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

Tue Jul 4 07:36:06 PDT 2017

Hi John,

thanks for the reply - I've attached the log.txt for the prm file I sent, along with the error output.

I have tried and played around with a great number of parameters to try and get this to work, but I think it is good to get some outside perspective.

Point 1 - thanks for that, I've applied that change to the models.

Point 2 - the vertical sides seems to be immune to the fluctuating velocity, the interior of the model has the blow up in velocity.

Point 3 - I'm just running a fixed mesh model now to see where it gets to. Will keep you posted.

Furthermore, I'm going to run a series of tests on reference viscosity after noticing this post:

https://github.com/geodynamics/aspect/issues/1814

Issues with linear solver convergence due to choice of Reference viscosity · Issue #1814 · geodynamics/aspect<https://github.com/geodynamics/aspect/issues/1814>
github.com
I've had some issues with choosing the "right" reference viscosity (in models with varying viscosity) in order to get convergence of the linear system and was wondering if there might be some way o...

Philip J. Heron
Junior Research Fellow
Dept. of Earth Sciences
Durham University
web: http://philheron.com<http://philheron.com/>

________________________________
From: Aspect-devel <aspect-devel-bounces at geodynamics.org> on behalf of John Naliboff <jbnaliboff at ucdavis.edu>
Sent: 04 July 2017 01:22:47
To: aspect-devel at geodynamics.org
Subject: Re: [aspect-devel] Velocity boundary conditions - lithosphere ext/compression

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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