## 2 Materials and Methods
### Experimental Description
In a previous study by [PERSON] and [PERSON] [43], it was not possible to evaluate the power generation efficiency in high wave height conditions because a rack gear with the shape of a straight rod attached to a flap was separated from the gearbox. Therefore, a curved, round rack gear, as depicted in Figure 3, was designed in this study so that the rack gear was hardly se \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Case No.**} & **Distance to the** & **Water Depth \(h\) (m)** & **Wave Period \(T\) (s)** & **Wave Height \(H\) (m)** \\  & **Reflection Wall \(D\) (m)** & **(Submergence Depth \(d\) (m))** & **Wave Period \(T\) (s)** & **Wave Height \(H\) (m)** \\ \hline \multirow{8}{*}{1–328} & \multirow{8}{*}{1.09} & 0.425 (\(-\)0.05) & 1.4 & 0.04 \\  & & & 1.8 & 0.08 \\  & & & 2.2 & 0.10 \\  & & & 2.6 & 0.12 \\  & & 0.475 (0.0) & & \\  & & 0.510 (+0.035) & 3.0 & 0.16 \\  & 1.45 & 0.525 (+0.05) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental conditions. Figure 2: Flap design with an inverted triangular prism shape: (**a**) front view and (**b**) side view. The round rack gear was manufactured by pasting a flexible rack gear (DR1-2000) made of plastic on top of an aluminum-based arch structure (central angle: 68\({}^{\circ}\), thickness: 0.02 m). To minimize the energy loss due to friction between the gears, in this study, a simplified PTO system that generated electricity in one direction by applying two rotary generators with a simple gear structure was adopted. Specifically, as depicted in Figure 4, it consisted of a shaft, gears 1-3, and a cam clutch. Gear 1 is fixed to the shaft and meshes with the rack gear, which is fixed to the upper part of the flap. When the flap reciprocates owing to the waves, the meshing of gear 1 with the rack gear shaft is rotated with the shaft. On the shaft, two cam clutches that rotate in only one direction are fixed. Each cam clutch rotates according to a ratchet mechanism when the direction of the white arrow (shown in Figure 4b) and that of the shaft rotation match. However, when the rotary shaft rotates in a direction opposite to the direction of the arrow, the cam clutch shifts to idling. The cam clutches are installed so that the effective rotation is in the opposite direction. Gear 2 is sandwiched and fixed to the outside of each cam clutch. When the cam clutch rotates, gear 2 rotates, and the meshing of gear 3 with gear 2 also rotates simultaneously. Gear 3 is connected to a rotary generator, and the generator operates when gear 3 rotates. The detailed specifications of the gear units are presented in Table 2.  
Figure 4: Simplified power take-off system with the flap: (**a**) full view and (**b**) detailed view. Figure 3: Curved, round rack gear attached to the upper part of the flap. When the flap rotates shoreward, gear 1 and the shaft rotate in the clockwise direction, as illustrated in Figure 4a. Additionally, gear 2 (on), depicted in Figure 4a in blue, rotates in the clockwise direction and gear 3 rotates in the counterclockwise direction. Finally, gear 3 activates one of the generators. When the flap rotates seaward, gear 2 (off) depicted in green, rotates in the counterclockwise direction, and gear 3 rotates in the clockwise direction. Thereafter, another generator is activated. As for the opposite directions, as described above, gear 2 does not rotate due to the idle rotation. Each generator is then inactivated. The cam clutch has the effect of not only rotating only in one direction but also reducing the effect of the starting torque of the rotary generator. The rotary generator generally exhibits the most considerable torque during activation from a stationary state. If two generators are installed without cam clutches, the damping effects of the PTO system increase two-fold, thereby making it difficult for the flap to rotate.