Study On Hydrodynamic Characteristics Of Hinged Floaters-type Wave Energy Dissipators

Over the last decades,flexible floating bodies both reducing waves and absorbing wave energy have gotten more and more attentions.In this paper,a kind of hinged floaters-type wave energy dissipator with independent intellectual property rights is proposed,capturing wave energy by the hinged floaters and consuming the absorbed energy through the power dissipation system,thus weakening the wave energy and then reducing the wave height.Both a numerical simulation and a physical experiment are carried out to study the operating and hydrodynamic characteristics of this type of device,and to validate the effectiveness and feasibility of this method of reducing waves.Based on the Reynolds-averaged Navier–Stokes(RANS)equation,the nonlinear multi-floating structure motion theory and the fluid-structure interaction theory,different mathematical models for the hydrodynamics of the hinged floaters-type wave energy dissipators with 3 and 4 degrees of freedom(DOF)are presented,which consider the constraints of a pile and a mooring system respectively.The models include the interaction of the hinged floaters,the viscous fluid,the power dissipation system and the restraining system.Finite volume method(FVM)is used to discrete the equations of fluid motion,while the Runge-Kutta(RK)method is employed to discrete the equations of structure motion.A dynamic mesh method of the structured mesh is applied to update the mesh every time step,therefore full coupling between the fluid and the structure is achieved.Hydrodynamic characteristics of the hinged twin-floater device with 3-DOF are analyzed numerically.Investigations into the effects of the damping coefficient,the wave parameter and the flow velocity on the performance of device with 3-DOF are included.The results show that there exists an optimal damping coefficient,where the power dissipation rate reaches the maximum value,whereas the wave transmission coefficient reaches the minimum value.The results also reveal that the differences in behavior exhibited by an inviscid fluid and a viscous fluid can be large and vary considerably,depending on the flow velocity.Numerical study on the hydrodynamic characteristics of the hinged twin-floater device with 4-DOF is carried out to examine the effects of stiffness of mooring rope,damping coefficient,hollow parameters,wave frequency and flow velocity on the performance of the device.The differences of the mechanisms of wave elimination between the solid and the hollow floaters are discussed.Results indicate that the viscous dissipation rate of hollow floaters is significantly larger than that of solid ones.The power dissipation rate per unit surface area and the total dissipation rate per unit surface area of hollow floaters are both larger than those of solid ones.Increasing of the stiffness of mooring rope significantly weakens the performance of the device on wave energy absorption.Physical model of the twin hinged floaters-type wave energy dissipator with adjustable longitudinal dimension is set up,and the performance of the device under various wave conditions is observed.On the one hand,the observation data can be applied to validate the numerical model,on the other hand,the comparison of the numerical and experimental results reveal that the numerical model investigates the complex interaction of viscous fluid,power dissipation system,constrained system and structures of nonlinear motion effectively.The results present that for a specified total longitudinal length,the difference in energy dissipation ratio between the two reciprocal fore-and-aft raft length ratios can be significant and varies considerably,depending on wave frequency,whereas the difference in wave transmission coefficient between two reciprocal fore-and-aft raft length ratios is very small almost regardless of wave frequency.