Wave Propagation through a Breakwater Gap
We initially evaluated the ability of BOUSS-2D to simulate the propagation
of waves through a gap into a rectangular harbor basin. The basin is 1,200 m
wide, 600 m long, and 10 m deep. The width of the opening at the harbor
entrance is 120 m.
The first case considered is a regular wave with period T = 7 s propagating in
a direction normal to the breakwaters. The corresponding ratio of the gap width,
, to wavelength, L
, is 2. Boussinesq model simulations
were carried out using
grid spacings ∆x = ∆y = 3 m and time-step size ∆t = 0.15 s. A 60-m-wide damp-
ing layer was placed around the perimeter of the basin to absorb outgoing waves.
Figure 8 shows a snapshot of the instantaneous water-surface elevation produced
by the BOUSS-2D model.
The normalized wave height distribution predicted by BOUSS-2D is com-
pared with the numerical solution of Isaacson and Qu (1990) in Figure 9.
Isaacson and Qu (1990) used a boundary integral technique to solve the 2-D
Helmholtz equation, which is a reduced form of the mild-slope equation for
water of constant depth. Good agreement is generally observed between the wave
height predictions from the numerical models. Small oscillations can be seen in
the Boussinesq model predictions, especially for the smaller wave height con-
tion coefficients of the order of 5 to 10 percent at the boundaries have been
observed to cause such oscillations in wave height contour lines (Isaacson and
We next investigated the propagation of irregular multidirectional waves
through the gap. The sea state is characterized by a JONSWAP wave spectrum
with peak period Tp = 7 s and peak enhancement factor γ = 3.3. A wrapped-
normal distribution with a standard deviation of 20 deg was used for the direc-
tional distribution of wave energy. The double-summation method was used to
synthesize time-histories of velocity fluxes along the incident wave boundary for
the BOUSS-2D simulations.
Figure 10 shows a snapshot of the instantaneous water-surface elevation
produced by the BOUSS-2D model. The normalized wave height distribution
predicted by BOUSS-2D is compared with the numerical solution of Isaacson
and Qu (1990) in Figure 11. Good agreement is observed. As expected, the
Chapter 5 Model Validation