[Dune] Dune-grid-how-to finitevolume.cc example

[Jö Fahlke]

Am Thu,  5. Feb 2015, 11:36:37 +0100 schrieb Christoph Grüninger:
> Date: Thu, 05 Feb 2015 11:36:37 +0100
> From: Christoph Grüninger <christoph.grueninger at iws.uni-stuttgart.de>
> To: CERRITO Samuel EUROGICIEL INGENIERIE <Samuel.CERRITO at cea.fr>,
>  "'dune at dune-project.org'" <dune at dune-project.org>
> Subject: Re: [Dune] Dune-grid-how-to finitevolume.cc example
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> 
> Hi Samuel,
> 
> by "transportproblem2.hh" you are referring to what file?
> Please specify the Dune module (I could image grid HowTo,
> PDELab, dune-FEM, and their howtos) and the file path.

Well, he did specify dune-grid-howto, in the subject.

> >// the boundary condition b on inflow boundary
> >template<int dimworld, class ct>
> >double b (const Dune::FieldVector<ct,dimworld>& x, double t)
> >{
> > return 0.0;
> > if (x.two_norm()<t+0.125)
> > return 1.0;
> > else
> > return 0.0;
> >}
> >
> >Can someone explain what is "t" here and what this boundary
> >condition represents physically speaking ?

See <http://www.dune-project.org/doc/grid-howto/grid-howto.pdf> equation
(6.6).  That very much looks like a Dirichlet boundary condition to me,
i.e. prescribed concentration.  "t" is the time.

Note that at some point someone apparently commited some changes he probably
did not intend to commit, propably for debugging, which is how the "return
0.0;" in the first line of the function body ended up there.  Due to this line
the boundary condition will always be zero.  To actually see something
interesting happening, you probably have to comment that line out (but keep
the "return 0.0;" in the final line...).

Regards,
Jö.

-- 
Jorrit (Jö) Fahlke, Institute for Computational und Applied Mathematics,
University of Münster, Orleans-Ring 10, D-48149 Münster
Tel: +49 251 83 35146 Fax: +49 251 83 32729

A mathematician is a device to turn coffee into theorems.
-- Paul Erdős
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