## 4 Simulation Results and Discussion
 \tag{58}\]  
Figure 8 shows the trajectory tracking results of the HAUV with a variable-sweep configuration during the diving process. Similarly, each of the three subgraphs in the figure has two parts: the upper part represents the tracking trajectory of the track angle, and the lower part represents the tracking error of the track angle. Conduct simulation tests on three different flight-path angle change rates. Still focusing on key time points of 1 s, 10 s, 15 s, etc., from the simulation results above, it can be seen that, similar to _case 1_, the variable-sweep level flight process of 5 s (starting with variable sweep) has no significant impact on the tracking of the controller. The difference is that the tracking error changes sharply after 15 s (when diving begins). As the diving flight-path angle increases, the convergence time of the tracking error increases, but within the limit of \([-0.6^{\circ},0.15^{\circ}]\), and the divergence is controlled during diving. Figure 9 shows the angle of rudder reflection of the HAUV when it changes sweepback during the level flight, and then dives into water. Similarly, the main focus is on the key time points in each subgraph, and there is no significant control input near 14 s to 15 s. From the reflection of the rudder angle at 15 s (starting to dive), it can be seen that the controller can quickly adjust the rudder. It can be analyzed that the aerodynamic parameter changes caused by the change in sweepback during the dive process have no impact on the control stability. Similarly, it is evident that as the flight-path angle increases when diving, the control input jitter of the angle of rudder reflection more frequently diverges. Figure 10 shows the change law of AOA and pitch angle rate under case 1, with a different sweepback angle rate. We can conclude that when \(\Delta\gamma\) increases at the same time, AOA and pitch angle's oscillations become more apparent. What is more, the disturbance increases suddenly when the dive begins, which affects the stability heavily in _case 2_. _Case 1_ and _case 2_ invoke controllers with the same performance, but the results are vastly different, indicating that the variable-sweep dive into the water scheme for _case 2_'s level flight process is not feasible. This is consistent with the natural behavior of kingfishers, gannets, and others entering the water to prey, who gradually fold their wings towards their body during the dive process (change sweepback of wings). In summary, the ADSC method used in this section has a certain degree of robustness for controlling systems with disturbances. In addition, the variable-sweep layout of the HAUV is more suitable for biomimetic diving with a variable-sweep strategy during the diving process. Figure 10: Under the phenomenon during plunge-diving, complete the change in variable sweepback fully and then ingress the water. Change laws of AOA and pitch angle rate of the variable-sweep HAUV in the plunge-diving process at different change rates of flight-path angle in _case 2_: (**a**) \(\Delta\gamma=\frac{\pi}{12}\). (**b**) \(\Delta\gamma=\frac{\pi}{6}\); (**c**) \(\Delta\gamma=\frac{\pi}{4}\). (**a**) Change law of AOA and pitch angle rate when \(\Delta\gamma=\frac{\pi}{12}\). (**b**) Change law of AOA and pitch angle rate when \(\Delta\gamma=\frac{\pi}{6}\). (**c**) Change law of AOA and pitch angle rate when \(\Delta\gamma=\frac{\pi}{4}\). Figure 9: The actual control input of angle of rudder reflection due to the variable\(-\)swept and plunge\(-\)diving process in _case 2_.