[aspect-devel] Van Keken et al. 2008 subduction benchmark

[John Naliboff]

Hi Max,

I haven't tried this benchmark specifically, but yesterday I tried a 
problem (GeoMod compression) with prescribed internal boundary 
conditions using the same plugin.

The internal velocity field I prescribed was quite simple compared to 
the subduction benchmark (uniform horizontal and vertical velocity), but 
time-dependent.  I had no solver issues when the internal velocity 
constraints did not vary with time, but immediately had solver issues 
once I incorporated time-dependence.

I'm not sure what the solution on my end is, but perhaps velocity-based 
mesh refinement (multiple initial refinement steps) in your case would 
help?

As I recall, mesh refinement in at least Peter's code (SEPRON-based) 
helped minimize pressure oscillations in the region of the 
discontinuity.  Susanne Buiter's code (SULEC, no AMR) also has similar 
issues to what you describe below with this benchmark.

Cheers,
John

*************************************************
John Naliboff
Assistant Project Scientist, CIG
Earth & Planetary Sciences Dept., UC Davis

On 10/27/2016 09:13 AM, Max Rudolph wrote:
> I was wondering if anyone has been successful in setting up the Van 
> Keken et al. 2008 subduction benchmark using ASPECT? I have been using 
> this as a starting point to set up a more complicated corner flow 
> model and have not yet been successful.
>
> This benchmark solution requires a rigid overriding plate and 
> kinematic subducting plate. There is a discontinuity along the 
> subduction interface. I tried imposing kinematic boundary conditions 
> on the left and bottom of the box and using Jonathan Perry-Houts' 
> prescribed velocity plugin (cookbooks/prescribed_velocity), but the 
> Stokes solver fails to converge. Looking at the pressure field, it's 
> not surprising to see very large oscillations in this region where the 
> velocity field is discontinuous. It occurred to me that using the 
> locally conservative discretization might help. However, when the 
> locally conservative discretization is enabled, the internal 
> prescribed velocities are no longer enforced anywhere. Is it obvious 
> why this might be the case?
>
> Regards,
> Max
>
>
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