New evolution equations for non-linear water waves in general bathymetry with application to steady travelling solutions in constant, but arbitrary, depth

Pages: 75 - 84, Issue Special, September 2007

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G. A. Athanassoulis - School of Naval Architecture & Marine Engineering, National Technical University of Athens, Heroon Polytechniou 9, Athens 15773, Greece (email)
K. A. Belibassakis - School of Technological Applications, Technological Educational Institute of Athens, Greece (email)

Abstract: A non-linear coupled-mode system of horizontal equations is derived with the aid of Luke’s [13] variational principle, which models the evolution of nonlinear water waves in intermediate depth and over a general bathymetry. The vertical structure of the wave field is exactly represented by means of a local-mode series expansion of the wave potential. This series contains the usual propagating and evanescent modes, plus two additional modes, the free-surface mode and the sloping-bottom mode, enabling to consistently treat the non-vertical end-conditions at the free-surface and the bottom boundaries. The system fully accounts for the effects of non-linearity and dispersion. The main features of this approach are the following: (i) various standard models of water-wave propagation are recovered by appropriate simplifications of the coupled-mode system, and (ii) a small number of modes (up to 5) are enough for the precise numerical solution, provided that the two new modes (the free-surface and the sloping-bottom ones) are included in the local-mode series. In the present work, the consistent coupled-mode system is applied to the numerical investigation of families of steady travelling wave solutions in constant depth, corresponding to a wide range of water depths, ranging from intermediate to shallow-water wave conditions.

Keywords:  nonlinear water waves, coupled modes.
Mathematics Subject Classification:  76B15, 76B07.

Received: September 2006;      Revised: February 2007;      Published: September 2007.