[MITgcm-support] Model based on exp4 experiment - stability problems

[MASSIMO NOVELLO (Yahoo)]

Thanks Dustin, I will follow your recommendation and check the log results. I had increased the values just to speed up the process.

With the analytical values on CFL condition the result is much lower than 1.
U is always lower than 0,01m/s
dt = 1s
dx =10m
C=0,001

If I increase dx to 100m the model works fine.

Cheers,
Massimo


On 01/07/2014, at 09:24, Dustin Carroll <dcarroll at uoregon.edu> wrote:

> Hi Massimo,
> 
> Since lowering your deltaT and increasing the horizontal grid spacing makes your model stable, I suspect you may be violating the CFL (see Courant-Friedrichs-Lewy) criterion for your model setup 
> 
> i.e you want C = (u*deltaT) / deltaX to be less than 1.
> 
> I would recommend changing your monitorFreq to a much smaller value, say start with 60 s. This way you can look at STDOUT.0000 and pinpoint where your model blows up. 
> 
> Watch your horizontal and vertical advective CLF numbers (advcfl_uvel_max, advcfl_vvel_max, advcfl_wvel_max) and make sure that they are not steadily increasing above 0.5. You want them to stabilize as the model integration progresses.
> 
> Cheers,
> Dustin Carroll
> 
> 
> 
> 
> 
> 
> On Jul 1, 2014, at 3:52 AM, MASSIMO NOVELLO (Yahoo) <massimonovello at yahoo.com.br> wrote:
> 
>> 
>>> Please, I will really appreciate if someone can help on what is wrong related to the stability of this model. It is based on exp4 experiment, and I made some changes to reflect a small Lagoon in Rio de Janeiro. If I change delX and delY to 198*1.E2 the model works fine. Also if I only change deltat to 1.E-4, the model also works, but I need more than  5 days to model a 5 days experiment. I tried to apply all the analytics formulas for stability (3.24, 3.25, 3.26, 3.27 and 3.28) and did not found wrong values.
>>> 
>>> I’m only looking at the flow when we have a constant wind of 2m/s
>>> 
>>> Many thanks,
>>> Massimo
>>> 
>>> # ====================
>>> # | Model parameters |
>>> # ====================
>>> #
>>> # Continuous equation parameters
>>> ################# ARQUIVO PTRACERS_SIZE.h POSSUI VALORES DEFAULT ##############
>>> 
>>> &PARM01
>>> tempStepping=.FALSE., 
>>> tempAdvection=.FALSE.,
>>> tempForcing=.FALSE.
>>> saltStepping=.FALSE.
>>> saltAdvection=.FALSE.
>>> saltForcing=.FALSE.
>>> Tref = 20., 20., 20., 20., 20., 20.,
>>> sRef = 14., 14., 14., 14., 14., 14.,
>>> viscAr=1.E-4,
>>> viscAh=5.E2,
>>> viscA4=1.E6,
>>> no_slip_sides=.FALSE.,
>>> no_slip_bottom=.FALSE.,
>>> diffKhT=1.E3,
>>> diffKrT=1.E-5,
>>> diffKhS=1.E3,
>>> diffKrS=1.E-5,
>>> saltAdvScheme=4,
>>> eosType='LINEAR',
>>> tAlpha=2.E-4,
>>> sBeta =0.E-4,
>>> gravity=9.81,
>>> f0=1.E-4,
>>> beta=0.E-11,
>>> nonHydrostatic=.FALSE.,
>>> rigidLid=.FALSE.,
>>> implicitFreeSurface=.TRUE.,
>>> exactConserv=.TRUE.,
>>> hFacMin=0.2,
>>> readBinaryPrec=64,
>>> globalFiles=.FALSE.,
>>> useSingleCpuIO=.TRUE.,
>>> &
>>> 
>>> &PARM02
>>> cg2dMaxIters=1000,
>>> cg2dTargetResidual=1.E-13,
>>> cg3dMaxIters=400,
>>> cg3dTargetResidual=1.E-13,
>>> &
>>> 
>>> &PARM03
>>> nIter0=0,
>>> nTimeSteps=432000,
>>> baseTime=0.,
>>> deltaT=1,
>>> startTime=0,
>>> abEps=0.1,
>>> momDissip_In_AB=.FALSE.,
>>> pChkptFreq = 600,
>>> chkptFreq = 0.0,
>>> dumpFreq = 20.0,
>>> monitorSelect = 3,
>>> monitorFreq = 300000.1,
>>> 
>>> periodicExternalForcing=.TRUE.,
>>> externForcingPeriod=3600.,
>>> externForcingCycle = 432000.,
>>> &
>>> 
>>> &PARM04
>>> usingCartesianGrid=.TRUE.,
>>> delX=198*1.E1,
>>> delY=210*1.E1,
>>> delR= 1, 1, 1, 2, 2, 2,
>>> &
>>> 
>>> # Input datasets
>>> &PARM05
>>> bathyFile='topog.bump',
>>> zonalWindFile='wind_x.bin',
>>> meridWindFile='wind_y.bin',
>>> &
>>> 
>> 
>> 
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