Short water surface waves generated by wind in a water tunnel have been measured by a optical technique that provides a synoptic picture of the water surface gradient over an area of water surface (Zhang && Cox 1994). These images of the surface gradient can be integrated to recover the shape of the water surface and find the two-dimensional wavenumber spectrum. Waveforms and two-dimensional structures of short wind waves have many interesting features: short and steep waves featuring sharp troughs and flat crests are very commonly seen and most of the short waves are far less steep than the limiting waveforms; waveforms that resemble capillary-gravity solitons are observed with a close match to the form theoretically predicted for potential flows (Longuet-Higgins 1989); capillaries are mainly found as parasitics on the downwind faces of gravity waves, and the longest wavelengths of those parasitic capillaries found are less than 1 cm; the phenomenon of capillary blockage (Phillips 1981) on dispersive freely travellingshort waves is also observed. The spectra of short waves generated by lowwinds show a characteristic dip at the transition wavenumber between thegravity and capillary regimes, and the dip becomes filled in as the wind increases. The spectral cut-off at high wavenumbers shows a power law behaviour with an exponent of about minus four. The wavenumber of the transition from the dip to the cut-off is not sensitive to the change of wind speed.
Capillary-gravity and capillary waves generated in a wind wave tank: observations and theories
Erzeugung von Kapillarschwere und Kapillarwellen in einem Windwellentank: Beobachtungen und Theorien
Journal of Fluid Mechanics ; 289 ; 51-82
1995
32 Seiten, 12 Bilder, 1 Tabelle, 53 Quellen
Aufsatz (Zeitschrift)
Englisch
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