Outlook

Abstract

Ideally, a numerical wave model should compute the 2d wave spectrum, starting from a postulated functional form of the three basic source function constituents S _in, S _nl, and S _ds, for a prescribed wind field and boundary conditions, without any prior information on the form of the resultant wave spectrum. In the present study, only the exact-nl model integrated the transport equation in this manner (with respect to one integration coordinate only). The first-generation DP models compute the initial growth rate from prescribed source functions, but presume a given limiting form for the equilibrium spectrum. The second-generation CH models assume a given quasi-equilibrium shape (or family of shapes) for the entire windsea spectrum, predicting only one, or at most a few, characteristic windsea parameters. Finally, attempts to integrate the full transport equation in second-generation CD models using simple parameterizations of S _nl lead to spectral instabilities at frequencies beyond the peak frequency, so that these models also have to assume a prescribed spectral shape over much of the windsea spectrum.