Changes in rays\u2019 swimming stability due to the phase difference between left and right pectoral fin movements

Hiroaki Sumikawa,Tasuku Miyoshi,Yoshikazu Naraoka,Takashi Fukue

doi:10.1038/s41598-022-05317-5

Hiroaki Sumikawa, Tasuku Miyoshi + Show 2 more

Open Access

https://doi.org/10.1038/s41598-022-05317-5

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Abstract

Swimming motions of rays that swim using undulation locomotion are not always symmetrical; there may be a phase difference between the left and right pectoral fins. However, few studies on the swimming of rays have mentioned left and right pectoral fin movements. Moreover, the effects of movements of the left and right pectoral fins on swimming have not been clarified. This paper describes a computational study of phase differences of pectoral fin movements in the swimming of rays with the validity of fluid analysis methods. The movement and shape of the ray were made based on previous biological research and pictures. An overset grid was used to reproduce the ray’s complex motions. The analysis was performed under four phase difference conditions: 0 T (T is the period), 0.25 T, 0.5 T, and 0.75 T. The results show that a phase difference between the left and right pectoral fin movements affects swimming stability and maneuverability but not propulsive efficiency. We suggest that the phase difference in pectoral fin movements is essential for the swimming of rays, and rays adjust the phase difference between the movement of the left and right pectoral fins to suit their purpose.

Highlights

Swimming motions of rays that swim using undulation locomotion are not always symmetrical; there may be a phase difference between the left and right pectoral fins
We hypothesized that the phase difference in the movement of the left and right pectoral fins during straight-line swimming would increase swimming stability and maneuverability
In order to verify our hypothesis, two questions were examined: (1) What is the effect of the phase difference between the movements of the left and right pectoral fins on undulation propulsion and (2) Why do stingrays swim straight ahead by phasing their left and right pectoral fin movements

Summary

Introduction

Swimming motions of rays that swim using undulation locomotion are not always symmetrical; there may be a phase difference between the left and right pectoral fins. In insects and rajiform and mobuliform rays, stability has been shown to be affected by changes in the amplitude and speed of the left and right pectoral fin movements and the bending angle of the pectoral fins[13,14,18,19,20] These previous studies were based on the assumption of turning, the amplitude and speed difference of the left and right pectoral fin movements are expected to maintain posture effectively even during straight-line swimming. It still is not clear whether the phase difference increased or decreased swimming stability and maneuverability. Those robots are better than propellers in waters littered with seaweed and plastic debris or in waters with high hydrostatic p ressure[23,24]

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