## 4 Discussion of Simulation Results
### Self-Propulsion Simulation
#### 4.1.3 Calculation of Wake Fraction in Self-Propulsion Point  
On the basis of calculating the average flow velocity of the inflow section, the wake fraction \(\omega\) of each self-propulsion point of the hybrid-driven underwater glider was further calculated. It should be noted that the inflow velocity defined in the wake fraction formula is the average axial velocity at the propeller disk surface. However, since the section area at the propeller disk surface cannot be effectively calculated, the average axial velocity at Section 1 at 0.16D upstream of the propeller disk was used to calculate the wake fraction. The wake fraction \(\omega\) of each hybrid-driven underwater glider in the self-propulsion point state is shown in Figure 23, and the value ranges from 0.11 to 0.13, in line with the value range of submarine wake fraction 0.10 to 0.25. From the analysis of Figure 23, except for the conventional propeller Kap00, under the same velocity, the current retention fraction of the hybrid-driven underwater glider under the self-propelled condition shows a trend of increasing first and then decreasing with the increase in the bending degree of the end plate of the series Kappel propeller. Among these, the hybrid-driven underwater  
Figure 22: Comparison of calculation results of self-propulsion points of each hybrid-driven underwater glider, actual advance speed \(V_{A}\) (**a**), actual advance speed coefficient \(J\) (**b**), thrust coefficient \(K_{T}\) and torque coefficient \(K_{Q}\) (**c**), and actual propulsion efficiency \(\eta\) (**d**).  
glider with the propeller Kap02 has the highest current retention fraction under the self-propelled condition, and the hybrid-driven underwater glider with the propeller Kap05 has the lowest current holding fraction under the self-propelled working condition, which indicates that it is within a certain range. Appropriately increasing the bending degree of the end plate of the series of Kappel propellers can effectively reduce the accompanying phenomenon of the hybrid-driven underwater glider in the process of self-propulsion, reduce the interference of the propeller in the wake field of the hull, and improve the overall self-propelled performance of the hybrid-driven underwater glider. For the same type of Kappel propeller, the mate current fraction of the mixed-drive underwater glider under self-propelled conditions changes inversely with the speed of the mixed-drive glider. With the increase in the bending degree of the end plate of the series of Kappel propellers, the gap between the trail fraction at 3 kn and the trail fraction at 6 kn is 5.25%, and the gap between the trail fraction at 3 kn and the trail fraction at 6 kn decreases by 4.87%, indicating that the difference between the trail fraction at 3 kn and the trail fraction at 6 kn decreases by 4.87%. This indicates that, within a certain range, the speed of the hybrid-driven underwater glider can be reduced by appropriately increasing the bending degree of the end plate of the Kappel propeller so as to achieve the same self-propelled effect.  
The hull efficiency of the self-propulsion point is shown in Table 8. Since the total resistance of the hybrid-driven underwater glider is close to the same as the propeller thrust under the condition of the self-propulsion point, the thrust derating fraction is close to zero numerically.