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[Anders Logg <logg@xxxxxxxxx>]

On Fri, May 07, 2010 at 02:39:41PM +0200, Patrick Riesen wrote:
> hello,
>
> i want to zero the normal velocity on a boundary part of my
> 2D-domain, so i used something like
>
> n = cell.n
> a = ... + inner(w,dot(v,n)*n)*ds(2) + ...
>
> in my form-file (w=testfunction, v=trialfunction).
>
> i marked the boundary part using the "exterior facet domains"
> meshfunction, which will be picked up in assemble(..):
>
> MeshFunction< uint >* _ext_facet_domains =
> mesh.data().create_mesh_function("exterior facet domains", 1)
>
> *_ext_facet_domains = 5;
> boundary.mark(*_ext_facet_domains, 2)
>
> can i do this? or what is wrong with the above way? because i don't
> get zero velocities...
>
> thank your for help,
>
> patrick

What if you add a (big) parameter in front of that term? Does it have
any effect at all on the solution?

I would also suggest writing the term as

  dot(w, n)*dot(v, n)*ds(2)

--
Anders

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