfepy? Is it a bug/feature?
  There is also the possibility that the formulations are not equivalent,
but I can't see it now.
- What is the difference between the [hypo]elastic term and e.g. diffusion?
(There is a time-derivative term in `time_poisson_interactive.py` together
with Dirichlet boundary conditions and everything seems to work.)
  Is it the fact that there is no term without time derivative in the
balance equation? I guess not - I tried to add an elastic term (multiplied
by either 0, 1e-4), but that doesn't change the results much.


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