## 4 Verification
### Verification of PFD and Reliability Assessment Program  
The [PERSON]'s duck type WEC converts the rotational energy absorbed by the rotor from the wave by the transmission principle of gear or pulley, a secondary energy conversion equipment, and transmits it to another axis through the shaft, so that the generator develops. In the meantime, the rotation can be amplified by equipment such as gearbox, hydraulic pump, and hydraulic motor. In this study, reliability assessment was performed for each of the three systems consisting of gear and pulley in the first stage of the secondary energy conversion mechanical system in the derived PFDs of Figures 5 and 6 for the Salter's duck type WEC. Table 4 shows the assumptions of specifications and efficiency for each equipment constituting the secondary energy conversion system, the efficiency of the output to the input, and the ratio of the RPM without loss [32, 33, 45, 46, 47]. The evaluated parameters for each stage of the system using the performance formula-based reliability assessment program developed in the previous chapter are as shown in Table 5. For reference, the input RPM delivered in stage 1 was assumed to be 1.0, because it is intended to assess the ratio of RPM and the efficiency at the final stage. Figure 8: GUI of reliability assessment program of secondary energy conversion mechanical system. As shown in Table 5, when a secondary energy conversion system is constructed including only pulleys or gears, the final RPM is low, but the efficiency is the highest. As the number of equipment-pieces of the system increases, RPM gradually increases, but the efficiency gradually decreases. Moreover, the hydraulic system generally does not exceed 90% in efficiency for both pump and motor, so it can be seen that the efficiency drops up to about 75% for systems including the hydraulic system. For this reason, it can be determined that a combination of mechanical systems is more suitable as a secondary energy conversion system of the existing Salter's duck type WEC. In the reliability assessment using the developed program, if reliability is assessed based on the specifications and efficiency of equipment, 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. Accordingly, difficulties in deriving an optimal energy conversion system may be solved through various applied PFDs. In addition, to compare the results when the ideal RPM of the final stage is the same due to the same rotational increase rate of the system, Table 6 shows the results of comparing four systems composed of equipment with different specifications so that the final RPM in the no loss state is derived identically. As shown in Table 6, the RPMs without loss of the final stage on the four PFDs are all the same at 8.0, but the final efficiency \(\times\) RPM value is different due to the difference in efficiency of the equipment constituting each system. The results of efficiency \(\times\) RPM show that PFD 1 is the highest, followed by PFD 4. From these results, it can be judged that PFD 1 composed only of gears and shafts is the most efficient system with low loss. However, an efficient system does not necessarily mean efficiency in