between currents and waves. For example, iterations are required to solve the
dispersion relationship including a current simultaneously with Snell's law
for refraction, as well as to determine the wave field in the presence of a
current (these two quantities are coupled through the governing equations).
NMLong-CW is thus computationally more demanding than NMLong.
NMLong-CW was evaluated by applying it to simulate several
hypothetical situations as well as laboratory and field data. The validation of
the NMLong-CW focused on the two major enhancements made in the
model, namely wave-current interaction and roller modeling. Data sets that
featured these two aspects were selected for comparison with the model.
Laboratory data from Smith et al. (1998) and Chawla and Kirby (1998, 1999)
were employed to investigate the wave transformation on an opposing
current, regarding both wave blocking and energy dissipation for waves
breaking on a current. These data sets included both monochromatic and
random waves. The laboratory data on the longshore current from Visser
(1982) was revisited to investigate the consequences of taking into account
full wave-current interaction as well as of including roller modeling.
Additionally, a more recently available data set of a similar kind to that of
Visser (1982) but of larger scale (monochromatic and random waves) was
employed (Hamilton and Ebersole 2001).
Three field data sets were included in the comparison, namely, Kraus and
Sasaki (1979), Kuriyama and Ozaki (1993), and Smith, Larson, and Kraus
(1993). These data sets involve more complicated profile shapes; in
particular, longshore bars were present across the profile in the two latter data
sets. Several sample calculations are also included to demonstrate the
capabilities of NMLong-CW to simulate the interaction between currents and
waves.
Report Content
Chapter 1 gives motivation for interest in the longshore current,
objectives of the study, and procedure employed. Chapter 2 is an updated
literature review of work relevant to enhancement of NMLong. The
theoretical foundation for the wave model is contained in Chapter 3, with
emphasis on the wave-current interaction. A short discussion of the wave
roller model is included, as well as comments to the numerical
implementation of the governing equations in the wave model. Evaluation of
the wave model is presented in Chapter 4.
The theory of the longshore current model is presented in Chapter 5,
mainly as a review of work in the original NMLong report (Kraus and Larson
1991). The longshore current model is evaluated in Chapter 6. Chapter 7
presents conclusions and an assessment of the capability of the model
NMLong-CW to simulate waves and currents in the nearshore.
3
Chapter 1 Introduction
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