A Fish-Like Propeller Integrated With Magnetorheological Shear Damping and Elastic Components

Scombrid fish possess superior-performance propulsion characteristics, attributed to the powerful contraction of the peduncle tendon muscle which effectively transmits energy to the caudal fin. Inspired by the bionic structure, we proposed a fish-like propeller consisting of a driving joint and a peduncle joint connected in series. The peduncle joint combines magnetorheological (MR) damping with elastic components and is actuated by a sine mechanism to replicate biological motion. The intensity of the damping mechanism enhances with frequency, which can compensate for the shortcomings of insufficient elastic intensity at high frequencies. The integration of both mechanisms aims to accomplish high propulsion across a wide frequency range. Then, an MR damper is constructed to imitate the tendon muscle of the peduncle. The shear stress of the MR fluid possesses online intensity adjustment capability by regulating the current of the inner coil, thereby affecting the damping torque output by the peduncle joint. Experimental results reveal that the controllable damping torque ranges from 49.3 to 134.4 mNm. A forward thrust dynamic model is built according to the Lagrangian method to explore the effect of the shear stress on propulsion. Simulated results indicate that at a specific frequency, an optimal shear stress exists that enables the system to achieve the best propulsion. Meanwhile, as frequency increases, the best propulsion gradually enhances, and the shear stress corresponding to the best propulsion also increases. Experimental results of four caudal fins with different aspect ratios (ARs) show that the shear stress should be further increased to accomplish best propulsion as AR decreases. The max average thrust of the fish-like propeller can reach 1.956 N at a frequency of 3 Hz.