INTRODUCTION

The WAM group is an international group of wave researchers, working on the joint development of a so-called third generation ocean wave model. This is a mode about the spectral shape and in which source terms are chosen to represent the different physical processes determining the evolution of ocean waves. After a short description of the model, first results from a two-day global test run with realistic winds will be discussed. In the second part of the chapter a short overview of the plans of the WAM group will be given. They comprise growth curve analysis, directional relaxation studies, shallow-water effects and data assimilation.

INTRODUCTION

There exists considerable interest in ocean wave research, and in the development and application of numerical wave models. This interest is strongly stimulated by demand. Worldwide offshore and coastal engineering project require good knowledge of local wave climates. In addition, shipping, fisheries and offshore operations depend on the availability of accurate wave forecasts. These are usually made with the help of numerical wave prediction models, which are also used to reconstruct wave climates, where observations are lacking.

In recent years, important developments have been made in ocean wave modeling. Our understanding of the dynamics of surface waves has increased significantly as a result of a series of field programs and because of experience with sequence of first - and second-generation wave models (JONSWAP, Hasselmann et al., 1973; SWAMP, Allender et al., 1984; SWIM, Bouws et al., 1985). The increasing understanding has led to an increasing sophistication of methods which, in turn, has led to increasing collaboration between different wave modeling groups. For example, the SWAMP study involved six European, two American and two Japanese research teams.

The European wave modelling community is currently in the process of developing a new third-generation wave model which may be expected to yield a further significant improvement in wave forecasting skill. The present proposal outlines a plan of action directed at further development of this third - generation model, its implementation in a global version on a central efficient vector-processing computer, and the development of regional versions of the model for regional use.

Present wave - predication models are based on the integration of the radiative transfer equation for the two - dimensional wave spectrum. Simple empirical wave - prediction tables relating wind or sea parameters such as the significant wave height and period to the wind speed, fetch and duration are still sometimes used in engineering applications, but they are often inadequate. The transfer equation described the propagation of the different wave components of the spectrum with different frequencies and propagation directions at their appropriate group velocities, and the change in the energies of these components produced by wind forcing, dissipation and higher - order non - liner wave - wave interaction. The models predict the full two - dimensional wave spectrum at every timestep and grid point. Present second - generation wave models have to make a - priori restrictions on the spectral shape, because an accurate representation of the non - linear transfer process was not yet available.

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