Re: [deal.II] Dirichlet boundary condition (homogeneous) on selected dofs
Krishanu, > I understood that the the Dirichlet boundary condition in this problem was > being applied on only the top surface. But what I am trying to implement > seems > a little different to me. I will try to explain in a little more detail with > an example in the following part. > > I have a a part of boundary with boundary indicator 2 which has two nodes. > Each node has 3 degrees of freedom: displacements along x and y, and pressure. > > I am trying to implement x displacement to be 0 on both the nodes on this > part > of the boundary, and y displacement to be 0 on only one of these nodes. I > felt > that this is a little different from step-22 as in that case all the degrees > of freedom corresponding to displacements on the part of the boundary (top > surface) were constrained. Yes, that should not be too difficult to do if you get the semantics right. First, VectorTools::interpolate_boundary_values() has an additional argument that lets you specify which vector components you want to constrain. So if you mark a part of the boundary as, say, boundary_id=1, then you can call VectorTools::interpolate_boundary_values() with an argument that makes sure that both x and y displacement are set to something. If a different part of the boundary, say with boundary_id=2, should have only the x-component constrained, then you just call VectorTools::interpolate_boundary_values() for that boundary but with a different optional argument that specifies that you only want to select the x-component. Regarding semantics: When you say "I have a a part of boundary with boundary indicator 2 which has two nodes", then this is the wrong way to approach the problem. Boundary conditions are posed on *parts of the boundary* (i.e., faces!), not at individual nodes. You should really think about this in terms of the domain boundary, not in terms of the mesh you use to discretize the domain. This also ensures that the right thing happens upon mesh refinement. 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/bc6e54ee-9d9e-6760-9653-db261ef7382c%40colostate.edu.
Re: [deal.II] Dirichlet boundary condition (homogeneous) on selected dofs
Thanks, Prof. Bangerth for your response. I understood that the the Dirichlet boundary condition in this problem was being applied on only the top surface. But what I am trying to implement seems a little different to me. I will try to explain in a little more detail with an example in the following part. I have a a part of boundary with boundary indicator 2 which has two nodes. Each node has 3 degrees of freedom: displacements along x and y, and pressure. I am trying to implement x displacement to be 0 on both the nodes on this part of the boundary, and y displacement to be 0 on only one of these nodes. I felt that this is a little different from step-22 as in that case all the degrees of freedom corresponding to displacements on the part of the boundary (top surface) were constrained. I would be happy to learn about your thoughts on this. Thanks, Krishanu On Sunday, 26 January 2020 09:12:24 UTC-6, Wolfgang Bangerth wrote: > > On 1/25/20 4:10 PM, Krishanu Sen wrote: > > > > I am able to understand that step-22 has Dirichlet boundary condition on > all > > the degrees of freedom corresponding to displacement components. But I > am > > trying to have the Dirichlet boundary conditions on only some of the > degrees > > of freedom (e. g. all x dofs on the boundary and only one (this one is > to > > prevent rigid body motion) of the y dofs). To do that, I think some > > modifications are needed in the BoundaryValues() function and the > part > > where 'interpolate_boundary_values' is used in the 'setup_dofs'. But I > am not > > able to figure out what the modifications would actually be. > > step-22 actually only uses Dirichlet boundary conditions on the top > surface. > This is done by setting different boundary indicators for the different > parts > of the boundary, and interpolating Dirichlet boundary conditions for only > one > of these boundary indicators. > > Best > W. > > -- > > Wolfgang Bangerth email: bang...@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/7fec7938-57f5-4f09-984d-4673ff2e3351%40googlegroups.com.
Re: [deal.II] Dirichlet boundary condition (homogeneous) on selected dofs
On 1/25/20 4:10 PM, Krishanu Sen wrote: > > I am able to understand that step-22 has Dirichlet boundary condition on all > the degrees of freedom corresponding to displacement components. But I am > trying to have the Dirichlet boundary conditions on only some of the degrees > of freedom (e. g. all x dofs on the boundary and only one (this one is to > prevent rigid body motion) of the y dofs). To do that, I think some > modifications are needed in the BoundaryValues() function and the part > where 'interpolate_boundary_values' is used in the 'setup_dofs'. But I am not > able to figure out what the modifications would actually be. step-22 actually only uses Dirichlet boundary conditions on the top surface. This is done by setting different boundary indicators for the different parts of the boundary, and interpolating Dirichlet boundary conditions for only one of these boundary indicators. 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/1630c99d-2ff4-46c8-aced-89165a2878fc%40colostate.edu.
