Hi, Bruno I am thinking of similar problem. Could I ask you one thing?
When you allowed slip on the top and bottom wall, did you implement any specific form of tangential velocity profile? or or just only u_y=0 (no flux) is implied? Thanks, Jaekwang On Saturday, February 17, 2018 at 4:46:32 PM UTC-6, Bruno Blais 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 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.
