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VOLUME 98 (2013) | ISSUE 9 |
PAGE 591
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On the persistence of breathers at deep water
F. Fedele
School of Civil and Environmental Engineering, School of Electrical and Computer Engineering, Georgia Institute of Technology, GA 30332 Atlanta, USA
Abstract
The long-time behavior of a perturbation to a uniform wavetrain of the compact
Zakharov equation is studied near the modulational instability threshold. A multiple-scale
analysis reveals that the perturbation evolves in accord with a focusing nonlinear
Schrodinger equation for values of wave steepness . The
long-time dynamics is characterized by interacting breathers, homoclinic orbits to an
unstable wavetrain. The associated Benjamin-Feir index is a decreasing function of
μ, and it vanishes at μ1. Above this threshold, the perturbation dynamics is of
defocusing type and breathers are suppressed. Thus, homoclinic orbits persist only for
small values of wave steepness , in agreement with recent experimental
and numerical observations of breathers.
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