# Experimental Validation of a Gyroscope Wave Energy Converter for Autonomous Underwater Vehicles
## 5 Parametric Analysis  
A wave period of 7 s was selected as the rated period in this paper, according to the RAO curve in Figure 2. This section analyzes the influence of different parameters on the output power of GWEC with the aim of increasing the energy conversion capability of GWEC as much as possible. Figure 5 shows a series of hot colormap arrays, which are all about the extracted average power of rotational speed and damping coefficient. The damping coefficient varies from 20 to 100 Nms/rad, and the flywheel rotational speed varies from 2000 to 10,000 rpm. The three sub-pictures are obtained under different wave amplitudes (\(A=8^{\circ}\), \(10^{\circ}\), and \(12^{\circ}\)).  
As expected, the energy output power increases as the pitch amplitude increases. As can be seen in Figure 5, for different wave amplitudes (Figure 5a \(A=8^{\circ}\); Figure 5b \(A=10^{\circ}\); Figure 5c \(A=12^{\circ}\)), the damping coefficient is between 30 and 40, and the rotational speed is \(\phi=8000\) rpm, which results in a higher power. Therefore, \(c_{y}=35\) Nms/rad is taken as the rated damping coefficient in this paper. An appropriate rotational speed can not only ensure the ideal output power, but also reduce the angular momentum and the power loss for maintaining the rotation of the flywheel compared to a larger rotational speed. The wave amplitude \(A=10^{\circ}\) is selected and combined with the above conditions, and from now on is defined the rated condition.  
Figure 4: Dry test workflow.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Values** & **Units** \\ \hline Platform working space & 0.4796 & m\({}^{3}\) \\ Motor power & 7.5 & kW \\ System flow rate & 48 & L/min \\ Cylinder maximum stroke & 280 & mm \\ Rated pressure & 10 & MPa \\ Pitch range & \(\pm 30\) & degree (\({}^{\circ}\)) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Supporting test parameters of the dry test platform.  
Figure 6 shows the performance of the system under wave period \(T=7\) s, pitch amplitude \(A=10^{\circ}\), flywheel rotational speed \(\dot{\varphi}=8000\) rpm and damping coefficient \(c_{y}=35\) Nms/rad. The torque is maximum in the \(x\) axis at 433 Nm, while the torque in the \(z\) axis is negligible compared to the other two axes. Under the influence of wave motion, the system's precession angular displacement, angular velocity and the period of the torque in the \(x\) and \(y\) directions are all the same as the wave period. It is worth noting that the periods of Figure 6f,g are both half of the wave period, while Figure 6g shows the output power of the system under rated conditions (the black line is the instantaneous power, and the blue is the average power), the peak power is 24.77 W and the average power is 9.66 W. In this paper, energy is obtained through a rotating PTO whose damping allows  
Figure 5: Hot colormap array of power output with different wave amplitudes under rated conditions: (**a**) \(A=8^{\circ}\); (**b**) \(A=10^{\circ}\); (**c**) \(A=12^{\circ}\).  
the conversion of wave energy into active power through the device, while reactive power is related to the spring effect. Therefore, from the perspective of power acquisition, the system output can also be improved by adjusting the stiffness and damping coefficient.