I realized that the mesh file I provided had an issue. The corner nodes of the tetrahedral elements coincided with a mid-face node of the hexahedron element. I've fixed that and uploaded a new mesh.
Thanks,
Alex
On Monday, November 7, 2022 at 3:25:25 PM UTC-5 Alex Quinlan wrote:
> Hello everyone,
> I have been reading the messages in this user group for a while, but this
> is my first post! I am hoping that you can help with my problem.
>
> 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 to implement some advanced functionality that the other
> programs don't have. I'm an engineer with some programming experience,
> though fairly new to C++.
>
> We are working with some complex geometries that are not practical to mesh
> with only hex elements. The meshes are generated externally, so I am
> trying to import the meshes into deal.ii. I have tried to do this in two
> general ways and run into problems with each, so I will split my post into
> 2 parts.
>
> 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?
>
>
> 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.
>
> The problem seems to arrive when I call dof_handler.distribute_dofs(fe);
> I've attached my modified version of the example program along with my
> simple mixed-element 3D mesh.
>
> Is there something that I am missing regarding the dof_handler when trying
> to use a 3D mixed-element mesh?
>
>
> Thanks very much,
> Alex
>
>
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mixed2top.msh
Description: Mesh model
