## 3 Experimental Results and Discussion
Figure 6: Real-time generated power, torque and rotational speed for RE 1 case. Figure 7: Mean power according to load torque for various regular wave conditions. Figure 9 plots the mean CWR of the hybrid wave energy converter according to the variation of the change in the load of the servo motor in regular wave conditions. As expressed in Equation (4), the CWR is the generated mean power measured during 2 min divided by the mean energy flux of the incident wave. \[\text{CWR}=\frac{P(\text{generated mean power})}{P_{w}(\text{incident wave energy})} \tag{4}\]  
For all the given regular wave conditions, the maximum CWR is developed for the load torque of the servo motor, ranging between 0.0077 Nm and 0.0385 Nm. The highest CWR (33.48%) is observed for regular wave case RE 1 with the shortest period, and the CWR tends to reduce with longer periods. Table 4 arranges the maximum CWR of mean and instant maximum power for each of the considered regular wave conditions. It appears that the maximum instant CWR can convert 66.28% of the incident wave energy into electric power for regular wave case RE 1. A larger CWR is observed for shorter wave periods. The ratio of the instant maximum  
Figure 8: Instant maximum power according to load torque for various regular wave conditions. Figure 9: CWR of mean power according to load torque for various regular wave conditions. CWR to the mean CWR (\(P_{ma}/P_{me}\)) ranges between 1.980 and 4.105, which indicates that the ratio tends to increase as much as the mean CWR decreases with longer periods of the incident wave. Figure 10 plots the real-time power generation characteristics for irregular wave case IRRE 1 with the largest variation in RPM and the highest generated power among the irregular wave conditions using PM spectrum. Figure 10 presents the real-time output measured during 5 min resulting from the incident irregular wave generated by attributing a mechanical load torque of 0.0231 Nm to the servo motor. The proposed hybrid wave energy converter is able to generate power by exhibiting the characteristics shown in Figure 6 that fit in real time with the characteristics of the incident wave since the irregular wave is the result of the combination of various regular waves. In addition, the RPM of the wave energy converter shows large variation according to the incident wave condition throughout the irregular wave tests, whereas the torque seems to have small variation. Consequently, it appears that the hybrid wave energy converter reacts very sensitively to the change in the incident wave height. A series of tests were conducted for nine load torques of the servo motor, namely 0.0 Nm, 0.0077 Nm, 0.0231 Nm, 0.0385 Nm, 0.0771 Nm, 0.1542 Nm, 0.2313 Nm, 0.3084 Nm and 0.3855 Nm, to evaluate the CWR of the hybrid wave energy converter for irregular wave conditions. Figures 11 and 12 plot, respectively, the mean power and instant maximum power generated during 5 min under irregular wave condition. Higher power appears to have been generated at load torques below 0.0771 Nm, whereas the generated power seems to experience gradual reduction beyond 0.0771 Nm. It is noteworthy that the mean generated power at load torque greater than 0.15 Nm exhibits very large values in irregular wave conditions differently from that in regular wave conditions. The mean generated \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Wave** & **Incident Wave** & **Generated Mean** & **Max. Mean** & **Instant Max.** & **Max. Instant** & \\
**Condition** & **Power, \(P_{in}\)** & **Power, \(P_{me}\)** & **CWR, \(P_{me}/P_{in}\)** & **Power, \(P_{ma}\)** & **CWR, \(P_{ma}\)/\(P_{in}\)** & **P\({}_{ma}\)/\(P_{me}\)** \\ \hline RE 1 & 338.66 & 113.39 & 0.3348 & 224.46 & 0.6628 & 1.98 \\ RE 2 & 280.19 & 54.69 & 0.1952 & 124.74 & 0.4452 & 2.281 \\ RE 3 & 295.17 & 14.13 & 0.0479 & 46.35 & 0.157 & 3.28 \\ RE 4 & 386.31 & 34.85 & 0.0902 & 100.57 & 0.2603 & 2.886 \\ RE 5 & 289.64 & 19.46 & 0.0672 & 60.51 & 0.2089 & 3.109 \\ RE 6 & 357.42 & 14.72 & 0.0412 & 60.43 & 0.1691 & 4.105 \\ \hline \end{tabular}
\end{table}