## 3 Results and Discussions
### Behavior Characteristics of the Flap  
The averaged power generation efficiency of the proposed WEC has a \(k_{e}\approx 0.3\) for pattern A as shown in Figure 18 and the highest \(k_{e}\) appeared at \(D/L\approx 0.32\). As discussed above, the position of \(D/L\approx 0.32\) is regarded as the position where the motion of the flap is maximized with a less phase discrepancy between the motion of the flap and the standing waves. In this section, the effects of the behavior characteristics of the flap on \(k_{e}\) are examined.  
Figure 19 illustrates screenshots of the behavior of the flap over \(t/T\) for the case of the highest \(k_{e}\) at \(D/L\approx 0.32\). The flap rotates to the right (offshore) at \(t/T=1/8\) by the reflected waves from the reflection wall, and the flap is tilted to the rightmost side at \(t/T=5/8\). Then, the flap rotates to the left side (shore side) again by the incident wave from the right side and is tilted to the leftmost side at \(t/T=9/8\) (=1/8) after \(t/T=8/8\). It is confirmed that the flap rotates without any delay during one wave period. Other cases of \(D/L\approx 0.32\) also demonstrate a tendency to rotate smoothly without stay when rotating in the opposite direction after being most inclined.  
Figures 20 and 21 depict screenshots of the flap motion over \(t/T\) for the cases of \(D/L\approx 0.25\). In Figure 20, it can be confirmed that the rotation of the flap is small between t/T = 1/8, 2/8, and t/T = 7/8, 8/8. Similarly, a slight rotation was observed during t/T = 4/8-6/8 in Figure 21, with the flap appearing to be stationary for a moment. These phenomena to be halted for a while on either side (shore side in Figure 20 or offshore side in Figure 21) are known as the latching of WEC and the latching effect has an impact on \(k_{e}\). Pattern D in this study is a kind of latching effect, and it becomes a stationary state without any rotating owing to the dominant latching effect at a certain point in time. In the wave energy recovery system used in this study, it is considered that the cycle of the incident, and reflected waves contributing to the flap motion and the cycle of the rotation behavior of the flap including the damping of PTO system, are synchronized at the position of \(D/L\approx 0.32\). Hence, there is no temporal stationary phenomenon during rotation at \(D/L\approx 0.32\) and it results in the smooth rotation of the rotary generator in both directions. Therefore, \(k_{e}\) increases at \(D/L\approx 0.32\). However, in other cases, it was regarded that was is a phase difference up to the force for operating the generator between the behavior of the flap and the waves near the flap so that the flap momentarily stopped. Consequently, the generator was stopped temporally during the latching phenomenon and it leads to decreased \(k_{e}\).  
Figure 19: Screenshots of the flap motions for the case of \(D=1.09\) m, \(h=0.425\) m, \(T=1.8\) s, and \(H_{i}=0.12\) m at (**a**) \(t/T=1/8\) to (**h**) 8/8. \(D/L\) is 0.3253 and \(k_{e}=0.76\). The blue arrow denotes the wave direction acting on the flap, and the white dotted line indicates the rotational neutral axis of the flap. The blue solid line denotes the water surface.  
Furthermore, the rotational center of the pendulum is inclined to the shore side in Figures 19 and 20, and the offshore side in Figure 21. The leaning phenomenon of the flap depends on \(D/L\) and \(h/h_{f}\) and affects the reflection coefficient \(k_{r}\) at the front of the flap. \(k_{r}\) is also influenced by the characteristics of the flap with the wide upper part inducing overflow and overtopping when waves pass above the flap, as depicted in Figure 19 (\(t/T=7/8\)) and Figure 21 (\(t/T=5/8\)). However, as these phenomena and the energy loss induced by the tilted pendulum occur irregularly for each condition, it is considered that there is no clear correlation between \(k_{e}\) and \(k_{r}\) in Figure 17.