[MITgcm-support] Wave damping

[Jean-Michel Campin]

Hi Patrick,

I guess your recent e-mail is related to this one.

If the waves are in the external mode, the fully implicit
time-stepping (backward in time) will damp the waves.
You could try the Crank-Nickelson time stepping:
 implicSurfPress=0.5,
 implicDiv2DFlow=0.5,
(see verification/adjustment.cs-32x32x1/input.nlfs/data)
that conserve the external mode energy.
But I am not so sure that it works well with the Non-Hydrostatic
option (In fact, I've never tried).

Jean-Michel

On Thu, Mar 15, 2007 at 02:23:47PM +0100, Patrick Rosendahl wrote:
> Hello all,
> 
> I am doing a non-hs simulation, where I generate waves at the one end of 
> the waterbody. On the other side there is a damping beach.
> 
> Now the problem. If I use a timestep of 1e-3
> - 1Hz waves travel with pretty much no damping.
> - 1.5Hz waves travel with very little damping
> - 2Hz waves are damped heavily, the profile of the wave peaks looks like 
> an exponential decay. Setting all the viscosities to 0.0 had no effect, 
> (including visc4 which is not in the file below.)
> 
> To remove the damping for 2Hz waves, I have to decrease the timestep to 
> 1e-4.
> 
> This seems weird to me, because the 2Hz waves travel slower than 1Hz 
> waves ("external mode"), and the wavemaker generated velocities are the 
> same (0.02 cm/s maximum vel in internal mode). Hence, the CFL criterion 
> is met "even better".
> 
> Is there some setting in the code, that damps short waves, depending on 
> the timestep? (Shapiro filter is turned off.)
> 
> Find my settings below.
> 
> Best regards,
> Patrick Rosendahl
> 
> 
> 
> -----------------------------------------------package.conf
> rw
> mdsio
> mnc
> obcs
> mom_fluxform
> generic_advdiff
> 
> 
> 
> -----------------------------------------------data
> # ====================
> # | Model parameters |
> # ====================
> #
> # Continuous equation parameters
>  &PARM01
>  tRef=135*20.0,
> # 1cm Salz
>  sRef=1*35.0,134*0.0,
>  viscAh=1.0E-6,
>  viscAz=1.0E-6,
>  no_slip_sides=.FALSE.,
>  no_slip_bottom=.TRUE.,
>  diffKhT=1.0E-7,
>  diffKzT=1.0E-6,
>  diffKhS=5.0E-7,
>  diffKzS=1.0E-6,
>  f0=0.0,
>  sBeta =0.,
>  gravity=9.81,
>  rhoConst=1000.0,
>  rhoNil=1000.0,
> # heatCapacity_Cp=3900.0,
>  rigidLid=.FALSE.,
>  implicitDiffusion=.TRUE.,
>  implicitViscosity=.TRUE.,
>  implicitFreeSurface=.TRUE.,
>  eosType='LINEAR',
>  nonHydrostatic=.TRUE.,
>  readBinaryPrec=32,
>  tempAdvScheme=4,
>  saltAdvScheme=4,
>  exactConserv=.TRUE.,
> # nonlinFreeSurf=3,
>  &
> 
> # Elliptic solver parameters
>  &PARM02
>  cg2dMaxIters=1000,
>  cg2dTargetResidual=1.E-13,
>  cg3dMaxIters=10,
>  cg3dTargetResidual=1.E-9,
>  &
> 
> # Time stepping parameters
>  &PARM03
>  nIter0=0,
>  nTimeSteps=40000,
>  deltaT=0.001,
>  abEps=0.1,
>  pChkptFreq=1.0,
>  chkptFreq=1.0,
>  dumpFreq=0.2,
>  monitorFreq=0.1,
> # outputTypesInclusive=.TRUE.,
>  &
> 
> # Gridding parameters
>  &PARM04
>  usingCartesianGrid=.TRUE.,
>  usingCylindricalGrid=.FALSE.,
>  usingCurvilinearGrid=.FALSE.,
>  delX=800*0.03,
>  dYspacing=0.1,
>  delZ=0.010,40*0.001,20*0.002,20*0.003,10*0.005,23*0.010,10*0.005,11*0.002,
>  &
> 
> # Input datasets
>  &PARM05
> # zonalWindFile='windstressx.const_0.1.bin.real*4',
> # hydrogThetaFile='thetaPol.bin',
>  bathyFile='depth.closedE_0.5.bin.real*4',
> # tCylIn  = 0
> # tCylOut  = 20
>  &
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support