## 1 Introduction  
Huge investments are being poured into new renewable energies as part of the Green New Deal policies launched worldwide to solve at once the economic problems triggered by the pandemic as well as the climate crisis caused by unusual temperature events. Among the ocean renewable energy resources, wave power generation is attracting interest since it is able to secure clean energy from the ocean, which occupies two-third of the earth surface. However, the amount of energy that can be produced by wave power generation is difficult to predict accurately because of the large variability and high irregularity of the incident waves. In addition, there is a multitude of problems starting from the design to the offshore installation of the structure, including its safety. Compared with standardized offshore wind power energy, research on wave power generation is still under course considering the power generation method, the type of installation and the offshore conditions [1]. Korea has also undertaken an analysis of the wave distribution characteristics in the Jeju area using the SWAN model simulation according to the variation of the seasonal cycle, wave height and wind direction in order to assess the wave power generation method and applicability considering the offshore conditions [2]. Wave energy converters can be classified as attenuator, oscillating water column and overtopping device with respect to the underlying energy absorption principle. The attenuator harvests energy through the movement of an object reacting sensitively to the up-and-down and rotational motions of the incident wave [3; 4; 5]. The attenuator offers high conversion efficiency since it makes direct use of the wave energy but is structurally unsafe because of its exposure to the wave. The oscillating water column generates electricity through a special air turbine such as the Wells turbine or the impulse turbine activated by the pumping of the air entrapped inside the chamber of the device caused by the variation of the water level inside the chamber following the periodic oscillation of the incident wave [6; 7; 8]. The oscillating water column offers safety and convenient maintenance of the structure but has relatively low energy conversion efficiency. Having a surface inclined in the direction of the incident wave and capturing the wave breaking into its storage reservoir, the overtopping device extracts energy by using the potential energy created by the difference between the mean sea level and the sea level [9; 10; 11]. The overtopping device presents a simple structure with outstanding safety but harvests electricity only beyond a definite water level. The PTO (Power Take-Off) of wave energy can be classified into hydraulic motor systems [12; 13], pneumatic air turbine transfer systems [14; 15], hydro-turbine transfer systems [16; 17], direct mechanical drive systems [18; 19] and direct linear electrical drive systems [20; 21]. Worldwide, 31 companies are actively working to exploit the direct mechanical drive system, whereas 21 companies have chosen the hydro-turbine transfer system as of 2020 [22]. The present study proposes a new hybrid wave energy converter composed of a horizontal cylinder and a swing plate to improve the wave energy conversion efficiency using both the potential energy (height) and kinetic energy (period) of the incident wave. The horizontal cylinder generates electrical energy by using the potential energy of the incident wave, whereas the swing plate produces electricity by using the kinetic energy of the water particles. Additional improvement is brought by additionally applying a direct mechanical drive system-based PTO converter. The power-generating performance of the proposed hybrid wave energy converter is evaluated experimentally through a hydraulic model test at a scale ratio of 0.3 in a two-dimensional wave tank using direct conversion by a dynamo PTO system.