Weakly Nonlinear Sea Surface Waves — Freak Waves and Deterministic Forecasting

Abstract

The material contained here is to a large extent motivated by the so-called Draupner “New Year Wave”, an extreme wave event that was recorded at the Draupner E platform in the central North Sea on January 1st 1995 [4], [5]. This location has an essentially uniform depth of 70 m. The platform is of jacket type and is not expected to modify the wave field in any significant way. The platform had been given a foundation of a novel type, and for this reason was instrumented with a large number of sensors measuring environmental data, structural and foundation response. We are particularly interested in measurements taken by a down looking laser-based wave sensor, recording surface elevation at a speed of 2.1333 Hz during 20 minutes of every hour. The full 20 minute time series recorded starting at 1520 GMT is shown in Figure 1 and a close-up of the extreme wave event is shown in Figure 2. To remove any doubt that the measurements are of good quality, Figure 3 shows an even finer close-up with the individual measurements indicated. It is clear that the extreme wave is not an isolated erroneous measurement. The minimum distance between the sensor and the water surface was 7.4 m.