Experimental study of fish-like bodies with passive tail and tunable stiffness

TL;DR

This study investigates how tunable tail stiffness affects the swimming performance of a fish-like robot, providing insights into optimizing bio-inspired underwater vehicle design.

Contribution

It introduces a robotic platform with adjustable tail stiffness to analyze its impact on swimming efficiency and kinematics, bridging gaps in previous robotic fish research.

Findings

Tuning tail stiffness influences thrust and power output.

The robot achieves self-propulsion speeds over 1 BL/s.

Deformation aligns with the traveling wave mechanism of real fish.

Abstract

Scombrid fishes and tuna are efficient swimmers capable of maximizing performance to escape predators and save energy during long journeys. A key aspect in achieving these goals is the flexibility of the tail, which the fish optimizes during swimming. Though, the robotic counterparts, although highly efficient, have partially investigated the importance of flexibility. We have designed and tested a fish-like robotic platform (of 30 cm in length) to quantify performance with a tail made flexible through a torsional spring placed at the peduncle. Body kinematics, forces, and power have been measured and compared with real fish. The platform can vary its frequency between 1 and 3 Hz, reaching self-propulsion conditions with speed over 1 BL/s and Strouhal number in the optimal range. We show that changing the frequency of the robot can influence the thrust and power achieved by the fish-like robot. Furthermore, by using appropriately tuned stiffness, the robot deforms in accordance with the travelling wave mechanism, which has been revealed to be the actual motion of real fish. These findings demonstrate the potential of tuning the stiffness in fish swimming and offer a basis for investigating fish-like flexibility in bio-inspired underwater vehicles.