Dear Wolfgang,
Thanks very much for your reply. I'm happy to hear that you think my
problems can be resolved without too much difficulty. I'd like to try
writing a patch for the mixed 3D meshes. I have done some development work
before, but I have never sent it out of our group; your advice on writing
the steps to write a patch would be most welcome!
I will re-review the relevant code and see if I can put together a general
plan on how to approach this.
Best regards,
Alex
On Wednesday, November 9, 2022 at 4:44:25 PM UTC-5 Wolfgang Bangerth wrote:
> Alex:
>
> > I am coming from a background of solid mechanics FEA and I've been using
> > CalculiX as an openSource program for some time. My group has decided
> > to switch to deal.ii
>
> Good choice -- we applaud you :-)
>
>
> > Part 1: Abaqus .inp format
> > I had success importing hex meshes from the abaqus <.inp> format, but it
> > seems that the UCD reader does not accept tet meshes. I am basing this
> > on the following bit of code in grid_in::read_ucd around Line 948
> >
> > if (((cell_type == "line") && (dim == 1)) ||
> > ((cell_type == "quad") && (dim == 2)) ||
> > ((cell_type == "hex") && (dim == 3)))
> > // found a cell
> > {
> >
> > The absence of
> > ((cell_type == "tet") && (dim == 3))
> > suggests that simplex elements are not supported when importing from
> > .inp. Am I correct in this conclusion. How difficult would it be for
> > me to add this functionality in?
>
> Not very difficult in all likelihood. The key difficulty in adding
> support for other cells in this function is that it uses the
> GeometryInfo<dim> class, which only provides information about hypercube
> cells. For example, we read vertex indices like this in that function:
> for (const unsigned int i : GeometryInfo<dim>::vertex_indices())
> in >> cells.back().vertices[GeometryInfo<dim>::ucd_to_deal[i]];
>
> This needs to be changed to account for the number of vertices a cell
> has, given the cell type, not the dimension. The right approach will be
> to use the ReferenceCell objects defined in namespace ReferenceCells
> (plural), and the other readers in that function will serve as guidance.
> You might want to take a look at the gmsh reader, for example.
>
>
> > Part 2: GMSH format
> > While looking at grid_in.cc, I saw that the MSH reader supported tet
> > elements. I found the FAQ page supplied these examples of simplex
> > meshes:
> https://www.dealii.org/developer/doxygen/deal.II/group__simplex.html
> >
> > I first ran the 2D simplex mesh example, and then I modified it to work
> > for 3D without much problem. Then, I switched to the mixed mesh, and
> > had success running the 2D example. However, I started having problems
> > when I switched to 3D. The mesh seems to import, but then I have issues
> > operating with it. I found several places within fe_simplex_p.cc (L714,
> > L759) where the dimension is asserted to be 2:
> >
> > AssertDimension(dim, 2);
> > This seems like a problem for a 3D analysis, so I am wondering if I need
> > to do something different so that this function doesn't get called.
>
> No, I think this is just not implemented. The function is called on
> mixed meshes when the library wants to know how elements of type
> FE_SimplexP on tetrahedra connect to another element types on other cell
> shapes (namely, on wedges and pyramids). The comparison is simply not
> implemented, but if you want to compute on mixed 3d meshes, you will
> have to implement the missing parts of this function. As long as you
> want to use the same polynomial degree on all cells, this should not
> even be particularly difficult and I would be happy to walk you through
> the necessary steps if you were interested in writing up a patch!
>
> Best
> Wolfgang
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth email: [email protected]
> www: http://www.math.colostate.edu/~bangerth/
>
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