[CIG-SHORT] Stress concentration near the fault tip

[Josimar Alves da Silva]

Dear Charles and Brad,

I removed the z-constraint on the upper right boundary of my domain the
problem seems to be fixed now.

You mention that the "first time step takes a huge number of iterations,
while subsequent steps only seem to need one iteration".  Could you give
some hints on how to improve this aspect of my simulation ?

Thank you
Josimar



On Mon, Nov 7, 2016 at 6:05 PM, Charles Williams <willic3 at gmail.com> wrote:

> Dear Josimar,
>
> See if removing the z-constraint helps your solution.  Looking at your
> log, the first time step takes a huge number of iterations, while
> subsequent steps only seem to need one iteration.
>
> I did not realize that you had gravity turned on.  That would provide
> sufficient normal stress to clamp the fault.  Also, you would not be able
> to apply tractions in the same place you are applying displacement BC.
>
> If the only purpose of having gravity in your problem is to provide normal
> stress on the fault, it is probably simpler to compute the overburden
> stress and apply it to the fault using db_initial_stress, and turn off
> gravity.  That would also mean you wouldn’t need the traction BC on the
> left side of your domain.
>
> Cheers,
> Charles
>
>
> On 8/11/2016, at 4:54 AM, Brad Aagaard <baagaard at usgs.gov> wrote:
>
> Josimar,
>
> Why are you constraining the tangential (z) displacement on the right hand
> side boundary? I think this may be causing the large tractions around the
> fault on the right hand side.
>
> You should not mark the buried edges of the fault on edges of the fault
> that reach the edges of the domain.
>
> Brad
>
>
> On 11/06/2016 04:31 PM, Josimar Alves da Silva wrote:
>
> Dear Charles,
>
> Thank you so much for the reply. I am attaching a figure with the
> correct boundary conditions.
>
> My questions is:
>
> 1) What causes the high normal and shear stresses near the fault tip ?
>
> Would it be possible that there is something wrong on the way I am
> parameterizing the fault edge ? I have tried turning on the "edges"
> command on the set up but I still observe the high stresses.
>
> My simulation only runs for 15 years. At the end of the simulation there
> is no fault displacement. However, only the high stress values indicated
> above. I wonder if this behavior is normal because the failure criteria
> was not met ?
>
> Best,
> Josimar
>
>
>
>
>
>
>
> On Sun, Nov 6, 2016 at 1:25 PM, Charles Williams <willic3 at gmail.com
> <mailto:willic3 at gmail.com <willic3 at gmail.com>>> wrote:
>
>    Dear Josimar,
>
>    I am somewhat confused about your boundary conditions.  Are any
>    conditions being placed on the top and bottom boundaries?  Also, it
>    appears that you are applying Neumann BC on the left boundary,
>    rather than the fixed displacement BC shown in your figure.  Is this
>    correct, or is something mislabelled?
>
>    Cheers,
>    Charles
>
>
>    On 5/11/2016, at 11:24 AM, Josimar Alves da Silva
>    <jsilva.mit at gmail.com <mailto:jsilva.mit at gmail.com
> <jsilva.mit at gmail.com>>> wrote:
>
>    Dear All,
>
>    I am running PyLith with a 2D fault friction model, including
>    gravitational effects.
>
>    I am finding stress concentration near the tip of the fault and I
>    would like to understand why this occurs. See attached figure.
>
>    On the link below Brad seems to address this issue, however it is
>    still not clear to me why this happens.
>
>    http://lists.geodynamics.org/pipermail/cig-short/2014-
> November/001924.html
>    <http://lists.geodynamics.org/pipermail/cig-short/2014-
> November/001924.html>
>
>    Details about my simulation are attached (log files, boundary
>    conditions...)
>
>    Thank you in advance for your time.
>    Best,
>    Josimar
>    <pylith_problem.pdf><log.out>__________________________
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>
>    Charles A. Williams
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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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