The aim of this study is to investigate the vertical motion reduction of a floating body, such as marina or ferry dock, by interaction between floating and submerged bodies.
Firstly, a numerical study on the heave reduction of a floating body connected with a submerged body by connection line was conducted in the potential-flow computational domain in regular and irregular wave condition. A two-degrees-of-freedom system was modeled to control the vertical motion of floating and submerged bodies. In this study, heave added mass, radiation damping and excitation force were obtained by solving radiation problem and diffraction problem of a floating body and a submerged body based on boundary element method. The drag force acting on the submerged body was applied to the equation of two-body motion to model the drag effect. A parametric study revealed variations in the frequency of the maximum floating body heave reduction according to the dimensions of the submerged body and stiffness of the connection line. Hence, a heave response amplitude operator (RAO) of the floating body can be regulated by a two-body interaction. And floating body’s response spectra and significant heave amplitudes were obtained by applying various irregular wave conditions. By comparing the ratios of the heave RAOs reduction and significant heave amplitudes of floating body for various submerged body and connection line conditions according to wave conditions, the optimal conditions for the maximum vertical motion reduction were predicted regarding the resonant frequency of single body motion.
Then, secondly, based on the results of theoretical analysis of two-body interaction from the numerical study, an experimental study on the reduction of vertical motion of floating body using floating and submerged bodies interaction was performed in a two-dimensional wave channel. To investigate the effect of two-body interaction on the vertical motion of the bodies, various incident wave conditions are applied for various connection line’s stiffness and dimension of a submerged body. In order to find an optimal condition for maximal vertical motion reduction, the area of heave RAO near the resonant frequency is compared under various model conditions. Finally, the optimal condition for maximal motion reduction of the floater can be assessed.