A robotic fish capable of fast underwater swimming and water leaping with high Froude number

• Published in: Ocean engineering 2023-01, Vol.268, p.113512, Article 113512
• Main Authors: Pham, Tan-Hanh, Nguyen, Khanh, Park, Hoon Cheol
• Format: Article
• Language: English
• Subjects: Froude number; Hydrodynamics; Leaping velocity; Robotic fish; Water leaping
• ISSN: 0029-8018; 1873-5258
• DOI: 10.1016/j.oceaneng.2022.113512

Natural underwater species outperform man-made underwater vehicles in many aspects. In this work, as our first effort to eventually mimic flying fish, a robotic fish capable of swimming fast and leaping out of water was developed, named KUFish. The thrust of KUFish was produced by a tail-beating mechanism driven by a DC motor in combination with reduction gears, four-bar linkage, and pulley-string mechanisms. The passive dynamic stability was implemented by the symmetric mass distribution, positive buoyancy, and lower center of gravity. A series of swimming experiments indicated that the KUFish could swim 0.68 m and leap out of the water with a speed of 1.35 m/s (6.1 BL/s) at an instant of 0.68 s after release. In addition to experimentation, a two-dimensional dynamic model was developed to predict the swimming behavior of the robot. The proposed dynamic model could reasonably capture the measured swimming performance of the robot before water leaping. The water leaping capability of the KUFish can be well supported by the computed Froude number of (1.08 or 0.92) in terms of the body faring length or robot length, respectively. The results from the current work can be useful for developing a flying-fish-like swimming robot in the future. •A fish-like swimming robot was designed employing a DC motor, gears, 4-bar linkage, and pulley-string mechanism.•The robotic fish demonstrated fast underwater swimming and water leaping.•The symmetric mass distribution, positive buoyancy, and lower center of gravity (CG) enhanced the passive dynamic stability.•The nose-up moment generated by misalignment of the CG and center of buoyancy was beneficial for fast water leaping.•This work confirmed that the Froude number = 1 is a good measure of the inclined water leaping.