Wave attenuation properties of double trapezoidal submerged breakwaters on flat-bed

Abstract

This paper investigates the wave attenuation properties of the double trapezoidal submerged breakwaters on the flat-bed by conducting physical experiments subjected to linear and cnoidal incident waves. The method of Goda’s two points is used to separate the heights of incident, reflected and transmitted waves based on the experimental data. The possible factors affecting the wave attenuation properties of the double trapezoidal submerged breakwaters (i.e., the relative submerged water depth, relative breakwater spacing, wave steepness and relative wave height) are investigated with respect to the reflection and transmission coefficients. The results show that there is a range, within which the breakwater spacing has little impact on the reflection coefficient, and the transmission coefficient tends to be a constant. The influence of the wave steepness is reduced while the breakwater spacing is too large or too small. Within the range of the relative wave height tested in this study, the reflection and transmission coefficients increase and decrease with the relative wave height, respectively. The double trapezoidal submerged breakwaters model indicates a good attenuation effect for larger wave steepness, big relative wave height and within the range of the relative breakwater spacing between 12.5 and 14 according to linear and cnoidal waves. The changes of wave energy spectra between the double submerged breakwaters on the flat-bed are investigated by the fast Fourier transform (FFT) method, showing that wave energy dissipation can be reached more effectively when the relative breakwater spacing is 12.5.

Keywords

linear wave / cnoidal wave / double trapezoidal submerged breakwaters / reflection coefficient / transmission coefficient / attenuation coefficient

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