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

[John Naliboff]

Hi all,

Juliane Dannberg and Rene Gassmoeller have recently implemented features in ASPECT that track finite strain through compositional fields or tracers.  

Tracking finite strain, or tensors in general, through compositional fields was initially a bit abstract, but is certainly appealing based on the relative speed of field vs tracer advection.  

As many people are likely interested in tracking time-dependent properties (strain, melt, CPO, etc), it seems like a general discussion of the details and applications of this method may be helpful to the broad user group.  

Juliane has already graciously offered to answer some initial questions.  To anyone interested, please chime in and add opinions or questions!

For reference, I’ve attached the files finite_strain.cc and finite_strain.prm from the finite_strain cookbook.

Below are some starter questions.

1.  In finite_strain.cc, each component of the strain tensor is assigned to and advected with a unique compositional field via the reaction term.  If one wishes to track additional properties, say CPO and melt, this will require additional unique compositional fields for each component.  At some point, will the advantages of using compositional fields over tracers be negated if too many compositional fields are present?

2. In finite_strain.prm the compositional fields for each component (4 total) of the 2-D strain tensor are assigned a value of 0 under the initial conditions section.  My interpretation is that this procedure allows the fields to track the strain through the reaction term, but the "volume fraction” of these fields in each cell is still effectively 0.  Is this interpretation correct?  If it is correct, that means composition dependent material models (ex: multicomponent.c) following this approach will not be affected by the compositional fields tracking strain unless they specifically use the reaction terms.

Ok, that seems like plenty to start with.  I hope the ensuing discussion proves useful to everyone!

Cheers,
John

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



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