USER MANUAL SWAN Cycle III version 40.72A

Definitions of variables 93
WLEN
The mean wavelength, defined as
( ∫ ∫ ) k
WLEN = 2π
p −1
E(σ,θ)dσdθ
∫ ∫ k p−1 E(σ,θ)dσdθ
STEEPNESS
BFI
As default, p = 1 (see command QUANTITY).
Wave steepness computed as HSIG/WLEN.
The Benjamin-Feir index or the steepness-over-randomness ratio,
defined as
BFI = √ 2π× STEEPNESS × QP
This index can be used to quantify the probability of freak waves.
QB Fraction of breakers in expression of Battjes and Janssen (1978).
TRANSP Energy transport with components P x = ρg ∫ ∫ c x E(σ,θ)dσdθ and
P y = ρg ∫ ∫ c y E(σ,θ)dσdθ with x and y the problem coordinate system,
except in the case of output with BLOCK command in combination
with command FRAME, where x and y relate to the x−axis and y−axis
of the output frame.
VEL
Current velocity components in x− and y−direction of the problem
coordinate system, except in the case of output with BLOCK command in
combination with command FRAME, where x and y relate to the x−axis
and y−axis of the output frame.
WIND Wind velocity components in x− and y−direction of the problem coordinate
sytem, except in the case of output with BLOCK command in combination
with command FRAME, where x and y relate to the x−axis and y−axis of
the output frame.
FORCE Wave-induced force per unit surface area (gradient of radiation stresses)
with x and y the problem coordinate system, except in the case of output
with BLOCK command in combination with command FRAME,
where x and y relate to the x−axis and y−axis of the output frame.
F x = − ∂Sxx
∂x
F y = − ∂Syx
∂x
− ∂Sxy
∂y
−
∂Syy
∂y
where S is the radiation stress tensor as given by
S xx = ρg ∫ ⌊n cos 2 θ + n − 1 2 ⌋Edσdθ
S xy = S yx = ρg ∫ n sin θ cos θEdσdθ