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[Anders Logg <logg@xxxxxxxxx>]

The support for automatically setting boundary conditions other than
simple Dirichlet conditions based on point values is not very good.

I suggest one of the following solutions:

1. Implement the boundary condition weakly (by a penalty).

2. Set the boundary conditions manually. If you know you have all the
degrees of freedom on vertices, you can do something similar as is
done in the function applyCommonBC() that you can find in the file
FEM.cpp (src/kernel/fem in the DOLFIN source tree).

/Anders


On Mon, Nov 06, 2006 at 06:20:39PM +0100, Michi Stöckli wrote:
> Hey hey,
> 
> I'm working on ALE in dolfin.
> 
> My code uses a discrete function for the mesh velocity,
> this means that the function can only be evaluated at vertices.
> 
> Problem is that, when we specify a boundary condition, all we receive
> are points and not vertices.
> 
> But for the proper calculation of the boundary, we need the mesh
> velocity since the fluid on the boundary moves at the same velocity as
> the mesh - this is the no-slip condition.
> 
> So the problem is, how do you evaluate the mesh velocity (a discrete
> function) at a point?
> 
> I.e., how do we set a boundary value using a discrete function?
> 
> Any suggestions are well appreciated.
> 
> /Michael
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