[CIG-SHORT] Dynamic faulting under gravity

Sun Nov 25 15:36:20 PST 2012

Hi Charles

Max. is around 12. I guess it has to be close to 1 or 2. Is that the only reason for nonconvergence of the nonlinear solver? 

CUBIT> quality volume all Condition No. global
 Hex quality, 24360 elements:
------------------------------------
   Function Name    Average      Std Dev      Minimum   (id)    Maximum  (id)
 -----------------  ---------    ---------    --------------    -------------
   Condition No.    1.118e+00    3.692e-01    1.000e+00 (2846)    1.231e+01 (24023)

In that case, I have no option but to refine the mesh throughout which will give me a huge number of cells. Then I won't be able to run it on my machine, for sure.

Can I use Pylith's refine mesh capability to help me here? Can it refine selectively in one material region?

Thanks and regards
Birendra

--- On Mon, 11/26/12, Charles Williams <willic3 at gmail.com> wrote:

From: Charles Williams <willic3 at gmail.com>
Subject: Re: [CIG-SHORT] Dynamic faulting under gravity
To: "Birendra jha" <bjha7333 at yahoo.com>
Cc: cig-short at geodynamics.org
Date: Monday, November 26, 2012, 3:32 AM

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
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