David,

I'm trying to compute the effective elastic properties of a heterogeneous, linear and a bi-periodic system (i.e., left-right and top-bottom periodic displacement fields). To this system, I would like to apply a global shearing by prescribing the displacement field of the surfaces in the form of Dirichlet BCs. This seems slightly contradictory since a bi-periodic system doesn't have surfaces.

However, we can still think of the global shearing as an average surface displacement around which periodic fluctuations occur (the origin of such fluctuations is due to heterogeneous elastic properties). This is illustrated in the picture below.


bitmap.png


I would like to know which is the best way to do this in deal.II (I have tried with make_periodicity_constraints and interpolate_boundary_values, but the problem is that, as I explain before, we set apparently contradictory constraints).

It seems to me like the correct boundary values are of the form

  u(left) = u(right) + offset

and similarly for the bottom/top. The point is that you encode the shearing in the 'offset', so you have a variation of periodic boundary conditions that includes this nonzero offset.

I believe that the make_periodicity_constraints() function takes such an offset argument. Have you tried that?

Best
 W.

--
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Wolfgang Bangerth          email:                 bange...@colostate.edu
                           www: http://www.math.colostate.edu/~bangerth/

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