NONLINEAR EVOLUTION OF DIRECTIONAL WAVE SPECTRA IN SHALLOW WATER

Okey Nwogu

Abstract


Nonlinear aspects of the transformation of a multidirectional wave field in shallow water are investigated using Boussinesq-type equations. Second-order interactions between different frequency components in an irregular sea state produce lower and higher harmonic components at the sum and difference frequencies of the primary waves. For water of constant depth, expressions are derived from the Boussinesq equations for the magnitude of the second-order waves induced by bidirectional, bichromatic waves. These are used to investigate the effect of the direction of wave propagation on the near-resonant interactions that occur in shallow water. For waves propagating in water of variable depth, a numerical model based on a time-domain solution of the governing equations is used to the predict the spatial evolution of the directional wave spectrum. The results of the numerical model are compared to experimental results for the propagation of bidirectional, bichromatic waves and irregular, multidirectional waves on a constant slope beach.

Keywords


nonlinear evolution; directional spectra; wave spectra; shallow water

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