# [aspect-devel] internal velocity boundary conditions

Magali Billen mibillen at ucdavis.edu
Fri May 15 09:29:02 PDT 2015

```Wolfgang,

On May 15, 2015, at 5:36 AM, Wolfgang Bangerth <bangerth at tamu.edu> wrote:

>
> Magali,
>
>> One of the issues with defining the velocities everywhere is that  we will
>> need to use a non-uniform grid for the fully-dynamic 3D models (that is higher
>> resolution near the slab/wedge and much coarser mesh in the lower mantle and
>> out near the edges of the boundary), and there’s not an easy way to define the
>> velocities on a non-uniform grid.
>
> The way you should think about the velocity is as a function v(x,y,z) that is defined everywhere. It is not enough to know about it at the vertices of the mesh, but on the upside, if you think of it as a function, then whether the mesh is uniform or not, has hanging nodes or not, etc, are all questions that do not matter.

Yes, I understand that. My problem is that given that the dip and position of the slab is not uniform, I can not come up
with an analytical expression to define it as a single function for all x, y, and z. I can come up with a way to define
the velocity analytically at each depth along profiles that are approximately perpendicular to the slab (instead of being actually perpendicular, I can align this along the mesh direction that is roughly perpendicular to the slab).  This is why,
I first asked about just defining the velocity on the slab, because there is not a good way to define the velocity analytically for a slab that varies in 3D.

>
>> - As a last step before running the “kinematic” simulation, we would like to
>> use the AMR-mesh coarsening to coarsen the mesh using the velocity gradient of
>> the prescribed velocity field (CAN WE DO THIS??).
>
> There are plugins for mesh refinement and coarsening. As long as you can algorithmically describe what you'd like to happen, it can be done in this framework.

Good… then I think we can make this approach work.

Thank you,
Magali

>
> Best
> W.
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth               email:            bangerth at math.tamu.edu
>                                www: http://www.math.tamu.edu/~bangerth/
>
> _______________________________________________
> Aspect-devel mailing list
> Aspect-devel at geodynamics.org
> http://lists.geodynamics.org/cgi-bin/mailman/listinfo/aspect-devel

--------------------------------------------------
Professor of Geophysics & UCD Chancellor Fellow
Earth & Planetary Sciences Dept., UC Davis
Davis, CA 95616
2129 Earth & Physical Sciences Bldg.
Office Phone: (530) 752-4169
http://mygeologypage.ucdavis.edu/billen/
--------------------------------------------------

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.geodynamics.org/pipermail/aspect-devel/attachments/20150515/bf7331ca/attachment.html>
```