Project Acronym: HyIV-Marintek-02
1. Title of
Research
Project
2 Facility -
Location
Experimental investigation of nonlinear wave interactions, wave turbulence and rogue waves
Ocean Basin Laboratory
Marintek
Marine Technology Centre
Otto Nielsens veg 10,
NO-7052 Trondheim, Norway
3 Summary The aims of this research were to isolate the mechanisms that lead to the creation of extreme waves and in particular rogue waves on the water surface. The tests were also designed to allow study the wave dynamics and statistical properties of extreme and rogue waves under conditions close to those found in an open sea. The mechanisms identified will be compared to theoretical wave turbulence models. Comparison of the test results with numerical model simulations based on wave turbulence theory will provide important information on the mechanisms responsible for freak wave formation and will constitute a basis for further development of the theory of this phenomenon.
Freak waves, i.e. events with crests larger than or equal to five times the standard deviation or wave heights larger than or equal to twice the significant wave height, were observed in each test. The number increased with increasing angle between the wave fields, and with reduction of directional spreading. This is also reflected in the tails of the wave height and wave crest distributions, which deviate increasingly from a Rayleigh distribution with growing distance from the wave paddle. The fourth order moment of the probability density function of the surface elevation, or kurtosis, was calculated from each surface elevation time series. The kurtosis is believed to be influenced by the nonlinear dynamics of free waves responsible for the formation of extreme events. The maximum observed kurtoses were above 3.0 (the Gaussian expectation) for each test. The observed kurtoses were compared with an estimate obtained by use of a second-order theory, which includes only the contribution of bound waves.
There was little difference between the observed and estimated values, indicating that the contribution of free waves is very small.
Unlike previously published findings for the crossing of irregular waves, the crossing angle does not appear to exert a significant influence on the kurtosis.

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Contact
Information
Rather, it seems that the degree of directional spreading is the most important parameter.
Dr. Suzana Ilic
Lancaster Environment Centre
Lancaster University
Tel.: +44 (0) 1524 510264
E-mail: s.ilic@lancaster.ac.uk
Photos

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Keywords
Reference to publications
Status
Bi-modal sea, Freak wave, Rogue wave, Crossing swell and wind waves
Ilic S, Luxmoore J, McClintock PVE, Efimov V, Stefanovska A, Fortes J, Santos J,
Capitao R, Kolmakov G, Pakodzi C, Stansberg CT, Nygaard I, and Mori N. ‘Freak waves in crossing directional seas: a laboratory experiment’, In EGU General
Assembly Conference Abstracts, vol. 15, p. 10029. 2013.
Experiments completed in June 2012. Analysis on-going