Re: [Anuga-user] boundary conditions and interior region tags

[Stephen R. <u86...@ud...>]

Hi Stefan,

> 1) If I use "anuga.Dirichlet_boundary([0, 0, 0])" (stage = 0), does
> ANUGA use the elevation at the boundary nodes, because there is no error
> rising? If so: what is the difference between
> "anuga.Dirichlet_boundary([0, 0, 0])" and
> "anuga.Transmissive_stage_zero_momentum_boundary(domain)"?

anuga.Dirichlet_boundary([0, 0, 0]) is very simple in that the value on the boundary is set to
0 stage , 0 xmomentum , 0 ymomentum. Depending on the flow_algorithm you are using, the elevation
at the boundary will either be the average of elevation at the interior and 0, or in hte later DE0
and DE1, a discontinuous jump in elevation will be used.

The Dirichlet will set stage and momenta to zero and the
Transmissive_stage_zero_momentum will set the momenta to zero and use the stage value in the
interior to set the boundary value.

> 2) Is it possible to set one of the above boundary conditions to an
> interior region so that the interior region acts as a sink? How do I
> assign boundary tags to this interior region?


You can use the procedures

create_mesh_from_regions or
create_domain_from_regions

to create interior hole(s).

The interior edges of the hole will be tagged "interior" and then you can
associate a boundary condition to the "interior" tag.

You can associate specific boundary tags using the hole_tags argument to
create_mesh_from_regions or create_domain_from_regions if you want multiple holes
with different tags and so the facility to set different BC to the different holes.

validation_tests/case_studies/merewether/runMerewether.py uses create_mesh_from_regions (line 99)
to set some interior holes and sets the BC to Reflective (line 182)

The unit test test_create_mesh_with_interior_holes_and_tags in test_mesh_interface.py  in
anuga/pmesh/tests folder demonstrate how to set hole_tags.

Cheers
Steve





On 30/01/15 23:56, Stefan Kummer wrote:
> Hi,
>
> I am an ANUGA-user and have questions on boundary conditions and
> boundary tags:
>
> 1) If I use "anuga.Dirichlet_boundary([0, 0, 0])" (stage = 0), does
> ANUGA use the elevation at the boundary nodes, because there is no error
> rising? If so: what is the difference between
> "anuga.Dirichlet_boundary([0, 0, 0])" and
> "anuga.Transmissive_stage_zero_momentum_boundary(domain)"?
>
> 2) Is it possible to set one of the above boundary conditions to an
> interior region so that the interior region acts as a sink? How do I
> assign boundary tags to this interior region?
>
> Thanks
> Stefan
>
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