MIKE 21 BW - Page 42

Examples
42 MIKE 21 BW - © DHI
Wave breaking is included in this 2DH module application and a wave event
occurring approximately 30 hours/month is considered (H
m0
= 4.0 m, T
p
= 9 s,
MWD= 270 ºN).
Model setup
The model bathymetry is illustrated in Figure 4.16 where the maximum depth
is 11.5 m and minimum depth is 1 m. The spatial resolution is 2 m. We will
consider a wave situation where substantial wave breaking will occur:
 Significant wave height, H
m0
= 4.0 m
 Peak wave period, T
p
= 9 s
 Standard JONSWAP spectrum
 Minimum wave period T
min
= 4.1 s
 Mean wave direction, MWD= 270ºN
 Cos
8
-directional spreading
The most energetic and breaking waves have a period around 9 s and are
resolved by the 20-40 points per wave length at depths 2-10 m, where the pri-
mary part of the waves will break. In most practical 2DH applications includ-
ing wave breaking, a grid spacing of 1-2 m is used for peak wave periods
larger than, say, 7s.
The model bathymetry is generated by using the Bathymetry Editor and alge-
braic manipulations in the Grid Editor.
As shown in Figure 4.17, a 20-point wide sponge layer has been set up at the
shoreline. Hence wave run-up is not considered in this example. The mini-
mum model depth of 1m is well inside the sponge layer. A 50 points wide
sponge layer is used for efficient wave absorption at the other boundaries.
The thickness of the sponge layer is here corresponding to one wave length
or more. The sponge layer map is generated using the MIKE 21 Toolbox
'Generate Sponge and Porosity Layer Maps' and algebraic manipulations in
the Grid Editor.