Faraday waves produced by periodic substrates: Mimicking the alligator water dance.

Abstract

Male alligators use surface waves to attract their mates. This phenomenon is colloquially known as the alligator’s water dance. Male alligators vibrate their lungs at very low frequencies, creating unique wavy patterns and fountains on the surface of the water. We hypothesize that the water dance phenomena are an expression of Faraday waves, arising from the instability of the plane fluid interface to wavy perturbations above a threshold vibration amplitude. We performed laboratory experiments to study how the corrugations covering the skin of an alligator affect the onset, efficiency, and pattern of Faraday waves. A three-dimensional (3-D) printed plate was modeled after a molding of an alligator’s back, mimicking the corrugation size, shape, and spacing. An electromagnetic induction transducer was used to vibrate this model plate normal to the water surface. Frequency sweep data were collected for a variety of amplitude settings. Sweeps were performed for different plate depths, with and without corrugations. Three diagnostics were employed: a piezoelectric hydrophone, an out-of-plane laser vibrometer, and a high-speed video. Onset, frequency, and pattern data will be presented as a function of driving parameters, and as a function of depth. Implications of this work for an eventual field experiment will be discussed.