dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Tue, Jan 15, 2008 at 12:42:29AM +0100, Murtazo Nazarov wrote:
> > On Tue, Jan 15, 2008 at 12:23:30AM +0100, Murtazo Nazarov wrote:
> >> > On Mon, Jan 14, 2008 at 08:57:34PM +0100, Murtazo Nazarov wrote:
> >> >> > Is there an obvious high level way to implement normal flow type
> >> >> > boundary conditions or symmetry type boundary conditions?
> >> >> >
> >> >> > -gideon
> >> >> >
> >> >>
> >> >> If you mean slip boundary condition which for normal velocity, it is
> >> >> already implemented and soon will be available with UNICORN.
> >> >>
> >> >> The slip with friction is also implemented.
> >> >>
> >> >> /murtazo
> >> >
> >> > How is this implemented and for which element types? Maybe it can be
> >> > added to DOLFIN.
> >> >
> >>
> >> It is implemented in the "stong" way as the Dirichlet BC. The idea is to
> >> put u*n = u1*n1 + u2*n2 + u3*n3 = 0, where u = (u1,u2,u3) velocity and n
> >> =
> >> (n1,n2,n3) normal to a boundary node. At the monent it works for simple
> >> (cylinder, cube, ...) and quite complex geometries (car), but we are
> >> testing it in different geometries. Then, it would be good to add it to
> >> DOLFIN.
> >
> > I mean how do you translate u1*n1 + u2*n2 + u3*n3 = 0 into an equation
> > for the degrees of freedom (which may or may not be u1, u2, u3), which
> > types of finite elements does this work for and how do you modify the
> > linear system?
> >
> 
> It is done for the linear system. The idea is almost the same as Dirichlet
> implementation, but here we change two (in 2D), three (in 3D)
> corresponding rows of the system.

ok, but how exactly do you make the modification?

> I think (I may be wrong) it has nothing to do with the types of
> finite elements.

ok, but some more information about how it's done would be
good (since this would be a good feature to add).

-- 
Anders