[CIG-SHORT] (no subject)

[Eunseo Choi]

Brad, thanks for the clarification!

Best regards,
Eunseo

On Thu, Aug 6, 2015 at 4:11 PM, Brad Aagaard <baagaard at usgs.gov> wrote:

> Eunseo,
>
> The stable time step in explicit time stepping comes from the CFL
> condition. With a viscoelastic material, the stability is reduced because
> the effective stiffness is higher at high frequencies.
>
> Regards,
> Brad
>
>
>
> On 08/06/2015 02:01 PM, Eunseo Choi wrote:
>
>> Thanks for the confirmation, Brad!
>>
>> I'll try a smaller time step but don't understand why it would work.
>> The time step I used was a stable one for the dynamic problem, ~0.01 sec,
>> which was already much smaller than relaxation times I tried, ~1 sec to ~1
>> year.
>>
>> Eunseo
>>
>>
>> On Thu, Aug 6, 2015 at 1:03 PM, Brad Aagaard <baagaard at usgs.gov> wrote:
>>
>> Eunseo,
>>>
>>> Attenuation for dynamic models is not yet implemented. This has been on
>>> the TODO list for a while but many other features have been a higher
>>> priority.
>>>
>>> If you try to use a viscoelastic model with a high viscosity, then you
>>> will likely need to reduce the time step. I am guessing that the
>>> instability you see is starting at a cell that is slightly more distorted
>>> so it has a smaller stable time step.
>>>
>>> Regards,
>>> Brad
>>>
>>>
>>> On 08/06/2015 09:17 AM, Eunseo Choi (echoi2) wrote:
>>>
>>> Can PyLith have attenuation in an explicit dynamic problem?
>>>>
>>>> I couldn't find how to do this anywhere in the v.2.1.0 manual.
>>>>
>>>>
>>>> So, I first tried MaxwellIsotropic3D expecting the relaxation effect
>>>> to do the job but even with a very high viscosity, an instability
>>>> kicks in around the boundary where a time-dependent traction BC is
>>>> applied. Maybe this material model works only in static or
>>>> quasi-static problems? Or is it more likely to be a mistake in my
>>>> problem setup?
>>>>
>>>>
>>>> I also read in PyLith's TO-DO list that the plan is to use the
>>>> generalized Maxwell model for attenuation. Is this the material model
>>>> I was supposed to use? Is it working in v.2.1.0 but just not being
>>>> discussed in the manual?
>>>>
>>>>
>>>> Thanks,
>>>>
>>>> Eunseo
>>>>
>>>>
>>>>
>>>>
>>>>
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>>
>>
>>
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