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The need for renewable energy has gained importance with growing concerns about climate change. Wave energy has attracted considerable attention owing to its sustainability potential. Reflection, refraction, diffraction, and shoaling of waves occur when waves propagate through a submerged structure. These mechanics, when properly utilized, can be employed to focus waves to a specific location and also to increase wave heights, by which wave energy is usually represented, for planning and designing wave farms. Wave focusing induced by a submerged crescent-shaped plate for different wave conditions, incident wave directions, and submerged depths mainly considering the potential applications of absorber wave-energy converters within the wave farm was investigated experimentally and numerically. All experimental regular wave conditions were controlled to be nonbreaking, and the numerical results were obtained by a 3D model, implemented through the boundary element method based on Airy wave theory. The results show that wave focusing appears behind the plate along the direction of the incident waves, and the locations of focused waves tend to be farther away from the plate for shorter-period waves. The maximum measured wave height can be 3.44 times higher than the incident wave height.

Wave attenuation for the purpose of coastal protection has been an important topic in coastal engineering. Wave attenuation in relation to the vortices induced by a solitary-like wave propagating over submerged breakwaters (BWs) is discussed in this paper. A series of hydraulic model experiments was conducted to investigate the occurrence of eddies, the types and combinations of submerged BWs, and related phenomena of the range expansion of vortices. The microscopic changes in the flow field, the variation of eddies, and the distributions of streamlines were analyzed using the particle image velocimetry (PIV) technique. The measured transmission and reflection coefficients, along with the concept of energy conservation, were also examined to support the results. The results indicate that the attenuated wave energy is related to the induced vortices, and show that the total relative vortex energy for rectangular submerged BWs is larger than that for undulating submerged BWs in both the single and composite sets. The magnitude of the maximum vorticity of the undulating BW sets is larger and more concentrated than that of the rectangular BW sets; however, the total vortex energy is slightly smaller owing to the narrower vortex area range.

Shih, R.-S. and Weng, W.-K., 0000. A study of long wave attenuation over composite undulating breakwaters. Journal of Coastal Research, 00(0), 000-000. Coconut Creek (Florida), ISSN 0749-0208.In this study, the wave attenuation of multiple impermeable sinusoidal profile breakwaters is investigated by a physical experiment conducted in a 21-m wave flume with a combination of breakwaters collocated with various widths (w) and heights (D). The breakwaters were arranged in different permutations and combinations (from one to three sets) on the bottom of various undulating slopes. The attenuation effect when waves propagated through the periodic-gradational undulating terrain was explored, and the optimization of various sinusoidal breakwaters was analyzed. This article discusses the properties of wave reflectance (K r ), transmittance (K t ), the energy loss coefficient (K L ), and the attenuation of composite terrain, including the optimal combinations of obstacles. The values of K r , K t , and K L were diverse because of various breakwater combinations and various wave conditions. The results indicated that the attenuation of long waves was effective and was affected by nonlinearity and dispersion. Wave decomposition occurred when a wave passed through the breakwaters; a high-frequency fluctuation appeared and dissipated the energy of long waves. The transmittance indicated that a composite of rapidly varying combinations was more favorable than a gradually varying section. Increasing the quantity of composite breakwaters also improved the attenuation effect on both the rapidly varying cases and the segmented gradually varying cases. The optimal combination required to eliminate the energy of long waves was also examined and confirmed using a solitary wave test. ADDITIONAL INDEX WORDS:Composite undulating breakwater, reflection coefficient, transmission coefficient, wave attenuation, long wave, solitary wave.

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