<div dir="ltr">On Thu, Oct 31, 2013 at 7:21 PM, Eric Lindsey <span dir="ltr"><<a href="mailto:elindsey@ucsd.edu" target="_blank">elindsey@ucsd.edu</a>></span> wrote:<br><div class="gmail_extra"><div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>Thanks very much for the help everyone.</div><div><br></div><div>Brad and Charles, thanks for pointing out the ill-posedness, I hadn't thought this through properly. After adding back some Dirichlet BC the solver does converge, in ~400 iterations. Thanks!</div>
<div><br></div><div>The initial stress field also works nicely. In this case I just want uniform compression and shear stress, so I can impose it with a simple spatialDB with just the 3 components; I believe this is compatible with the Airy stress function. I had some confusion getting the other boundary conditions to be compatible with this setup as you mentioned, but think I've got it worked out -- the two sides with no Dirichlet BC need a Neumann condition to maintain the initial normal stress.</div>
<div><br></div><div>Matt, I'm just using the linux binary package (1.9.0) -- but I grabbed a clone from git, and tried out these solvers. They both converged in only 3-5 iterations, but run much slower (~2min instead of ~1sec). I'm not sure what the metric is for a "better" solver I guess?</div>
</div></blockquote><div><br></div><div>For any performance question, you need to send</div><div><br></div><div> a) The output of --petsc.log_summary</div><div><br></div><div> b) The output of --petsc.ksp_view</div><div>
<br></div><div> c) The output of --petsc.ksp_monitor</div><div><br></div><div>So there are slides that go with the files that explain the options. I find 2min and 1s hard to believe. You can always</div><div>try them on the same benchmark problems that we used in the paper.</div>
<div><br></div><div> Thanks,</div><div><br></div><div> Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>Thanks,</div><div>
Eric</div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Thu, Oct 31, 2013 at 1:12 PM, Charles Williams <span dir="ltr"><<a href="mailto:willic3@gmail.com" target="_blank">willic3@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">Hi Eric,<div><br></div><div>Sorry to be slow in responding. I just had a look at your problem, and it appears that you have changed all the BC to Neumann, which means that your displacements are completely unconstrained. This is an ill-posed problem, and I wouldn't expect it to work. I'm not quite sure what you're trying to represent, but I'm wondering whether initial stresses might be what you want. Alternatively, you need to pin at least 3 DOF (to prevent translation/rotation). Usually, with traction BC there is some sort of symmetry, so you could probably fix one of your boundaries. I'm assuming your traction variations aren't that complicated, however, which means you could use an Airy stress function to describe the stresses within the domain (see, for example, the elasticity book by Timoshenko). Your displacement BC would have to be compatible, though.</div>
<div><br></div><div>Cheers,</div><div>Charles</div><div><br></div><div><br><div><div><div><div>On 31/10/2013, at 11:43 AM, Eric Lindsey wrote:</div><br></div></div><blockquote type="cite"><div><div><div dir="ltr">
<div>Hi,</div><div><br></div><div>I'd like to apply background stresses to a simple elastic 2D plane strain model in pylith, then add fault slip or other quasistatic deformation; later I'll modify the material properties etc. Of course the stresses also cause some deformation in the volume that I'd like to ignore. So I'm imposing the slip at the second time step, with the hopes of subtracting out the deformation from the first time step. (Is this the right way to do this?)</div>
<div><br></div><div>However, I noticed that the effects from the boundary conditions continue to increase, and then oscillate, and don't stabilize until I let it run to the 8th step or so (ideally I'd only use 2 time steps, I think). I think the problem is with the solver's convergence; I see the message </div>
<div><br></div><div>...</div><div>499 KSP Residual norm 9.952574507238e-04</div><div>500 KSP Residual norm 9.952555275971e-04</div><div>Linear solve did not converge due to DIVERGED_ITS iterations 500</div><div><br></div>
<div>I've taken most of the configuration straight from examples/2d/greensfns/strikeslip, and just modified the boundary conditions from Dirichlet to Neumann. Config file is attached; any advice would be great.</div>
<div>
<br></div><div>Thanks,</div><div>Eric</div><div><br></div></div>
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