## 3 Numerical Simulations
### Simulation Results and Analysis of the Proposed System
Figure 8: Description of single and dual floating bodies: (**a**) Single sphere: front; (**b**) Single present body: front; (**c**) Top view of single sphere/present body: front; (**d**) Single sphere: rear; (**e**) Single present body: rear; (**f**) Top view of a single sphere/present body: rear; (**g**) Side view of a dual present body; (**h**) Top view of a dual present body. Figure 9: Pitch RAOs of various floating bodies by the present body-nonlinear method. Table 1 lists the average significant wave height, average peak period, and percentage of overall availability. The direction of all incident waves was the same to estimate the potential maximum power production. Based on the actual sea data, a representative significant wave height of 1.28 m and a peak period of 5.46 s (=1.15 rad/s) were selected. The water depth was 50 m, and the applied seawater density was 1025 kg/m\({}^{3}\). A PM spectrum was applied to generate a time history of the incident wave. The wave direction was fixed in the \(x\)-axis direction, and 130 regular component waves were superposed. The frequency range was 0.7 rad/s to 3.4 rad/s, excluding values less than 1% of the maximum spectrum value under the corresponding environmental condition. A simulation result of 3600 s after a 100-s ramping period was used for further analysis. Figure 11a shows the generated incident wave time series applied in this study. For validation, the theoretical PM spectrum and the regenerated spectrum obtained using the fast Fourier transform (FFT) with smoothing from the time series were compared (Figure 11b). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multicolumn{2}{c}{**Average Significant**} & \multirow{2}{*}{**Average Peak Period [s]**} & \multirow{2}{*}{**Overall Availability [\%]**} \\  & **Wave Height [m]** & & \\ \hline
2017 & 1.387 & 5.65 & 99.41 \\
2018 & 1.211 & 5.28 & 98.75 \\
2019 & 1.150 & 5.24 & 93.96 \\
2020 & 1.182 & 5.33 & 89.93 \\
2021 & 1.446 & 5.80 & 99.34 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Five-year average winter wave data in Buan measured by the KMA [44]. Figure 11: Description of the input wave: (**a**) Time history of wave elevation; (**b**) Wave spectrum. Figure 10: Wave buoy location in the Korean nearshore area: Buan. Figure 12 shows the bottom-fixed foundation structure with two WECs, and Table 2 lists the detailed structural properties of the platform. The platform consisted of 122 nodal points and 124 three-dimensional beam elements, and the deck was supported by four legs. The nodal points at the bottom are fixed to the seabed. The structural elements were all slender, and the Morison equation could be used. The inertia and drag coefficients of each leg were 2.0 and 1.0, respectively, which is typical for such slender cylindrical elements. The deck weight was 980 kN, and it acted equally on each leg. Two floating buoys in Figure 7 were connected to the foundation structure, as described in the previous sections. \begin{table}
\begin{tabular}{c c c c} \hline
**Component** & **Description** & **Value** & **Unit** \\ \hline \multirow{8}{*}{Platform} & Deck size (x \(\times\) y \(\times\) z) & 3 \(\times\) 2.4 \(\times\) 2 & m \\  & Leg height & 52.6 & m \\  & Diameter of leg member & 0.45 & m \\  & Thickness of leg member & 12 & mm \\  & Inertia coefficient & 2.0 & - \\  & Drag coefficient & 1.0 & - \\  & Deck weight & 980 & kN \\  & Structural weight per unit volume & 78.6 & kN/m\({}^{3}\) \\  & Modulus of elasticity & \(2.1\times 10^{8}\) & kN/m\({}^{2}\) \\  & Modulus of rigidity & \(8.33\times 10^{7}\) & kN/m\({}^{2}\) \\  & Number of elements & 124 & - \\  & Number of nodal points & 122 & - \\ \hline \multirow{8}{*}{Float} & Diameter & 2.0 & m \\  & Draft & 1.0 & m \\  & Mass & 2147 & kg \\ \cline{1-1}  & Damping coefficient of a & 100 & kN-m/(rad/s) \\ \cline{1-1}  & rotational damper & 8520 & - \\ \cline{1-1}  & Number of elements & 124 & - \\ \cline{1-1}  & Number of nodal points & 122 & - \\ \hline \end{tabular}
\end{table}