MIKE 21 BW, User Manual, Page: 71 / 196

2DH Boussinesq Wave Module - Examples
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4.2.7 Rip channel
Purpose of the example
The next two examples concentrate on wave breaking, run-up and wave-
induced currents. This can be done without the traditional splitting of the phe-
nomena into a wave problem and a current problem. In both examples we
consider waves normally incident on a plane sloping beach, but with some
alongshore non-uniformity to trigger nearshore circulation. In the first exam-
ple, a rip channel is present while the second example (section 4.2.8) con-
cerns a detached breakwater parallel to the shoreline.
Laboratory experiments are available for both examples as described in
Sørensen et al (1998)
(1)
. This paper includes detailed comparisons between
Boussinesq model results and laboratory measurements. The two examples
included in the DHI Software installation are very similar to the cases consid-
ered in Sørensen et al (1998). However, the examples here are considered
as prototypes of the laboratory experiments by use of a Froude scaling of
1:40.
Model setup
The first example is chosen according to laboratory experiments reported by
Hamm (1992a, b), see reference in Sørensen et al (1998). The size of model
area is 1200 m x 1200 m and the bathymetry is shown in Figure 4.43. It con-
sists of a plane sloping beach of 1:30 with a rip channel excavated along the
centre line. The maximum water depth is 20 m at the offshore boundary.
We will consider regular, unidirectional incident waves with a period of 7.9 s
(1.25 s in the laboratory) and a wave height of 2.8 m (0.07 m in the labora-
tory) at the offshore boundary. Wave direction is 270 ºN.
The spatial resolution is 2 m. As the primary part of the waves is expected to
break where Hmax ~ 0.8
.
h (experience rule for regular waves), the wave
breaking is initiated at 3.5-4 m water depth. At this depth the waves are
resolved by approximately 25 grid points per wave length.
As illustrated in Figure 4.44 a 50 points wide sponge layer is used for wave
absorption at the offshore boundary and behind the slot used to modelling the
run-up process. The thickness of the sponge layer is corresponding to one
wave length or more. No sponge layer is used along the lateral boundaries in
order to avoid wave radiation into the sponge layer.
1 A link to this paper is available from the MIKE 21 Documentation Index