[CIG-SHORT] Smoothing Issues

[Charles Williams]

Dear Nick,

I can see several potential issues with your problem setup.  First, this is a fairly coarse mesh and it is too regular, which can cause problems.  The setup you are using could be prone to locking.  You should also have much finer resolution in the vicinity of your density contrast in the center.  Also, it is possible that the Poisson’s ratio you are using is too high.  Does the checkerboarding go away if you use a smaller value?  Finally, you probably want to extend your lower boundary to avoid edge effects.

Also, it appears to me that you have mixed up the names for upper_crust and lower_crust in your output filenames.

Do you have access to a meshing package such as Trelis or Cubit?  I believe it might be easier to obtain a better mesh that way.  Interestingly, when you use the mesh quality filter in Paraview on your mesh (using condition number for tets), there is a checkerboard pattern that somewhat mimics the stress pattern you see.  This may also be affecting your solution.

Cheers,
Charles

> On 26/10/2016, at 10:10 AM, Nick Wogan <nicholaswogan at gmail.com> wrote:
> 
> Thank you very much for the feedback,
> 
> Attached is config/mesh/spacialdb file, and an image that provides a cross-section of the model giving material properties. I am using unusual material properties. Large parts of the model are youngs mod = 0.1 and Poisson's Ratio = 0.49
> 
> The problem is as follows. There is an upper crust that has typical elastic material properties, and a lower crust that has young's mod = 0.1 and Poisson's Ratio = 0.49. In the center top of the upper crust there is a small chunk of low density. The displacement output looks great, only the stress output looks checkered in certain areas.
> 
> I checked the quality of the mesh. Here is the Lagrit output:
> 
> epsilon1, epsilonaspect: 4.6113656E-11  9.8059273E-32
> elements with aspect ratio < .01:                      0
> elements with aspect ratio b/w .01 and .02:      0
> ...
> elements with aspect ration b/w .2 and .5 :       0
> elements with aspect ratio b/w .5 and 1. :         314844
> min aspect ratio = 0.3795E+00     max aspect ratio = 0.7107E+00
> 
> Thanks you again,
> Nick
> 
> 
> ​
>  Checkered.zip <https://drive.google.com/file/d/0BxnRdwFIDyn5U01aZEYzUURrSzg/view?usp=drive_web>​
> 
> On Wed, Oct 19, 2016 at 4:40 PM, Nick Wogan <nicholaswogan at gmail.com <mailto:nicholaswogan at gmail.com>> wrote:
> Hi Pylith,
> 
> I am having issues with the Pylith output lacking smoothness. It is very clear in the attached photo plotting stress_zz that there are large jumps in stress that are unexpected. Is this "checker-boarding" something that can be fixed?
> 
> Let me know if I should send the mesh, cfg, spacialdb files.
> 
> Thanks!
> 
> Nick Wogan
> Research Assistant
> University of Oregon
> 
> <Setup.png>_______________________________________________
> CIG-SHORT mailing list
> CIG-SHORT at geodynamics.org
> http://lists.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 <mailto:C.Williams at gns.cri.nz>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.geodynamics.org/pipermail/cig-short/attachments/20161026/94c8f22b/attachment.html>