[CIG-SHORT] Dynamic faulting under gravity

[Brad Aagaard]

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
>>>
>>
>>
>