## 3 Experimental Results and Discussion

Table 4: Maximum CWR of mean and instant maximum power for regular wave conditions. Figure 10: Real-time generated power, torque and rotational speed for IRRE 1 case. power does not experience sharp decreases even when the period of the incident wave becomes longer. Accordingly, the proposed hybrid wave energy converter can provide very stable power generation under irregular wave conditions similar to that occurring actually in a marine environment. In Figure 12, the values of the instant maximum generated power show irregularity unlike the similar mean power curves observed in regular wave conditions. This last observation indicates that the power generation reflects the irregular characteristic of the incident wave. Figure 13 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 irregular wave conditions. The CWR is expressed as the generated mean power measured during 5 min divided by the mean energy flux of the incident wave. For the considered irregular wave conditions, the maximum CWR occurs when the load torque of the servo motor ranges between 0.0077 Nm and 0.0385 Nm, and the CWR tends to reduce proportionally to the increase in the applied load torque. Moreover, the largest CWR (48.87%) is observed for irregular wave case IRRE 1 with a short period, which represents an improvement by about 1.46 times compared with the regular wave condition (33.48%). It appears also that the reduction ratio of the  
Figure 11: Mean power according to load torque for various irregular wave conditions. Figure 12: Maximum power according to load torque for various irregular wave conditions. CWR with longer periods is smaller for the irregular wave condition than for the regular wave condition. Table 5 arranges the maximum CWR of the mean and instant maximum power for each of the considered irregular wave conditions. The ratio of the instant maximum CWR to the mean CWR (\(P_{ma}/P_{me}\)) ranges between 1.980 and 4.105. Considering that the ratio of the mean height to the maximum height of a common incident irregular wave ranges between 2.56 and 3.2 (\(H_{\text{max}}=(1.6\sim 2.0)H_{1/3}=(1.6\sim 2.0)\times 1.6\overline{H}=(2.56 \sim 3.2)\overline{H}\)), it appears that the proposed hybrid wave energy converter reacts very sensitively to the change in the incident wave height. Figure 14 compares the real time power, mean incident energy and mean generated power measured during 5 min for irregular wave case IRRE 1 that exhibited the highest power generation among the tests. The real-time measured power is sorted in descending order to verify the frequency and level of the output. In view of the distribution of the sorted values computed at time steps of 0.1 s, the generated power exceeding the energy of the incident wave represents approximately 16.91% of the whole set, and the generated power exceeding the mean power represents about 32.43% of the whole set. This indicates that the clutch gears adopted to improve the CWR of the proposed hybrid wave energy converter are very efficient in irregular wave conditions. The CWR of previous wave energy converters provided limited mean power generation or were within a narrow load range. Additionally, by applying a dynamo PTO system, this study could propose wide-ranging mean power and instant maximum power by the hybrid wave energy converter and acquire diversified data necessary for the design of the wave energy converter.