Estimating Bimodal Frequency-Direction Spectra From Surface Buoy Data Recorded During Tropical Cyclones

[+] Author and Article Information
K. C. Ewans

Shell International Deepwater Services, P.O. Box 3006, 2280 MH Rijswijk, The Netherlands

T. van der Vlugt

Radac, Papelaan 85s, 2252 EG Voorschoten, The Netherlands

J. Offshore Mech. Arct. Eng 121(3), 172-180 (Aug 01, 1999) (9 pages) doi:10.1115/1.2829562 History: Received October 01, 1998; Revised May 18, 1999; Online December 17, 2007


Techniques for computing wave frequency-direction spectra are evaluated using wave buoy data recorded on the North West Shelf of Australia. Frequency-direction spectra are computed by each of four techniques and compared with the wave directionality expected at the measurement location, based on the meteorological conditions prevailing at the time. Particular emphasis is placed on the wave conditions occurring during tropical cyclones. Such sea states show strong directional bimodality, consisting largely of a cyclone-generated swell component and a local wind sea. The cyclone swell can be expected to have a narrow beam width when the cyclone is several hundred kilometers from the location. It is found that the bimodality is well indicated by a unimodal/bimodality parameter; and of the four techniques for computing the frequency-direction spectrum, the maximum entropy method is best at reproducing the directional bimodality while maintaining the narrow directional spreading in the cyclone swell.

Copyright © 1999 by The American Society of Mechanical Engineers
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