Hello, My gmsh mesh produces 3 physical groups which are independent. Say my simulation is the flow around a cylinder. The cylinder is a physical group (0), the inlet (say left wall) is a class inheriting from the Function class which sets the X component to 1 and the Y component to 0 and uses the velocity mask. Finally the physical group(2) is supposed to be the top and the bottom boundary which would be slip. The last part (the right wall) I wish to leave as a free boundary condition so it is not put in any physical group. Everything works if I put the physical group(2) as a dirichlet boundary condition (and if I adapt the velocity profile of the inlet so that it matches the 0 on the top and bottom wall using for instance a parabolic inlet profile).
Does the order in which I apply the nonzero and zero constraints matter? Currently I apply the inlet and then the no-slip in the nonzero_constraints, thus the bottom and top wall appear after the inlet. Afterward the cylinder is put in the zero constraints. Thanks you very much Best regards Bruno On Sunday, 18 February 2018 11:58:40 UTC-5, Timo Heister wrote: > > Are you setting the conditions correctly for the zero_constraints and > the nonzero_constraints and are you sure you are not applying other > boundary conditions on that wall (for example with > interpolate_boundary_values())? > > On Sat, Feb 17, 2018 at 5:46 PM, Bruno Blais <blais...@gmail.com > <javascript:>> wrote: > > Hello everyone, > > > > I believe this may sound like a relatively dumb question, but I thank > you > > for your time. > > I am using a (slightly) modified version of step-57 to solve certain > steady > > state Navier-Stokes problem. > > I have had relatively good success and showed that i could recover the > > appropriate order of convergence on manufactured solutions and obtained > good > > solutions on problems like a backward facing step, as such I am > confident > > that the residual / jacobian matrix / linear solver / Schur complement > > aspect is ok. Anyway, I did not modify anything from Step-57 when it > comes > > to the Schur complement / solution of the linear system. > > > > My core issue arises when I try to replace one of my homogenous or > > non-homogenous dirichlet boundary condition with a > > no_normal_flux_constraints to impose slip instead of no-slip on a > boundary. > > Simply, I can say that I implement it by adding an additional constraint > in > > the setup_dofs member function of step-57 such as: > > > > std::set<types::boundary_id> no_normal_flux_boundaries; > > > > no_normal_flux_boundaries.insert (2); /* here 2 is a Physical Line in my > > gmsh mesh */ > > > > VectorTools::compute_no_normal_flux_constraints (dof_handler, 0, > > > > > no_normal_flux_boundaries, > > > > nonzero_constraints > > > > ); > > > > > > Now everything compiles , but the iterative solver (GMRES in this case) > for > > the system matrix does not converge anymore with this set of boundary > > conditions. My general problem is well-posed and if I replace these > boundary > > with regular Dirichlet I get an expected solution. > > Clearly, I am doing something wrong, but I must admit my lack of > knowledge > > on the issue. Could it be related to the way for system matrix and the > Schur > > complement is formed which is rendered not-ok in this case for no-flux > > boundaries? > > I know the example is made with Dirichlet (homogenous or not) boundary > in > > mind, so clearly I am missing something when it comes to changing one of > > these boundaries to a slip. > > > > I thank you greatly for your time, > > Best regards, > > Bruno > > > > > > -- > > The deal.II project is located at > https://urldefense.proofpoint.com/v2/url?u=http-3A__www.dealii.org_&d=DwIBaQ&c=Ngd-ta5yRYsqeUsEDgxhcqsYYY1Xs5ogLxWPA_2Wlc4&r=4k7iKXbjGC8LfYxVJJXiaYVu6FRWmEjX38S7JmlS9Vw&m=ulWuM0dNK_XHF-DL_x2EvT8bMSBuSrV4XKcqEfBiLm8&s=-4wmXq2eve0gPycm8fOaR7d-hpgfjIE1aPscZQsUILk&e= > > > For mailing list/forum options, see > > > https://urldefense.proofpoint.com/v2/url?u=https-3A__groups.google.com_d_forum_dealii-3Fhl-3Den&d=DwIBaQ&c=Ngd-ta5yRYsqeUsEDgxhcqsYYY1Xs5ogLxWPA_2Wlc4&r=4k7iKXbjGC8LfYxVJJXiaYVu6FRWmEjX38S7JmlS9Vw&m=ulWuM0dNK_XHF-DL_x2EvT8bMSBuSrV4XKcqEfBiLm8&s=shEU_TxDkAEzy7XeIgIrmbDaeclYOji85cAxehiBlJE&e= > > > --- > > 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+un...@googlegroups.com <javascript:>. > > For more options, visit > https://urldefense.proofpoint.com/v2/url?u=https-3A__groups.google.com_d_optout&d=DwIBaQ&c=Ngd-ta5yRYsqeUsEDgxhcqsYYY1Xs5ogLxWPA_2Wlc4&r=4k7iKXbjGC8LfYxVJJXiaYVu6FRWmEjX38S7JmlS9Vw&m=ulWuM0dNK_XHF-DL_x2EvT8bMSBuSrV4XKcqEfBiLm8&s=IGenO_6vTVuLZb24YoNS8UKHad1Gw628aXOYYblETro&e= > > . > > > > -- > Timo Heister > http://www.math.clemson.edu/~heister/ > -- 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. For more options, visit https://groups.google.com/d/optout.
