USER MANUAL SWAN Cycle III version 40.72A

54 Chapter 4
With this command the user wants to choose the Cumulative Steepness Method (CSM)
for approximating whitecapping (see Scientific/Technical documentation) and not the formulation
of Komen et al. (1984) and not Janssen (1991a).
[cst] the tuneable coefficient Cwc
st
Default: [cst] = 4.0.
[pow] power m.
Default: [pow] = 2.0.
Note that the CSM method in SWAN is still in its experimental phase. Its results are
promising, but the method still suffers some numerical problems.
QUADrupl [iquad] [lambda] [Cnl4] [Csh1] [Csh2] [Csh3]
With this option the user can influence the computation of nonlinear quadruplet wave
interactions. Default: the quadruplets are included in the computations. Can be deactivated
with command OFF QUAD. Note that the DIA approximation of the quadruplet
interactions is a poor approximation for long-crested waves and frequency resolutions very
different from 10% (see command CGRID).
[iquad]
[lambda]
[Cnl4]
[Csh1]
[Csh2]
the quadruplets can be integrated by four different numerical procedures:
= 1 semi-implicit computation of the nonlinear transfer with DIA per sweep
= 2 fully explicit computation of the nonlinear transfer with DIA per sweep
= 3 fully explicit computation of the nonlinear transfer with DIA per iteration
= 8 fully explicit computation of the nonlinear transfer with DIA per iteration,
but neighbouring interactions are interpolated in piecewise constant manner.
other techniques for the computation of quadruplets are
= 4 Multiple DIA
= 6 FD-RIAM
= 51 XNL (deep water transfer)
= 52 XNL (deep water transfer with WAM depth scaling)
= 53 XNL (finite depth transfer)
Default: [iquad] = 2.
coefficient for quadruplet configuration in case of DIA.
Default: [lambda]=0.25.
proportionality coefficient for quadruplet interactions in case of DIA.
Default: [Cnl4]=3 × 10 7 .
coefficient for shallow water scaling in case of DIA.
Default: [Csh1]=5.5.
coefficient for shallow water scaling in case of DIA.
Default: [Csh2]=6/7.