In addition to what Wolfgang mentioned, I was wondering how you were managing the pressure constant in this case. This may severely hinder your "apparent" convergence, especially for pressure.
On Wednesday, October 1, 2025 at 1:26:35 a.m. UTC+2 Wolfgang Bangerth wrote: > > On 9/30/25 13:38, HC Zhang wrote: > > I am solving the Stokes equations using Raviart–Thomas elements in > > deal.II. When the boundary conditions are homogeneous Dirichlet, > > everything works fine and I observe the expected convergence behavior. > > > > However, when I switch to inhomogeneous Dirichlet boundary conditions, I > > encounter problems: although I apply > > ``VectorTools::project_boundary_values_div_conforming(...)`` to set the > > boundary values, the pressure error does not converge. > > > > Has anyone experienced a similar issue, or could point me to the right > > way of handling inhomogeneous Dirichlet conditions for the Stokes > > problem with RT elements? Am I missing an additional step to make the > > pressure converge? > > > > Any advice or references would be very much appreciated. > > HC: I think there isn't enough information here. For example, I'm not > even sure what variable you're providing boundary values. > > Regardless, what have you tried already? When you compare the computed > and the exact solution, which variable differs? The velocity or the > pressure? If you look at a visualization of the solution, in which > specific ways does the computed solution differ from the expected one? > Is it offset by a constant? Are the boundary values completely wrong? > For example, do you expect the boundary values to be g(x) but they are > zero? When you say "the pressure error does not converge", does that > mean that it doesn't converge to the right value, or that it in fact > *diverges*? > > I often find it useful to be specific in which ways the solution does > not match my expectations when trying to find errors. > > Best > W. > > -- 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]. To view this discussion visit https://groups.google.com/d/msgid/dealii/e7ea8efc-0080-4135-a083-116df6053abbn%40googlegroups.com.
