[CIG-SHORT] Convergence problem with Neumann BCs

[Eric Lindsey]

Hi,

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?)

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

...
499 KSP Residual norm 9.952574507238e-04
500 KSP Residual norm 9.952555275971e-04
Linear solve did not converge due to DIVERGED_ITS iterations 500

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.

Thanks,
Eric
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