[aspect-devel] boundary pb

[Cedric Thieulot]

Hi all, 

Anne, Menno and myself have been trying to run a model very similar to the convection-box.prm setup (based after the Blankenbach 1989 paper) albeit with a more 
complex rheology. Indeed, the setup involves a nonlinear visco-plastic rheology and it kept yielding all afternoon abnormal results in the right corner of the box. 
Visually abnormal, but also quantitatively abnormal when compared to the same setup ran with my ELEFANT code. 
In order to fix ideas, we decided to start all over again, and ran a few timesteps of the convection-box.prm setup … and witnessed the same 
abnormal behaviour for three versions of ASPECT (one from two weeks ago, i.e. the virtual box made for the GFZ workshop, one from a few weeks back,
and one from last december). 
As you know, the convection-box is a buoyancy-driven experiment where the temperature field is initially prescribed to be  T(x,z)=(1-z)-0.01*cos(pi*x)*sin(pi*x)
so that one expects the velocity field to be symmetric at t=0  (in magnitude, not direction). However attached are some screen captures of what we obtain.
Please keep in mind that we get the convection-box.prm from git (or svn for the older version), that we do not modify it at all and that the file prescribes free slip on all sides. 
So why does the velocity field display a kink on the right boundary ? 
Also by changing the temperature field to T(x,z)=(1-z)+0.01*cos(pi*x)*sin(pi*x) , the kink is reversed, as if there was a velocity prescribed on the boundary no matter what…
Do you have any idea where this could come from ? Can someone replicate this probem with their version by running 1 timestep of the convection-box experiment ?

Kind regards, 

Cedric, Anne & Menno


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