A Hemispherical Motor Oscillator for Experiments on Swimming and Flying of Small Animals

[+] Author and Article Information
Promode Bandyopadhyay

Naval Undersea Warfare Center Division, Newport, RI 02841

1Corresponding author.

ASME doi:10.1115/1.4040523 History: Received November 09, 2017; Revised May 18, 2018


The propulsors of organisms from paramecia to dolphins have ball-and-socket jointed bases that allow large-amplitude, low-friction swings. Their olivo-cerebellar control also remains unchanged. Yet, the propulsive surfaces of small animals vary widely from flagellar filaments (0 < Re < 5) to flapping fins (Re > 20) with an intermediate range of Reynolds number (5 < Re < 20) where both types are present in the same swimming animal. Analysis suggests that these unsteady surfaces are mechanical oscillators coupled to their nonlinear wakes. A low-friction-driven oscillator that can interact with the oscillators of models or live swimming and flying animals could help us understand the hydro-structural events prompting evolution of such surfaces at specific Re values. A gearless underdamped hemispherical motor oscillator is described where efficiency increases by a factor of eight as the forces drop by a factor of ten from 10 N. The efficiencies at 0.8 N are comparable to the total thermal efficiencies of flies, and the quality factor is comparable. The fin oscillations of penguins, Clione antarctica and flies are reproduced. When flapping at 0.3 Hz, the oscillator would respond to all wake nonlinearities. Abrupt fin turning is modeled by switching the roll and pitch phase difference between -p/2 and p/2 in successive quadrants. Defining the fish-wake lock-in error as the difference between Triantafyllou's fish Strouhal number and the tangent of the vortex-shedding angle, an experiment is discussed for measuring the minimum drag of live fish.

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