[CIG-SHORT] PyLith Convergence issue - DIVERGED_FUNCTION_COUNT and CONVERGED_SNORM_RELATIVE
Brad Aagaard
baagaard at usgs.gov
Fri Jun 23 07:00:03 PDT 2017
On 06/23/2017 06:24 AM, Josimar Alves da Silva wrote:
> Brad,
>
> Just to let you know that I sorted it out this problem.
>
> I set "open_free_surface=True" instead of False. My understanding
> regarding why it was not working is because I am applying tensile
> tractions on the fault to balance out the normal stress, however this
> could potentially cause a problem with the fault node that is on edge of
> the domain (right side on the fault, on the interface between the
> displacement BC and the zero displacement BC of my geometry). Do you
> think this could potentially be the problem ? I
Maybe. It is difficult to diagnose some of these issues without a better
understanding of what you are trying to model. For example, I don't
understand why you are applying tensile tractions. A simple sketch of
what you are trying to model would help. We can talk about this at the
workshop next week.
In setting up a new fault friction example, I may be encountering some
similar issues to what you are finding related to rate- and
state-friction and convergence issues for a through-going fault. I have
several ideas on what the source of this might be, but need to do some
more testing to zero in on the problem (I doubt I will be able to get to
this before next week).
Regards,
Brad
>
> I haven't changed anything on the solver parameterization. You can find
> all the log files and the pylith_parameters.json file here:
> https://www.dropbox.com/sh/by2vgqadgbsk1fs/AACENG_kCXygHa3dsdEyNAf-a?dl=0
>
> thank you,
> Josimar
>
>
> On Thu, Jun 22, 2017 at 5:49 PM, Josimar Alves da Silva
> <jsilva.mit at gmail.com <mailto:jsilva.mit at gmail.com>> wrote:
>
> Brad,
>
> Thanks for the remind. Here it is:
> https://www.dropbox.com/sh/sxiburbvru670n3/AAD3sLLHVPp-E-FKo4oQwf23a?dl=0
> <https://www.dropbox.com/sh/sxiburbvru670n3/AAD3sLLHVPp-E-FKo4oQwf23a?dl=0>
>
> thank you
> Josimar
>
> On Thu, Jun 22, 2017 at 5:28 PM, Brad Aagaard <baagaard at usgs.gov
> <mailto:baagaard at usgs.gov>> wrote:
>
> Josimar,
>
> Please send the pylith_parameters.json file that PyLith generates.
>
> Thanks,
> Brad
>
>
> On 06/22/2017 02:19 PM, Josimar Alves da Silva wrote:
>
> Matt,
>
> Thanks for the help. Here is the log file with more
> information:
> https://www.dropbox.com/s/qnpk055o9xg38j1/log.out?dl=0
> <https://www.dropbox.com/s/qnpk055o9xg38j1/log.out?dl=0>
>
> Let me know if you need anything else.
>
> thank you,
> Josimar
>
> On Thu, Jun 22, 2017 at 3:21 PM, Matthew Knepley
> <knepley at rice.edu <mailto:knepley at rice.edu>
> <mailto:knepley at rice.edu <mailto:knepley at rice.edu>>> wrote:
>
> On Thu, Jun 22, 2017 at 12:10 PM, Josimar Alves da Silva
> <jsilva.mit at gmail.com <mailto:jsilva.mit at gmail.com>
> <mailto:jsilva.mit at gmail.com <mailto:jsilva.mit at gmail.com>>>
> wrote:
>
> Matt,
>
> Thank you so much for the help. I followed up on
> your suggestions:
>
> 1) Using snes_max_funcs=10000 did not help. The
> simulation does
> not go beyond iteration #5000. It stopped at the
> same time step
> as the previous one.
>
>
> Note this has to be in the [petsc] section. Please add
> snes_view.
> Then we can see exactly what the setting were.
> It would also be good to add snes_converged_reason
>
> I looked at the log. It makes as much as progress as it
> will ever
> make after 2 iterates, thus I think there
> is a problem with interplay of tolerances here.
>
> 2) Can you comment a little bit on how can I
> improve my initial
> guess, as you mentioned here : "if your initial
> guess is not
> good enough they can fail". What you mean about it ?
>
>
> I mean if you are taking time steps so big that the
> last solution is
> not close to the next one, the solves will be harder.
>
> Matt
>
> The log file is attached.
>
> thank you so much in advance,
> Josimar
>
>
>
>
> On Thu, Jun 22, 2017 at 11:33 AM, Matthew Knepley
> <knepley at rice.edu <mailto:knepley at rice.edu>
> <mailto:knepley at rice.edu <mailto:knepley at rice.edu>>> wrote:
>
> On Wed, Jun 21, 2017 at 6:25 PM, Josimar Alves
> da Silva
> <jsilva.mit at gmail.com
> <mailto:jsilva.mit at gmail.com> <mailto:jsilva.mit at gmail.com
> <mailto:jsilva.mit at gmail.com>>> wrote:
>
> Dear Brad, Matt and Charles,
>
> I am working on a 2-D quasi-static,
> elastic, simulation
> using rate and state friction model.
>
> The simulation runs fine for many time
> steps, then at
> some point I get the error below related to
> DIVERGED_FUNCTION_COUNT.
>
> Nonlinear solve did not converge due to
> DIVERGED_FUNCTION_COUNT iterations 5000
>
> All the log files, along with the .cfg
> files, model
> geometry and boundary conditions as well as a
> convergence plot for the SNES residual can
> be found on
> the attached .zip file.
>
> I have some questions that I would like to
> have your input:
>
> 1) Is it possible to extend the maximum
> value for
> DIVERGED_FUNCTION_COUNT ? Note that I have
> snes_max_it
> =10000 but SNES still stops at 5000 value.
>
>
>
> snes_max_funcs 10000
>
> 2) Looking at the convergence plots that I have
> attached, I noticed that the time step that
> fails
> contains iterations that actually increase the
> residual,instead of decreasing it. Would
> you know what
> is causing this behavior ?
>
>
> There is no guarantee of decrease with a
> general nonlinear
> problem.
>
> 3) There are several time steps that
> converge with
> tolerances smaller than what I ask for
> using the
> snes_atol (see figure attached). At these
> time steps I
> get the following
>
> Line search: Aborted due to ynorm < stol*xnorm
> (9.933794721748e-10 < 1.046238089915e-09)
> and inadequate
> full step.
>
> Nonlinear solve converged due to
> CONVERGED_SNORM_RELATIVE iterations 694
>
>
> This means that even a very short step length
> gave no
> residual decrease, also known as "stagnation".
> Here is the
> nonlinear
> solver is just not working.
>
> We have no convergence theory for the friction
> problems, and
> if your initial guess is not good enough they
> can fail. We
> want to explore
> more powerful solvers for these, but after we
> get a revised
> formulation in place.
>
> Thanks,
>
> Matt
>
> Note that I am using
> snes_error_if_not_converged =true.
>
> Could you please comment on why this is
> happening and
> how I would fix this issue ? Does it affect
> the next
> time steps after it ?
>
> Let me know if you need any further
> information.
>
> Thank you so much for you help in advance,
> Best
> Josimar
>
>
>
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