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Observations of a nonlinear solitary wave packet in the Kelvin wake of a ship

Published online by Cambridge University Press:  26 April 2006

Ellen D. Brown
Affiliation:
Science Applications International Corporation, San Diego, CA 92121, USA
Steven B. Buchsbaum
Affiliation:
Science Applications International Corporation, San Diego, CA 92121, USA Scripps Institution of Oceanography, San Diego, CA 92093, USA
Robert E. Hall
Affiliation:
Science Applications International Corporation, San Diego, CA 92121, USA
John P. Penhune
Affiliation:
Science Applications International Corporation, San Diego, CA 92121, USA
Kurt F. Schmitt
Affiliation:
Science Applications International Corporation, San Diego, CA 92121, USA
Kenneth M. Watson
Affiliation:
Scripps Institution of Oceanography, San Diego, CA 92093, USA
Donald C. Wyatt
Affiliation:
Science Applications International Corporation, San Diego, CA 92121, USA Department of Applied Mechanics and Engineering Sciences, University of California, San Diego, CA 92093, USA

Abstract

Thirty data sets of wavestaff measurements of a solitary feature in the Kelvin wake of the Coast Guard cutter Point Brower are analysed. The average characteristics of the feature between 1 and 4 km aft of the ship are shown to be consistent with those of an oblique nonlinear solitary wave packet. The ship speed is 7.7 m/s (Froude number 0.49) and the waves that comprise the packet have an average frequency of 3.28 rad/s. The ship speed and the wave frequency, together with Kelvin wake kinematics, imply that the feature appears at an average wake half-angle of 10.9°. The packet does not exhibit linear dispersion beyond 1 km aft of the ship and its average width is 8.9 m (measured at e−1 of the peak variance). The average amplitude is 1.1 times the theoretical amplitude of an oblique nonlinear solitary wave packet with the observed width. There is considerable variability from run to run, and there is evidence of dispersive spreading before 1 km aft of the ship. An aerial photograph shows a sinuous fluctuation of the feature; possible explanations for the fluctuation include small variations in initial conditions or a sinuous instability. The solitary feature is a possible explanation for the long bright lines observed in SEASAT SAR images in light to moderate winds and observed in sun glitter photos taken from the space shuttle.

Type
Research Article
Copyright
© 1989 Cambridge University Press

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