ABSTRACT
Bioinspired thrusters designed to mimic the propulsive capabilities and mechanisms of fish locomotion pose an alternative to conventional screw propellers which are typically used as the main propulsion system of autonomous underwater vehicles (AUVs). Incorporating certain biomimetic features in the design of a thruster, such as fish-propulsion kinematics and chordwise flexibility, has the potential to enhance the propulsive efficiency and extend the overall operational capabilities of the AUV that comes with certain limitations in terms of power supply. In this work a flapping-foil thruster that undergoes prescribed heaving and pitching motions about its pivot axis, travelling at a constant speed and operating as the main propulsion system of the ocean vehicle is examined. The response of the chordwise flexible thruster is evaluated using a coupled BEM-FEM fluid-structure interaction solver that addresses the unsteady lifting flow problem of passively deforming hydrofoils, and based on the parameters of the system the quantifies the propulsive performance of the thruster. A step-optimization process is proposed to optimally tune kinematic parameters, determine an improved thickness profile and select the material property distribution chordwise in order to further enhance the propulsive performance of the thruster. The optimization problems are solved using genetic algorithms. Finally, a comparative analysis between a rigid and the optimal flexible thruster illustrates the potential of performance enhancement due to chordwise flexibility.
