EXTREME MULTI-DIRECTIONAL WAVES

T.B. Johannessen, C. Swan

Abstract


The present paper concerns the nonlinear description of large waves in which the wave energy is spread in both the frequency and the directional domains. A new series of experimental observations are briefly described in which a large number of deep-water focused wave groups were generated in a large wave basin. For each combination of frequency bandwidth and directional spread the intensity of the wave, measured in terms of a linear amplitude sum, was varied from a near-linear condition to the limit of incipient wave breaking. Comparisons between this laboratory data and a new fully nonlinear, multi-directional, numerical model are used to validate the modelling procedure and highlight the importance of the directionality. In particular, the results show that for a given linear amplitude sum an increase in the directional spread leads to a reduction in the magnitude of the nonlinear wave-wave interactions. Conversely, the maximum nonlinear crest elevation, observed just prior to the onset of wave breaking, increases with the directional spread assuming the frequency bandwidth remains constant. From a practical perspective, the paper demonstrates that an accurate representation of an extreme ocean wave requires a model that incorporates nonlinearity, unsteadiness and directionality. The present model satisfies these requirements.

Keywords


extreme waves; multidirectional waves

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