[GeoMechanicsApplication] Degrees of freedom should be freed in between stages

[rfaasse]

As a user, I would like to be able to run a multi-stage analysis, where I fix degrees of freedom in one stage, and free them in the next.

Background
This issue was found by an external user (see #12277). A 2-stage problem was presented, where displacements were fixed in the first stage and should be free in the second. However, the dofs were never freed.

As seen in the comment thread of this issue, python versions of the processes in question (ApplyComponentTableProcess & ApplyConstantScalarValueProcess) do free the DoF. The code can be found in:
https://github.com/KratosMultiphysics/Kratos/blob/master/kratos/python_scripts/assign_scalar_variable_process.py#L134-L144

A similar function on Finalize or FinalizeSolutionStep needs to be added to the C++ processes we rely upon (exact location needs to be discussed, but the processes in question only implement the Initialize function, not the InitializeSolutionStep, so for symmetry's sake, implementing it in the Finalize function would seem more logical).

We could use the reported case LysmerBoundaries-K0.zip as a test case (but might want to create a simpler one).

Acceptance Criteria
Given A user runs a two-stage analysis, where some DoF are fixed in the first stage using the ApplyComponentTableProcess or the ApplyConstantScalarValueProcess
When The user doesn't fix said DoF in the second stage
Then They are free in the second stage.

[RiccardoRossi]

Hi,

this is a bit strange to me. In principle degrees of freedom are fixed by processes in the InitializeSolutionStep and are freed in the FinalizeSolutionStep ... so that they should be definitely free between one stage and the other

[rfaasse]

Hi @RiccardoRossi,
Thank you for reaching out! We are using our ApplyVectorConstraintTableProcess which makes use of the ApplyComponentTableProcess and/or ApplyConstantScalarValueProcess from Kratos Core.

However, they don't seem to have an override for the FinalizeSolutionStep or Finalize, therefore at least the process itself doesn't seem to free the dofs if I'm correct.

Is this something that could be implemented in the core processes?

[RiccardoRossi]

to my understanding the expected behavioru is what is shown in here

Kratos/kratos/python_scripts/assign_scalar_variable_process.py

Line 143 in e55171c

fixity_status = False

(variables freed in the ExecuteFinalizeSolutionStep).

pinging @KratosMultiphysics/technical-committee for comments

[roigcarlo]

As far as I can see @rfaasse is correct. The ApplyConstantScalarValueProcess does not free anything previously fixed.

My understanding is that they can not make use of the process we would normally use for that (assign_scalar_variable_process.py) as it only exists in python.

If we want the dofs to become free we have to implement the ExecuteOnFinalize as we do with the Assign_scalar_variable_process

[rfaasse]

That is a good point @RiccardoRossi, I didn't know this functionality was there in the python process. However, as @roigcarlo mentioned, indeed for the case described here, we can rely only on the C++ implementation of the processes and therefore, cannot use the python implementation of finalize solution step.

It would help us a lot if that functionality could be moved to the C++ process (that would hold for ApplyComponentTableProcess as well as ApplyConstantScalarValueProcess).

FYI @mcgicjn2 @avdg81 @WPK4FEM on the issue of freeing dofs.

[WPK4FEM]

dirichlet release stage.zip

1 element problem. stage 1 comprresses with a Dirichlet condition vertically. stage 2 does not have this Top Dirichlet condition. Stage 2 should show springback, so going back to zero vertical stresses and total displacements zero.