4 Verification of Wave Model
Introduction
To evaluate the enhanced wave calculation routine in NMLong-CW, two
data sets originating from laboratory experiments involving the interaction
between currents and waves were employed. Both data sets encompassed the
transformation of waves on an opposing current, with breaking and
dissipation on the current. In the data set reported by Smith et al. (1998;
referred to as the CHL-I data set in the following), wave breaking on the
current occurred in shallow water, and only random waves were run. The
other data set originates from Chawla and Kirby (1999; referred to as the
C&K data set) and encompasses both monochromatic and random waves,
with breaking taking place in intermediate to deep water. Thus, the C&K
data included little or no influence of the bottom profile on the wave
transformation, whereas the influence of the profile on the wave
transformation and breaking was significant in the CHL-I data. Although
NMLong-CW was not developed for application to deep water, it is of
interest to explore the limitations of the model by simulating the C&K data.
Also, the number of data sets available for evaluating the capability of
NMLong-CW to reproduce the influence of a strong current on the wave
transformation is limited, making it necessary to employ all existing data sets
to demonstrate reliability of the model.
In the following, a short description is first given of the CHL-I
experiments after which the simulation results with NMLong-CW are shown
for four representative runs. Similarly, the C&K experiments are discussed,
and the simulation results are displayed for four monochromatic and four
random tests, chosen to represent various features of the observed wave
transformation. After the comparisons with the laboratory data, a
hypothetical case is simulated to illustrate the effects of ebb and flood current
on the wave transformation at an inlet. The input data for these simulations
were selected to correspond to the conditions at Shinnecock Inlet, Long
Island, NY.
CHL-I Data
Smith et al. (1998) measured wave breaking on a current at an idealized
inlet in the laboratory. A 1:50 scale model of an inlet was constructed in a
46-m-wide by 99-m-long concrete basin with 0.6-m-high walls. The parallel
jetties at the inlet had a spacing of 3.66 m and extended 5.5 m offshore. A
seaward flowing (ebb) current Uc was generated between the jetties that
eventually diffused as it propagated offshore. The water depth was constant
in the inlet (about 0.09 m), and seaward of the jetties the profile followed an
equilibrium shape according to Dean (1977). The experimental conditions
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Chapter 4 Verification of Wave Model
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