[MITgcm-support] Specify W velocity with OBCS?

[David Hebert]

Thanks Matt, I appreciate the explanation.

By "swirl" I mean the motion of a jet induced by a rotating propeller. 
The jet would have some angular velocity in addition to an axial velocity.

David

Matthew Mazloff wrote:
> Hi David,
>
> It is just a nice feature of the c-grid and obcs implementation that I 
> really think the W and P in the center point of the obcs does not 
> effect the interior in the hydrostatic mode.  If you are using 
> non-hydrostatic and have terms like Wxx this may become an issue...and 
> as the MITgcm currently does not have the capability of prescribing W 
> you could either
> 1) carefully choose tangential velocity so W get is what you want
> 2) implement the code so that W is overwritten after it is solved for 
> by divergence of tangential velocity
> 3) use sponge layers to limit effect of whatever is happening right on 
> the boundary
>
>
> good luck
> Matt
>
> ps> Not sure what you mean by a "swirl", maybe someone else can help 
> you with that.
>
>
> On Jan 14, 2008, at 2:17 PM, David Hebert wrote:
>
>> Hi Matt,
>>
>> Thanks for your response. I can see that  a point on a boundary 
>> wouldn't be solved for since it is specified, but wouldn't it affect 
>> the adjacent interior point somehow? I probably should note that I am 
>> using the model in non-hydrostatic mode.
>>
>> My previous question stems from wanting to specify a jet on the 
>> boundary. Implementing a "Top Hat" jet on the west boundary using 
>> OBWuFile seems to work. If I wanted to model a jet with swirl I was 
>> thinking I would specify all three velocity components on the 
>> boundary. A Google search for 'MITgcm OBWwFile' gives a few hits, so 
>> I thought it would be possible to specify vertical velocity on the 
>> boundary.  Perhaps this was possible in the past? If not, it looks 
>> like something I will have to add to the code.
>>
>> As m. schaferkotter noted, the namelist in 
>> MITgcm/pkg/obcs/obcs_readparms.F does not have any W velocity 
>> boundary files.
>>
>> Thanks,
>>
>> David
>>
>> Matthew Mazloff wrote:
>>> Hi David,
>>>
>>> I do not believe W (and P) on the open boundary comes into the 
>>> dynamics.  If W on this point is solved for (and thus given as 
>>> output) it will be because there is some divergence in the 
>>> prescribed tangential velocity....but this doesn't effect the interior.
>>>
>>> -Matt
>>>
>>>
>>> On Jan 14, 2008, at 11:06 AM, David Hebert wrote:
>>>
>>>> All,
>>>>
>>>> Is there a way so specify W velocity using OBCS and EXF? When I 
>>>> specify 'OBWwFile = w.bin' in data.obcs, I get an error saying it 
>>>> is not found in namelist:
>>>>
>>>> PGFIO-F-239/namelist read/unit=11/entity name is not member of group.
>>>> File name = /tmp/FTNwcP5jg7mUsXg8    formatted, sequential access   
>>>> record = 17
>>>> In source file obcs_readparms.f, at line number 1989
>>>>
>>>> Thanks,
>>>>
>>>> David
>>>>
>>>>
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>>
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