[aspect-devel] Velocity boundary conditions - lithosphere ext/compression

[John Naliboff]

Hi Philip,

Yes, certainly happy to help on this front! A few things to discuss.

1. Unrelated to your issue, I completely forgot that there is a small 
bug with the heat production term in this cookbook that Anne Glerum 
pointed out to me a week or two ago. This will cause the crust to cool 
more rapidly than it should over time, but it is not readily apparent 
over 10's of Myr with advection on. This is unrelated to the anomalous 
velocities in your model, but I will push a fix for this this evening or 
tomorrow morning. Apologies to all who are currently using the cookbook 
example. The quick fix is to change the "Initial concentrations crust" 
parameter from 1 to 1e6. Alternatively, the "fix" I'll push tomorrow 
will allow you to set different constant heating rates for each 
compositional layer (see "compositional heating" method).

2.Onto your issue. I've run a similar extension model (1000 x 600 km) 
with similar boundary conditions along the sides (balanced inflow 
outflow) and the velocity field was stable over time. Are your 
horizontal velocities fluctuating throughout the model or near the 
vertical sides?

3. In similar models I used a fixed mesh (no AMR). Have you tried the 
model with a fixed mesh? Very likely to be unrelated, but might be worth 
using a fixed mesh to see if the error occurs at a similar time and 
place in the model.

3. I'm running your parameter file now, but in the meantime can you send 
the log.txt file from the output folder?

Regardless of the root issue, we can get this worked out quickly. If the 
issue is not readily apparent, we can start from a similar working input 
file and compare the differences.

Thanks for sending in this question to the "devel" email list. Really 
helpful for others to see where issues are cropping up!

Cheers,
John

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

On 07/03/2017 08:14 AM, HERON, PHILIP J. wrote:
>
> Hello all,
>
>
> I was just extending the 'continental_extension.prm' cookbook to 
> include sub-lithosphere mantle, and have ran into issues of 
> convergence. I wonder if anyone on the group could help!
>
>
> I've attached the extended cont extension model, I was wondering if 
> anyone could point me in the right directions of how to get it to 
> converge. The issue is that after 10-15 timesteps velocities within 
> the model start to blow up.
>
>
> I feel that the temperature profile initially is fine. Although 
> applying a variable horizontal velocity to the boundary, the initial 
> horizontal velocity field is smooth. However, almost immediately the 
> horizontal velocity starts to fluctuate.
>
>
> Are there better techniques to be able to get this  model to converge? 
> Am I missing something simple? I've played around with a few different 
> things but with little luck.
>
>
> Thanks in advance!
>
>
> Phil
>
>
>
>
>
>
>
> Philip J. Heron
> Junior Research Fellow
> Dept. of Earth Sciences
> Durham University
> web: http://philheron.com <http://philheron.com/>
>
>
>
> _______________________________________________
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