[CIG-SHORT] Linear convergence for nonplanar faults

[Charles Williams]

Dear Josimar,

Try setting your length scale to 500 m and see if that improves your convergence.

Cheers,
Charles


> On 9/11/2016, at 9:19 AM, Josimar Alves da Silva <jsilva.mit at gmail.com> wrote:
> 
> 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 <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 <mailto: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 <mailto: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/2012-September/001123.html>
>> 
>> http://lists.geodynamics.org/pipermail/cig-short/2008-December/000453.html <http://lists.geodynamics.org/pipermail/cig-short/2008-December/000453.html>
>> 
>> http://lists.geodynamics.org/pipermail/cig-short/2013-March/001320.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 <mailto:C.Williams at gns.cri.nz>
> 
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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 <mailto:C.Williams at gns.cri.nz>
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