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

Dustin Carroll dcarroll at uoregon.edu
Tue Jul 1 08:24:15 EDT 2014


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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