Advances in Autonomous Underwater Drones

Dear Colleagues,

The demand for the autonomous underwater drone market is rising at a considerable rate, and the market value is predicted to reach over USD 2.5 billion by 2028. Underwater drones are not only advanced robots that operate in the ocean, but they are also a new type of vehicle to be used in ocean research. The characteristics of water and air are significantly different. Therefore, the resistance and other characteristics affecting underwater drones have significant differences. The traditional underwater drones have a torpedo-like shape due to their low resistance and suitability for long-distance trajectories. However, even if the configuration type is a full-drive unmanned submersible, when it performs high-speed manoeuvring tasks, its auxiliary thrusters cannot meet the expected control requirements and will also enter the under-actuation mode. Recently, many new types of underwater drones have appeared with different shapes and driving units, such as cross-medium, multi-rotor, and soft robotic fish. The navigation, guidance, driving device, and control technology of the unmanned submersible are the basis and prerequisite for completing a series of underwater special operations. Due to the complex underwater operating environment and irregular shapes, it is often difficult to accurately obtain the hydrodynamic coefficients of autonomous underwater drones, resulting in inaccurate system dynamic models and even issues affected by unknown time-varying disturbances such as ocean currents. In addition, there are usually weak observations, weak perceptions, and weak communication constraints, rendering full-state feedback control infeasible. Moreover, the quality and colour of underwater images are usually low due to various environmental factors, such as light. Autonomous underwater drones rely on vision sensors to perceive their surroundings and make appropriate motion decisions when performing underwater movements. Therefore, in-depth research on new types of underwater drones has important engineering value and theoretical significance. The new concept of underwater drones has many scientific issues, e.g., cross-medium mechanisms, new propulsion mechanisms, and new materials that are worthy of in-depth research by scholars.

Advances in sensors, design, power, computer vision, and AI-based technologies can pave the way to operate these drones for extended periods of time and can be used to monitor and assess the health of underwater ecosystems without the need for human divers, which are costly and dangerous. These devices can explore areas that are too deep, too dangerous, or previously untouched. Underwater drones can help cover more ground in a shorter period of time and collect data more accurately. These devices can perform otherwise impossible tasks such as mapping the ocean floor, locating lost or abandoned objects, and finding rare or endangered species and territories. The demand for autonomous underwater drones is increasing in several diverse applications, such as (1) reef monitoring; (2) environmental monitoring and mapping; (3) offshore windfarm inspection; (4) object detection and tracking; (5) simultaneous localisation and mapping (SLAM); (6) bio-inspired design and collaboration; and 6) seabed pipeline inspection.

The purpose of this Special Issue is to publish cutting-edge advances in technologies and applications related to works in the design of drones, driving mechanisms, control algorithms, and navigation algorithms, as well as energy, materials, and other fields, which are in line with the scope of journal submissions. This Special Issue has great appeal and can promote the development of underwater drone technology research.

Dr. Daxiong Ji
Dr. Asiya Khan
Dr. Pablo Borja
Dr. Dena Bazazian
Dr. Mohd Hisham Bin Nordin
Guest Editors

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