[CIG-SHORT] Stress concentration near the fault tip

[Charles Williams]

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 <mailto: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>
>> <mailto:willic3 at gmail.com <mailto: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> <mailto:jsilva.mit at gmail.com <mailto: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>
>>>    <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>_______________________________________________
>>>    CIG-SHORT mailing list
>>>    CIG-SHORT at geodynamics.org <mailto:CIG-SHORT at geodynamics.org> <mailto:CIG-SHORT at geodynamics.org <mailto:CIG-SHORT at geodynamics.org>>
>>>    http://lists.geodynamics.org/cgi-bin/mailman/listinfo/cig-short <http://lists.geodynamics.org/cgi-bin/mailman/listinfo/cig-short>
>>>    <http://lists.geodynamics.org/cgi-bin/mailman/listinfo/cig-short <http://lists.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 <mailto:C.Williams at gns.cri.nz> <mailto: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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