dolfin team mailing list archive

[Johan Jansson <johanjan@xxxxxxxxxxxxxxxx>]

On Thu, Jul 07, 2005 at 05:44:44PM +0200, Garth N. Wells wrote:
> Quoting jhoffman@xxxxxxxxxxx:
> 
> > Maybe it would be a good idea to be able to create several Boundary
> > objects.? As it is now, the default is to create one Boundary (in
> > InitBoundary) which is the total Boundary. Instead maybe one would like to
> > be able to create different Boundary objects for different boundary
> > conditions. The iteration would then be over the different Boundary
> > objects individually.
> > 
> > /Johan
> 
> 
> This is an idea which could solve some problems I have. A simple
> example is a prescribed displacement in the middle of a plate. The
> nodes to which the bc is applied is not located on the boundary of
> the mesh.
> 
> Garth
> 

Isn't it possible to model this with the density coefficient?
Typically a dirichlet boundary condition models that the material
outside the domain has an infinite density. But you don't need
boundary conditions to model this, you can simply assign a very large
density coefficient to portions of the domain, and then the interface
to the rest of the domain will behave like a dirichlet boundary
condition.

I think it's a good general principle to make use of coefficients
where possible, instead of solving problems by introducing special
cases in the solver. This means that the solver is kept simple, which
makes it easier to optimize and manage. There are cases where this is
not always possible though, so I understand the need for implementing
boundary conditions.

  Johan