Shih, R.-S. and Weng, W.-K., 2016. A study of long wave attenuation over composite undulating breakwaters.

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.