[MITgcm-support] Re:How to reduce a reflection wave from OBCs!

[Samar Khatiwala]

Hi

Just to add to this discussion ... radiation BCs are definitely the  
way to go. (As one of the
developers of the Orlanski package, I would of course say that.) But  
its not foolproof. For the
barotropically forced internal wave problem, it took some serious  
effort to get the waves to
radiate out correctly (i.e., make it compare favorably with  
analytical solutions). This is documented
in a 2003 DSR paper on internal tide generation:
http://www.ldeo.columbia.edu/~spk/Papers/KhatiwalaInternalTidesDSR03.pdf

Last I looked, the basic orlanski code does not have the various  
hacks needed to radiate out
only the "baroclinic" component. It took some doing to get this  
right. If people don't want to reinvent
the wheel, I'll be happy to post this code somewhere. There is also  
code to compute topographic
drag etc. (taking into account the lopped cell topo, subtracting out  
the barotropic component, ...).

Samar

On Feb 11, 2006, at 12:46 PM, Jennifer MacKinnon wrote:

> Hi,
>
> I've been struggling with similar issues regarding internal waves  
> and boundary conditions.  My solution so far is to clamp the  
> barotropic velocities to be whatever you like (a simple sinusoid in  
> your case), but allow baroclinic velocities as well as T and S to  
> radiate internal-waves out of the domain using the Orlanski  
> radiation option.  This requires a little bit of monkeying with  
> orlanski_west.F and orlanski_east.F, but is fairly  
> straightforward.  Let me know if you'd like a copy of my modified  
> files.
>
> Cheers,
>
> Jen
>
> ---------------------------------------------------------------
> Dr. Jennifer MacKinnon
> Physical Oceanography Research Division
> Scripps Institution of Oceanography
> http://www-pord.ucsd.edu/~jen/
> 858-822-3716
>
>
>>
>> From: Van Thinh Nguyen <vtnguyen at moisie.math.uwaterloo.ca>
>> Date: February 10, 2006 12:25:54 PM PST
>> To: mitgcm-support at mitgcm.org
>> Subject: [MITgcm-support] How to reduce a reflection wave from OBCs!
>> Reply-To: mitgcm-support at mitgcm.org
>>
>>
>> Dear all,
>>
>> I would like to simulate internal waves generated by tidal forcing  
>> over a depression bump in a open channel (opened at east & west).  
>> My case is similar to exp4, but it's limited in 2D. The tidal  
>> current is from the East to West with u=Uo*sin(omega*t). At west  
>> and east OBCs I set:
>>
>> OBWu=Uo*sin(omega*t)
>> OBWv=0.
>> OBWt=tRef
>> OBWs=sRef
>>
>> OBWw=0. for nonhydrostatic
>> OBWeta=Eta=0.
>>
>> At Eastern OBC is set the same above.
>>
>> I extended the length of domain from 60km, 120km, ...
>> the depth of domain H=80m (shallow), depth of bump=50%*H.
>>
>> I got refection waves from both OBCs, because Temperature profile  
>> (linearized in depth) is fixed at these OBCs (always =tRef),  
>> however the temperature profile in inner domain has changed.
>>
>> Anyone may have an idea to help me to fix this problem?
>>
>> Thanks so much for your helps,
>>
>> Van Thinh
>>
>>
>> From: Dmitri Leonov <dleonov at ocean.washington.edu>
>> Date: February 10, 2006 12:51:35 PM PST
>> To: mitgcm-support at mitgcm.org
>> Subject: Re: [MITgcm-support] How to reduce a reflection wave from  
>> OBCs!
>> Reply-To: mitgcm-support at mitgcm.org
>>
>>
>> Hello Van Thinh,
>>
>> I've used sponge boundary conditions for a similar problem. My  
>> data.obcs file looks like this
>>
>> &OBCS_PARM01
>> OB_Iwest=1,
>> OB_Ieast=-1,
>> useOBCSsponge=.TRUE.,
>> &
>>
>> &OBCS_PARM03
>> spongeThickness=10,
>> # inverse relax. coef's (seconds)
>> Urelaxobcsinner = 0.0,
>> Urelaxobcsbound = 32.0,
>> Vrelaxobcsinner = 0.0,
>> Vrelaxobcsbound = 32.0,
>> &
>>
>> You may want to try it.
>>
>> Dmitri
>>
>>
>
>
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