[CIG-SHORT] Initial stress conditions

[Eric Lindsey]

OK, I think I've resolved it - you were right that the shear tractions in
the two cases were different; in the case of applied initial stresses, the
final shear stress throughout the domain (and on the fault) was close to
zero. So it seems that Pylith simply relaxed all the initial shear stress
before allowing the fault to slip, because I had a free-slip boundary on
one side.  I resolved this by adding an extra Neumann boundary condition on
that side to maintain the shear stress at the boundary. In retrospect this
is obvious, but somehow it wasn't intuitive to me how these two stress
conditions would interact.

Thanks again,
Eric



On Wed, Nov 6, 2013 at 1:31 PM, Brad Aagaard <baagaard at usgs.gov> wrote:

> Eric,
>
> You can examine the fault tractions to see if they are consistent between
> the case when you use BC and when you use an initial stress field. They
> should be the same if everything is setup consistently. This is what I have
> done for the SCEC dynamic spontaneous rupture benchmarks where I needed an
> initial stress field over the domain for an elastoplastic rheology.
>
> Regards,
> Brad
>
>
>
> On 11/06/2013 01:22 PM, Eric Lindsey wrote:
>
>> It seems I don't understand what the initial stress conditions imposed by
>>
>> [pylithapp.timedependent.materials.elastic]
>> db_initial_stress
>>
>> are doing. I've got a dynamic fault with static friction that will slip
>> when I impose Dirichlet or Neumann BC that introduce a large enough shear
>> stress (I took most of the configuration from
>> examples/3d/hex8/step11.cfg),
>> but if I impose these initial stresses instead of the extra boundary
>> conditions, I get no slip! What's going on here - am I misunderstanding
>> the
>> purpose of initial stress?
>>
>> Thanks,
>> Eric
>>
>>
>>
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