Coastal Engineering Journal

A new model for nearshore nonlinear water wave is established through the Galerkin Chebyshev spectral approach on the vertical direction. The model is based on the spatial-temporal separation conception. The Galerkin Chebyshev spectral approach is applied to solve the Laplace equation, while the Zakharov's expression of the free surface boundary condition is considered as the evolution equation of the free surface and integrated temporally. The accuracy and efficiency of the model are confirmed by the results of simulation of water waves over even bottom, nonlinear wave shoaling and harmonic generation over a submerged bar. Finally, the model is used to study the wave blocking phenomenon due to strong opposing currents. Both the location of the blocking point and the wave structure near the point are well presented.

Wave setup and longshore currents on planar beaches induced by directional spectral waves have been computed for beach slopes ranging from 1/100 to 1/10, waves with deepwater wave steepness from 0.005 to 0.08 and offshore incident angles from 1° to 70°. The author's random wave breaking model PEGBIS (Parabolic Equation with Gradational Breaker Index for Spectral waves) is employed for the evaluation of wave attenuation by breaking. Prediction formulas are empirically derived for estimation of the wave setup at the shoreline and the cross-shore distribution of longshore currents on the basis of numerical computation results. Effects of spectral peakedness and directional spreading, surface roller, and turbulent eddy viscosity on wave setup and longshore currents are examined. The formulas have shown the capability to predict the wave setup and longshore currents observed in several field measurements fairly well.

This paper analyses the influence on the measured mean overtopping discharge of the duration of physical model tests of wave overtopping, bearing in mind the practical purpose of the studies, and the required accuracy of the measurements. The case study of the South Breakwater of Póvoa de Varzim Harbor, Portugal, is used to investigate this subject. During the two-dimensional physical model tests, three main target test conditions were used. For each one, different wave trains were utilized, all conforming to the same target JONSWAP spectrum, and three different test durations were employed. The number of random waves ranged from about 300 to 2400. Then, one of the three main test conditions was again used, but for twelve different test durations. In this case, the number of waves ranged from about 150 to 1900.

The results suggest that the convergence of the mean overtopping discharge to a constant value with increasing test duration is not obvious. Regardless of the test duration, the information obtained with a single test gives limited information about the expected mean discharge, as the mean overtopping discharge varies even for the same wave and structure characteristics. Consequently, more information is obtained on the mean discharge if several tests of the same short duration (but with different time series) are undertaken rather than if one test of long duration is carried out.

The response characteristics of a discus data buoy under the action of nonlinear waves are investigated through an experimental set-up in a wave tank. The details of the model, instrumentation, testing conditions and the analysis of the results are presented and discussed in this paper. The nonlinear waves were generated in the wave tank such that their characteristics fall under the Cnoidal and Stokes wave theory regions. The measured wave elevation and responses of the buoy model were analyzed qualitatively through phase-portrait and, quantitatively through spectral and harmonic analysis. In addition, the effects of the nonlinear wave height, wave period and Ursell parameter, U_r, on the response characteristics of the buoy model are addressed. Using a linear Transfer Function (TF) obtained from linear waves, an attempt to estimate the nonlinear-wave spectral density from the buoy model dynamics is made and the uncertainties in such predictions are detailed.