[CIG-SHORT] Anisotropy in Pylith

[Charles Williams]

Hi Ravi,

At present, the general recipe for a rheological model is:

1.  Write the C++ code that does the actual work, using one of the existing models as a template.
2.  Write the top-level Python, which generally defines the parameters used by the model.
3.  Write a SWIG binding for the model, which will look very much like the bindings for the other materials.

It’s not generally very difficult.  Things to think about:

1.  Is the model linear or nonlinear?
2.  What parameters are needed to define the model, and what is the easiest way to specify them?
3.  Is it easy to spatially vary the parameters?  As an example, take a look at the power-law viscoelastic material.  We had to reformulate that model because the usual parameterization made the units of the parameters dependent on the power-law exponent.

I haven’t looked at the models you mention, but I would guess it wouldn’t be too hard to do.  At some point, just having anisotropic elasticity would also be nice.

Cheers,
Charles


On 25/08/2014, at 7:54 am, Ravi Kanda <rkanda at usu.edu> wrote:

> Hi Brad, Charles, and Matt,
> 
> I am back in the U.S. now and doing a new postdoc at USU (working with Tony Lowry).  My focus here is on incorporating 'in-situ' rheological models (from geophysical observations) into regional models of crustal and lithospheric scale deformation.  We are planning to include the use of Pylith in an NSF proposal, and have a quick question regarding handling bulk anisotropy in Pylith.  I could not find info on this in the latest manual or the short-term tectonics email archives (e.g. Google search for "anisotrop* site:geodynamics.org/pipermail/cig-short" yielded nothing).
> 
> My understanding from the manual is that currently, only isotropic (elastic or viscoelastic) bulk constitutive relations are implemented.  I am trying to figure out if Pylith has hooks to handle anisotropic viscosity in viscoelastic materials.  That is, would it be possible to simply add an anisotropic bulk constitutive model - something that provides a stress-strain(-rate) constitutive relation for different components? I am thinking of the approach in Muhlhaus et al, 2002a,b (references below), which uses only two anisotropic directions represented by normal and shear viscosity. If that is the way to go, are there potential pitfalls, or issues related to solvers that I need to be aware of?
> 
> Also, are anisotropic materials in the plans for future versions of Pylith?  If so, how far down the line?
> 
> Thanks much for your time!
> Ravi.
> ================
> REFERENCES:
> ================
> H.-B. Muhlhaus, F. Dufour, L. Moresi, and B. Hobbs. 2002a.
> A director theory for visco-elastic folding instabilities in multilayered rock. Int. Jour. Solids. Struct., 39:3675–3691.
> H.-B. Muhlhaus, L. Moresi, B. Hobbs, and F. Dufour. 2002b.
> Large Amplitude Folding in Finely Layered Viscoelastic Rock Structures. Pure Appl. Geophys., 159:2311–2333.
> 
> 
> -- 
> ---------------------------------------------------------------------
> Ravi Kanda
> Post-Doctoral Researcher
> Department of Geology
> Utah State University
> 4505 Old Main Hill
> Logan UT 84322-4505
> --------------------------
> Web Page: http://www.usu.edu/geo/rkanda/
> 
> ----------------------------------------------------------------------
> For a human being, the unexamined life is not worth living - SOCRATES
> ----------------------------------------------------------------------
> 

Charles A. Williams
Scientist
GNS Science
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PO Box 30368
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C.Williams at gns.cri.nz


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