A saturation-dependent dissipation function for wind-wave modelling applications.

Jose Henrique G. M. Alves

Thesis submitted to the School of Mathematics in the fulfillment of the requirements for the degree of Doctor of Philosophy in Applied Mathematics (Physical Oceanography). Sydney, Australia, December 2000.


This study reports on a new formulation of the spectral dissipation source term Sds for wind -wave modelling applications. This new form of Sds features a nonlinear dependence on the lo cal wave spectrum, expressed in terms of the azimuthally integrated saturation parameter B(k) = k^4 F(k). The basic form of this saturation-dependent Sds is based on a new framework for t he onset of deep-water wave breaking due to the nonlinear modulation of wave groups. The new form of Sds is succesfully validated through numerical experiments that include exact nonlinear computations of fetch-limited wind-wave evolution and hindcasts of two-dimensional wave fields ma de with an operational wind-wave model. The newly-proposed form of Sds generates integral spectral parameters that agree more closel y with observations when compared to other dissipation source terms used in state-of-the-art wind -wave models. It also provides more flexibility in controlling properties of the wave spectrum wi thin the high wavenumber range. Tests using a variety of wind speeds, three commonly-used wind in put source functions and two alternative full-development evolution limits further demonstrate th e robustness and flexibility of the new saturation-dependent dissipation source term. Finally, im proved wave hindcasts obtained with an implementation of the new form of Sds in a version of the WAM model demonstrate its potential usefulness in operational wind-wave forecasting applications.

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