dolfin team mailing list archive

["Murtazo Nazarov" <murtazo@xxxxxxxxxxx>]

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

/murtazo