[MITgcm-support] open boundaries!

[Matthew Robert Mazloff]

Hi Van Thinh,

As you know, you tell the model you have an open western boundary by writing in
data.obcs:
 OB_Iwest=   55*1

You can then prescribe a u velocity component by adding to this file:

useOBCSprescribe=.TRUE.,
OBNuFile='UNBC.bin',

This can have multiple records in it...and then in data.exf you add
obcsWstartdate1     = 19920101,
obcsWstartdate2     = 000000,
obcsWperiod         = 2635200.0,

which tells the model to switch to the next velocity record every 2635200.0
seconds.

A better way to impliment your function would be to write a new routine.  The
model sets the U velocity on the open western boundary to
OBWu.  This is read in when the routine OBCS_PRESCRIBE_READ executes

 call EXF_SET_OBCS_YZ(  OBWu, OBWu0, OBWu1, OBWufile, 'u'
     I                     , fac, first, changed, count0, count1
     I                     , mycurrenttime, mycurrentiter, mythid )

Here you could change this call to

 call VAN_THINHS_FUNCTION(  OBWu, OBWu0, OBWu1, OBWufile, 'u'
     I                     , fac, first, changed, count0, count1
     I                     , mycurrenttime, mycurrentiter, mythid )

and in the routine VAN_THINHS_FUNCTION, OBWu is set from your function.  The
same can be done for the eastern boundary.

Good luck,
Matt



Van Thinh Nguyen wrote:

>Hi Stefano and Patrick,
>
>I took a look on MITgcm Support Archives to find how to set up OBCs,
>however I still confuse in setting up some parameters.
>
>My test case is almost the same as exp4:
>
>Flow in a channel over a bump with
>- north and south boundaries are walls
>- west & east are OBs
>I would like to set the tidal forcing at west OB with velocity component
>U=Uo*cos(omega*t). (Uo=0.025; omega=2*pi/43200)
>
>Could you please give a hint how can I set these inputs?
>
>Thanks so much for your helps,
>
>Van Thinh
>----------------
>
>
>On Mon, 26 Sep 2005, Stefano Querin wrote:
>
>>Hi Van-Thinh,
>>maybe the best thing you can do is to take a look to the files in the CVS
>>repository (or directly in your /pkg/obcs folder if you have a recent
>>version of the code). Some routines have short and useful comments that help
>>the user in the preliminar obcs tests.
>>Basically (and in very few words), you can impose:
>>- constant OBCs (obcs_calc.F sets u, v, w and eta to zero, and T, S to tRef
>>and sRef);
>>- radiating (passive) OBCs for momentum and tracers following Orlanski (see
>>Orlanski, 1976);
>>- time varying (active) OBCs using the obcs package (set
>>useOBCSprescribe=.TRUE.,) together with exf and cal.
>>
>>You can also define a sponge (or better, nudging?) layer on the OB (setting
>>useOBCSsponge=.TRUE., sponge thickness and relaxation parameters) and/or
>>prescribe the net flow across the OB using the useOBCSbalance option.
>>
>>A useful example is in:
>>
>>http://mitgcm.org/cgi-bin/viewcvs.cgi/MITgcm_contrib/heimbach/obcs_prescribe/
>>
>>As the old obcs/README said, happy open-boundarying!
>>
>>Cheers,
>>
>>Stefano
>>
>>
>>----- Original Message -----
>>From: "Van Thinh Nguyen" <vtnguyen at moisie.math.uwaterloo.ca>
>>To: <mitgcm-support at mitgcm.org>
>>Sent: Monday, September 26, 2005 6:26 PM
>>Subject: [MITgcm-support] open boundaries!
>>
>>
>>>Dear MITgcm-supporters & users,
>>>
>>>Could someone please explain for me more detail about how to set up an
>>>open boundary conditions. For instance, in exp4:
>>>
>>>when we set in data.obcs:
>>>
>>>"OB_Jnorth=80*-1" to define a face where OB is appied, however I still
>>>don't know which boundary condition is appied here (Neumann?).
>>>
>>>And what is the "useOrlanski" in OB option?
>>>
>>>There are probably some docu around in MITgcm users' manuals (I actually
>>>took a look but haven't found), if someone know please give me a hint?
>>>
>>>Thanks a lot!
>>>
>>>Van Thinh
>>>_______________________________________________
>>>MITgcm-support mailing list
>>>MITgcm-support at mitgcm.org
>>>http://mitgcm.org/mailman/listinfo/mitgcm-support
>>>
>>_______________________________________________
>>MITgcm-support mailing list
>>MITgcm-support at mitgcm.org
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>>
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