[Libmesh-devel] Periodic boundary conditions

[Roy S. <roy...@ic...>]

I've just added support for using DofMap constraints to impose
periodic boundary conditions.  There's been some interest in this on
the mailing lists in the past, so if anyone would like to test it out:


Download the latest CVS.  (Or just "cvs update" an existing tree and
possibly "make distclean" to be safe)

Run "./configure --enable-everything" (or just "--enable-periodic"
along with whatever other options you need), and recompile.

Create a mesh with boundary ids corresponding to each side of the
periodic boundary.  The coarse mesh needs to be conforming across the
boundary.

Add code like the following (which works with build_square's
boundary ids on a square of width W, height H) before
equation_systems.init():

   PeriodicBoundary p1, p2;
   p1.myboundary = 0;      // Bottom
   p1.pairedboundary = 2;  // Top
   p1.translation_vector = RealVectorValue(0, H);
   p2.myboundary = 3;      // Left
   p2.pairedboundary = 1;  // Right
   p2.translation_vector = RealVectorValue(W, 0);
   mysystem.get_dof_map().add_periodic_boundary(p1);
   mysystem.get_dof_map().add_periodic_boundary(p2);


In theory, this feature should work even with non-straight boundaries,
periodic boundaries that meet at corners, adaptive refinement (except
that level-1 rules aren't yet enforced between boundaries), C0 and C1
elements, etc.  In practice, I've only tested it on one application
on a uniform square grid, and it'll probably break if you look at it
funny.  Send any bug reports to libmesh-devel.

API suggestions are appreciated too.  I've currently got the
PeriodicBoundaries defined in the DofMap, but one could argue that it
should be a property of a Mesh or that it should be per-variable.
---
Roy