The development and utilization of wave energy, heralded as a potential leading source of clean energy worldwide, have garnered considerable attention from the global research community. Among the diverse array of wave energy converters (WECs), the raft-type WEC stands out for its potential to efficiently harness and utilize wave energy, offering high energy conversion rates and a broad frequency response range. This paper delves into the evaluation of a raft-type WEC’s performance in various mooring configurations under different wave conditions. Our analysis primarily focuses on the dynamics of the two-body WEC using a weakly nonlinear three-dimensional potential flow solver. The considered device comprises two interconnected floating barges, incorporating a power take-off system at the hinged connection point. This investigation involves the use of equivalent linear damping to model the power take-off (PTO) system. To validate the numerical simulations, we conduct physical model experiments with WECs. Additionally, the coupling of the raft-type WEC’s dynamics and its mooring dynamics was examined, highlighting the performance differences between various mooring systems through a comparative analysis.

Vortex-induced vibration (VIV) of bluff bodies is one type of flow-induced vibration phenomenon, and the possibility of using it to harvest hydrokinetic energy from marine currents has recently been revealed. To develop an optimal harvester, various parameters such as mass ratio, structural stiffness, and inflow velocity need to be explored, resulting in a large number of test cases. This study primarily aims to examine the validity of a parameter optimization approach to maximize the energy capture efficiency using VIV. The Box–Behnken design response-surface method (RSM-BBD) applied in the present study, for an optimization purpose, allows for us to efficiently explore these parameters, consequently reducing the number of experiments. The proper combinations of these operating variables were then identified in this regard. Within this algorithm, the spring stiffness, the reduced velocity, and the vibrator diameter are set as level factors. Correspondingly, the energy conversion efficiency was taken as the observed value of the target. The predicted results were validated by comparing the optimized parameters to values collected from the literature, as well as to our simulations using a computational-fluid dynamics (CFD) model. Generally, the optimal operating conditions predicted using the response-surface method agreed well with those simulated using our CFD model. The number of experiments was successfully reduced somewhat, and the operating conditions that lead to the highest efficiency of energy harvesting using VIV were determined.

It has been known that the cross-sectional shape of a column oscillator significantly influences its vibrational characteristics and energy conversion capacity, and can alter the nature of flow-excited vibration (FIV). Whether the addition of appendages to oscillators with different cross-sectional shapes enhances energy conversion capacity remains uncertain. In this study, the vibration characteristics and energy capture capabilities of an elastically supported oscillator with a semicircular appendage, suitable for low-speed seafloor current environments, are investigated. Experiments were conducted at zero degrees incidence for Reynolds numbers ranging from 5.041 × 10³ to 7.562 × 10⁴, resulting in turbulent wake conditions. The hydrodynamic properties of the oscillators were evaluated through statistical analysis, Proper Orthogonal Decomposition (POD), and vortex core identification of Particle Image Velocimetry (PIV) fields. The energy capture capability of the oscillator was assessed through statistical analysis of its vibration displacement, frequency, and amplitude. The study's results indicate that an oscillator with symmetric sharp attachments and without vortex reattachment is favorable for galloping with self-excitation. Under equivalent conditions, the Circular-T-shaped oscillator demonstrates superior energy conversion capacity compared to existing models, with the galloping branch being the most efficient for energy conversion; the peak efficiency is 24.5% (Ur = 14.5). This study provides some baseline data and optimization solutions for flow-induced motion power generation.