Abstract

Freshwater stingrays undulate their flexible disc-like pectoral fins to perform cruising, manoeuvring, and other motions. This undulatory propulsion has a higher propulsive efficiency and more precise manoeuvrability than most other species at low swimming velocity. In the current study, a new robotic fish inspired by the freshwater stingray was developed and tested. First, the morphology and kinematic patterns of the freshwater stingray were presented. A kinematic model of the pectoral fin was established based on several assumptions. Then a robotic stingray with an undulatory pectoral fin was designed and developed. Experiments were conducted to investigate the effects of various fin actuation parameters on its linear swimming velocity and the forces generated by the robotic stingray. The controllable fin parameters include oscillation frequency, wave number, maximal angular deflection of the fin rays, and the amplitude pattern of the pectoral fin. The experimental results indicate that the developed prototype is able to generate adequate thrust for self-propulsion. Linear swimming velocity and surge force increase rapidly with oscillation frequency, angular deflection, and wave number. A maximum velocity of 4.3 cm·s⁻¹ (nearly 0.18 Body Lengths per second (BL·s⁻¹)) and a maximum surge force of 102 mN are achieved at an oscillation frequency of 0.5 Hz, a wave number of 1, a maximum angular deflection of 30°, and an equal amplitude pattern. The sway force of the robotic fish fluctuates around 0 mN. The heave force varies with wave number and reaches its minimum at a wave number of 1.