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.
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