RESUMO
In this Letter, we experimentally demonstrate self-organization of small tracers under the action of longitudinal Faraday waves in a narrow container. We observe a steady current formation dividing the interface in small cells given by Faraday-wave symmetries. These streaming currents rotate in each cell, and their circulation increases with wave amplitude. This streaming flow drives the tracers to form patterns, whose shapes depend on the Faraday-wave amplitude: From low to high amplitudes, we find tracers dispersed on vortices, narrow rotating rings, and a hedgehoglike pattern. We first describe the main pattern features and characterize the wave and tracers' motion. We then show experimentally that the main source of the streaming flow is the spatiotemporal-dependent shear at the wall contact line created by the Faraday wave itself. We end by presenting a 2D compressible advection model that considers the minimal ingredients present in the Faraday experiment, namely, the stationary circulation, the stretching component due to the oscillatory wave, and a steady converging field, which combined produce the observed self-organized patterns.
RESUMO
We report on the numerical and theoretical study of the subcritical bifurcation of parametrically amplified waves appearing at the interface between two immiscible incompressible fluids when the layer of the lower fluid is very shallow. As a critical control parameter is surpassed, small amplitude surface waves bifurcate subcritically toward highly nonlinear ones with twice their amplitude. We relate this hysteresis with the change of shear stress using a simple stress balance, in agreement with numerical results.
RESUMO
A direct numerical simulation of Faraday waves is carried out in a minimal hexagonal domain. Over long times, we observe the alternation of patterns we call quasihexagons and beaded stripes. The symmetries and spatial Fourier spectra of these patterns are analyzed.
