NONLINEAR RANDOM OCEAN WAVES: PREDICTION AND COMPARISON WITH DATA

Second-order nonlinear models have been increasingly used in recent years to model nonlinear processes in offshore engineering. We develop convenient analytic formulae to predict the nonlinearities in waves and to predict the crest height distribution in a specified wave condition. We apply such models to study the properties of random ocean waves. These include measured waves both in wave tanks and in field. Statistics comparison between model and measurements include: moment comparisons, comparison of distributions of wave elevations, crest heights, wave heights, and conditional distributions of local wave parameters, for example, crest height given wave heights, wave periods given crest heights, among others. We find the second-order model predictions to agree quite closely with the field measurements, while the wave tank statistics seem to be underpredicted by the second-order model. Finally, we solve the inverse problem, in which we identify the underlying first-order wave components, which when run through the second-order wave predictor matches the measured wave histories time point by time point.