Among the various wave power systems, Salter's duck (rotor) is one of the most effective wave absorbers for extracting wave energy. The rotor shape is designed such that the front part faces the direction of the incident wave, which forces it to bob up and down due to wave-induced water particle motion, whereas the rear part, which is mostly circular in shape, reflects no waves. The asymmetric geometric shape of the duck makes it absorb energy efficiently. In the present study, the rotor was investigated using WAMIT (a program based on the linear potential flow theory in three-dimensional diffraction/radiation analyses) in the frequency domain and verified using OrcaFlex (design and analysis program of marine system) in the time domain. Then, an experimental investigation was conducted to assess the performance of the rotor motion based on the model scale in a two-dimensional (2D) wave tank. Initially, a free decay test (FDT) was carried out to obtain the viscous damping coefficient. The pitch response was extracted from the experimental time series in a periodic regular wave for two different wave heights (1 cm and 3 cm). In addition, the viscous damping coefficient was calculated from the FDT result and fluid forces, obtained from WAMIT, are incorporated into the final response of the rotor. Finally, a comparative study based on experimental and numerical results (WAMIT & OrcaFlex) was performed to confirm the performance reliability of the designed rotor.

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A wave energy converter (WEC) that generates electrical energy from wave energy is a subject of high research interest in academia. Salter's duck, which is a pitch-type WEC positioned on the water surface to primarily convert wave energy into rotational kinetic energy of a floating body (rotor), is one of the oldest WECs and has been researched since the 1970s (Salter et al., 1975). Salter's duck maximizes wave energy absorption by designing the front and rear shapes differently and thus is theoretically known to have nearly 90% energy absorption efficiency (Swift-Hook et al., 1975). Several recent studies in South Korea have designed Salter's duck-type WECs suitable for the western waters of Jeju Island. The design parameters and performance of a rotor have been verified through a parametric study of optimal motion performance using the wave data of the western waters of Jeju Island (Poguluri and Bae, 2018), a study on estimating viscous coefficients of a rotor using computational fluid dynamics (CFD) (Poguluri et al., 2019a), and a numerical and experimental study on the linear behavior of a rotor (Kim et al., 2019a). These previous studies, however, focused on only one WEC rotor, so the effects of hydrodynamic interactions between adjacent modules must be analyzed considering how multiple WECs are simultaneously installed in the seas in general (Kim et al., 2020). Previous studies on analyzing dynamic behavior by arranging multipleWECs include an analysis of multiple cylindrical WECs in a heaving motion in the frequency domain (Lee et al., 2018) and in the time domain (Bae and Lee, 2017) as well as a study on optimal arrangement for improving the overall performance of multiple cylindrical WECs (Kim and Bae, 2019b). In these studies, a multibody analysis was performed for cylindrical WECs in the frequency domain to which a linear potential theory was applied, based on which the motion performance of individual WECs was evaluated by solving the coupled equations of motion in the time domain. An approach for computing performance changes and interactions may be effective for multiple cylindrical WECs with a fairly weak nonlinearity of motions; however, there are limitations in examining performance changes and interactions of arrayed WEC rotors based only on linear potential theory, because asymmetrical WEC rotors applied in this study have a

This study primarily investigates an optimum energy conversion efficiency of asymmetric wave energy converter (WEC). A power take-off (PTO) system that provides a constant load torque opposite to pitch motion was implemented. Incident wave conditions were selected based on the measured data in the western sea of Jeju Island, South Korea. An optimum torque was calculated by comparing the time-averaged extracted power with various PTO load torque. InterDyMFoam solver based on Reynolds-averaged Navier-Stokes (RANS) equations were used in an OpenFOAM v4.0 framework—an open-source computational fluid dynamics model—against the experimental results derived from the wave flume. The upward pitch excursion was induced by wave force due to the asymmetric WEC characteristics; however, the downward pitch excursion depends on its weight. Numerically, the PTO torque was only loaded in uni-direction against the upward pitch motion. Moreover, the optimum PTO torque was estimated by comparing the time-averaged extracted power. Finally, the optimum PTO torque was evaluated by an irregular wave as a function of significant wave height. The optimum PTO provides design information about the asymmetric wave energy converter to improve energy conversion efficiency.

The aim of the research presented here is to develop a new experimental device which would permit the study of multiscale and vertically-variable oceanographic flows using a system called the Hydraulic-Control Wave-maker (HCW). Both the inlet and outlet flume boundaries are composed of an adjustable set of vertical baffles. Each baffle is connected to an individual flow control system, such that the vertical distribution of flow is entirely controllable. In such a system, any arbitrary flow can be reasonably created, and different sets of baffles can be connected to different reservoirs to create vertical density profiles. In this study, before constructing the experimental device, numerical analyses to verify the method of HCW, such as its ability to generate waves are carried out. Moreover, the small physical model with one baffle connected to our own flow control system is developed by ourselves. Long and short sine wave are generated by a small-scale HCW and the snapshots are presented. In practical, thus, The possibility of system can be confirmed.