Relation between occurrence probability of freak waves and kurtosis/skewness in unidirectional wave trains under single-peak spectra

Wang, Lei; Zhou, Binzhen; Jin, Peng; Li, Jinxuan; Liu, Shuxue; Ducrozet, Guillaume

doi:10.1016/j.oceaneng.2022.110813

Cited by 8 publications

(4 citation statements)

References 28 publications

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“…As known, kurtosis gradually increases with the wave propagation, then decreases slightly, and finally tends to be stable in a unidirectional sea state [45]. However, in a multi-directional sea state, the spatial evolution of kurtosis is unclear, such as the information on the maximum kurtosis and its corresponding area.…”

Section: Spatial Evolution Of Kurtosismentioning

confidence: 97%

Nonlinear statistical characteristics of the multi-directional waves with equivalent energy

Wang,

Ding,

Zhou

et al. 2023

Physics of Fluids

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Directional distribution is believed to have a significant impact on the statistical characteristics in multi-directional sea states. In real sea states, short-crested waves are discrete not only in frequency but also in direction. For the former one, they are well explained in unidirectional mode, but for the latter one, they are not. In this paper, the kurtosis of short-crested waves with equivalent energy is first discussed. Unimodal-spectrum-multi-direction sea states and bimodal-spectrum-multi-direction sea states are simulated for a long time in a numerical wave basin based on the high-order spectral method. In the equivalent sea-swell sea state, the spatial evolution of kurtosis becomes more inhomogeneous, along with the maximum value of kurtosis being larger and the area where the maximum value occurs wider in the configuration with a crossing angle β = 40° than that with β = 0°, while little variations in swell-dominated and wind-sea-dominated states. A positive linear correlation between wavelet group steepness and kurtosis is obtained in a unimodal sea state, but not applied to a crossing sea state characterized by a bimodal spectrum. The exceedance probability of wave height and wave crest distribution at maximum kurtosis is also given. These findings can help predict the probability of extreme waves occurring, guiding the selection of ocean engineering sites to avoid extreme configurations.

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Section: Spatial Evolution Of Kurtosismentioning

confidence: 97%

Nonlinear statistical characteristics of the multi-directional waves with equivalent energy

Wang,

Ding,

Zhou

et al. 2023

Physics of Fluids

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“…Table 2 shows one set of examples, described by equivalent energy but different intermodal distances (ID), with their corresponding spectra provided in Figure 3. In this study, the occurrence probability of freak waves is defined as the probability at H i /H s ≥ 2 in the exceedance probability, also applied in their work by Wang et al [17]. After the long-time numerical simulation considering various wave configurations, we processed data such as statistics to assess the wave height using a zero-crossing method, calculate the exceedance probability distribution of wave height, and so on.…”

Section: Construction Of Datasetsmentioning

confidence: 99%

“…In addition to theoretical predictions, traditional numerical methods were also available, such as the commonly used high-order spectral method [15]. Taking full nonlinearity into account, the numerically simulated results were closer to real values, but they took a long time to simulate and process [16,17]. The above methods could neither quickly nor accurately predict the occurrence probability of freak waves under a given application.…”

Section: Introductionmentioning

confidence: 99%

Prediction of the Occurrence Probability of Freak Waves in Unidirectional Sea State Using Deep Learning

Zhou,

Wang,

Ding

et al. 2023

JMSE

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Predicting extreme waves can foresee the hydrodynamic environment of marine engineering, critical for avoiding disaster risks. Till now, there are barely any available models that can rapidly and accurately predict the occurrence probability of freak waves in a given state. This paper develops a trained model based on the Back Propagation (BP) neural network, with wave parameters of unidirectional sea state fed into the model, such as significant wave height, wave period, spectral type, and the intermodal distance of the peak frequencies. A rapid and accurate model optimized for predicting the occurrence probability of freak waves in a unidirectional sea state, from unimodal to bimodal configuration, is achieved by iterating to reduce accumulation errors. Compared to the regression and least-squares boosting trees, the optimized model performs much better in accurately predicting the occurrence probability of freak waves. Irrespective of whether in unimodal or bimodal sea state, this optimized model is competitive in calculation accuracy compared to theoretical models such as Rayleigh prediction and MER prediction, improved by at least 41%. The established model based on the BP neural network can quickly predict the threshold of freak waves in a given sea state, guiding practical engineering applications.

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“…In recent years, as giant waves [1], known as one of the most astonishing marine disasters [2][3], take place with a frequency much higher than expected [4] [5][6] [7], studies on extreme waves become a hot issue. Several physical mechanisms to reveal these extreme events have been summarized as geometrical or spatial focusing, spatial-temporal focusing, wave-current interaction, modulation instability, soliton collision, and so on.…”

Section: Introductionmentioning

confidence: 99%

Experimental study on the interactions between wave groups in double-wave-group focusing

et al. 2023

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Nonlinear interactions in wave-group focusing are regarded as one of the main mechanisms in the generation of destructive extreme waves. In real seas, the wideband bimodal state is a typical configuration, containing interactions within a single wave group and between different wave groups. The former has been well uncovered under the assumption of narrow bandwidth, but the latter is poorly understood. In this paper, physical experiments are conducted to reveal the physics of double-wave-group focusing considering various energy distributions. Superposed wavemaker signals generated by the iteration method are applied to produce a double-wave-group focusing with the interactions being decomposed. Results of the wavelet-based bicoherence spectrum show that double-wave-group focusing is distinguished from the linear superposition of two single-wave-group focusing mainly in the nonlinear interactions induced by the second-order sum harmonics. Under the assumption of equivalent energy, interactions of the second-order sum harmonics between the lower frequency group and higher frequency group cannot be ignored in swell-dominated states, and lesser linear interactions and stronger nonlinear interactions are observed while the spectral distribution of the double-wave-group is more asymmetrical. This work is anticipated to contribute to the understanding of the generation mechanism of extreme waves driven by strong nonlinearity.

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Relation between occurrence probability of freak waves and kurtosis/skewness in unidirectional wave trains under single-peak spectra

Cited by 8 publications

References 28 publications

Nonlinear statistical characteristics of the multi-directional waves with equivalent energy

Nonlinear statistical characteristics of the multi-directional waves with equivalent energy

Prediction of the Occurrence Probability of Freak Waves in Unidirectional Sea State Using Deep Learning

Experimental study on the interactions between wave groups in double-wave-group focusing

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