[petsc-users] Multi-physics meshes with PETSc DM?

[Matthew Knepley]

On Sat, Jul 30, 2016 at 12:19 PM, Andrew Ho <andrewh0 at uw.edu> wrote:

> I am trying to solve a multi-physics problem consisting of some physics on
> a rectangular domain which is split in half such that one set of physics is
> solved on the left, and the other set of physics is solved on the right.
>
> Each set has their own set of variable components, and I would like to not
> allocate both variable sets across the entire domain because the physics in
> one subdomain happens to have lots of components per mesh element, which
> the other subdomain doesn't need except to compute boundary interactions.
>
> For testing right now, I am using the attached gmsh file to generate a
> mesh with 2 physical groups to represent each subdomain (called "left" and
> "right"). It has periodic boundaries on all sides.
>
> However, when I try to load the generated mesh into PETSc using the
> *DMPlexCreateFromFile* function, PETSc complains that the mesh is not a
> valid Gmsh file. I've attached the sample mesh, as well as the error
> message PETSc spits out.
>
> Here's the relevant code (should be a complete working example) which
> re-creates what I'm doing:
>
> #include <petsc.h>
>
>
>> int main(int argc, char** argv)
>> {
>>   PetscInitialize(&argc, &argv, NULL, "multi physics testing");
>>   DM dm;
>>   CHKERRQ(DMPlexCreateFromFile(PETSC_COMM_WORLD, "periodic_square.msh",
>> PETSC_TRUE, &dm));
>>   PetscFinalize();
>> }
>
>
> What is the correct procedure for creating a multi-physics mesh using
> PETSc DM objects for mesh management?
>


1) I don't use Physical Groups from GMsh since its unclear how this would
be reflected in the discretization

2) You should make a PetscSection representing your data layout, which is
discussed in the manual and in the tutorials.
    The number of dofs on different cells/edges/vertices will be different
across the mesh (it sounds like from your description).

3) Obviously this means the closures of different cells will be different
sizes. I am not sure how your assembly is setup to handle this.

  Matt

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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