You should first try with a direct solver (hopefully the problem is small enough),<br>--petsc.pc_type=lu --petsc.ksp_type=preonly<br><br> Matt<br><br><div class="gmail_quote">On Wed, Dec 10, 2008 at 10:49 AM, Tabrez Ali <span dir="ltr"><<a href="mailto:stali@purdue.edu">stali@purdue.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Brad/Charles<br>
<br>
Thanks for your reply. Yes the residuals do increase after each time<br>
step. I have a low dipping fault which curves from very shallow dip to<br>
somewhat steeper dip (as in shallow subduction).<br>
<br>
If I specify slip on the steeper part then things work fine. Things also<br>
work fine when I dont specify slip on this particular fault but have<br>
other faults/BC's in place (on the same mesh).<br>
<br>
Its slip on the shallow part which seems to mess it up.<br>
<br>
Also my mesh quality isnt that bad. I do have a few elements with aspect<br>
ratios of 50+ (in cubit) but nothing greater than 100. And my material<br>
property for the fault is the same as used in the examples/benchmarks.<br>
<br>
Regards<br>
<font color="#888888">Tabrez<br>
</font><div><div></div><div class="Wj3C7c"><br>
Brad Aagaard wrote:<br>
> Tabrez-<br>
><br>
> Does the solution blow up (residual increases) or just fail to converge<br>
> (residual approaches some value)? If the solution blows up, something is<br>
> wrong. Either the problem is not setup correctly or there is a bug.<br>
><br>
> There are a number of things that can cause the solution to converge very<br>
> slowly. In addition to the mesh quality issue that Charles pointed out, some<br>
> other things you might look into include:<br>
><br>
> (1) Do you get the same behavior with a coarser mesh?<br>
><br>
> (2) Does the solution converge when you omit the fault in the parameters<br>
> (i.e., use the same mesh but don't have any fault interface conditions)? If<br>
> you have zero displacement BC, try simple compression without a fault.<br>
><br>
> (3) What is Poisson's ratio? Do any cells have a Poisson ratio greater than<br>
> 0.45 (only values greater than about 0.48 should cause problems)?<br>
><br>
> (4) What physical properties are you using for the fault (this affects the<br>
> conditioning of the system and can affect convergence if they are not<br>
> reasonable)? In a test problem, the solution converged slightly faster for<br>
> uniform physical properties for the fault (only used to condition the system)<br>
> compared with the actual 3-D variation.<br>
><br>
> Brad<br>
><br>
><br>
> On Wednesday 10 December 2008 12:05:31 am Charles Williams wrote:<br>
><br>
>> I would look at the element quality in the mesh. You can do this in<br>
>> ParaView. The low angles may be giving you poorly-formed elements,<br>
>> and this could cause problems. I doubt that incorrect fault<br>
>> parameters is causing the problem, unless you're doing something<br>
>> that's giving you very large strains.<br>
>><br>
>> Charles<br>
>><br>
>> On Dec 10, 2008, at 6:43 PM, Tabrez Ali wrote:<br>
>><br>
>>> Brad/PyLith Users<br>
>>><br>
>>> It seems that whenever I use a low angle thrust fault (very low dip)<br>
>>> the<br>
>>> solution (to the quasi-static problem) after a certain number of time<br>
>>> steps fails to converge and blows up. Can wrong fault parameters<br>
>>> such as<br>
>>> up_dir or normal_dir also cause this?<br>
>>><br>
>>> Regards<br>
>>> Tabrez<br>
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>>><br>
>> Charles A. Williams<br>
>> Scientist<br>
>> GNS Science<br>
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>><br>
><br>
><br>
><br>
<br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>
-- Norbert Wiener<br>