[aspect-devel] Dynamic topography

Lev Karatun lev.karatun at gmail.com
Thu Oct 19 20:41:07 PDT 2017

Thank you everyone for the responses!

I kind of realized dynamic topography should be around zero when free
surface in enabled, but in reality in some of my models it was not
(reaching hundreds and even thousands of meters). I assume it means the
errors were high when the surface displacements were calculated? Should I
be worried about it? Is there a way to fight it? I tried decreasing the
free surface solver tolerance, but it didn't help.

Best regards,
Lev Karatun.

2017-10-19 15:23 GMT-04:00 Rene Gassmoeller <rene.gassmoeller at mailbox.org>:

> As Ian mentioned, unfortunately there is currently no option to do this.
> There is an open issue for this fact: https://github.com/geodynamics
> /aspect/issues/1270, and it is on the list of things that 'should be
> done', but never get done, because there are always more important things
> to do. If anyone wants to go ahead with this issue, we would be grateful
> for it :-).
> Best,
> Rene
> On 10/19/2017 11:18 AM, Ian Rose wrote:
> A bit of context: I agree that the naming of the "topography" and "dynamic
> topography" postprocessors are a bit confusing (the distinction is
> described in the manual, section A.114). They are that way largely for
> historical reasons, as Jacky and I were working on those at roughly the
> same time and did not coordinate naming efforts. But yes, what Wolfgang and
> Timo say is correct: they are measuring different things. With a free
> surface, you expect the dynamic topgraphy to be near zero, since we are
> enforcing no-stress boundary conditions there!
> As to your other question, Lev: the "topography" postprocessor should
> provide an option to output the full topography, rather than just min/max
> values. It's just that nobody has put in the work to do the parallel I/O
> for it.
> Cheers,
> Ian
> On Thu, Oct 19, 2017 at 9:50 AM, Timo Heister <heister at clemson.edu> wrote:
>> > Or are you saying that the topography you output is due to the moving
>> > boundary? In that case, if the boundary would move in perfect response
>> to
>> > the fluid stress underneath, then the "dynamic topography" computed in
>> each
>> > time step would actually be zero, because there are no excess stresses
>> that
>> > aren't already accommodated by the displaced surface!
>> To add to Wolfgang's reply:
>> This is basically how the free surface implementation works, we
>> compute how much fluid wants to move through the surface and move the
>> surface accordingly.
>> --
>> Timo Heister
>> http://www.math.clemson.edu/~heister/
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> --
> Rene Gassmoellerhttp://www.math.colostate.edu/~gassmoel/
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