[Seminar] Colloquia 4/28/2009

[Amy Barnes]

Dept of Physics & Astronomy
Lewis Hall Rm 101
Tuesday April 28, 2009
4:00 pm



Victor Sanchez-Morcillo
Departamento de Física Aplicada
Universidad Politécnica de Valencia, Spain

Parametric Instability and the Emergence of Complexity in Acoustics

Michael Faraday, when experimenting with a vertically oscillated fluid
layer, incidentally observed in 1831 two phenomena that have attracted the
attention of scientists for long time, and are still a hot topic of
research. First, he observed that the fluid surface oscillated at a
frequency half that of the imposed vertical oscillation, (which is now
recognized as the parametric instability). The most common example of this
phenomenon is found in a playground swing. Secondly, the spatial
distribution of the fluid along the surface showed beautiful ordered
patterns, with different symmetries, similar to those arising from natural
processes such as ripples on sand dunes. Similar patterns can also be
created in the lab where variables can be controlled and investigated.
Nowadays it is accepted that both parametric instability and pattern
formation are found in most of the scientific disciplines, and therefore its
description has a universal character (It is ubiquitous in Physics.).

In the talk the most typical features of these phenomena will be reviewed,
with a particular emphasis on systems based on the Faraday mechanism (those
driven by an external harmonic vibration). Examples of parametrically
driven, spatially extended acoustical systems include both the chain of
coupled pendula, and the ultrasonic resonant cavity filled with a fluid.

The talk will be mostly descriptive, with images and animations illustrating
the basic features of parametric systems.

ALL GRADUATE STUDENTS ARE REQUIRED TO ATTEND