[CIG-SEISMO] anti-damping in viscoelastic simulation, it crashes

[Yingzi Ying]

Dear Dimitri,

Thanks for explaining.

Yes, the PDE would be a different type. I tried to use Qs=60 and 
recorded the signal just for a very short time period. That running did 
not blow up. It was quite strange.

I will investigate another one or two cases. I may give up if it does 
not work finally.

Great thanks & Best regards,
Yingzi
On 10/20/2015 03:36 PM, Dimitri Komatitsch wrote:
>
> Dear Yingzi,
>
> PS (important): that is unrelated to SPECFEM, it would be true in any
> other explicit time scheme and related code as well.
>
> Best regards,
> Dimitri.
>
> On 10/20/2015 04:35 PM, Dimitri Komatitsch wrote:
>>
>> Dear Yingzi,
>>
>> Unfortunately that is known for being unconditionally unstable
>> (mathematically), i.e. impossible; when you amplify the signal you also
>> amplify the noise and the scheme quickly blows up.
>>
>> Best regards,
>> Dimitri.
>>
>> On 10/20/2015 03:23 PM, Yingzi Ying wrote:
>>> Dear Dimitri and All,
>>>
>>> I am going to realise a function in viscoelastic simulation with
>>> SPECFEM2D. I would like to build an anti-damping material, in which the
>>> wave amplitude can increase rather than decrease during propagation,
>>> i.e., an inverse process of visco-attenuation. Such processing is
>>> physically meaningless but might be useful in signal processing.
>>>
>>> I added following 3 lines in "compute_forces_viscoelastic.F90"
>>>
>>> e1_sum  = -e1_sum
>>> e11_sum = -e11_sum
>>> e13_sum = -e13_sum
>>>
>>> but the modified code is not stable and crashes.
>>>
>>> I have tried to reduce the mesh size and time step, but it still
>>> crashes(may be not small enough). Should I use double precision instead
>>> and decrease the amplification factor of the SOURCE?
>>>
>>> Do you have any suggestion?
>>>
>>> Best regards,
>>> Yingzi
>>> _______________________________________________
>>> CIG-SEISMO mailing list
>>> CIG-SEISMO at geodynamics.org
>>> http://lists.geodynamics.org/cgi-bin/mailman/listinfo/cig-seismo
>>
>