[MITgcm-support] variables (.)_F1 in obcs_calc.F

[Jody Klymak]

Hi Mario,

So you basically just want a channel flow, which is something I and others do all the time for “wake” experiments from underwater bathymetry.

For that case, on both boundaries I would use a sponge that relaxes the model velocities slowly to the desired velocity. Orlanski is fine in 2-d with the lowest mode, but will not really do a good job on lateral variations, whereas a relatively careful sponge will do very well at the expense of some grid cells. I also try to make the sponge far away from the active region by slowly telescoping the grid away from the obstacle.  This means the sponge can be many wavelengths from the obstacle.  You just have to be sure that your telescoping doesn’t cause spurious reflections, so the change in each dx needs to be gradual (I think 1% or so is fine for my applications).

I’m not clear however if you are trying to simulate the surface wake.  I’m not at all certain how well the MITgcm does at non-linear surface waves, nor how you can damp them away.  I think sea surface height is usually inferred, so its a bit of a nuisance to apply a sponge to.  Maybe someone on here can pipe up on the GCMs ability to resolve surface waves, but its not something a lot of large-scale ocean modellers usually do.

Hope that helps.

Cheers,   Jody



> On 25 Feb 2016, at  9:13 AM, Duran Camejo, Mario FORNATL, SP <mduranca at nps.edu> wrote:
> 
> Hello Martin,
> 
> I hadn't got an answer yet, thank you very much for replying!
> 
> I will try to explain my question a little better. I'm using MITgcm although, as you say, it is not meant to simulated watercrafts moving in the ocean, because 
> I'm interested in the evolution of the wakes (after a watercraft) and for that  I think MITgcm is an extraordinary tool. The way to simulate a watercraft 
> accelerating through a fixed box in the ocean is by "injecting momentum" to the fluid inside the box, namely, setting some additional velocity in a small parcel of the fluid 
> every time step and updating the boundary conditions for the zonal velocity in the west every time step too (watercraft is moving east to west which is equivalent to 
> assume that the fluid is moving west to east and the watercraft is at rest), whereas keeping Orlanski open boundary conditions in the east to allow the free development 
> of the wakes. Maybe it wouldn't be necessary to go through the F1 variables for updating the BC in the west because the time-evolving BC there might be 
> straightforwardly calculated in obcs_calc.F. Any suggestion will be greatly appreciated!
> 
> Anyway I will take a look to “verification/exp4”. 
> 
> Best regards,
> Mario
> 
> 
> -----Original Message-----
> From: Martin Losch [mailto:Martin.Losch at awi.de] 
> Sent: Thursday, February 25, 2016 6:51 AM
> To: MITgcm Support
> Subject: Re: [MITgcm-support] variables (.)_F1 in obcs_calc.F
> 
> Mario,
> 
> did you get an answer? I am afraid that your question is not clear.
> - the MITgcm is not meant to simulated watercrafts moving in the ocean, you could probably used some of the technology and introduce fixed geometry representing a watercraft, but I am sure that there is better software for that
> - the *_F1 variables are passed to the model via MPI from a parent model into which the current model is nested. This is a feature that is not used very often and I don’t know how well this is maintained. For a more typical application of the obcs-packace see “verification/exp4”
> 
> Martin
> 
>> On 17 Feb 2016, at 23:57, Duran Camejo, Mario FORNATL, SP <mduranca at nps.edu> wrote:
>> 
>> Dear MITgcm users,
>> 
>> I'm doing some simulations of watercrafts moving in the ocean. For 
>> that, I'm trying to produce time- dependent boundary conditions 
>> through the code obcs_calc.F  and I would like to know where the variables (.)_F1 are being calculated.
>> 
>> I will greatly appreciate any help!!!
>> 
>> Mario
>> 
>> _______________________________________________
>> MITgcm-support mailing list
>> MITgcm-support at mitgcm.org
>> http://mitgcm.org/mailman/listinfo/mitgcm-support
> 
> 
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--
Jody Klymak    
http://web.uvic.ca/~jklymak/