[aspect-devel] Aspect melt_fraction

[Juliane Dannberg]

On 06/12/2014 05:28 AM, Wolfgang Bangerth wrote:
> On 03/14/2014 03:00 PM, Magali Billen wrote:
>> I think it would be great to have a module for calculating melt fraction
>> in the main branch. This doesn't come up for every problem, but there's
>> often a problem that you're working on and then part way through you
>> realize that melt fraction might be helpful.
>
> Juliane has been making more progress on this.

Just to give a short update on this:

I think the melt postprocessor that calculates the melt fraction is 
already in the main version of aspect for a few months. However, in the 
last weeks I tested it and it should now calculate the melt fraction 
exactly as in the sources of the melting models (to have a look at the 
p-T-diagrams, you can run the tests melt_postprocessor_peridotite and 
melt_postprocessor_pyroxenite).

If there are no compositional fields, this postprocessor will visualize 
the melt fraction of peridotite (calculated using the anhydrous model of 
the Katz, 2003 paper). If there is at least one compositional field, the 
postprocessor assumes that the  first compositional field is the content 
of pyroxenite, and will visualize the melt fraction for a mixture of 
peridotite and pyroxenite (using the melting model of Sobolev, 2011 for 
pyroxenite).
All the parameters that were used in these calculations can be changed 
in the input file, too, the most relevant maybe being the mass fraction 
of Cpx in peridotite in the Katz melting model ("Mass fraction cpx"), 
which right now has a default of 15%. (The code is implemented in 
source/postprocess/visualization/melt_fraction.cc.)

In addition, to make the rheology dependent on melt fraction, we now 
have the possibility to access the calculation of a postprocessor from 
the material model. So to access the melt postprocessor, you could use 
the function "find_postprocessor ()" (in 
include/aspect/simulator_access.h) to get the postprocessor calculation. 
(Wolfgang, is this how it works? I never used it myself...). However, 
this would not include latent heat effects.

I am also working on a material model that has a melt fraction 
calculation and includes the effects of latent heat of melting. Right 
now this is only in my branch of Aspect, but as soon as it is working 
and tested, I will contribute it back to the main version.

>
>> for example,
>> being able to have rheology depend on melt fraction would require
>> calculating melt fraction first.
>
> If your melt doesn't migrate, this is already possible. Juliane is 
> working on models where melt is also migrating.

Yes, we also started to work on including melt migration. Right now this 
is only in my Aspect branch and it is not finished yet. We already added 
the equations, but are still in the stage of testing. I definitely plan 
on contributing it back to the main version, however, it may take some 
time until everything is working and tested.

Best,
Juliane