[CIG-SHORT] Dynamic faulting under gravity

Sun Nov 25 18:36:24 PST 2012

Hi Brad

Now, I simplified my grid to have a maximum condition number of 1.09. Still, it does not converge with a displacement of -2 cm on the +x face.

I have attached the 3 files.

Thanks
Birendra

--- On Mon, 11/26/12, Brad Aagaard <baagaard at usgs.gov> wrote:

> From: Brad Aagaard <baagaard at usgs.gov>
> Subject: Re: [CIG-SHORT] Dynamic faulting under gravity
> To: cig-short at geodynamics.org
> Date: Monday, November 26, 2012, 5:14 AM
> Birendra,
> 
> A condition number of 12 is very large and is likely a
> significant 
> factor in the poor rate of convergence. You have two general
> options for 
> trying to resolve very small scale geometric features: (1)
> create a mesh 
> that resolves those features (and hopefully coarsens with
> distance) or 
> (2) switch to adaptive mesh refinement methods.
> 
> For (1) you should switch to an unstructured mesh. Using a
> structured 
> mesh would be inappropriate because it would use so much
> memory. For (2) 
> I would recommend switching to deal.II.
> 
> The refine meshing feature in PyLith refines an entire mesh
> uniformly.
> 
> Regards,
> Brad
> 
> 
> On 11/25/2012 03:36 PM, Birendra jha wrote:
> > 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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> > CIG-SHORT at geodynamics.org
> > http://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
> >
> >
> >
> > _______________________________________________
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> > CIG-SHORT at geodynamics.org
> > http://geodynamics.org/cgi-bin/mailman/listinfo/cig-short
> >
> 
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