[CIG-SHORT] Linear convergence for nonplanar faults

[Josimar Alves da Silva]

Charles,

I forgot to mention it. The mesh dimension are 350 km x 80 km.

When building the mesh in Trellis, I set the size of the elements on the
fault to 500m . Would this be the smallest element on my mesh ?

Note that I used 0.01cm because on the Pylith website (
https://wiki.geodynamics.org/software:pylith:help:hints) it says:

length_scale = DISCRETIZATION_SIZE or DISPLACEMENT_MAGNITUDE

Since I expect displacements magnitudes on the order of mm to cm, then
that's why used length_scale=0.01 cm.

Let me know what you think about it.

Thank you
Josimar




On Tue, Nov 8, 2016 at 2:49 PM, Charles Williams <willic3 at gmail.com> wrote:

> Dear Josimar,
>
> What are the dimensions of your mesh, and what is the size of the small
> elements close to the fault?  It’s possible that your nondimensionalization
> is incorrect.  The default for PyLith (I think) is 1 km for distance.  If
> your elements are considerably smaller than this, you may need to change
> that value.
>
> Cheers,
> Charles
>
>
> On 9/11/2016, at 8:00 AM, Josimar Alves da Silva <jsilva.mit at gmail.com>
> wrote:
>
> Dear Brad, Matt and Charles,
>
> I am running Pylith for a 2D friction model with gravity for a nonplanar
> fault. I am finding that the linear solver does not converge when the fault
> is included on the model. When the fault is not included on the model the
> linear solver takes roughly 500 to 1000 iterations to converge. Please
> refer to the attached "log_no_fault.cfg" file.
>
> The three links below show previous discussions on linear convergence:
>
> http://lists.geodynamics.org/pipermail/cig-short/2012-
> September/001123.html
>
> http://lists.geodynamics.org/pipermail/cig-short/2008-December/000453.html
>
> http://lists.geodynamics.org/pipermail/cig-short/2013-March/001320.html
>
>
> As pointed out by Charles previously and also discussed on the links
> above, overall, it seems that there are 3 main causes for convergence
> issues: 1) Poor quality mesh; 2) incorrect solver settings; 3) Poor
> setup/initial conditions.
>
> For my set up, I am unable to make the linear solver to converge.
>
> This is what I have done so far, based on recommendations from previous
> discussions:
>
> 1) Make sure that the mesh has condition number and aspect ratios <1.5.
> Please see attached presentation for histograms.
> 2) used the solver parameters shown on share/settings/solver_
> fault_fieldsplit.cfg
>
> I would like to know if there is anything else that I can do in order to
> make the linear solver to converge. Any other advices to improve my
> simulation would be very much appreciated.
>
> You can find attached the pylith .cfg files that I am using and also the
> log files for the case without the fault (log_no_fault.out) and with the
> fault (log_with_fault.out).
>
> I run my simulation using:
>
> 1) pylith no_fault.cfg > log_nor_fault.out
> 2) pylith no_fault.cfg   fault.cfg > log_with_fault.out
>
>
> Thank you in advance for you help,
> Josimar
>
> <fault.cfg><no_fault.cfg><pylithapp.cfg><log_no_fault.out>
> <log_with_fault.out><mesh_information.pdf>______________
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>
> 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
>
>
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