## 6 Test Results and Discussion
Figure 12: Results in case 2.  
resistive load applied in these experiments is approximately the optimum value in case 2. The largest overall efficiency achieved is about 39.22% in case 2. These experimental results are compatible with Equation (28) and linear wave theory in [29]. The inertial supplementary brings the natural frequency of the PTO system close to the excited wave frequencies. Therefore, the PTO system reaches close to the resonance area. As a result of hydrodynamic behavior, the elevation of the floating buoy is increased. Figure 13: Results in case 3. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author. **Conflicts of Interest:** The authors declare no conflict of interest. **Nomenclature** \begin{tabular}{l l} \(a\) & Buoy radius (m) \\ \(A\) & Wave amplitude (m) \\ \(A_{0}\) & The water plane area of the buoy at rest (m\({}^{2}\)) \\ \(b\) & The draft of initial position (m) \\ \(C_{d}\) & The drag coefficient \\ \(c_{F}\) & Force transition approximation coefficient (s/rad) \\ \(C_{g}\) & The group velocity (m/s) \\ \(D(kh)\) & The depth functions \\ \(d\) & The captured width (m) \\ \(E\) & The mean wave energy density per unit horizontal area (J/m\({}^{2}\)) \\ \(E_{g}\) & The generated energy (J) \\ \(F_{br}\) & The breakaway friction force (N) \\ \(F_{c}\) & The Coulomb friction force (N) \\ \(F_{e}\) & The excitation force (N) \\ \(F_{f}\) & Friction force from the PTO system (N) \\ \(F_{g}\) & The induced force by generator (N) \\ \(F_{h}\) & The hydrodynamic force (N) \\ \(F_{s}\) & The hydrostatic restoring force (N) \\ \(F_{\text{sup}}\) & The supplementary force (N) \\ \(F_{\text{PTO}}\) & The resistive force from the PTO system (N) \\ \(F_{r}\) & Radiation force (N) \\ \(F_{p}\) & Viscous force (N) \\ \(f_{3}\) & The excitation force coefficient \\ \(f_{v}\) & The viscous friction coefficient \\ \(g\) & Gravitational acceleration (m/s\({}^{2}\)) \\ \(H\) & Wave height (m) \\ \(h\) & Water depth (m) \\ \(l_{0}\) & The initial inertia (kg:m\({}^{2}\)) \\ \(l_{a}\) & The added inertia (kg:m\({}^{2}\)) \\ \(l_{fl}\) & Equivalent inertia of the flywheel (kg:m\({}^{2}\)) \\ \(l_{s}\) & The supplementary inertia (kg:m\({}^{2}\)) \\ \(i_{GB}\) & The gear ratio \\ \(k\) & The angular repetency (rad/m) \\ \(l_{1}\) & Center distance of the left mass (m) \\ \(l_{2}\) & Center distance of the right mass (m) \\ \(l_{a}\) & The arm length (m) \\ \(m_{a}\) & The added mass (kg) \\ \(m_{b}\) & The buoy mass (including support structure) (kg) \\ \(m_{1}\) & The added mass on the left side (kg) \\ \(m_{2}\) & The added mass on the right side (kg) \\ \(n\) & The rotational speed of driving shaft (rad/s) \\ \(\eta\) & Wave elevation (m) \\ \(\eta_{O}\) & The overall efficiency \\ \(R_{r}\) & The radiation damping coefficient \\ \(R_{g}\) & The torque coefficient from generator (Nms/rad) \\ \(P_{g}\) & The generated power (kW) \\ \(P_{m}\) & The mean wave power (kW/m) \\ \(P_{w}\) & The wave power interacted with the buoy (kW) \\ \(\rho\) & Water density (kg/m\({}^{3}\)) \\ \(S_{b}\) & The buoyancy stiffness (N/m) \\ \(T_{d}\) & The driving torque of the generator's shaft (Nm) \\ \end{tabular}