Autonomous Underwater Vehicles (AUVs) are the mainstream equipment for underwater scientific research and engineering. However, it remains a great challenge for AUVs to carry out near-seabed operations because of their poor maneuverability. In this paper, a new design for a high-maneuverability disc-shaped AUV is proposed, namely, the Autonomous Underwater Helicopter (AUH). We designed the AUH’s propulsion system through dynamic analysis based on the unique disc shape. The experimental prototype was built by mechatronics technology, after which several motion experiments were carried out to demonstrate the high maneuverability. We find that the prototype has high maneuverability: it can cruise at 0.8 m/s (about 1.5 knots), at least; its turning radius is zero and its turning speed is at least 20 deg/s; and the motion of specific curves in a small range was completed. It is demonstrated that over-actuation is not necessary for the high-maneuverability AUH because of its unique disc shape. A propulsion system consisting of four propellers and a buoyancy adjustment system is used for the highly maneuverable AUH. In addition, the AUH may be a solution for near-seafloor operations.

The autonomous underwater helicopter, shortly referred to as AUH, is a newly developed underwater platform with a unique disc shape. An autonomous underwater helicopter with a suboptimal disc shape is presented in this paper. It adopts a multirotor configuration and stable fins to overcome the shape shortcoming for motion stabilization. Its motion analysis and mathematical model have been introduced accordingly. Computational Fluid Dynamics (CFD) simulation is carried out to evaluate fins’ hydrodynamic performance. Proportional integral derivative (PID) and sliding mode fuzzy (SMF) control are adopted for controller design. Finally, the controller is applied on this AUH and extensively tested in various simulations and experiments, and the results illustrate the high stabilization and robustness of the controller and the hovering stability and manoeuvrability of AUH.

Artificial upwelling is a geoengineering method to repair and improve marine ecosystems, and its operation requires long-term and continuous temperature field observation. However, existing methods are rarely seen to accomplish such observation. In this study, we investigate the coastal acoustic tomography (CAT) to obtain the long-term horizontal temperature field of an artificial upwelling area in an anechoic tank. We conduct four sets of experiments with different CAT station numbers and compare their data with those collected from temperature sensors. By analyzing the travel time from the CAT experiments, the horizontal temperature field of the upwelling area could be mapped. The CAT results and the comparison results show that the surface temperature of the observed area decreases by approximately 3 °C after upwelling, while the temperature of where the CAT is deployed decreases by about 1 °C; the temperature is lowest at the center of the upwelling area. Increasing the number of stations and station spacing would improve the temperature mapping accuracy. Therefore, the feasibility of using the CAT system to observe artificial upwelling is proved valid. This study indicates the potential application of CAT in temperature field observation in artificial upwelling area in the sea.

Autonomous underwater helicopter, referred to as AUH, has high maneuverability in the horizontal plane and stable movement in the vertical direction due to its disc shape. Thus, the AUH demonstrates great advantages when working in scenarios that require high accuracy of horizontal movement, fixed height and depth, operation near the seafloor, and so on. In this paper, we propose a new design for an autonomous underwater helicopter with three thrusters in the vertical direction (three-vertical-thrusters), so it is equipped with fewer thrusters while maintaining maneuverability and motion stability. The three-vertical-thruster AUH not only achieves stable attitude control, but also reduces the number of thrusters, enabling the AUH to save space, reduce drag, and decrease power consumption. The three-vertical-thruster structure is designed first and compared with the existing four-vertical-thrusters type to verify its advantages through dynamic analysis and hydrodynamic simulation. The three-vertical-thruster AUH is then modelled, and a compensation method is proposed for its more complex control. The three-vertical-thruster AUH’s controllability and stability are also verified by experiments on the basis of the experimental prototypes.