[CIG-LONG] FW: Convergence issues with long-term extension models
Tim Rawling
tim at modeltheearth.com
Fri Mar 12 20:54:21 PST 2010
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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