[MITgcm-support] How to use OBCS and add the Sponges layer?

[Matthew Mazloff]

Hi Chunyan


Mostly fine...although I don't know of anyone who has used Orlanski or  
obcs balance succesfully so as a first start you may want to turn  
these off and then experiment with them later...so try:

> C This include hooks to the Orlanski Open Boundary Radiation code
> #undef ALLOW_ORLANSKI
>
> C balance barotropic velocity
> #undef ALLOW_OBCS_BALANCE


and then of course
>  useOrlanskiEast=.FLASE.,
>  useOBCSbalance=.FALSE.,


Also I would use
  useOBCSprescribe=.TRUE.,
not sure if "1" works

and also, you give
>  OBEuFile = 'OBzonalU.bin',
but you also need to give
> OBWuFile = 'OBzonalU.bin',


As for  PARM03 put something like:
&OBCS_PARM03
  Urelaxobcsinner=864000.E0,
  Urelaxobcsbound=43200.E0,
  Vrelaxobcsinner=864000.E0,
  Vrelaxobcsbound=43200.E0,
  spongeThickness=15,
  &

and I would recommend give V,T,and S too -- even if they are trivial

Hope that is everything and not too confusing,
Matt





On Jan 13, 2011, at 1:58 AM, Chun-Yan Zhou wrote:

> Dear all,
>
> I am trying to do quite a simple configuration: The model domain  
> covers a continental slope and neighbouring parts of the deep ocean  
> and shelf. A barotropic tidal flow into the model domain from the  
> east open boundary (2D problem, no y-dependency, no Coriolis). My  
> basin is 300km across and I use dx=500m and dz=100*25m (i.e. grid  
> dimensions is 600x1x100).
> Furthermore, I want to add a sponge-layer (50 Km width) at the  
> lateral boundary of the deep ocean (the west boundary) to absorb the  
> baroclinic fields.
>   I have read the OBCS package in the manual and the examples but  
> still can not understand well.
> OBCS_OPTIONS.h
> #include "CPP_OPTIONS.h"
>
> #ifdef ALLOW_OBCS
>
> C Enable individual open boundaries
> #undef ALLOW_OBCS_NORTH
> #undef ALLOW_OBCS_SOUTH
> #define ALLOW_OBCS_EAST
> #define ALLOW_OBCS_WEST
>
> C This include hooks to the Orlanski Open Boundary Radiation code
> #define ALLOW_ORLANSKI
>
> C Enable OB values to be prescribed via external fields that are read
> C from a file
> #define ALLOW_OBCS_PRESCRIBE
>
> C This includes hooks to sponge layer treatment of uvel, vvel
> #define ALLOW_OBCS_SPONGE
>
> C balance barotropic velocity
> #define ALLOW_OBCS_BALANCE
>
> C     The following five CPP options are experimental and aim to deal
> C     with artifacts due to the low-frequency specification of sea-ice
> C     boundary conditions compared to the model forcing frequency.
> C     Ice convergence at edges can cause model to blow up.  The
> C     following CPP option fixes this problem at the expense of less
> C     accurate boundary conditions.
> #undef OBCS_SEAICE_AVOID_CONVERGENCE
>
> C     Smooth the component of sea-ice velocity perpendicular to the  
> edge.
> #undef OBCS_SEAICE_SMOOTH_UVICE_PERP
>
> C     Smooth the component of sea ice velocity parallel to the edge.
> #undef OBCS_SEAICE_SMOOTH_UVICE_PAR
>
> C     Smooth the tracer sea-ice variables near the edges.
> #undef OBCS_SEAICE_SMOOTH_EDGE
>
> C     Compute rather than specify seaice velocities at the edges.
> #undef OBCS_SEAICE_COMPUTE_UVICE
>
> #endif /* ALLOW_OBCS */
> #endif /* OBCS_OPTIONS_H */
>
>
> Data.obcs
> # Open-boundaries
>  &OBCS_PARM01
>  OB_Ieast=600*1, ( is this right?)
>  OB_Iwest=1*1,  ( is this right?)
>  useOrlanskiEast=.TRUE.,
>  useOBCSbalance=.TRUE.,
>  useOBCSsponge=.TRUE.,
>  #
>  useOBCSprescribe=1,
>  #
>  OBEuFile = 'OBzonalU.bin',
>  &
>
> # Orlanski parameters
>  &OBCS_PARM02
>  Cmax=0.45,
>  cVelTimeScale=1000.,
>  &
>
>  # Sponge-layer parameters
>  &OBCS_PARM03
>  spongeThickness=100,
>   Urelaxobcsinner = long relaxation time scale of your choice,
>   Urelaxobcsbound= short relaxation time scale,(is there any method  
> to give these two parameters?)
>   spongeThickness = # grid points,( how to describe the sponges  
> position between (1,1 and 100,1)? )
>
>  &
>
> I am appreciate any help/advices; if you need more info let me know.
> Thanks in advance.
> Chunyan
>
>
> Chunyan Zhou
> Division of Civil Engineering
> School of Engineering, Physics and Mathematics
> College of Art, Science and Engineering
> Fulton Building
> University of Dundee
> Dundee DD1 4HN
>
>
>
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