[aspect-devel] Tracking time-dependent properties through compositional fields (general discussion)

[Wolfgang Bangerth]

John,

> Wolfgang - The ‘volume fraction’ I was referring to is the percentage of a
> specific composition in an element, which is then used to compute the overall
> (averaged) material properties for a composition-dependent material model.
>   The terminology is specific to a section of code in the
> composition-dependent material models (multicomponent, diffusion_dislocation,
> etc).

I see. I think this results from an overly literal reading of the word 
"compositional". This is how we had originally envisioned these fields to be 
used, but that is no longer the case -- in situations like the strain, these 
fields have completely different meanings, and volume fractions and similar 
terms then have no meaning any more.


> I’ll keep thinking over ways to make the separation of compositional fields
> (tracking strain/etc vs affecting material behavior).  I’d like to make this
> is a simple as possible so that users don’t accidentally mix up what fields
> are doing what.

I think the way to do this is to not use magic numbers in material models (and 
other parts of the implementation) to pick one compositional field out of them 
all, but instead to use the named approach Juliane pointed out. This way, it 
no longer matters whether the "strain" is the first of the fourth 
compositional field -- the material model will simply use the one that has 
that name, whichever number that corresponds to.

In case the user has not assigned any of the compositional fields the name 
"strain", she will simply get an error (rightfully so).

Best
  W.

-- 
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Wolfgang Bangerth               email:            bangerth at math.tamu.edu
                                 www: http://www.math.tamu.edu/~bangerth/