Morphing median fin enhances untethered bionic robotic tuna's linear acceleration and turning maneuverability

TL;DR

This study demonstrates that a morphing median fin on a robotic tuna significantly improves acceleration and maneuverability, providing insights into fish fin behavior and advancing underwater robot design.

Contribution

Developed a foldable dorsal fin robotic tuna that mimics real tuna fin behavior, revealing effects on acceleration, maneuverability, and efficiency during swimming.

Findings

Erecting the dorsal fin reduces head heave by 50%.

Erecting the dorsal fin enhances linear acceleration by 15.7%.

Turning angular velocity increases by 32.78%.

Abstract

Median fins of fish-like swimmers play a crucial role in linear acceleration and maneuvering processes. However, few research focused on untethered robotic fish experiments. Imitating the behaviour of real tuna, we developed a free-swimming bionic tuna with a foldable dorsal fin. The erection of dorsal fin, at proper conditions, can reduce head heave by 50%, enhance linear acceleration by 15.7%, increase turning angular velocity by 32.78%, and turning radius decreasing by 33.13%. Conversely, erecting the dorsal fin increases the wetted surface area, resulting in decreased maximum speed and efficiency during steady swimming phase. This finding partially explains why tuna erect their median fins during maneuvers or acceleration and fold them afterward to reduce drag. In addition, we verified that folding the median fins after acceleration does not significantly affect locomotion efficiency. This study supports the application of morphing median fins in undulating underwater robots and helps to further understand the impact of median fins on fish locomotion.