Identification of the trade-off between speed and efficiency in undulatory swimming using a bio-inspired robot

Abstract

Anguilliform swimmers, like eels or lampreys, are highly efficient swimmers. Key to understanding their performances is the relationship between the body's kinematics and resulting swimming speed and efficiency. But, we cannot prescribe kinematics to living fish, and it is challenging to measure their power consumption. Here, we characterise the swimming speed and cost of transport of a free-swimming undulatory bio-inspired robot as we vary its kinematic parameters, including joint amplitude, body wavelength, and frequency. We identify a trade-off between speed and efficiency. Speed, in terms of stride length, scales with the maximum tail angle, described by the newly proposed specific tail amplitude and reaches a maximum value around the specific tail amplitude of unity. Efficiency needs a whole-body motion, travelling wave-like kinematics, and lower specific tail amplitudes. Our results suggest that live eels choose efficiency over speed and provide insights into the key characteristics affecting undulatory swimming performance.

Complex Modal Characteristic Analysis of a Tensegrity Robotic Fish’s Body Waves

“…The kinematics analysis of fish swimming using the traveling wave is a hot topic in the fields of swimming dynamics and fluid mechanics [55][56][57]. In the field of bionic robotic fish, scholars have experimentally observed that robotic fish performs better [21][22][23]58,59] when the traveling wave is the dominant component of the fish body wave. However, it is challenging to analyze the traveling wave and standing wave.…”

“…In the case of a low traveling index, the predominant motion is the standing wave, which displaces the surrounding fluid laterally. Its momentum flux typically occurs in the lateral direction, potentially impacting swimming efficiency [23]. Furthermore, Anastasiadis and Ijspeert et al [23] pointed out that a higher traveling index can reduce the cost of transport (COT) of robotic fish.…”

“…Its momentum flux typically occurs in the lateral direction, potentially impacting swimming efficiency [23]. Furthermore, Anastasiadis and Ijspeert et al [23] pointed out that a higher traveling index can reduce the cost of transport (COT) of robotic fish. The prerequisite to achieving high efficiency is the adoption of pure traveling wave-like body undulations.…”