## 2 Materials and Methods
### Experimental Description
In contrast, by making the cam clutch contribute to the idle rotation in a direction opposite to the effective rotating direction, the damping effects on the motion of a flap by two generators can be reduced to that of one in the effective rotation direction. A brushless direct current (BLDC) geared motor developed by Nakatsu MFG Co. Ltd. in Sayama City, Japan (NS-37 SGJ-25-24J36 SBLA1), which can control the rotation speed as a generator, was utilized as a rotary generator (hereafter, referred to BLDC generator). It can be used as a generator by removing the drive circuit inside the motor, thereby limiting the reverse flow of the current. The BLDC generator is composed of a BLDC generator and a gear head. General direct current generators have a brush that plays the role of passing current from a commutator rotating inside the generator to an external circuit. As the brush brings the commutator in contact with the switch, it is prone to wear due to friction and needs to be replaced regularly, thereby generating high maintenance costs. In contrast, the BLDC generator has the advantage of low maintenance cost and high power generation efficiency because there is no brush inside the generator, causing less friction. Additionally, BLDC generators can retain uniform torque over a wide speed range in comparison to alternating current (AC) generators, which induce torque loss when the rotation speed increases. The gear head can decelerate or accelerate the rotation speed by combining gears with different numbers of teeth. When two gears mesh with each other, the ratio of the rotation angle to angular velocity is the reciprocal of the ratio of the number of teeth. For example, when a gear with a large number of teeth (90) and a gear with a small number of teeth (20) mesh with each other, the angular velocity of the smaller gear is 4.5 times that of the larger gear (e.g., the larger gear rotates 240\({}^{\circ}\) when the smaller gear rotates 3 times). However, the torque of the larger gear with low rotational speed becomes 4.5 times that of the smaller gear, making the rotation of the WEC difficult. The gear head can increase the amount of power generation by accelerating the rotational speed inside the generator with relatively low rotations outside the generator. If the force that rotates the generator increases, the optimum rotational speed should be controlled based on the marine environments. Generators can be classified into single-phase and multi-phase generators. As the number of phases increases, power losses can be reduced. However, the required electrical equipment and construction costs increase significantly. Three-phase generators that can supply power most comfortably while minimizing power losses are commonly used not only in daily life but also in power plants. Therefore, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Internal** & **External** & **Width** & **Number of** & **Total Length** \\  & **Diameter** & **(mm)** & **(mm)** & **Teeth** & **(mm)** \\ \hline \hline \begin{tabular}{c} \end{tabular} & - & - & 5 & - & 560 \\ \begin{tabular}{c} \end{tabular} & 15 & 60 & & 60 & - \\ \begin{tabular}{c} \end{tabular} & 35 & 60 & & 60 & - \\ \begin{tabular}{c} \end{tabular} & 15 & 35 & 10 & - & - \\ \
\begin{tabular}{c} \end{tabular} & 6 & 18 & & 18 & - \\
\begin{tabular}{c} \end{tabular} & - & - & - & - & 600 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Specification of respective parts in PTO system. a three-phase BLDC generator was used in this study. Although the current waveform of a three-phase BLDC generator has a regular change in the polarity of the (+) and (-) poles, such as the AC in an AC generator, electricity rectifies the three-phase AC into DC. Consequently, the voltage increases by \(\sqrt{3}\) times. In this experiment, the voltage produced by the generator was rectified using a three-phase bridge rectifier (TOSHIBA, 30L6P45), and the rectified voltage was measured using a data logger.