[CIG-SEISMO] variable mesh spacing

[Dimitri Komatitsch]

Hi Nicholas,

Yes, when there is varying bathymetry i.e. a non-flat ocean bottom, 
having a geometrically non-conforming mesh in the horizontal direction 
at the ocean bottom interface is difficult to do, one needs to ensure 
the conservation of total energy in the numerical scheme along that 
interface and that is hard to enforce. There is a really nice recent 
paper about this https://hal.inria.fr/hal-01255188 showing that it is 
not so easy.

However in the case of a flat interface no such instabilities arise and 
the classical SEM can handle that easily; that is not implemented in the 
current code but I have a (very) old version from 15 years ago in which 
I did that. I still have it somewhere, however it will lack all the 
modern features of the current code; if you feel like trying to merge 
them I can send it to you.

When doing that ideally one should also use time sub-stepping, which is 
also difficult to do properly (see e.g. 
http://komatitsch.free.fr/preprints/CMES_time_substepping_2009.pdf ).

Best wishes,
Dimitri.

On 25/03/2016 14:15, Nicholas Mancinelli wrote:
> Hi,
>
> I’m trying to use SPECFEM2D to simulate elastic wave propagation in the crust and lithosphere while including effects from reverberations in the water column.  Can you point me to a good method to generate a fine mesh (for the water column) atop a coarser mesh (for the lithosphere)?  It does not appear that the built-in (i.e., internal) mesher is capable of generating mesh layers with varying numbers of elements in the x-direction.
>
> Thanks in advance for any advice!
>
> Nick
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-- 
Dimitri Komatitsch
CNRS Research Director (DR CNRS), Laboratory of Mechanics and Acoustics,
UPR 7051, Marseille, France    http://komatitsch.free.fr