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Observations of the directional spectrum relaxation of wavefields in slowly and rapidly turning winds

Tsanis Giannis, F. Brissette

Πλήρης Εγγραφή

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Περίληψη

A so called “Exact Form” of the Maximum Likelihood Method is used to obtain directional spectrum estimates from a 3-meter NDBC discus buoy, part of the Surface Wave Dynamics Experiment (SWADE) field array. The method was used to look at the response of wavefields to turning winds with various wind shift gradients. For slowly turning winds, the spectrum was found to smoothly adjust to the wind changes. As the wind shift gradient increased, a portion of the spectral energy was found to be decoupled from the wind while the bulk of the spectrum smoothly adjusted to the new wind direc- tion. Finally, for even larger wind shift gradients, the preexisting spectrum was completely decoupled from the wind and decayed separately, as a new spectrum consistent with the wind direction was gen- erated. These observations confirm theoretical results previously obtained from a third generation wave model. The relaxation of waves in turning winds was investigated using a simple relaxation model. Correlation coefficients obtained in this study are higher than previously published studies, especially for lower values of the wave age, and a relationship between the relaxation parameter and the wave age is observed.

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