Star-Shaped Waves
J. Rajchenbach et al., Phys. Rev. Lett. (2013)
Observation of Star-Shaped Surface Gravity Waves
Published February 28, 2013
The ocean can produce exotic wave forms, such as “freak”
waves, when normal waves combine in just the right way. These unusual
wave patterns can—theoretically—take on a variety of different shapes,
but researchers have so far only managed to produce a few distinct cases
in the lab. As reported in Physical Review Letters,
Jean Rajchenbach and colleagues at CNRS and the University of Nice in
France have produced star- and polygon-shaped standing waves by
vertically shaking a vessel filled with liquid oil.
Ocean waves and similar fluid waves are called surface gravity waves because the main restoring force is gravity. The basic equations describing these waves are nonlinear, which means that waves of different wavelengths can interact with each other and, under certain conditions, form unusual patterns, such as long-lasting solitary waves (solitons), U-shaped, and X-shaped waves. Such wave forms sometimes have important counterparts in other scientific domains, from optics to cold-atom physics.
To explore novel nonlinear possibilities, Rajchenbach and his collaborators placed a thin layer of silicon oil in a flat vessel and shook it up and down at a rate of around10
hertz. They initially observed circularly symmetric standing waves, but
as they increased the shaking amplitude, the wave crests formed edges
and vertices in an alternating pattern of five-pointed stars and
pentagons. Varying the fluid depth and the shaking parameters produced
other star-polygon shapes with three, four, and six sides. However, the
vessel shape was not a factor, as identical patterns appeared in both
circular and rectangular vessels. The authors explain how the observed
shapes could arise from a resonant nonlinear interaction between three
different waves generated by the shaking action. – Michael Schirber
Ocean waves and similar fluid waves are called surface gravity waves because the main restoring force is gravity. The basic equations describing these waves are nonlinear, which means that waves of different wavelengths can interact with each other and, under certain conditions, form unusual patterns, such as long-lasting solitary waves (solitons), U-shaped, and X-shaped waves. Such wave forms sometimes have important counterparts in other scientific domains, from optics to cold-atom physics.
To explore novel nonlinear possibilities, Rajchenbach and his collaborators placed a thin layer of silicon oil in a flat vessel and shook it up and down at a rate of around
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