[MITgcm-support] viscAh & viscAz?

[Van Thinh Nguyen]

Hi Baylor,

Thanks so much for your info. Because now I can stop my searching on the 
code.
Since I was not sure what you mentioned me by last email about implementing
of Smagorinsky & Leith scheme with non-hydrostatic mode, so I did a lot of
running tests and tried to look inside the code. I'm not sure that I am right,
but it seems to me the smagonrinsky & leith work fine with non-hydrostatic
mode. From the documentation (2.20.1.3), I know that smagorinky is not yet
implemented for the vertical viscosity in the code. It's really nice to 
hear that it's comming soon.

Thanks again,

Van Thinh

---------------------------------------------

On Tue, 20 Jun 2006, Baylor Fox-Kemper wrote:

> Hi Van Thinh,
>  I just checked in a version of the code that should do the right thing with 
> Leith and nonhydrostatic.  Smagorinsky will also work, but it will only 
> calculate horizontal viscosities, not the vertical.  That will be coming 
> soon!
>  Cheers,
>     -Baylor
>
>
> On Jun 14, 2006, at 11:14 AM, Van Thinh Nguyen wrote:
>
>> Hi Baylor,
>> 
>> When I run the non-hydrostatic mode with the option of Smagorinsky and 
>> Leith, the program had no warning or error, it just crashed after 1/2 tidal 
>> period (22320 s), it happened the same when i played only with viscAh & 
>> viscAz (increased to 1.). And with the option of Smagorinsky & Leith, it 
>> shows a great reduce the noises with the low values of viscAh &
>> viscAz (10-5). So I'm not sure that Smagorinsky & Leith wouldn't work with 
>> non-hydrostatic?
>> 
>> In case to run non-hydrostatic mode with Smagorinsky and/or Leith, some 
>> works have to be implemented, could you please give me some hints which 
>> subroutines have to be concerned?
>> 
>> Thanks a lot!
>> 
>> Van Thinh
>> 
>> -------------------------------------------
>> 
>> On Fri, 9 Jun 2006, Baylor Fox-Kemper wrote:
>> 
>>> Hi Van Thinh,
>>> Are you using non-hydrostatic mode?  If so, Leith and Smagorinsky are not 
>>> yet implemented, and you can only use viscAh or viscA4.
>>> If you are using hydrostatic mode, and you are at O(10m) resolution, it is 
>>> probably most sensible to be using the Smagorinsky scheme.  You should be 
>>> able to run it with no other viscosities.  If you are having trouble with 
>>> noise, you might try adding some biharmonic viscosity.
>>> Try this to get started:
>>> 
>>> &PARM01
>>> viscAr=5.E -5,
>>> # This is harmonic Smagorinsky Coefficient
>>> # 0.2-0.9=value from 3-d turbulence theory; Smagorinsky (1993)
>>> # 2.2-4=stable oceanic values (Griffies and Hallberg, 2000)
>>> # 1.0 smag is approximately the same as 1.85 leith+leithd
>>> # for this grid spacing
>>> viscC2Smag=1.0,
>>> viscC4Smag=1.0,
>>> # This is the max Viscosity used, be it Smag or Leith, and it scales
>>> # with grid size and timestep
>>> viscAhGridMax=0.5,
>>> viscA4GridMax=0.5,
>>> 
>>> implicitDiffusion=.TRUE.,
>>> implicitViscosity=.TRUE.,
>>> 
>>> # These two might be particularly useful, depending on your problem
>>> usejamartwetpoints=.TRUE.,
>>> staggerTimeStep=.TRUE.,
>>> 
>>> # You should stick with the 33, it reduces noise.
>>> tempAdvScheme=33,
>>> saltAdvScheme=33,
>>> nonHydrostatic=.FALSE.,
>>> &
>>> 
>>> You can play with the values of the Smagorinsky coefficients to see what 
>>> effect they have.
>>> 
>>> If you are using nonhydrostatic mode, let me know (I am overdue on setting 
>>> up the variable viscosity for nonhydrostatic mode anyway!)
>>> Cheers,
>>> -Baylor
>>> 
>>> On Jun 8, 2006, at 3:37 PM, Van Thinh Nguyen wrote:
>>> 
>>>> Dear all,
>>>> In oder to reduce the noises, I am playing with parameters viscAh & 
>>>> viscAz, so I have some questions, could someone please help me?
>>>> 1. From the documentation, we can have two ways to set viscAh:
>>>>  a. By estimating velocity & grid scale
>>>>  b. By using viscAhReMax and/or viscC2Smag (or maybe combine with Leith
>>>>     viscosity)
>>>> So, I understand that when I use option b) then I don't need to set
>>>> viscAh or viscAz in &PARM01, is that correct?
>>>> 2. Here are some options in data file:
>>>> &PARM01
>>>> #
>>>> viscAz=1.E-5,
>>>> viscAh=1.E-5,
>>>> tempAdvScheme=33,
>>>> viscA4=0.E12,
>>>> diffK4T=0.E4,
>>>> diffKhT=1.E-5,
>>>> diffKzT=1.E-5,
>>>> diffK4S=0.E4,
>>>> diffKhS=1.E-5,
>>>> diffKzS=1.E-5,
>>>> implicitDiffusion=.TRUE.,
>>>> implicitViscosity=.TRUE.,
>>>> viscC2leith=1.,
>>>> viscC2leithd=1.,
>>>> ##
>>>> &
>>>> &PARM04
>>>> viscC2Gmag=4.,
>>>> viscAhGridMax=0.5,
>>>> &
>>>> I even try to increase viscAh & viscAz (to 1.E-1), as well as increase 
>>>> viscC2leith=viscC2leithd=1.
>>>> but I still get noises.
>>>> I know that you should know my simulation (problem &domain length scale) 
>>>> related to grid space (dX=10m) & time step (1s). However, I just wanna 
>>>> know
>>>> that my above options are correct or anything in conflict.
>>>> My problem has to be dealed with the range of viscAh=1.E-6 & 
>>>> viscAz=1.E-6, but I got stuck in this simulation due to the noises.
>>>> Thanks so much for your helps.
>>>> Van Thinh
>>>> -----------------------------------------------------
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