# Development of Modular Bio-Inspired Autonomous Underwater Vehicle for Close Subsea Asset Inspection
## 2 Motivation and Background  
Traditionally, offshore infrastructure such as wind turbines has been inspected in person by humans, with the associated risks to safety in inclement weather and changing underwater conditions. More recently, automated inspection systems such as drones above the water and underwater vehicles have been developed, but with limited autonomy and loitering time. Human intervention to control an underwater vehicle can be quite beneficial, especially during complex inspection tasks, which require human judgement and intuition. ROVs have been in existence since 60 s [14], and received international attention following the aftermath of the Deepwater Horizon disaster in the Gulf of Mexico in 2010 [15]. In this disaster, human operators sent ROVs fitted out with a saw and manipulators to cut and cap an oil well head at a depth of one mile. The precise control, flexibility and ability to have dangerous jobs done at great depths make ROVs an ideal solution for such inspection tasks in open water. ROVs enable unique access to the underwater world and can also have robotic arms for object manipulation to provide a safe alternative to perform otherwise costly and dangerous tasks. Since they are tethered, their advantage over AUVs will, however, be restricted by the complexity of the underwater infrastructure. Unlike ROVs, AUVs have no human intervention in their control loop, and they run more independently. AUVs are traditionally used to gather oceanographic data using cameras, SONAR and other sensing instruments. Using advanced control algorithms, AUVs can run in an autopilot mode for hours and even days without receiving constant operator guidance. REX II [16] from MIT is a unique AUV that can run autonomously and through a remote operator. While loitering autonomously, REX II can transmit video images over a wireless channel using a tethered buoy equipped with a radio modem, which is also used in the manual operating mode to enable remote control by an operator. Odyssey IV is an AUV with a pioneered concept known as hovering [17]. It is capable of remaining stationary anywhere up to 6000 m depth. After AUVs became able to reach great depths and hover around in the oceans, the ability to operate over a longer period of time and cover an extended range were the next features to improve. AUVs can, otherwise, catch only brief glimpses in time and space of the underwater world. Thus, a newer class of more recent AUVs such as Autosub-Long-Range [18] and HUGIN-AUV [19] were developed to push beyond their powers of endurance for longer ranges and larger sensor payloads. This class of AUVs is particularly useful in offshore surveying applications. Although the aforementioned sophisticated AUVs are extremely capable, they are not the optimal platform to operate in shallow water and inspect assets closely in critical locations due to their relatively large size, unbending bodies. Because of the limitations of AUVs and constraints of ROVs in certain applications, a new, low-cost, bendable vehicle was needed to efficiently perform research missions in shallow water and inspect subsea assets. This requirement is what initiated the design for RoboFish, a low-cost, modular, hovering AUV or wireless ROV. The concept of a flexible subsea vehicle comprising a chain of joints that are collectively able to change shape was previously successfully implemented by Eelume-AS [20]. Eelume demonstrated dexterity and hyper-redundancy that has not been commercially available before in the inspection, maintenance and repair (IMR) applications. During IMR, the vehicle is able to transit over distances and hover around using ducted lateral and vertical thrusters attached along its flexible body. Unlike Eelume, RoboFish does not use any thrusters and has the ability to run both autonomously and remotely controlled by means of an acoustic communication system. Fish-like robots have been an active research area due to the remarkable physical mobility of fish in nature.