A new reciprocating straight propulsion for high propulsive hydrodynamic efficiency

The majority of underwater vehicles currently use screw propellers as propulsion method. Despite screw propellers are being promoted to increase the efficiency through better designs and technologies, the circumferential flow caused by the rotation of screw propeller results in wasted energy. This paper proposes an ideal reciprocating straight propulsion paradigm that eliminates this waste by implementing straight backward thrust based on a foldable mechanism. This mechanism can implement a maximized propulsion during the propelling stroke and a minimized resistance during recovery by folding and unfolding the mechanism, which can be adjusted passively via the relative motion between the thruster mechanism and water avoiding using sensors and actuations. This principle makes the reciprocating straight propulsion simple and reliable to be achieved in practice. Besides, a modularized propulsion system with four identical independently thrusters based on the proposed mechanism was proposed, achieving various motion modes in underwater vehicles. The proposed propulsion mechanism was theoretically analyzed and verified through simulations and prototype tests. In mooring tests, the thrust provided by the proposed mechanism is similar to the simulation results. The propulsion performance indicator of an underwater vehicle with the proposed propulsor reached 66 %. The mechanism could turn even with one-sided propulsion.