[MITgcm-support] question on sponge-layer/mpi

[Patrick Heimbach]

Hi Theo,

I can't give a detailed answer right now (short on time),
but hope the following helps you to get further.

Once you're in parallel, the i,j indices are
local indices for each processor tile.
Thus, you are making the error to apply the open boundaries
locally at every processor tile boundary rather than
globally only once at your domain boundary.

Have a look e.g. in 
pkg/obcs/obcs_apply_ts.F
where you'll see that open boundary conditions
are applied only where the global array indices (e.g. OB_Jn)
require it.

-Patrick



Quoting Theo Gerkema <Theo.Gerkema at hmg.inpg.fr>:

> Hi,
> 
> Could someone help me sorting out the following problem:
> in external_forcing.F I've added a sponge-layer; the sponge
> covers (say) the first 100 points of the basin:
> 
>       DO j=jMin,jMax
>        DO i=iMin,iMax
>         rayleighz(i,j,kLev,bi,bj)=0.
>        ENDDO
>       ENDDO
>       DO j=jMin,jMax
>        DO i=1,100
>         rayleighz(i,j,kLev,bi,bj)=0.1*(100-i)/100.
>        ENDDO
>       ENDDO
> 
> It works selectively on the baroclinic field (tides):
> 
>         DO j=jMin,jMax
>         DO i=iMin+1,iMax-1
>          gU(i,j,kLev,bi,bj) = gU(i,j,kLev,bi,bj)
>      &   -rayleighz(i,j,kLev,bi,bj)*
>      &    abs(uVel(i+1,j,kLev,bi,bj)-uVel(i-1,j,kLev,bi,bj))*
>      &    uVel(i,j,kLev,bi,bj)
>         ENDDO
>        ENDDO
> 
> This works well, but I've now started doing runs in parallel,
> and if I run the code on for example two processors, an additional
> sponge-layer appears halfway the basin (ie at the left end of the 2nd
> sub-domain), rendering the results meaningless.
> Is there a way I can avoid the repetition of the sponge in parallel
> runs? Many thanks!
> 
> -- Theo.
> 
> 
> ***
> 
> Theo GERKEMA
> LEGI (Laboratoire des Ecoulements Géophysiques et Industriels)
> BP 53
> 38041 GRENOBLE Cedex 9
> FRANCE
> 
> tel: +33 (0)4 76 82 50 45
> fax: +33 (0)4 76 82 52 71
> theo.gerkema at hmg.inpg.fr
> 
> http://www.nioz.nl/nioz_nl/a5923dfa5bb47febe911cbfa4048961c.php
> 
> ~
> 
> 
> 
> 
> 
> 
> 
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--------------------------------------------------------
Patrick Heimbach   Massachusetts Institute of Technology
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FAX: +1/617/253-4464             77 Massachusetts Avenue
mailto:heimbach at mit.edu               Cambridge MA 02139
http://www.mit.edu/~heimbach/                        USA