The Influence of the Peduncle on Swimming Performance in Biological Tuna and Tuna-Inspired Artificial Propulsors

Designers of unmanned underwater vehicles (UUVs) are increasingly turning to aquatic animals that use lift-based propulsion for inspiration. This is because of the significant advantage they have over traditional rotary propeller systems, such as efficiency and maneuverability. Thunniforms have been identified as fast, economical swimmers. If the performance of the next generation of UUVs is to achieve these biological performance metrics, it is essential that we understand and quantify the key mechanisms that contribute to their superior swimming performance. Significant efforts have been directed toward quantifying the morphometrics, kinematics, and material properties of thunniform swimmers. Through careful dissection, it was observed that the peduncle region of tuna and tuna-like fish allows for a degree a freedom. This motivated studies of the biology and artificial propulsors to quantify the role this subsystem has on speed, work done, and economy. Results show that the peduncle joint significantly improves performance: boosting speed and decreasing power compared to a fish without it and was reproduced in an artificial tuna-like platform. Additionally, modulating the joint stiffness and bend angle has profound effects on performance with preferred kinematics depending on swimming speed. These findings can inform the tail design of a high-performing UUV based on the biomechanics of a tuna.