On 4/15/19 9:51 AM, jane....@jandj-ltd.com wrote:
>
> I can get a table if it would be useful.
In the end, *you* need to convince yourself that something works or doesn't
work. A table is a useful tool :-)
> I see what you mean in terms of convergence. I guess I was looking for the
> accuracy pointwise on a boundary where the Dirichlet condition for the
> pressure is imposed weakly. In my case, the value of the output on the
> boundary was important, which is why I was looking at the value of the
> pressure on the boundary.
I understand why it is important to have an accurate solution. But before
accuracy comes convergence.
> I will try using Q2-Q2 elements, though I realise that this doesn't change
> the
> application of the BC itself, so the issues may be the same, but definitely
> worth a try.
Correct. But it also has a higher convergence rate than the low-order RT
element -- which is known to work, but converge really slowly. The lowest
order RT element is really not a particularly good choice for anything at all.
> For a neumann boundary condition though (my problem has that on another
> boundary), am I correct in thinking that project_boundary_values doesn't
> allow
> for component masking? the condition is only on u = f(grad p) and not on p
> itself so I would need something similar to component masking the velocities.
I think this is true. The function in the library doesn't allow you to choose
a component mask -- there is a discussion on this on the mailing list sometime
in the last couple of weeks, if you want to read up on it.
You might have to write something yourself that does the projection.
Best
WB
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Wolfgang Bangerth email: bange...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/
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