Kinematics in a manta-like robot for one-degree-of-freedom intermittent propulsion

Mantas demonstrate effective swimming techniques, employing intermittent flapping and gliding to enhance propulsion during cruising, inspiring people to mimic these motion patterns to minimize energy consumption. This paper simulates a one-degree-of-freedom intermittent propulsion system using the immersed boundary-lattice Boltzmann method (IB-LBM). The kinematics of a manta-like robot are analyzed while varying the parameters of intermittent flapping and gliding, including the Strouhal number (St), wave number (N_w), gliding timing (t_g), and duty cycle (dc). A cone-shaped reverse Kármán vortex jet is produced in the wake, transitioning from 2-S to 2-P as St increases, and the force distribution on the fin surface shifts toward the trailing edge, enhancing the thrust component and improving propulsion efficiency. The propulsive velocity increases rapidly when St is less than 0.7 and changes insignificantly when St is above 0.8, while efficiency peaks when St is in [0.4, 0.6]. Regarding intermittent propulsion, when the fin tip is close to the mid-plane at the gliding moment, the cumulative distance traveled is significantly greater than when the fin tip is at the peaks (upstroke/downstroke) during continuous intermittent cycles. It has been observed that the ability to maintain gliding velocity significantly decreases when dc exceeds 0.5. Additionally, the kinematics of the manta-like robot are fitted based on the simulation data. The conclusions of this paper can be used as a reference for the high-precision intermittent propulsion control of manta-like robots.