[MITgcm-support] ALLOW_ADDFLUID option and U, V momentum equation

[Jason Goodman]

The source/sink terms affect the momentum equation through the pressure 
field.  If I have a tank of water with a hose running into it, how does 
the water already in the tank "know" to move away from the hose spigot?  
Pressure.  Adding fluid increases the pressure at the source, which 
causes a pressure gradient pushing nearby water away.

The standard MITGCM solves to find the pressure field needed to make the 
velocity field non-divergent.  When ALLOW_ADDFLUID is on, it solves for 
the pressure field needed to make the velocity field have a prescribed 
divergence: that pressure field then appears in the momentum equation to 
push water around.

I don't think there *should* be any other terms added to the momentum 
equations.

JCG

On 8/26/2011 12:44 PM, Angela Marie Zalucha wrote:
> Kumar,
>
> You're right, the fluid source/sink is assumed not to affect the 
> momentum equations.  For planetary applications this term is small, I 
> don't know about the ocean.
>
>   Angela
>
>
>
> On Thu, 25 Aug 2011, Krishnakumar Rajagopalan wrote:
>
>> Hi All,
>>
>> We have been customizing the 4x4 global ocean simulation 
>> (tutorial_global_oce_latlon) to include sources/sinks  using the 
>> ALLOW_ADDFLUID option. Checking with grep " ALLOW_ADDFLUID"  *.F,  it 
>> seems that  sources do not explicitly appear in the U or V momentum 
>> equations.  If indeed these equations are formally unchanged when the 
>> source/sink switch is on,  are we correct assuming that this version 
>> of MITgcm does not have a provision for (input) source momentum? A 
>> source could have an initial vertical momentum as well, although such 
>> cases may be more relevant for non-hydrostatic runs.
>> Thanks a lot
>> Kumar
>>
>
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