MIKE 21 BW - Page 96

Examples
96 MIKE 21 BW - © DHI
Figure 4.64 Model results. Time series of input and simulated surface elevation at a
P(150) for irregular (left panels) and regular waves (right panels)
The wave reflection coefficient can be estimated from the model results
shown in Figure 4.65. In case of monochromatic and linear waves the reflec-
tion coefficient R can be estimated, using the formula:
(4.1)
where a
max
and a
min
is the maximum and minimum value of the envelope
amplitude, respectively. From Figure 4.65 is found that a
max
 0.65 m and a
min
 0.32, which results in a reflection coefficient of about 0.34. This value is a
little smaller than the expected value of about 0.40 cf. Figure 4.65, which is
mainly due to the wave non-linearity. The incoming waves are not perfectly
linear (as can be seen from the missing wave profile symmetry in
Figure 4.65), which is assumed in the theory for the Calculation of Reflection
coefficient program and for the above formula.
Figure 4.65 Model results. The left panel shows an envelope plot of the surface ele-
vation (corresponding to one wave period) in case of regular waves.
The right panel shows line series of the significant wave height at two
different times in case of irregular waves
In case of irregular and linear waves the reflection coefficient R can be esti-
mated using the formula (based on wave energy considerations):
(4.2)
R
a
max
a
min
–
a
max
a
min
+
-----------------------------=
R
H
m0
H
m0,i
------------


2
1–=