[CIG-SHORT] Question about accuracy in Pylith
Brad Aagaard
baagaard at usgs.gov
Fri Oct 14 12:05:55 PDT 2016
Demian,
For a quasi-static problem the global accuracy of the solution should
not be controlled by the worse cells. You should aim for a condition
number of about 2.0 or less. I strongly recommend using ParaView to see
if there is a correlation between condition number (or aspect ratio) and
the local fluctuations in stress/strain that you see. If there is a
correlation, this should tell you what condition number to aim for.
Regards,
Brad
On 10/14/2016 11:58 AM, Demian Gomez wrote:
> Hi Brad,
>
> Thanks. Here's the output for the mesh quality:
>
> Tet quality, 3297540 elements:
>
> Condition No. ranges from 1.000e+00 to 4.650e+00 (3297540 entities)
>
> Red ranges from 4.128e+00 to 4.650e+00 (3 entities)
>
> Magenta ranges from 3.607e+00 to 4.128e+00 (69 entities)
>
> DkYellow ranges from 3.086e+00 to 3.607e+00 (196 entities)
>
> Yellow ranges from 2.564e+00 to 3.086e+00 (862 entities)
>
> Green ranges from 2.043e+00 to 2.564e+00 (4427 entities)
>
> Cyan ranges from 1.521e+00 to 2.043e+00 (75597 entities)
>
> Blue ranges from 1.000e+00 to 1.521e+00 (3216386 entities)
>
>
> The highest Co. number is 4.65 and there are only 3 elements, mostly on
> the edges. Can this distort all the solution? Also, although we want all
> the elements to be as close to 1 as possible, is there an acceptable
> range limit?
>
>
> Thank you,
>
> Demián
>
>
> --
> *Dr. Demián D. Gómez*
> Postdoctoral Researcher
> The Ohio State University - School of Earth Sciences
> 275 Mendenhall Laboratory
> 125 South Oval Mall
> Columbus, Ohio 43210
> Cell: +1 (901) 900-7324
> email: gomez.124 at osu.edu <mailto:gomez.124 at osu.edu>
>
>
> On Fri, Oct 14, 2016 at 2:28 PM, Brad Aagaard <baagaard at usgs.gov
> <mailto:baagaard at usgs.gov>> wrote:
>
> Demian,
>
> Have you looked at mesh quality (aspect and condition numbers close
> to 1.0)? Distorted cells (slivers, squashed tets, etc) will be
> stiffer and may cause local stress/strain concentrations. My guess
> is that your 2-D mesh has better quality. Look to see if there is a
> correlation between condition number or aspect ratio and the kinks,
> etc in your stress field (you can do this in ParaView). If so, then
> spend some time playing with the bias value, cell size, and
> smoothing to improve the mesh quality.
>
> Regards,
> Brad
>
>
>
> On 10/14/2016 11:17 AM, Demian Gomez wrote:
>
> Dear Brad, Matt and Charles,
>
> I have a question regarding the accuracy of the solution using
> tets. I
> have a model with a biased tet mesh (4 km at the fault and 160
> km at the
> edges, ~2200 km away) from which I am trying to get the strain and
> stress on some depth profiles at ~ 400 km from the fault. I am
> running
> Pylith with the refiner on (only one level) to refine my mesh and
> improve the resolution.
>
> The problem I'm having is that when I plot the strains and
> stresses, the
> plots are very "noisy" (see profiles_70.png). The displacement
> looks ok,
> maybe a few bumps and kinks here and there, but acceptable. I think
> these small displacement kinks are translating into the "noise" and
> larger kinks in strain and stress. I did tests in 2D (on a cross
> section
> of my 3D model) to figure out the best discretization size, and
> if I use
> a mesh with constant element size (say, 1 km), then everything
> is smooth
> and nice (see profiles_70_2D.png). However, a 3D model of the
> size that
> I need meshed with 1 km elements is huge and very impractical.
> Moreover,
> there shouldn't be any problems with using a biased mesh since
> there are
> examples within Pylith were you guys use this type of mesh.
>
> I know that I can improve the accuracy by using hexes, but
> unfortunately
> I've been trying to mesh my model with hexes (in Trelis) without any
> success. The model has the shape of a spherical cap and
> apparently there
> is something that Trelis doesn't like about this geometry. No
> matter how
> I divide and subdivide the model to help the mesher, there is
> always one
> volume that I cannot mesh. With tets, however, it works fine.
>
> Do you have any suggestions on what can I try to improve these
> results,
> without increasing the number of elements? I am at the limit of
> resources in terms of the model size (right now I'm at 125 GB of
> required memory to run my model). I could start using the HPC but it
> seems that there should be another way to solve this problem
> other than
> "brute force", i.e. making the model larger and using a bigger
> computer.
> You may also have suggestions regarding the meshing process. I would
> appreciate any advise that can help me to solve my problem. Let
> me know
> if there is any additional information you may need that I did
> not include.
>
> Cheers,
> Demián
>
> PS: I've attached the cfg files, just in case you want to see
> how I'm
> running the problem.
>
> --
> *Dr. Demián D. Gómez*
> Postdoctoral Researcher
> The Ohio State University - School of Earth Sciences
> 275 Mendenhall Laboratory
> 125 South Oval Mall
> Columbus, Ohio 43210
> Cell: +1 (901) 900-7324 <tel:%2B1%20%28901%29%20900-7324>
> email: gomez.124 at osu.edu <mailto:gomez.124 at osu.edu>
> <mailto:gomez.124 at osu.edu <mailto:gomez.124 at osu.edu>>
>
>
>
> _______________________________________________
> CIG-SHORT mailing list
> CIG-SHORT at geodynamics.org <mailto:CIG-SHORT at geodynamics.org>
> http://lists.geodynamics.org/cgi-bin/mailman/listinfo/cig-short
> <http://lists.geodynamics.org/cgi-bin/mailman/listinfo/cig-short>
>
>
> _______________________________________________
> CIG-SHORT mailing list
> CIG-SHORT at geodynamics.org <mailto:CIG-SHORT at geodynamics.org>
> http://lists.geodynamics.org/cgi-bin/mailman/listinfo/cig-short
> <http://lists.geodynamics.org/cgi-bin/mailman/listinfo/cig-short>
>
>
>
>
> _______________________________________________
> CIG-SHORT mailing list
> CIG-SHORT at geodynamics.org
> http://lists.geodynamics.org/cgi-bin/mailman/listinfo/cig-short
>
More information about the CIG-SHORT
mailing list