[MITgcm-support] very large velocity near the land boundary

[Martin Losch]

Hi,

I suggest that you turn on some kind of boundary friction:

 no_slip_sides=.FALSE., ( maybe this one = .true., too)
 no_slip_bottom=.TRUE.,
 bottomDragQuadratic = some positive number, e.g. 0.0025 or whatever you think is appropriate for tidal modelling.

to dissipate the energy in shallow water.


BTW:
why do you have: 
inexact equations?
>  metricTerms=.FALSE.,
No rotation?
>  omega=0., 
you can set hFacMin to probbably 0.1 to 0.3
For tidal simulations I would recommend a different time stepping scheme that does not damp fast tidal waves, see the "internal_wave" example ( implicSurfPress=0.5, implicDiv2DFlow=0.5,) and the documentation: <http://mitgcm.org/public/r2_manual/latest/online_documents/node41.html>
(In general, there is a lot to find in the documentation!)

Martin

 
On Nov 20, 2011, at 7:17 PM, Chun-Yan Zhou wrote:

> Hi all,
> I use a realistic topography in order to study the tidal effect. I have smoothed the topography a lot, and add the barotropical tidal velocity (velocity magnitude=0.2m/s ) in the east boundary. But I got very large velocity near the land boundary (up to 8m/s). I then reduced the minimum water depth to 10m, still got the similar problem. I don't know how to deal with the land boundary. The data is attached. Any suggestion is much appreciated!
>    
> # ====================
> # | Model parameters |
> # ====================
> #
> # Continuous equation parameters
>  &PARM01
>  viscAh=1.E2,
>  viscAz=1.E-3,
>  no_slip_sides=.FALSE.,
>  no_slip_bottom=.FALSE.,
>  diffKhT=1.E2,
>  diffKzT=1.E-3,
>  diffKhS=0.E2,
>  diffKzS=0.E-5,
>  tAlpha=2.E-4,
>  sBeta =0.,
>  omega=0.,
>  gravity=9.81,
>  eosType='LINEAR',
>  tempStepping=.TRUE.,
>  rigidLid=.FALSE.,
>  implicitFreeSurface=.TRUE.,
>  readBinaryPrec=64,
>  writeBinaryPrec=64,
>  metricTerms=.FALSE.,
>  hFacMin=0.5,
>  exactConserv=.TRUE.,
>  &
> 
> # Elliptic solver parameters
>  &PARM02
>  cg2dMaxIters=1000,
>  cg2dTargetResidual=1.E-13,
>  &
> 
> # Time stepping parameters
>  &PARM03
>  startTime=0.,
>  endTime=44714.,
>  deltaT=44.714,
>  cAdjFreq=0.,
>  abEps=0.02,
>  pChkptFreq=0.0,
>  chkptFreq=0.0,
> #dumpFreq=7200.0,
>  dumpFreq=447.14,
> #taveFreq=86400.0,
>  monitorFreq=3600.,
>  periodicExternalForcing=.TRUE.,
>  externForcingPeriod=447.14,
>  externForcingCycle=44714.,
>  &
> 
> # Gridding parameters
>  &PARM04
>  usingSphericalPolarGrid=.TRUE.,
>  delX=108*0.1,
>  delY=140*0.1,
>  delZ=10*3.,10*7.,20*25.,
>  ygOrigin=27.1,
>  &
> 
> # Input datasets
>  &PARM05
> bathyFile='topog.slope',
> hydrogThetaFile='T.init',
>  &
> 
> 
> # Open-boundaries
>  &OBCS_PARM01
>  OB_Ieast=140*-1,
>  OB_Jsouth=108*1,
>  useOrlanskiEast=.TRUE.,
>  useOrlanskiSouth=.TRUE.,
>  useOBCSprescribe=.TRUE.,
>  OBEuFile = 'OBEU.bin',
>  &
> # Orlanski parameters
>  &OBCS_PARM02
>  Cmax=0.45,
>  cVelTimeScale=1000.,
>  &
> 
> 
> Chunyan Zhou
> Division of Civil Engineering
> School of Engineering, Physics and Mathematics
> College of Art, Science and Engineering
> Fulton Building
> University of Dundee
> Dundee DD1 4HN
> 
> 
> 
> The University of Dundee is a registered Scottish charity, No: SC015096
> 
> <depthrun2.jpg><velocity surface.jpg><Eta.jpg>_______________________________________________
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