[MITgcm-support] Too short time step ?!
Menemenlis, Dimitris (3248)
Dimitris.Menemenlis at jpl.nasa.gov
Wed Jul 7 11:53:16 EDT 2010
One more comment, is that depending on your initial conditions, it is often necessary to initially integrate the model with shorter deltat for a few day, to dissipate any instabilities that might be present in your initial conditions.
On Jul 6, 2010, at 7:40 PM, 张正光 wrote:
> Dear mitgcm-support team,
> Hi, I'm Zhang.
> I'm modeling the overflow, now I'm running a idealized case, but I have to set my time step very short (dt=120s) in order to run my case, otherwise, it will go crazy or shut down.
> I'v checked the "Numerical Stability Criteria", which told me I can use a much longer time step.
> I'm confused, and my case need to be integrated for 30-50year, so use dt=120s will cost too much computer time. What can I do to use a longer time step?
> My grid size: dx=25km, dy=50km, dz=100m (uniform grid)
> and I think give you my "data" file maybe better:
>
> # ====================
> # | Model parameters |
> # ====================
> #
> # Continuous equation parameters
> &PARM01
> tRef=40*20.,
> sRef=40*35.,
> viscA4=0.0E4,
> viscAh=1.E-2,
> viscAz=1.E-3,
> no_slip_sides=.TRUE.,
> no_slip_bottom=.TRUE.,
> diffK4T=0.E4,
> diffKhT=0.E-2,
> diffKzT=0.E-3,
> diffK4S=0.E4,
> diffKhS=0.E-2,
> diffKzS=0.E-5,
> f0=0.e-5,
> beta=0.E-11,
> rhonil=1035.,
> rhoConstFresh=1000.,
> eosType = 'JMD95Z',
> rigidLid=.FALSE.,
> implicitFreeSurface=.TRUE.,
> hFacMin=0.05,
> nonHydrostatic=.TRUE.,
> readBinaryPrec=64,
> #- not safe to use globalFiles in multi-processors runs
> #globalFiles=.TRUE.,
> bottomDragLinear=0.E-4,
> bottomDragQuadratic=0.003,
> tempAdvScheme=33,
> &
>
> # Elliptic solver parameters
> &PARM02
> cg2dMaxIters=300,
> cg2dTargetResidual=1.E-13,
> cg3dMaxIters=400,
> cg3dTargetResidual=1.E-8,
> &
>
> # Time stepping parameters
> &PARM03
> niter0=0,
> nTimeSteps=10000,
> #nTimeSteps=20000,
> deltaT=600.0,
> abEps=0.01,
> pChkptFreq=120000000.0,
> chkptFreq=600000.0,
> dumpFreq=600000.0,
> #dumpFreq=120000.0,
> taveFreq=600000.0,
> tauThetaClimRelax=100000.0,
> monitorFreq=6000.,
> # staggerTimeStep=.TRUE.,
> &
>
> # Gridding parameters
> &PARM04
> usingCartesianGrid=.TRUE.,
> usingSphericalPolarGrid=.FALSE.,
> delXfile='dx.bin',
> delYfile='dy.bin',
> # dYspacing=200.,
> delZ=40*100.0,
> &
>
> # Input datasets
> &PARM05
> bathyFile='topog.slope',
> hydrogThetaFile='T.init',
> surfQfile='Qnet.forcing',
> thetaClimFile='SST.bin',
> diffKrFile='diffK.bin'
> #hydrogThetaFile='T.pickup',
> #hydrogSaltFile='S.pikup',
> #uVelInitFile='U.pickup',
> #vVelInitFile='V.pickup',
> #pSurfInitFile='Eta.pickup',
> &
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