Performance of the Wave Energy Dissipation of a Floating Breakwater with Truss Structures and the Quantification of Transmission Coefficients

The wave absorption performance of a new type of steel floating breakwater with truss (FBT), which is composed of a box-type pontoon and truss structures, has been investigated experimentally. The truss structures are attached to the front and the rear of the pontoon, and exaggerate wave energy dissipation due to wave breaking. Flow visualization has revealed that the front truss breaks the incident waves and effectively converts wave energy to turbulent energy. Image analysis of the motions of the FBT and determination of the transmission coefficient K(t) showed efficient dissipation of wave energy resulting from the truss structure. K(t) is also discussed and quantified with the aid of dimensional analysis. Values of K(t) are plotted against the ratio of the water depth h to the wavelength of incident waves L, and the profiles obtained are normalized by introducing values of h/L at which K(t) equals 0.5, i.e., (h/L)(0.5). Normalization gives a universal empirical expression for K(t), and empirical expressions of (h/L)(0.5) are also obtained by independently changing the shape parameters and the wave steepness. A graphic chart of (h/L)(0.5) is provided so K(t) of the FBT can be evaluated easily. This data-reduction method developed for the quantification of K(t) may be applicable for other floating breakwaters as well as for this new type.