Page 39: of Marine Technology Magazine (November 2017)

The Author The Author

In 1984 Darryl Symonds started his Frederic Dias received a PhD in Civil career at Teledyne RD Instruments and Environmental Engineering from (TRDI) located in San Diego. During the University of Wisconsin in 1986. this career he has worked as an He started his career in the U.S. assembler, technician, customer before coming back to France to join service manager and, starting just CNRS in 1990. In 2000, he moved over 17 years ago, he became the to Ecole Normale Superieure de

Director of the Marine Measure- Cachan and has been a Professor of ments Product Lines (MMPL). Applied Mathematics since. a result nonlinear focusing due to modu- beams provides an opportunity to con- group. Short time scale directional dis- lational instability is diminished. The struct directional estimates for short tribution shows that the 22m wave group recorded extreme wave is 22m peak to time scales or even individual events. had a particular direction but that the trough, but does not show any character- A successful investigation into the di- directional grouping in and around the istic nonlinear features such as depleted rectional properties of groups of large peak was not different than the rest of adjacent waves or unusual steepness. amplitude waves was performed using the storm. Measurements also showed

Instead it appears more like a standard time-frequency decomposition methods that the directional variability of this wave group produced by superposition. applied to the surface-track and subsur- storm was signi? cant making it unlikely

What we saw during this extreme event face velocities measured by the Sentinel that nonlinear models like modulational is a group of waves that is moving and V. instability are responsible for this event grows in amplitude to reach a maximum An independent measure of wave di- because they require a quasi-single di- before it decays. rection was produced through a concept rection.

A key quantity to understand the for- created by Brandon Strong, an engineer These ? gures provide an overview of mation of extreme waves is the wave at TRDI. This new measure compared the entire deployment in 2015, where directional spectrum. While traditional well to proven methods. a signi? cant wave height greater than statistical approaches have been devel- Time frequency decomposition re- 10m and maximum wave height greater oped to derive wave directional spectra, vealed details in wave direction on short than 22m was measured, and the ex- the array of ? ve direct surface tracking time scales necessary to isolate a wave treme wave direction.

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Marine Technology Reporter 39

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