[CIG-SHORT] Initial stress conditions

[Eric Lindsey]

Thanks, I think that's a good idea to write it out. I'm learning to be more
careful in setting these models up!

Eric


On Wed, Nov 6, 2013 at 3:47 PM, Brad Aagaard <baagaard at usgs.gov> wrote:

> Eric,
>
> I will look at the manual to see if we can improve the description of
> using the initial stresses.
>
> My recommended approach is to write down the stress field in the domain
> and make sure your BC are consistent. Then check the stress and fault
> traction output to make sure they are consistent with what you set as
> parameters. If they don't agree, then something is wrong in the simulation
> setup. Carefully examining all the various diagnostic output is how I catch
> most of my errors in setting up simulations.
>
> Regards,
> Brad
>
>
>
> On 11/06/2013 03:34 PM, Eric Lindsey wrote:
>
>> 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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>>
>>
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