Can I use 3D prism elements (extruded triangles) in deal.ii?

[Amit Singh]

Hi.

I am considering deal.ii for some nonlinear elasticity and fracture analysis.

From what I read in the documentation, deal.ii supports hexahedral elements much better than tetrahedral elements. My geometry looks as shown in the attached picture. The actual geometry is a boolean difference of a big sphere and a small sphere. But to exploit symmetry I am considering only one-eighth of the sphere.

 I am struggling to create a mesh that has only hexahedral elements. The best I was able to attain was a vast majority of the elements were hexahedral but there were some prism elements at the poles.

Therefore, my question is can I use prism elements in deal.ii? (Or if there is a clever way to mesh this geometry with just hexahedral elements kindly let me know.)

Regards,

Amit

[Paras Kumar]

HI Amit,

Focusing on the question of mesh generation, it is possible to generate an automated HEX mesh using Gmsh, but since that mesh is based on Delaunay based approaches, quality may not be very good. See discussions in this thread: https://groups.google.com/g/dealii/c/o_xXAur2Ao8/m/vlAjFs5ECQAJ

Alternatively, if you just want to mesh this specific geometry, you could also get a structured (good looking) HEX mesh using the transfinite mesh approach available in Gmsh.

In my limited knowledge, cf. [https://www.dealii.org/current/doxygen/deal.II/group__simplex.html], it seems that the simplex support is still experimental. As mentioned in the link, it might be helpful to look at the tests/simplex folder. The developers can maybe provide more precise answer here.

Best,

Paras

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[Bruno Turcksin]

Amit,

I think that GridGenerator::quarter_hyper_shell is what you want.

Best,

Bruno

[Wells, David]

Hi Amit,

If you are interested in using symmetry then I suspect you may also want to use periodic boundary conditions on the "internal" faces of the octant. For an example of how this works (e.g., periodic boundary conditions containing a rotation) check out step-45:

https://dealii.org/developer/doxygen/deal.II/step_45.html

Best,

David

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From: dea...@googlegroups.com <dea...@googlegroups.com> on behalf of Bruno Turcksin <bruno.t...@gmail.com>
Sent: Friday, June 24, 2022 9:33 AM
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Subject: Re: [deal.II] Can I use 3D prism elements (extruded triangles) in deal.ii?

 

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[hkch...@gmail.com]

Hi Amit,

To generate hexahedral mesh, in Gmsh, you can split the volume into three part like this ,and use transfinite command on curve, surface and volume, and recombine the surface to get the hexahedral cell.

Best

Chen

[Amit Singh]

Thank you very much for your replies Paras, and David!

@Bruno: Yes that is indeed what I am looking for!

@Chen: Awesome! Thank you very much for sharing the trick.

The deal.ii community is so amazing and helpful!

Best,

Amit