[MITgcm-support] cell size variation

[Jean-Michel Campin]

Hi,

Just a comment:
 z* would be a good solution but it's still not yet
in the code for Non-Hydrostatic set-up.

Jean-Michel

On Thu, Apr 10, 2008 at 10:06:08AM +0200, Martin Losch wrote:
> Patrick,
> 
> your upper layer thickness dz(1) (or drF(1) in MITgcm-lingo) should  
> be much larger than your maximum expected wave height, otherwise, the  
> surface layer is going to drain. I'd go with waveheight < 20% drF(1)  
> at least.
> 
> I am not sure if this works with non-hydrostatic dynamics, but maybe  
> you want to try the r*-coordinate (something like a surface following  
> sigma-coordinate) for your experiments?
> 
> Martin
> 
> On 9 Apr 2008, at 12:28, Patrick Rosendahl wrote:
> >Thank you, I get much better results!
> >
> >Next thing I was wandering, if that equation has to be fulfilled  
> >for zero-level (no waves) only? I have ~6cm waves in a 5cm upper  
> >layer (the wave reduces it to 5-3=2cm and enlarges it to 5+3=8cm).
> >Is there a rule-of-thumb for the maximum streching of the upper  
> >most layer?
> >
> >Best,
> >Patrick
> >
> >Martin Losch wrote:
> >>the rule of thumb is:
> >>abs(delz(k+1)/delz(k)) < 1.4
> >>In your case: 0.03/0.005 = 6
> >>Martin
> >>On 9 Apr 2008, at 10:34, Patrick Rosendahl wrote:
> >>>Hello all,
> >>>
> >>>I get unstable results with the following configuration in free-  
> >>>surface and non-hydrostatic mode:
> >>>
> >>>delZ=1*0.03,100*0.005,
> >>>
> >>>The depth is 0.5m, divided into a 3cm upper layer (that will   
> >>>contain the free surface), and the rest is divided into 5mm layers.
> >>>
> >>>
> >>>In the mail "Re: [MITgcm-support] z coordinate" from Baylor Fox-  
> >>>Kemper:
> >>>>Hi Rima,
> >>>>  The MITgcm is not accurate when you change the delZ so  
> >>>rapidly.   You
> >>>>are much better off using the 20 levels, if you can afford to  
> >>>run it
> >>>>that way.  If not, you can make a few levels of delz=30m, then
> >>>>gradually increase until you reach bottom.  The grid size shouldn't
> >>>>increase too rapidly from level to level, approximately 20% at  
> >>>most.
> >>>>This will be even more important in nonhydrostatic mode.
> >>>>   -Baylor
> >>>
> >>>
> >>>Is there a guide for the cell thickness? Is 20% really necessary?
> >>>
> >>>Best,
> >>>Patrick
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