The important of verifying the calibrating numerical models, before using them to predict design criteria, is well known. A verification scheme for wave refraction models has recently been developed.

Two of the latest wave refraction models have been acquired and tested. The first is based on a parabolic approximation method, using a finite difference technique, which includes the effects of combined refraction/diffraction, wave-current interaction, partial and full wave breaking and non-liner effects. The second is a simpler model based on the wave action equations, and includes the effects of wave refraction, shoaling, partial breaking and bottom friction.

The first model is most useful over coastal areas (up to 200 km 2) but is relatively expensive to run compared with the wave action model. The second model, although less rigorous in its solution of the physical equations, is more useful over much large areas (up to 200 km 2).

The method has been carefully designed to test all aspects of model performance. This includes :

  1. Verification against laboratory data (where traditional ray techniques break down)

  2. Sensitivity tests against hypothetical bathymetries for several input/boundary conditions.

  3. Verification against two field data sets, both including the measurement of directional spectra

This chapter outlines the test procedure and presents the results using the two models described above. It also highlights area where development work on the models was necessary, and where future work is required. Development of the modelling techniques is continuing.

INTRODUCTION

The designer of offshore and coastal structures requires local estimates of wave forces and elevations, while often the only available wave data are from offshore locations. It then becomes necessary to propagate waves from regions where they are known to areas of design interest.

Numerous techniques have been developed to calculate the transformation of waves as they propagate from offshore generation areas to the coast. For a single wave train, ray tracing has been the most popular technique (e.g. Griswold, 193). This technique has two major disadvantages the wave rays do not often provide a uniformly dense grid of wave heights and directions; and the presence of caustics makes the interpretation of the results difficult.

Recently, wave propagation models of various levels of sophistication have been produced. For example, in this project, a wave action model and a parabolic model, both of which produce wave information on a rectangular grid, have been examined. The aim of this study was to design and develop a verification procedure that could be systematically applied to any wave propagation model, in order to provide a thorough examination of the model's performance. The procedure, as developed, identifies the model's ability to include the relevant physical processes, such as wave refraction, diffraction, shoaling, wave breaking, non-linear effects and frictional attenuation. An end-product of the verification procedure is a guide to the setting-up and use of the model, including the selection of grid spacing, the value of variable coefficients, and the applicability of the model to various types of bathymetry.

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