dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Feb 13, 2008 at 08:52:29PM +0100, Dag Lindbo wrote:
> >> On Tue, Feb 12, 2008 at 10:23:09AM +0100, Dag Lindbo wrote:
> >>> Hello all!
> >>>
> >>> In the stokes demo (taylor-hood), I notice spurious pressure spikes
> >>> near
> >>> the corners. What is causing these?
> >>>
> >>> I changed to a paraboloc inflow profile (consistent with the no-slip
> >>> BCs),
> >>> but the problem remains. Further, I ran the same problem on a
> >>> unitsquare
> >>> mesh (see plot attached). The pressure spikes are large. Is the demo
> >>> problem ill posed?
> >>>
> >>> Thanks!
> >>> Dag Lindbo, KTH
> >>
> >> I would also suspect the boundary conditions for the velocity
> >> to be the problem, but if you still see the spikes with a parabolic
> >> inflow profile (which is zero at the no-slip boundaries) then I have
> >> no idea.
> >>
> >
> > Is this in all corners? Could you send a plot?
> >
> > /Johan
> 
> Problem solved. Thanks for the help! The error is that the facets adjacent
> to the corners no get properly marked for noslip BC.
> 
> Fix to get the correct subdomain markers, in demo/mesh/subdomain/main.cpp:
> 
> class Noslip : public SubDomain
>   {
>     bool inside(const real* x, bool on_boundary) const
>     {
>       return (x[1] > 1.0 - DOLFIN_EPS || x[1] < DOLFIN_EPS) && on_boundary;
>     }
>   };
> 
> /Dag & Shilpa

Then you don't get no-slip on the dolphin which makes the solution
look pretty dull, don't you think?

-- 
Anders