dolfin team mailing list archive

["Garth N. Wells" <g.n.wells@xxxxxxxxxxxxxxx>]

Quoting 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.
> 

Hi Johan,

I don't quite follow this. Could you expand?

Garth


> 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
> 
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