freak wave
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2022 ◽  
Vol 82 ◽  
pp. 103148
Author(s):  
Fanxu Zeng ◽  
Ningchuan Zhang ◽  
Guoxing Huang ◽  
Qian Gu ◽  
Wenbo Pan
Keyword(s):  

2021 ◽  
Vol 9 (11) ◽  
pp. 1266
Author(s):  
Fali Huo ◽  
Hongkun Yang ◽  
Zhi Yao ◽  
Kang An ◽  
Sheng Xu

Freak waves have great peak energy, short duration, great contingency, and strong nonlinear characteristics, and can cause severe damage to ships and marine structures. In this study, numerical simulations in conjunction with experimental tests are applied to study air gap response and wave slamming loads of a semi-submersible offshore platform under a freak wave. A three-dimensional wave tank, which is created based on the computational fluid dynamics (CFD) method, is applied to study the hydrodynamic responses of a semi-submersible platform. The numerical model of the tank and offshore platform system are checked according to the experimental results. A typical freak wave is modelled in numerical wave tanks by the linear superposition method, and its significant wave height is 13.03 m. It is found that the freak wave is closely associated with the wave slamming. The appearance of the freak wave gives rise to a negative air, gap which appears on the side of the back wave surface at the bottom of the deck box, and considerable slamming pressure is generated. Furthermore, the wave run up at the junction of the column and the buoyancy tank is also seen due to the freak wave.


2021 ◽  
Vol 927 ◽  
Author(s):  
Mateusz Kluczek ◽  
David Andrade ◽  
Michael Stiassnie

The problem of unidirectional shoaling of a water-wave field with a narrow energy spectrum is treated by using a new Alber equation. The stability of the linear stationary solution to small non-stationary disturbances is analysed; and numerical solutions for its subsequent long-distance evolution are presented. The results quantify the physics which causes the gradual decay in the probability of freak-wave occurrence, when moving from deep to shallow coastal waters.


2021 ◽  
Vol 3 (397) ◽  
pp. 65-74
Author(s):  
V. Maslov ◽  

Object and purpose of research. This paper describes physical modeling of interaction process of abnormal wave (freak wave) with a marine floating structure in a seakeeping tank of the Krylov State Research Center. Freak wave is extremely dangerous because of the difference from wind waves by an unusually steep front slope and a gentle trough. Freak wave appears suddenly and collapses rapidly. Research of effect process features is necessary for understanding and analysis of the object behavior at extreme sea conditions. As experiment results it was necessary to obtain empirical data of sea object motions and accelerations at interaction with freak wave on different course angles and speeds. The obtained physical experiment results will be the foundation of theoretical studies and numerical calculation methods. Materials and methods. Physical modeling of the interaction process of freak wave with a marine floating structure was conducted in a deep seakeeping tank. Freak wave was generated by the linear superposition method of four twodimensional unidirectional regular waves with variable steepness in frequency range of 2 to 6 rad/s. To create a control signal was using special software. Wave packets were formed consisting of a sequence of a four harmonicas with a given frequency, height and duration. For parameters registration of freak wave were used string probes installed with a certain step along the length of the tank. A marine floating structure model was fixed by elastic fastening system in a window of a tow cart. For measure the motions of marine floating structure and its accelerations in define points at encounter with freak wave the contactless optic system and two-component acceleration sensors (accelerometers) were used. Cases of structure interaction with freak wave at different course angles and speeds were considered. Main results. As result of physical experimental data of floating structure motions in the interaction with freak wave in conditions of regular sea state at five course angles with speed and without speed were obtained. Dependencies of roll, pitch and heave motions at different course angles and various speeds were built. Similar dependencies of vertical and transverse accelerations on a stem also were built. Comparative analysis of results with data, which were obtained on intensive irregular sea state (spectrum JONSWAP) at identical experiment conditions, and also with foreign results was carried out. Conclusions. The greatest roll and maximum accelerations are registered at alongside position to abnormal wave, but cargo vessel has a sufficient reserve of dynamic stability to withstand such an impulse effect. The values of roll motion and accelerations on irregular sea state are close to the parameters measured at freak wave effect. This similarity is explained by rocking effect of periodic impact of irregular sea state, the proximity of natural period of roll oscillations to average period of waves and sufficiently high waves. In comparison with foreign researches, a wider range of heading angles and speeds is considered, and data about accelerations in a stem are obtained.


2021 ◽  
Vol 290 ◽  
pp. 02013
Author(s):  
Yu Xiang-jun ◽  
Li Qing-hong ◽  
Li Mao-lin

Freak waves are both extremely large waves and highly transient time. Such a wave may lead to damage of ships to deaths. In this paper, to describe the connection between freak wave and wave essential factor, we use WAVEWATCH III model simulating “New Year Wave” in the North Sea to explore freak wave, with the importing of ECMWF re-analysis wind field. By this way, we successfully simulate the formation of freak wave in the random wave. Analysis shows large wave steepness and small directional spread angle are necessary conditions for freak waves to easily occur. By analyzing the wave spectrum, it is found that the wave energy is distributed in a small range, and the propagation direction is relatively concentrated.


Author(s):  
P. V. Anakhov

In linear theory the formation of extreme waves their existence is interpreted as a local superposition of surface monochromatic waves. Natural water areas are resonators that have their own set of natural oscillations – standing waves of stable spatial structure and fixed period. In the spectra of waves of many water bodies of World Ocean observed double high waves, this is explained by the tidal-seiche resonance. During a storm, the energy of natural oscillations increases ten times the background energy, during a tsunami it can increase up to three orders of magnitude. Examples of the effects of natural oscillations on the coast are given, and it is reported about the increased probability of the occurrence on the coast freak waves. Additionally, it is noted that natural oscillations in water mass are a normal state for any body of water at any time of its existence. The corresponding indices of the water fluctuations of the water basins are given. The events of extreme waves during the accidents at DniproHES (Zaporizhia) on August 18, 1941, and the Kurenivsky dam (Kyiv) on March 13, 1961, are presented. The excitement of the freak wave can be interpreted as enhancing the natural oscillations of the water basin, represented by standing waves of stable spatial structure, fixed period and high probability of waves in the water body. This does not contradict the linear theory of the resonant formation of abnormally high waves. The purpose of the article is to investigate possible sources of the excitement of freak waves, the results are proposed to be implemented in the development of countermeasures to the destructive process. However, the waves carry out both destructive and creative work. A task is presented, which involves the development of measures to stimulate extreme waves. This will increase electricity generation. Affiliation of dam-break waves to freak waves can be doubtful. However, they formally correspond to the classical condition of double exceeding the significant wave height. Most water basins are integral anthropogenic sites. The variability of both natural and anthropogenic environments forces the overriding of systematization and definition. It is proposed to attribute extreme waves of dam-break waves to freak waves.


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