[aspect-devel] ASPECT question

[Eric Heien]

On Apr 24, 2014, at 5:50 AM, Timo Heister <heister at clemson.edu> wrote:

> (sending to the mailing list)
> 
>> I had a quick question about ASPECT.  I’m working on recreating the 2008 Zhong spherical shell benchmarks which involve temperature dependent viscosity jumps up to the order of 1e7.  I notice in the simple material model there is an upper and lower bound on viscosity temperature dependence of 1e2 and 1e-2.  Is there a particular reason for this limit?
> 
> This was introduced by Rene way back. I guess it makes sense to limit
> in in some way to make the model solvable.
> 
>> If the limit is in the code then the solver fails to converge for large thermal viscosity exponents after a few hundred steps, but if I remove these bounds it appears to work fine.
> 
> What is your viscosity range in that case? I haven't tested 'very
> large' viscosity contrasts yet. There might be stuff that needs
> changing in ASPECT to make it work. One thing you can try is using a
> constant viscosity per cell for example.

It starts to fail for viscosity ranges around 1e5 and above.  I don’t think this is because of the large range, but rather because of the sharp cutoff in viscosity change caused by the min(max(…)) in simple.cc:43.  If I turn off this limit then large viscosity ranges up to at least 1e7 work fine.

For now I’ll change the limits in my own code.  I just wanted to make sure there wasn’t a particular reason (e.g. invalid results) the limits were there in the first place.

-Eric