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Read Full Article (file size: 740079 bytes) Cited by
JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 109,
C12002,
doi:10.1029/2004JC002612,
2004
Laboratory measurements of limiting freak waves on currents
Chin H. Wu
Department of Civil and Environmental Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA
Aifeng Yao
Department of Civil and Environmental Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA
Abstract
The results of laboratory measurements on limiting freak waves in the presence of currents are reported. Both dispersive spatial-temporal
focusing and wave-current interaction are used to generate freak waves in a partial random wave field in the presence of currents.
Wave group structure, for example, spectral slope and frequency bandwidth, is found to be critical to the formation and the
geometric properties of freak waves. A nondimensional spectral bandwidth is shown to well represent wave group structure and
proves to be a good indicator in determining limiting freak wave characteristics. The role of a co-existing current in the
freak wave formation is recognized. Experimental results confirm that a random wave field does not prevent freak wave formation
due to dispersive focusing. Strong opposing currents inducing partial wave blocking significantly elevate the limiting steepness
and asymmetry of freak waves. At the location where a freak wave occurs, the Fourier spectrum exhibits local energy transfer
to high-frequency waves. The Hilbert-Huang spectrum, a time-frequency-amplitude spectrum, depicts both the temporal and spectral
evolution of freak waves. A strong correlation between the magnitude of interwave instantaneous frequency modulation and the
freak wave nonlinearity (steepness) is observed. The experimental results provide an explanation to address the occurrence
and characteristic of freak waves in consideration of the onset of wave breaking.
Received 20
July
2004;
accepted 11
October
2004;
published 3
December
2004.
Keywords: freak waves;
rogue waves;
dispersive focusing;
wave-current interaction;
time-frequency analysis;
Hilbert-Huang Transformation (HHT).
Index Terms: 4504 Oceanography: Physical: Air/sea interactions (0312); 4546 Oceanography: Physical: Nearshore processes; 4560 Oceanography: Physical: Surface waves and tides (1255); 4572 Oceanography: Physical: Upper ocean processes.
Read Full Article (file size: 740079 bytes) Cited by
Citation: Wu, C. H., and A. Yao
(2004),
Laboratory measurements of limiting freak waves on currents,
J. Geophys. Res.,
109,
C12002,
doi:10.1029/2004JC002612.
Copyright 2004 by the American Geophysical Union.
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