Coastal Engineering Journal

A three-dimensional numerical model based on the potential wave theory is developed for nonlinear irregular wave motion. The σ-transformation is employed to map the irregular and time-dependent domain of definition of the physical problem onto a strip of unit width so as to facilitate the implementation of the free surface and bottom boundary conditions. The finite difference method is used to solve the governing equations in the mapped coordinates. Non-reflective wave-generation is realized by combining virtual sources and a sponge layer. The numerical model is verified by the known solutions for nonlinear regular and irregular waves in water of constant depth. Standing waves in front of a vertical wall, runup of long waves on a sloping beach, and wave decomposition phenomenon over submerged bars are also studied. The model is also applied to a three-dimensional problem of nonlinear wave transformation over an elliptical shoal. The computational results are shown to agree well with the experimental data.

The major aspects of interactive effects between irregular waves and a soft muddy bed, i.e. wave height attenuation and mud mass transport, are examined using numerical simulation and laboratory experiments. The irregular waves are simulated by spectral calculation method and joint distribution of wave height and wave period. The possibility of applying the representative wave method is also examined. The constitutive equations of visco-elastic-plastic model are selected for the complex rheological behavior of fluid mud. A series of wave flume experiments have been performed to obtain the required data for the verification of the numerical model. The results of the numerical model are also compared with the laboratory data of Zhang and Zhao [1999]. It is concluded that both wave spectra modeling and individual wave analysis are capable to simulate the interactive effects between irregular waves and fluid mud. The wave energy dissipation can also be simulated by using common representative waves. However, mean wave is the only representative wave that offers an acceptable approximation for the prediction of mud mass transport.

An X-band nautical radar system was employed to observe the wave field during a storm around the research pier HORS in Hasaki, Japan. The radar system provides instantaneous distributions of wave crests in the near-shore region, with image sequences comprising a clear spatial and temporal variation of the wave pattern. The spectra of radar echo signals and water surface elevations from wave gauge records were compared, and a relatively high coherence for a particular bandwidth was observed. A sequence of radar images was filtered at the dominant frequency, which was used to estimate the wavenumber distribution of the refraction field. The Fast Fourier Transform (FFT) and Maximum Entropy Method (MEM) were used to estimate the wavenumbers. The estimated wave angles were then compared with linear refraction analyses. The water depths along the pier were also estimated using the linear dispersion relationship and compared with the surveyed depths. The linear estimates of hydrodynamic parameters during the passage of the storm are presented in this paper to demonstrate the potential of radar measurements in capturing essential characteristics of coastal dynamics.

This paper addresses wave forces applied to vertical caisson breakwaters. Design diagrams are proposed to evaluate the reduction of the wave force induced by breaking and non-breaking short-crested oblique waves with increasing horizontal length of the caisson units. Results are derived by testing a model of a typical Italian vertical breakwater with a moderately high rubble mound in the CRF-LSF (Wallingford, UK) wave basin equipped with a multidirectional wave generator. Seven adjacent caisson modules were instrumented with synchronized force transducers. Non-breaking and breaking wave loads are distinguished on the basis of the frequency content. The reduction factor of the load per unit span is derived by the measured spatial correlation, following the argument developed by G. I. Taylor for random movements.

This study investigates the coupling field of grouped wind waves and their associated long waves in the surf and swash zones. Based on the calculated wave fields, the contributions of the wind waves and the long waves on the sediment transport efficiency are discussed. Spatial variations of the incident grouped wind waves propagating over a plane slope are calculated based on time-dependent mild slope equation. Generation of the long waves is reproduced based on a time-varying breakpoint model proposed by Symonds et al. [1982]. In order to obtain the long wave solutions extending over the landward region from the still water shoreline, calculations using nonlinear shallow water equations are connected to the Symonds' model invoking a moving boundary treatment. The Shields parameters under composition of the grouped wind waves and the associated long waves are evaluated to assess the mobility of the bottom sediment. The results show that the long waves have greater sediment transport efficiency over the grouped wind waves in the swash zone.