[CIG-LONG] FW: Convergence issues with long-term extension models
Tim Rawling
tim at modeltheearth.com
Sat Mar 13 13:49:44 PST 2010
Hi cig-long group
sorry for the email I sent earlier, I meant for it to go just to Gilly
but I am happy for any suggestions from the group. I am new to using
Gale but have been working with Gilly on some problems related to
collision and closure of asymmetric basins constrained by some deep
reflection seismic we acquired recently. I am now extending the work
Gilly did a little by looking at how the variation in rheology of that
accreted basement may have effected the geometry of a subsequent
extensional event.
I am currently trying to set up a model that has a pre-existing
weakness that cuts diagonally across the model volume (a relay fault if
you like). The shape would intersect the model front and right
boundaries but not the back or left boundaries. Is it possible to
create a shape like this in 3D using PolygonShape or is there are
better way to do it that anyone can suggest?
Cheers and thanks
Tim
---------------------------------------------
Dr Tim Rawling
Manager Earth Systems Modelling
GeoScience Victoria
Dreams of mountains as in their
sleep they brood on things eternal
---------------------------------------------
On Sat, 13 Mar 2010 15:54:21 +1100
Tim Rawling <tim at modeltheearth.com> wrote:
> Hi Gilly
>
> I hope you are well?
>
> I am still playing with Gale and am starting to get my head around it
> a bit. I would be keen to have a chat with you at some stage if you
> have some time to make sure what I am doing is appropriate and fits
> with the work you did with us. Ill also send you a copy of a talk I
> have put together that I think we could elaborate on in "that" paper
> we have spoken about to give you an idea where I am going with it.
>
> I do have a question for you about this email you sent to the Gale
> list though too. Is the compressible material just so that Gale does
> not have compute the failure on a model boundary? Does it matter how
> thick it is?
>
> Also did you use the PolygonShape argument to create the diverging
> crustal blocks in the Y-direction in the model you did for us?
>
> Cheers and thanks
> Tim
>
> On Thu, 11 Mar 2010 10:03:21 +0800
> <Guillaume.Duclaux at csiro.au> wrote:
>
> > Here is my reply to John.
> >
> >
> > ________________________________
> > From: Duclaux, Guillaume (CESRE, Kensington)
> > Sent: Thursday, 11 March 2010 9:06 AM
> > To: 'John Naliboff'
> > Cc: nicolas.riel at free.fr
> > Subject: RE: [CIG-LONG] Convergence issues with long-term extension
> > models
> >
> > Hi John,
> >
> > There's a hidden magical compressibility function in
> > Gale/Underworld.
> >
> > In the component part of your script, create a new shape (let say
> > called "compressibleShape") at the top of the model, then define
> > it's rheology and mechanical properties.
> >
> > You can create a new viscosity. As you suggested, a low viscosity
> > works. You may have to do some testing. In case your model
> > resolution is too low, you'll find an instability between the
> > compressible layer and the upper crust with particles "flying'
> > upward.
> >
> > <struct name="compressibleViscous">
> > <param name="Type">MaterialViscosity</param>
> > <param name="eta0">1e-4</param>
> > </struct>
> >
> > Then define the compressibility function:
> >
> > <struct name="compresibility">
> > <param name="Type">Compressible</param>
> > <param name="GeometryMesh">mesh-linear</param>
> > <param name="StiffnessMatrix">c_matrix</param>
> > <param name="Swarm">picIntegrationPoints</param>
> > <param name="oneOnLambda">10.0</param> <!-this is
> > the 'compressibility factor, 1/lambda. It has to be set between 0
> > and 10. As a rule of thumb, the larger 1/lambda (ie 10), the more
> > compressible --> </struct>
> >
> > and apply the compressible material properties to the
> > compressibleShape material:
> >
> > <struct name="compressibleRheology">
> > <param name="Type">RheologyMaterial</param>
> > <param name="Shape">compressibleShape</param>
> > <param name="density">XX</param> <!-do some testing, but 0
> > works usually fine --> <list name="Rheology">
> > <param>compressibleViscous</param>
> > <!-- <param>storeViscosity</param>
> > <param>storeStress</param> --> <!-this is optional, dunno if
> > you're outputting Stress and Viscosity for the particles --> </list>
> > <param name="Compressible">compresibility</param>
> > </struct>
> >
> > Ge it a shot, and let me know if you have any trouble with this
> > function.
> >
> > Cheers
> >
> > Gilly
> > ________________________________________________
> >
> > Dr Guillaume Duclaux
> > CSIRO Earth Science and Resource Engineering
> > Visiting address: ARRC, 26 Dick Perry Av., Kensington WA 6151
> > Postal address: PO Box 1130, Bentley WA 6102, Australia
> > Ph: + 61 8 6436 8728 Fax: + 61 8 6436 8555 Web:
> > www.csiro.au<http://www.csiro.au>
> >
> > ________________________________
> > From: John Naliboff [mailto:jbnaliboff at gmail.com] On Behalf Of John
> > Naliboff Sent: Thursday, 11 March 2010 8:29 AM
> > To: Duclaux, Guillaume (CESRE, Kensington)
> > Cc: nicolas.riel at free.fr
> > Subject: Re: [CIG-LONG] Convergence issues with long-term extension
> > models
> >
> > Hi again Gilly,
> >
> > Apologies for the second email.
> >
> > When implementing the compressible layer, did you simply specify a
> > low-viscosity/low-density region and then not subtract the
> > hydrostatic term from this region (i.e. hydrostatic term still
> > subtracted from the lithosphere)?
> >
> > This is the only way I could think of to create a quasi-compressible
> > layer with the current version of Gale (1.4.1). If used another
> > method to create the compressible layer, however, any tips would be
> > great!
> >
> > Cheers,
> > John
> >
> >
> >
> > On Mar 10, 2010, at 9:32 AM, John Naliboff wrote:
> >
> >
> > Hi Gilly,
> >
> > Thanks for the suggestion and I'll give the compressible layer a
> > shot today!
> >
> > John
> >
> >
> > On Mar 10, 2010, at 12:20 AM,
> > <Guillaume.Duclaux at csiro.au<mailto:Guillaume.Duclaux at csiro.au>>
> > wrote:
> >
> >
> > Hi John,
> >
> > Have you tried adding a compressible layer at the surface of the
> > model?
> >
> > Nicolas Riel and I ran some extension models recently and found out
> > that the only way to achieve large deformation is to use such
> > compressible layer.
> >
> > The initial geometry of the model is as follow with the compressible
> > layer in red:
> >
> > <image003.jpg>
> >
> > so you can extend the model quite extensively (the compressible has
> > been removed for visualisation)
> >
> > <image004.jpg>
> >
> > Give it a go!
> >
> > Cheers
> >
> > gilly
> >
> > ________________________________________________
> >
> > Dr Guillaume Duclaux
> > CSIRO Earth Science and Resource Engineering
> > Visiting address: ARRC, 26 Dick Perry Av., Kensington WA 6151
> > Postal address: PO Box 1130, Bentley WA 6102, Australia
> > Ph: + 61 8 6436 8728 Fax: + 61 8 6436 8555 Web:
> > www.csiro.au<http://www.csiro.au/>
> >
> >
> >
> > ________________________________
> > From:
> > cig-long-bounces at geodynamics.org<mailto:cig-long-bounces at geodynamics.org>
> > [mailto:cig-long-bounces at geodynamics.org] On Behalf Of John Naliboff
> > Sent: Wednesday, 10 March 2010 3:03 PM To:
> > cig-long at geodynamics.org<mailto:cig-long at geodynamics.org> Subject:
> > [CIG-LONG] Convergence issues with long-term extension models Hello
> > all,
> >
> > I'm hoping to get some input on convergence problems I'm having with
> > 2D long-term extension models.
> >
> > The models are designed following Wijns et al. 2005 (EPSL), who
> > modeled extension of a brittle upper crust overlying a viscous lower
> > crust using Underworld. The initial geometry is 160 km (width) x 60
> > km (depth) and the upper crust follows a yielding law similar to the
> > DruckerPrager yield criterion. The boundary conditions are
> > free-slip on all sides, although a weak, low-density layer is
> > present above the upper crust (i.e. top of lithosphere should
> > behave in a similar fashion to a true free-surface). Extension is
> > driven by a fixed velocity of 3 cm/yr applied to the right side of
> > the 2D box. The models in the paper are run up to roughly 80%
> > extension (~ 4 Myr).
> >
> > The simulations I'm running mimic the models above very closely,
> > although I'm using an upper free-surface rather than placing a weak,
> > low-density layer above the upper crust and specifying free-slip on
> > the top boundary.
> >
> > In short, the problem I'm encountering reproducing the long-term
> > extension models is that my simulations stop converging after ~ 1-2
> > Myr (~ 25%-40% extension). In terms of specific error messages, the
> > problem is almost always related to the Stokes Uzawa Solver (ex:
> > uzawaRhsScale has illegal value 'inf', etc).
> >
> > In terms of the model output, by 1-2 Myr very large strain rate
> > gradients have developed at the model surface roughly following
> > horst and grabben structures. I think this may be the source of the
> > convergence issue, but at this point I'm really not certain.
> >
> > After initially having convergence issues with a resolution of 1 km
> > and 30 particles per cell (ppc), I systematically increased the
> > resolution up 0.25 km with 60 ppc, but all the models still stopped
> > converging between 1-2 Myr. I also tried decreasing the time step by
> > 2 (dtFactor = 0.5) and turning off the pressure and velocity
> > interpolation onto the new mesh, neither of which had any
> > significant effect on the total run time before the models stopped
> > converging. In all of the cases above I used the MUMPS solver,
> > which performed better than the default solver.
> >
> > The convergence issue is also not likely related to the specific
> > upper crustal yielding rheology, as I've tried both DruckerPrager,
> > VonMises and the yielding law used in the Wijns et al. models.
> >
> > Finally, I tried using a free-slip top boundary with a weak,
> > low-density layer above the upper crust, but this produced a whole
> > different set of issues.
> >
> > Thanks in advance to anyone who has some ideas/input on the
> > convergence issues and I've attached a sample input file (resolution
> > = 0.5 km, ppc = 60) if that helps at all.
> >
> > Cheers,
> > John Naliboff
> >
> >
>
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