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 <[email protected]> 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 [email protected]. > 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
