[CIG-SHORT] on the viscosity coefficient

Ikuo Cho ikuo-chou at aist.go.jp
Wed Mar 17 03:03:48 PDT 2010


I discussed with my colleague, Yuta Abe, on the fit between the final
output from PyLith 1.4.2 and an analytical solution.

Yuta Abe Wrote:
> By the way, the final output of the PyLith program coincided with
the analytical solution.

 We found that an input parameter for the analytical calculation was
 incorrect when he wrote the above report, and consequently analytical
solution does not fit the  numerical results. He did use a value of A_T
as both the "powerlaw-coefficient" for PyLith and a parameter value for
the analytical calculation, although he had to use values of A_T and
(3/2)**n A_T for the "powerlaw-coefficient" and the analytical
calculation, respectively.
(As the result, he observed a good fit between the numerical and
analytical solutions.)

I wanted to ask from this fact the possibility that the
"powerlaw-coefficient" is actually defined by A_T'=(3/2)**n A_T,
instead of A_T defined in (5.75) in PyLith 1.4.2.
Is it difficult to check?

By the way, I recently installed PyLith from the repository. I also made
comparison between the numerical and the analytic solutions for the same
problem. (I noticed a small difference in the definition of A_T between
the released and repository versions.)
They showed a good fit in this case. 

Ikuo Cho

On Fri, 5 Mar 2010 07:14:30 +1300
Charles Williams <willic3 at gmail.com> wrote:

> Dear Yuta Abe,
> I will look at the code and the manual to see if there is a problem.  As I mentioned in a previous e-mail to cig-short, we are changing the input parameters for power-law materials, so 'eta' will no longer be a parameter in upcoming versions.  I will let you know what I find out about version 1.4.2, though.
> I'm glad the final output matches the analytical solution.  Would it be possible for you to describe the problem?  It may be useful as an example problem or benchmark.
> Cheers,
> Charles
> On 4/03/2010, at 9:07 PM, Yuta Abe wrote:
> > Dear PyLith Developers:
> > 
> >  I have a question about the viscosity_coefficient "eta", which is one of the physical properties that you get in the output "cel_info_fields" when you carry out analysis of a power-law viscoelastic material using PyLith 1.4.2.
> > 
 > >  I thought the values of "eta" could be calculated using the equations (5.74), (5.75) and (5.76) by substituting the power-law coefficient "At" and the power-law exponent n. I substituted "At"=1.99e-41 and n=3 into those equations, and obtained " eta"=1.77e+13 as a result. However, the value of "eta" in info.vtk file which was obtained as an automatic output of the PyLith program for the same values of "At"=1.99e-41 and n=3 was "eta"=1.77e+18, 100,000 times as large as the above value. By the way, the final output of the PyLith program coincided with the analytical solution.
> > 
> > I would like to find out the origin of this difference, so please kindly tell me how the value of "eta" is calculated within the PyLith program.
> > 
> > 
> > ------------------------------------------------------
> > Yuta ABE
> > Active Fault and Earthquake Reserch Center
> > National Institute of Advanced Industrial Science and Technology,Japan
> > tel; +81-29-861-3686
> > email; yuta-abe at aist.go.jp
> > -------------------------------------------------------  
> > _______________________________________________
> > CIG-SHORT mailing list
> > CIG-SHORT at geodynamics.org
> > http://geodynamics.org/cgi-bin/mailman/listinfo/cig-short
> Charles A. Williams
> Scientist
> GNS Science
> 1 Fairway Drive, Avalon
> PO Box 30368
> Lower Hutt  5040
> New Zealand
> ph (office): 0064-4570-4566
> fax (office): 0064-4570-4600
> C.Williams at gns.cri.nz

Ikuo Cho  ( ikuo-chou at aist.go.jp )
Geological Survey of Japan,
National Institute of Advanced Industrial Science and Technology
Tsukuba Central 7, Tsukuba 305-8567 Japan
Tel +81-29-861-3891, Fax +81-29-861-3682

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