Biomimetics is the area in which the engineering concepts of living beings are translated to solve human problems efficiently. In recent years, Autonomous Underwater Vehicles(AUVs) have been designed by mimicking fishes like whales, tuna, dolphins, rays, etc. They have high propulsive efficiency, are silent in operation, have fewer wake signatures, and are very good maneuvers. These inherent advantages of nature motivate the researchers to pick a biomimetic design for underwater vehicle development. At the same time, conventional propeller-operated systems have an efficiency range of 55-65%, are subject to noise operation, and encounter cavitation problems during operation. Concerning AUV applications, they are mainly used for surveillance, security, and surveying tasks, which require longer endurance and stealth operation. The other uses of the AUVs and ROVs are underwater exploratio n, underwater pipeline inspection, search and rescue missions, and offshore structure health monitoring. These wide ranges of applications require more stable, highly maneuverable vehicles, necessitating the significance of bio-mimetic design. While imitating fish into AUV, certain changes are made to the AUV shape and size to account for the lack of available space, the constraints of the propulsion mechanism, and the difficulty in achieving flexible behavior like actual fishes.

In the present work, a Thunniform fish-type AUV is modeled with a lunate tail fin as a main propulsor. The performance of the caudal fin is analyzed in open water conditions, and the parameters are optimized to the maximum performance conditions. Numerically simulated open-water tests (Fin studies without front body) are carried out by varying the oscillation frequency, phase between oscillations, amplitude, and aspect ratio of the foil. A typical thunniform fishtail motion is mimicked here with the help of two rotary actuators. The three-dimensional numerical simulations are carried out using a RANSE solver-based commercial software STARCCM+. With the optimized parameters, the self-propelled motion of the bio-inspired vehicle is simulated to investigate the body effect on fin performance and understand the vehicle’s behavior during self-propulsion. Finally, the impact of the design changes on AUVs’ performance is examined and presented in detail.