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An analytical model has been developed that can predict the scattering of irregular waves normally incident upon an array of vertical cylinders. To examine the predictability of the developed model, laboratory experiments have been made for the reflection and transmission of irregular waves from arrays of circular cylinders with various diameters and gap widths. Though the overall agreement between measurement and calculation is fairly good, the model tends to over- and under-predict the reflection and transmission coefficients, respectively, as the gap width decreases. The model also underestimates the energy loss coefficients for small gap widths because it neglects the evanescent waves near the cylinders. The peaks of the measured spectra of the reflected and transmitted waves slightly shift towards higher frequencies compared with that of the incident wave spectrum probably because of the generation of shorter period waves due to the interference of the cylinders. Both model and experimental data show that the wave reflection and transmission become larger and smaller, respectively, as the wave steepness increases, which is a desirable feature of the cylinder breakwaters.

Statistics of breaking waves across the surf zone are reanalyzed on the basis of various sets of field and laboratory data so as to provide coastal engineers with reliable information on breaking waves. The breaker index or the ratio of wave height to water depth is to be expressed as a function of the two parameters of beach slope and relative depth, and Goda's breaker index formula is revised slightly to reduce the slope effect. The breaker index for regular waves has inherent variability as expressed with the coefficient of variability, which increases from 6% to 14% as the beach slope becomes steep up to 1/10. The incipient breaking height of the significant wave is about 30% lower than that of regular waves, but the ratio of significant wave height to water depth gradually increases within the surf zone toward the shoreline. The wave height distribution is the narrowest in the middle of the surf zone, but it returns to the Rayleigh distribution near the shoreline owing to wave regeneration after breaking. The nonlinearity of random waves is strongest at the outer edge of the surf zone, but it is destroyed by the wave breaking process inside the surf zone. The ratios of statistical wave heights H_1/10, H_1/3 and H_rms to the spectral significant wave height H_m0 are shown to increase as the wave nonlinearity parameter increases up to the outer edge of the surf zone.

There are extensive studies on the topic of dynamic interaction between moored floating structures and waves, but the majority of the existing studies concerned the in-place condition of the moored floating system. There are few studies concerned the dynamic response of moored structures during the installation phase, especially for the case of immersion of moored tunnel element. In this study, scale model tests were performed to investigate the motion responses of the immersing tunnel element and hoist tensions between the element and pontoons under random waves. The heave motions of the tunnel were compared under various immersing depths. The comparison showed that the heave of the tunnel element was most severe during the stage of freeboard elimination, which reinforced the conclusion drawn by Song et al. [2014]. The experimental measurements quantitatively clarified the dynamic tensions on the hoist wires between the tunnel element and pontoons under different wave climates, immersion depths and negative buoyancy. In addition, with the quantitative information, the study recommends the operational parameters for the tunnel element immersion.

On a basis of experiments the evolution of irregular waves (wave group structure) in coastal zone are studied. It was revealed that during the transformation of the waves the amplitude-frequency structure of individual waves varies quasi-periodically in space and in time due to nonlinear interactions between harmonics. The phase shift between the first and second harmonics strongly depend on the main direction of energy transfer. The ratio between the amplitudes of the first and second harmonics of waves also varies in time: waves with small first harmonics can have large higher harmonics, and there is the effect of "filling" of intervals between wave groups with large amplitudes of first harmonics by wave groups with large amplitudes of highest wave harmonics. It was shown that construction of the model describing variability of individual waves in a coastal zone is possible only at an initial stage of deformation of waves.