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

[Pat Gallacher]

Hi,

I am having problems with internal waves reflecting off the open 
boundaries in the MITgcm code. I'd appreciate a copy of your code to 
address the problem.

Thanks,
Pat

------------------------------------------------------
Patrick C. Gallacher, PhD    gallacher at nrlssc.navy.mil
Oceanographer    Nonhydrostatic Coastal Ocean Modeling
Naval Research Laboratory        Phone: (228) 688-5315
Code 7331                    Secretary: (228) 688-4733
Stennis Space Center, MS 39529     FAX: (228) 688-5997
------------------------------------------------------



Samar Khatiwala wrote:

> 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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>
>
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