[CIG-LONG] Hydrostatic Term

[Walter Landry]

erik.a.kneller at exxonmobil.com wrote:
> 
> Hi Walter,
> 
> Thank you for the clarification. Gale appears to be an impressive package
> that is moving in interesting directions.
> 
> If a good guess for the hydrostatic term is necessary for good performance,
> it would be useful to have Gale automatically calculate the hydrostatic
> term based on the distribution of density at a given time step.
> 
> This would, for example, be very helpful when modeling continental
> extension or contraction and crustal thickness is modified significantly
> during deformation.

The profile does not have to be exact, but it should not be wildly
wrong.  So if there is some thinning of the crust, leading to an
upwelling of the mantle, the original profile will still work ok.
With isostasy, the pressure at the bottom of the crust will not
change.  The tibet example does not have isostasy, and so I had to
move the bottom boundary up to keep the average pressure at the bottom
correct.

But in general, I agree that it would be useful to automatically
compute a profile.  Users should really not have to worry this kind of
numerical issue.  Gale would have to compute an average profile over
the entire mesh and numerically integrate it.  That requires syncing
over multiple processors, so it is not entirely trivial.

> I would also like to suggest adding a benchmark or example model for Gale
> consisting of a model similar to the Tibet example with coupling between
> the heat and Stokes equations and stress boundary conditions that mimic
> isostasy. This simple benchmark would be a good test of whether or not Gale
> can be applied to dynamic high-strain geologic systems. Is such a benchmark
> in the works?

Have you looked at the example in input/examples/rifting.xml?  It is,
unfortunately, not documented in the manual, but I think it has
everything you want.

Cheers,
Walter Landry
walter at geodynamics.org