Performance of an F-type floating breakwater: A numerical and experimental study

Abstract

Floating breakwaters are structures with large ratio of length to breadth. The profile of an floating breakwater is the key to the hydrodynamic properties of it. In this work, a new kind of an F-type floating breakwater is presented. Its profile is asymmetric and looks like the English letter “F.” We present both numerical and experimental findings on this F-type floating breakwater. Based on linear potential-flow theory, first, the boundary-element method is presented to study the interaction problem of a two-dimensional floating body with waves. Following that, the two-dimensional experiments are conducted in a wave flume to measure the diffracted and radiated waves, the resulting transmission and reflection coefficients, and the motion responses of the F-type floating breakwater. It is shown that the experimental data are, in general, in good agreement with the numerical predictions. The transmission coefficients that are measured and calculated are under 0.5 when the ratio of B/λ (the ratio of model breadth to wavelength), when the F-type floating breakwater is fixed, is larger than 0.18. The ratio of B/λ, when the F-type floating breakwater is allowed to slide vertically only, is larger than 0.2 and the ratio of B/λ, when the F-type floating breakwater is allowed to rotate and slide, is larger than 0.22. To understand how the profile geometry can affect the performance of the F-type floating breakwater, a parametric study of the F-type floating breakwater’s main dimensions, including its profile breadth, draft, and angle, is conducted on the wave transmission coefficient. It is found that the transmission coefficients are particularly sensitive to the change in draft for certain sea conditions. These results are important since seeking the optimal principal dimensions can ensure minimum volume of displacement, thereby using less material and reducing the cost of construction sharply.

Keywords

F-type floating breakwater boundary-element method hydrodynamic coefficients model tests transmission coefficients reflection coefficients motion responses potential theory

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