[MITgcm-support] viscAh & viscAz?
Baylor Fox-Kemper
baylor at MIT.EDU
Tue Jun 20 20:54:29 EDT 2006
Hi Van Thinh,
Just to be sure, you should use the most recent version of the
code. I am quite sure that what is implemented there is better for
nonhydrostatic runs.
Cheers,
-Baylor
On Jun 20, 2006, at 5:44 PM, Van Thinh Nguyen wrote:
> 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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