## 5 Conclusions  
Although a lot of research studies have been conducted on the viewpoint of energy conversion of the wave power generator, among them, research on the system analysis and concept design based on reliability assessment for the secondary energy conversion system has not. Accordingly, in this study, the secondary energy conversion system was analyzed and generalized using the IDEF0 method, and equipment and PFD needed for the design of the system were derived. Therefore, the efficiency DB and formula of the mechanical equipment were built, and a program for reliability assessment was developed and verified using this. The main results are summarized as follows: \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **PFD** \\ **(Secondary Energy** \\ **Conversion System)** \\ \end{tabular} } & \multicolumn{6}{c}{**Stage**} \\ \cline{2-11}  & \multicolumn{3}{c}{**1**} & \multicolumn{3}{c}{**2**} & \multicolumn{3}{c}{**3**} & \multicolumn{3}{c}{**4**} & \multicolumn{3}{c}{**Final**} \\ \cline{2-11}  & \(N_{1}\) & \(N_{2}\) & \(\eta\) & \(W_{r}\) & \(W_{e}\) & \(W_{r}\) & \(W_{e}\) & \(W_{r}\) & \(W_{e}\) & \(\dfrac{\text{RPM}}{\text{(No Loss)}}\) & \(\eta\times\text{RPM}\) \\ \hline \begin{tabular}{c} PFD 1 \\ (Gears–Shaft) \\ \end{tabular} & 80 & 10 & 0.98 & 1.0 & 1.0 & - & - & 0.98 & 8.0 & 7.84 & 2.0 \\ \begin{tabular}{c} PFD 2 \\ (Gears– \\ \end{tabular} & 20 & 10 & 0.98 & 4.0 & 0.96 & 1.0 & 1.0 & 0.94 & 8.0 & 7.52 & 8.0 \\ \
\begin{tabular}{c} PFD 3 \\ (Gears–H \\ Pump–H Motor) \\ \end{tabular} & 20 & 10 & 0.98 & 2.0 & 0.85 & 2.0 & 0.90 & 0.75 & 8.0 & 6.0 & 8.0 \\
\begin{tabular}{c} PFD 4 \\ (Pulley–Shaft) \\ \end{tabular} & 0.8 & 0.1 & 0.97 & 1.0 & 1.0 & - & - & 0.97 & 8.0 & 7.76 & 2.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Efficiency and RPM of the system having the same rotational increase rate. * In this study, verification of the derived PFD and the developed reliability assessment programs for conceptual design were performed by using Salter's duck type WEC. As a result of the analysis based on the assessed reliability, it can be seen that as the number of components in the system increases, the final efficiency gradually decreases. In addition, in the case of a system including a hydraulic system, the efficiency decreases to about 75%. For this reason, it can be determined that the mechanical system is more suitable as a secondary energy conversion system of the existing Salter's duck type WEC. In conclusion, it is judged that reliability of various PFDs can be assessed at the conceptual design stage, and the most suitable energy conversion system can be constructed. * In addition, PFDs having the same rotational increase rate were compared. As for system performance, RPM increases gradually as the number of equipment-pieces in the system increases. Therefore, for the systems used in other movable object type WEC, it is judged that more efficient design is possible if the design is performed by combining the conceptual design process suggested in this study and economic evaluation such as CAPEX and OPEX related to the system efficiency. * As a result, the conceptual design process derived from this study is shown in Figure 9. The process proceeds in the order of constructing the system based on the PFD derived through system analysis through IDEF0 and assessing the reliability of the constructed system using the performance formula of the equipment constituting the system. In addition, if a hybrid system that applies both a mechanical system and a hydraulic system is designed based on reliability assessment using a DB of equipment, it is expected that a more seamless conceptual design and reliability assessment will be possible. Finally, the subject of this study is in the unique field of wave power systems.