# [aspect-devel] internal velocity boundary conditions

Magali Billen mibillen at ucdavis.edu
Fri May 15 13:35:41 PDT 2015

```Okay. I see what you mean. Its possible I could come up with a way to do that (hmm - okay 10 minutes later, I think I have figured it out - I will discuss with Scott before the Hackathon).

However, I still think using the prescribed velocity field to coarsen the mesh before solving is useful in this case, because its an easy way to determine how the mesh should go from fine to coarse around a distorted 3D shape. It would also allow for easily testing different grids by just adjusting the coarsening parameter.

-Magali

On May 15, 2015, at 12:31 PM, Wolfgang Bangerth <bangerth at tamu.edu> wrote:

> On 05/15/2015 11:29 AM, Magali Billen wrote:
>>
>> 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.
>
> Right, but that's also not necessary -- it doesn't have to be an analytical expression, it simply needs to be a function where if I give you a point (x,y,z), you return to me a velocity (u,v,w). This may very well be a velocity that's interpolated between points, or simply the velocity from the nearest one of the points for which you know the velocity.
>
> In other words, it just needs to be a function we can evaluate everywhere. It doesn't have to be known analytically.
>
> Best
> Wolfgang
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth               email:            bangerth at math.tamu.edu
>                                www: http://www.math.tamu.edu/~bangerth/
>
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