ABSTRACT

Rogue waves are extraordinarily large waves in the ocean, which are widely recognized as great threats to human's oceanic activities. To better understand their effects on marine structures, it is necessary to generate rogue waves, which has similar features as reality, in laboratory or numerical wave tank. To reproduce its unique features, several methods for generating rogue waves are proposed. The most commonly used approaches include NewWave, focusing wave and Peregrine breather, which are all adopted in extensive researches in this area. Nevertheless, the differences between them have not been studied quantitatively. This paper presents a numerical investigation of the rogue waves simulated in a numerical wave tank based on a fully nonlinear potential theory. Quantitative discussions on the differences between the rogue waves generated by different approaches are carried out.

INTRODUCTION

Rogue waves have been increasingly recognized as great threats to human's oceanic activities. Records of accidents due to rogue waves have been reported recently (Liu, 2007; Nikolkina & Didenkulova, 2012). A good review about the rogue waves could be found in the book by Kharif, et al. (2009) and the recent paper by Adcock & Taylor (2014).

The rogue wave is commonly defined as the wave with maximum wave height exceeding 2 times of significant wave height (Hs) and/or the maximum wave amplitude exceeding 1.25 Hs (Skourup, et al., 1996), where the significant wave height is defined as the mean value of the 1/3 highest waves in a sea state (or 4 times the standard deviation). Thus, it is expected to result in massive energy or load on marine structures, and therefore, attracts great attentions from offshore/marine engineering communities. Great efforts have been devoted to numerically or experimentally modelling the rogue waves and their interaction with structures.

However, reproducing the rogue waves in laboratory or numerical wave tank is not simply to generate a giant wave with height exceeding 2Hs. One also need to consider another remarkable feature of the rogue waves in statistics, as described by Akhmediev, et al. (2009), that they ‘appear from nowhere and disappear without a trace’. Three commonly used approaches, NewWave, focusing wave and Peregrine breather, have been developed, incorporating above-mentioned features of rogue waves.

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