[MITgcm-support] Wave damping

[Patrick Rosendahl]

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
  &