[aspect-devel] free surface with non-zero surface pressure

[Carolyn Branecky]

Hi Wolfgang,

Thank you for your detailed response!  If I decide to go this route, I'll
follow up with the community after AGU.

Cheers,
Carolyn

On Dec 8, 2016 9:55 PM, "Wolfgang Bangerth" <bangerth at tamu.edu> wrote:

>
> Carolyn & John,
> great question indeed.
>
> Currently, it is not possible to mix a free surface and traction boundary
>> condition.  However, as you pointed out this feature would be very useful
>> for
>> a number of applications and I do not see any reason why it can't be
>> implemented.
>>
>> I think this kind of feature would likely be implemented as an added
>> option to
>> the free surface portions of the code or as a new boundary condition
>> model/option.  Others will have a much better idea of exactly how/where
>> this
>> should be done.
>>
>
> There are basically two places where you have to do something. The first
> is that you still have to add the traction boundary terms even though it's
> a free boundary. This should not be very difficult: you could define a new
> type of boundary, say "free surface with traction", and then the place
> where we add the terms for tractions that currently reads
>   if (boundary is a traction boundary)
> would simply have to be extended to say
>   if (boundary is a traction boundary
>       or
>       boundary is a free boundary with traction)
>
> The second place is where we currently compute the response of the
> boundary to the internal stresses. Right now, it uses the entire normal
> component of the stress to move the boundary. In your case, it needs to use
>   "normal component of stress"   minus   "prescribed traction"
> to move the boundary.
>
>
> Neither of these two places (plus the addition of a new kind of boundary)
> are going to be very difficult. You just need to find the right places to
> add the necessary code. I suspect this can be done with not much more than
> 100 lines of additional code.
>
> If you want to go this route, feel free to ask the mailing list for
> concrete questions on how each of the steps above can be implemented and
> where! Ask early and often, as it's easier to first discuss a design then
> implement it, than it is to implement something that later needs to be
> rewritten in response to comments from the developer community :-)
>
> Cheers
>  W.
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth          email:                 bangerth at colostate.edu
>                            www: http://www.math.colostate.edu/~bangerth/
>
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