## 2 Hybrid Wave Energy Converter and Test Method
### Two-Dimensional Wave Tank and Hydraulic Model Test Conditions  
The hydraulic test was conducted in the two-dimensional wave-current-tide complex wave tank at the Experimental Center for Coastal and Harbor Engineering located in the Yeosu Campus of Chonnam National University. The wave tank presents a length of 100 m, a width of 2 m and a height of 3 m that can produce a maximum regular wave height of 130 cm, a wave period of 0.5 to 8.0 s and a maximum current velocity of 1.0 m/s. As shown in Figure 4, three capacity-type wave gauges were attached to the front of the column frame of the converter at 2.5 m and 5.5 m and in the rear at 3.0 m to measure the height of the incident wave produced by the wave generator. The hybrid wave energy converter was installed at a spot about 70 m from the wave generator. A water depth of 1.5 m in the tank was applied according to the law of similarity with a scale of 0.3. Table 1 arranges the detailed specifications of the fabricated reduced-scale prototype of the hybrid wave energy converter with a similitude of 0.3 that was installed in the wave tank. Figure 4: Two-dimensional wave tank: (**a**) definition sketch; (**b**) photograph of test. Tests were performed for six regular waves listed in Table 2 and six irregular waves using the PM spectrum (Pierson-Moskowitz spectrum) listed in Table 3 to consider various incident wave conditions. As shown in Figure 5, the tests were repeated 3 times for each wave period and height to compute the mean wave period and mean wave height. The mean incident energy flux for the regular waves is defined as follows [24]. \[P_{wre}=\frac{1}{8}\rho gH^{2}c_{g}, \tag{2}\]  
\[c_{g}=\frac{1}{2}\bigg{(}1+\frac{2 kh}{\text{sinh2}kh}\bigg{)}\frac{L}{T}\]  
where \(P_{wre}\) = energy flux of regular wave; \(\rho\) = density of water; \(g\) = gravitational acceleration; \(H\) = incident wave height; \(c_{g}\) = group velocity; \(L\) = wave length; \(k\) = wave number (\(2\pi/L\)); \(h\) = water depth and \(T\) = wave period. Irregular waves are represented as the superposition of regular waves. The mean energy flux of an irregular wave in shallow water can be expressed as follows:  
\[P_{wir}\approx\frac{\rho g}{64\pi}\bigg{[}\text{tanh}\bigg{(}\frac{4\pi^{2}h}{ gT_{e}^{2}}\bigg{)}^{3/4}\bigg{]}^{2/3}T_{e}H_{s}^{2} \tag{3}\] \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Wave Gen A** & **Length (mm)** & **Diameter (mm)** & **Wing Length (mm)** & **No. of Wings** & **Weight (N)** & **Draft (mm)** \\ \hline Horizontal & 1000 & 600 & 90 & 16 & 467.071 & 135 \\ cylinder & (3333) & (2000) & (300) & (16) & (17,298.9) & (450) \\ \hline
**Wave Gen B** & **Length (mm)** & **Height (mm)** & **Thickness (mm)** & **Weight (N)** \\ \hline Swing plate & 1000 & 450 & 20 & 568.786 \\  & (3333) & (1500) & (66.666) & (21,066.1) \\ \hline \hline \end{tabular} Values in parentheses indicate real values.  
\end{table} 
Table 1: Detailed specifications of hybrid wave energy converter. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Designation** & **Wave Period,** & **Wave Height,** & **Wave Length,** & **Wave Steepness,** & **Group Velocity,** & **Energy Flux,** \(P_{wre}\) \\  & **\(T\) (s)** & **\(H\) (m)** & **\(L\) (m)** & **H/L** & \(c_{g}\) (m/s)** & **(W)** \\ \hline RE 1 & 2.742 (5.006) & 0.330 (1.099) & 9.105 (30.551) & 1/27.609 & 2.542 & 338.66 \\ RE 2 & 3.291 (6.009) & 0.282 (0.939) & 11.444 (38.147) & 1/40.640 & 2.884 & 280.19 \\ RE 3 & 3.846 (7.022) & 0.278 (0.927) & 13.743 (45.809) & 1/49.417 & 3.116 & 295.17 \\ RE 4 & 4.379 (7.995) & 0.311 (1.035) & 15.910 (53.034) & 1/51.224 & 3.269 & 386.31 \\ RE 5 & 4.930 (9.001) & 0.264 (0.881) & 18.123 (60.409) & 1/68.543 & 3.382 & 289.64 \\ RE 6 & 6.572 (11.999) & 0.286 (0.952) & 24.617 (82.058) & 1/86.164 & 3.575 & 357.42 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Regular wave conditions for experimental test.