RE: [deal.II] How to define boundary conditions on edges and vertices in 3D?

[Michael Li]

Thanks for confirming that. It saves me from keeping trying to define boundary conditions by setting boundary id on edges or vertices. I was too excited to think it is possible to do that when reading the code line(j)->set_boundary_id(2) in grid_generator.cc. Maybe it is just to distinct the edges with different boundary_ids for other use.   There are still many scenarios that we want to fix some points in the domain. I wonder if we can make use of the AffineConstraints class to deal with Dirichlet boundary conditions though it is not possible for Neumman BCs.   Best, Michael   From: Wolfgang Bangerth Sent: Thursday, June 10, 2021 10:41 AM To: dealii@googlegroups.com Subject: Re: [deal.II] How to define boundary conditions on edges and vertices in 3D?   On 6/10/21 8:31 AM, Michael Lee wrote: > 1) thin plate under pressure with *four edges simply supported*. > 2) thin plate under pressure with *four corner points simply supported*. > 2021-06-10_082227.png > For the first one, I tried the following code, but it seems boundary condition > only works with face not on edge.   That is correct. Mathematically, you can only prescribe boundary conditions on portions of the boundary (i.e., on *faces*) but not on edges in 3d or vertices in 2d/3d. What is easy to do in deal.II matches what is mathematically possible.   Now, you will ask why other software packages allow you to do what is not easy in deal.II. The answer is that other packages generally use a fixed mesh, and on a fixed mesh, prescribing boundary conditions on a vertex is roughly equivalent to prescribing boundary conditions on the adjacent faces. That's ok if you keep the mesh fixed, but it means that you are changing the kind of boundary conditions every time you change the mesh if you use software that uses adaptive mesh refinement.   So my suggestion would be to think about the physical situation you want to model, and translate that into prescribing boundary conditions on faces instead of edges/vertices.   Best   W.   -- ------------------------------------------------------------------------ Wolfgang Bangerth          email:                 bange...@colostate.edu                             www: http://www.math.colostate.edu/~bangerth/   -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/9e09474b-1e3f-7fbf-7527-01f6cdd256ef%40colostate.edu.   -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/89FC6FE0-6F24-4447-B995-03F9B36D0E84%40hxcore.ol.