[petsc-users] DMPlex with spring elements

[Matthew Knepley]

On Tue, Sep 23, 2014 at 4:01 PM, Miguel Angel Salazar de Troya <
salazardetroya at gmail.com> wrote:

> Hi all
>
> I was wondering if it could be possible to build a model similar to the
> example snes/ex12.c, but with spring elements (for elasticity) instead of
> simplicial elements. Spring elements in a grid, therefore each element
> would have two nodes and each node two components. There would be more
> differences, because instead of calling the functions f0,f1,g0,g1,g2 and g3
> to build the residual and the jacobian, I would call a routine that would
> build the residual vector and the jacobian matrix directly. I would not
> have shape functions whatsoever. My problem is discrete, I don't have a PDE
> and my equations are algebraic. What is the best way in petsc to solve this
> problem? Is there any example that I can follow? Thanks in advance
>

Yes, ex12 is fairly specific to FEM. However, I think the right tools for
what you want are
DMPlex and PetscSection. Here is how I would proceed:

  1) Make a DMPlex that encodes a simple network that you wish to simulate

  2) Make a PetscSection that gets the data layout right. Its hard from the
above
      for me to understand where you degrees of freedom actually are. This
is usually
      the hard part.

  3) Calculate the residual, so you can check an exact solution. Here you
use the
      PetscSectionGetDof/Offset() for each mesh piece that you are
interested in. Again,
      its hard to be more specific when I do not understand your
discretization.

  Thanks,

    Matt


> Miguel
>
>
>
> --
> *Miguel Angel Salazar de Troya*
> Graduate Research Assistant
> Department of Mechanical Science and Engineering
> University of Illinois at Urbana-Champaign
> (217) 550-2360
> salaza11 at illinois.edu
>
>


-- 
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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