Wave interaction with a symmetrical dual-pendulum floating breakwater: An analytical study

A symmetrical dual-pendulum floating breakwater (SDP-FB) is proposed, consisting of a box-type floating body with two pendulums symmetrically suspended beneath it, yielding five degrees of freedom: global surge and heave, box pitch, and antisymmetric and symmetric pendulum pitch. Based on linear potential flow theory, the wave diffraction and radiation problems are solved using the matched eigenfunction expansion method. Hydrodynamic coefficients are obtained, and the equations of motion yield the response amplitude operators and the transmission coefficient. Following validation against published numerical and experimental results, the effects of the pendulum mass ratio, separation distance, and pendulum length on hydrodynamic performance are systematically investigated. The results indicate that the dual pendulums mainly modify the surge response of the floating box, while the heave response is nearly unaffected. The separation distance primarily controls the position and depth of the low-transmission trough and the effective wavenumber range of low transmission, particularly at larger mass ratios. A large mass ratio combined with a large separation distance produces the widest low-transmission wavenumber range for the considered pendulum length. Compared with box-type and single-pendulum floating breakwaters, the SDP-FB achieves a lower transmission coefficient and a wider effective wavenumber range, especially in the intermediate-to-high wavenumber range.