Specifying internal "boundary" conditions

Mélanie Gérault

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Sep 18, 2019, 11:34:12 AM9/18/19

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Hi,

I am wondering if anyone has ever implemented/used internal boundary conditions in deal.II. I need to impose displacements inside of a domain. I am assuming that it is feasible with the code, but please let me know if I am wrong.

And in case I need to do it from scratch, I would also appreciate any suggestion you may have.

Thanks a lot!

Mélanie

Bruno Turcksin

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Sep 18, 2019, 1:58:39 PM9/18/19

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Mélanie,

I am not sure I understand exactly what you want to do but often people who want internal boundary conditions, really just want to impose some constraints to a few dofs. This can be done using AffineConstraints. I am sure that you have seen it in the tutorials where it is used to constrain hanging nodes and to impose Dirichlet boundary condition. Basically, you can create one yourself to impose any constraint you want on any dofs.

I hope this help.

Bruno

Mélanie Gérault

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Sep 19, 2019, 1:55:31 PM9/19/19

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Dear Bruno,

Thank you, that helps a lot.

Melanie

Rene Gassmöller

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Sep 19, 2019, 6:42:13 PM9/19/19

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Hi Melanie,

we also have a few examples in ASPECT that probably do what you are aiming for. E.g. the cookbook prescribed_velocity (https://github.com/geodynamics/aspect/blob/master/cookbooks/prescribed_velocity/prescribed_velocity.cc#L295) uses the `add_line` and `set_inhomogeneity` functions to constrain the value of the solution to a particular value at a particular location. There we still use the deprecated ConstraintMatrix object (that should be replaced by the AffineConstraints Bruno mentioned), but the process is more or less identical. Let me know if you want to do something similar, but for the temperature, I have some code for that elsewhere.