Design of a Thunniform Swimming Robot in a Multiphysics Environment

Bio-inspired solutions devised for Autonomous Underwater Robots are currently investigated by researchers worldwide as a source of propulsive improvement. Despite the efforts made to pursue the substantial potential payoffs of marine animals’ locomotion, the performances of biological systems are still far to reach. In order to address this very ambitious objective, the authors of this work have designed and manufactured a series of ostraciiform swimming robots in the last three years. However, the aim to pursue the highest propulsive efficiency to maximize the robot autonomy, has driven them to improve their design by moving from ostraciiform to thunniform locomotion. In order to properly size the robot bio-inspired thruster – i.e. the caudal fin – and its actuation system, the performances of a flapping foil have been deeply investigated by means of computational fluid dynamics techniques. The numerical predictions led to the optimal design of a transmission mechanism capable to convert the continuous rotation of a single motor in the harmonic roto-translation of the robot thruster, a motion law closely resembling the fin kinematics in thunniform locomotion. Furthermore, in order to compute the robot resulting motion, the propulsive forces and torque generated by the flapping thruster have been integrated in a multibody model which accounts both for the mass distribution of the robotic fish and the hydrodynamic forces due to the relative motion between its segmented body and the surrounding fluid. The performed dynamic analysis allowed to compute the robot total efficiency in the cruising condition.