[CIG-SHORT] Dynamic faulting under gravity

[Charles Williams]

Hi Birendra,

What sort of maximum condition number values are you getting?  There still appear to be some very flat cells in your mesh.

Cheers,
Charles


On 25/11/2012, at 5:53 PM, Birendra jha wrote:

> Hi all
> 
> I removed gravity (and initial stress), improved the aspect ratio of my grid (condition number is much better now), still the nonlinear solver is not converging (linear solver converges in <50 iterations). SNES Function Norm decreases for first 2 iterations then increases (from 2.8E-02 to 3.08E-02 in 4 iterations).
> 
> I have the attached the 3 files necessary to run the problem.
> 
> Problem description: a slanted fault in a box domain. Dynamic fault. Static friction model with 0 cohesion.
> Boundary condition: roller boundary on -x, +y, -y. Dirichlet displacement on +x of -1 cm to apply compression on the fault.
> 
> Please help!
> 
> Thanks and regards
> Birendra
> 
> --- On Thu, 11/22/12, Brad Aagaard <baagaard at usgs.gov> wrote:
> 
>> From: Brad Aagaard <baagaard at usgs.gov>
>> Subject: Re: Dynamic faulting under gravity
>> To: "Birendra jha" <bjha7333 at yahoo.com>
>> Cc: cig-short at geodynamics.org
>> Date: Thursday, November 22, 2012, 3:18 AM
>> Birendra,
>> 
>> You have very flat hex cells in your mesh. This results in a
>> very poorly 
>> conditioned system. I think this prevents getting a decent
>> guess for the 
>> slip, so the nonlinear solve fails to converge.
>> 
>> It looks like you are trying to resolve very small scale
>> geometric 
>> features with a coarse hexahedral mesh. I think you will
>> need a mesh 
>> with much closer to cube-like cells to get the nonlinear
>> solve to converge.
>> 
>> Regards,
>> Brad
>> 
>> 
>> On 11/20/2012 11:32 AM, Birendra jha wrote:
>>> Hi,
>>> 
>>> With that, the linear solver converges but nonlinear
>> solver didn't converge in 100 iterations.
>>> To improve the gravity modeling, I also modified the
>> boundary conditions such that now I have zero normal
>> displacement on +x,-x,+y,-y,-z faces except the fault nodes
>> on +y,-y,-z faces. With this setup, in absence of fault
>> model in pylith, the case runs fine with almost 0
>> displacement everywhere except on the fault nodes which are
>> free. This is as expected. But with fault friction, it does
>> not converge. The unconverged solution also shows large
>> displacements on the fault nodes, I am just not sure if the
>> numbers are accurate.
>>> 
>>> The modified files are attached.
>>> 
>>> Thanks
>>> Birendra
>>> 
>>> --- On Tue, 11/20/12, Brad Aagaard <baagaard at usgs.gov>
>> wrote:
>>> 
>>>> From: Brad Aagaard <baagaard at usgs.gov>
>>>> Subject: Re: Dynamic faulting under gravity
>>>> To: "Birendra jha" <bjha7333 at yahoo.com>
>>>> Cc: cig-short at geodynamics.org
>>>> Date: Tuesday, November 20, 2012, 10:28 PM
>>>> Birendra,
>>>> 
>>>> The linear solve did not converge. If the linear
>> solves
>>>> within the
>>>> nonlinear solve doesn't converge, the nonlinear
>> solve won't
>>>> converge.
>>>> You are using ASM for the preconditioner. Try using
>> the
>>>> field split
>>>> preconditioner with ML on the elastic part and the
>> custom
>>>> fault
>>>> preconditioner. See examples/3d/tet4/step04 for
>> PETSc
>>>> settings.
>>>> 
>>>> Brad
>>>> 
>>>> On 11/19/2012 09:36 PM, Birendra jha wrote:
>>>>> Dear all
>>>>> 
>>>>> I have a relatively simple case of a slanted
>> fault
>>>> plane (along y axis) inside a layered box. I am
>> using
>>>> FaultCohesiveDyn with static friction model (please
>> see the
>>>> attached file). +x, -x boundaries are fixed in x,y
>>>> directions and bottom is fixed in z direction. y
>> faces are
>>>> free.
>>>>> I have gravity on and I use
>> initial_stress.spatialdb
>>>> with a density of 2400 kg/m3.
>>>>> 
>>>>> The nonlinear solver is not converging. Can you
>> please
>>>> help? What am I missing? There are four thin layers
>> in the
>>>> grid sandwiched between thick layers above and
>> below. Is
>>>> that the problem?
>>>>> 
>>>>> I am using the Pylith 1.8.0 windows binary.
>>>>> 
>>>>> Thanks and regards
>>>>> Birendra
>>>>> 
>>>> 
>>>> 
>>> 
>> 
> <faultedgrid3.zip>_______________________________________________
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Charles A. Williams
Scientist
GNS Science
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PO Box 30368
Lower Hutt  5040
New Zealand
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C.Williams at gns.cri.nz

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