## 4 Simulation Results
### Vehicle Performing a Complete Mission  
This section highlights the simulations encompassing the behaviors of the system in various complex scenarios, using a constant depth survey and constant altitude survey as representative of possible missions, and exploiting the features of task priority framework. These two mission scenarios, which are performed and studied in the following sections, will exploit all the behaviors of the system that were discussed in Section 3. The ability to dock onto a moving docking station is also evaluated in this study. As previously mentioned, a lawn mower profile-based survey is done at constant depth and constant altitude exploiting the LOS path following algorithm [53]. Once the vehicle completes the survey, it homes in to the moving docking station and finally docks. The \(\mathcal{A}_{p}\), \(\mathcal{A}_{sd}\) (for  
Figure 10: X300: (**a**) Maneuver showing the vehicle performing docking into a tight space, starting in front of the moving docking station. (**b**) Maneuver showing the vehicle performing docking into a tight space, starting from close proximity of the moving docking station and going around the dock structure without collision. Figure 9: X300: (**a**) Maneuver showing the vehicle performing docking to a docking station, going around without collision, (**b**) Maneuver showing the vehicle performing docking into a tight space inside a moving docking station, starting from a distance. constant depth path following mission), \(\mathcal{A}_{sa}\) (for constant altitude path following mission), \(\mathcal{A}_{a}\), and \(\mathcal{A}_{d}\) actions are used for the missions. Some possible ways of docking approaches are depicted in Figure 5. In the missions, we present docking approaches similar to the scenarios taken from [32; 33] where the vehicle docks to the moving docking stations from the top and side, respectively. However the classic approach is to dock from the aft of the docking station, e.g., to dock to a towed [31] or funnel-shaped [23] docking station which was already presented in Figures 9b and 10. The dock moves with a constant heading throughout the mission. Ocean current disturbances are also introduced in the following mission simulations. The missions are carried out as follows. A lawn mower profile is chosen for the survey mission as depicted in Figure 11. Waypoints are inserted wherever the vehicle needs to make a turn during the mission. The waypoint locations, vehicle initial position and orientation, the dock velocity, and the ocean current velocity used in the simulations are reported in Table 3. The vehicle starts from the home location and proceeds towards the 1 st way-point by following and aligning to the system velocities with the help of action \(\mathcal{A}_{p}\). The vehicle transits via each way-point using LOS based control at constant depth using \(\mathcal{A}_{sd}\) action or constant altitude using \(\mathcal{A}_{sa}\) action, along with the \(\mathcal{A}_{a}\) action. At every stage of the mission, the vehicle reactively avoids the obstacles along its path. A minimum altitude is always maintained to avoid crashing into the seafloor or any bottom structures and while traveling close to seafloor, the vehicle follows the terrain to avoid crashing into it when maneuvering over rough terrain. Once the vehicle completes its mission, the homing stage will start using the action \(\mathcal{A}_{p}\). The action will drive the AUV to the associated pre-docking position, defined w.r.t. the docking station as stated earlier. Thanks to the tasks defined in action \(\mathcal{A}_{p}\), the vehicle will align its heading to the system velocities as it proceeds towards the pre-docking position, while gradually aligning to the terminal orientation too. Once the misalignment errors are within the acceptable range, the vehicle surges or translates towards the final dock position with the help of action \(\mathcal{A}_{d}\).