dolfin team mailing list archive

["Shilpa Khatri" <khatri@xxxxxxxxxxxx>]

We were just trying to take care of the spikes that were due to the facets
closets to the corners not being included in the no slip condition on the
boundary. We did not try to get the no slip on the dolfin, but I would
assume you could do that by just adding in another statement in the code.
Shilpa

On Feb 13, 2008 11:56 PM, Anders Logg <logg@xxxxxxxxx> wrote:

> 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
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-- 
Shilpa M Khatri
Courant Institute of Mathematics - NYU
Royal Institute of Technology (KTH) - Sweden