## EVENT DETAILS AND ABSTRACT

**Interdisciplinary Seminar in Nonlinear Science**
**Title:** New Structures in a Shaking Fluid

**Speaker:** Professor J. Fineberg

**Speaker Info:** Hebrew U., Israel

**Brief Description:**

**Special Note**:

**Abstract:**

We describe experimental studies of two types of nonlinear structures
that appear on the surface of a fluid when, like the well-known Faraday
instability, a thin fluid layer is subjected to a spatially uniform,
periodic acceleration.
When a fluid is sufficiently dissipative, the dominant fluid state
observed for single frequency excitation is that of highly localized,
soliton-like structures that propagate along the two dimensional
surface. These structures, harmonically coupled to the external driving
frequency, are observed above a critical intrinsic "dissipation" in the
system (i.e. the ratio of the viscous boundary layer height to the depth
of the fluid layer) for a wide range of fluid viscosities and system
parameters. These highly localized nonlinear states, unlike classical
solitons, propagate at a single constant velocity for given fluid
parameters and their existence is dependent on the highly dissipative
character of the system. The properties of these states are discussed.
A different type of nonlinear state is excited when the fluid is made
less dissipative and driven via two simultaneous frequencies. Nonlinear
waves with basic wavenumbers, k1 and k2, are then simultaneously excited
via two-frequency parametric excitation of a fluid surface. Three new
multi-wave states are observed: (1) a superlattice state composed of k1
and k2 whose relative orientation is governed by a temporal resonance
condition, (2) a superlattice built entirely of wavenumbers k1 and k1/2,
and (3) a state is composed of wavenumbers of lengths k1 and k2, that
are uncorrelated in both space and time. The three states exhibit
interesting temporal as well as spatial behavior and are observed in a
variety of frequency combinations.

**Date:** Friday, October 9, 1998

**Time:** 2:00pm

**Where:** Tech M416

**Contact Person:** Prof. Riecke

**Contact email:** h-riecke@nwu.edu

**Contact Phone:** 847-491-8316

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