Steepness and asymmetry of the largest waves in storm sea states

Soares, C. Guedes; Cherneva, Z.; Antão, E.M.

doi:10.1016/j.oceaneng.2003.10.014

Cited by 72 publications

(9 citation statements)

References 13 publications

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“…Other properties of the individual wave are given in Guedes Soares et al (2004). Despite being very steep, there is no obvious sign in the data that the wave was breaking.…”

Section: Introductionmentioning

confidence: 99%

Did the Draupner wave occur in a crossing sea?

et al. 2011

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The 'New Year Wave' was recorded at the Draupner platform in the North Sea and is a rare high-quality measurement of a 'freak' or 'rogue' wave. The wave has been the subject of much interest and numerous studies. Despite this, the event has still not been satisfactorily explained. One piece of information that was not directly measured at the platform, but which is vital to understanding the nonlinear dynamics is the wave's directional spreading. This paper investigates the directionality of the Draupner wave and concludes it might have resulted from two wave-groups crossing, whose mean wave directions were separated by about 90• or more. This result has been deduced from a set-up of the low-frequency second-order difference waves under the giant wave, which can be explained only if two wave systems are propagating at such an angle. To check whether second-order theory is satisfactory for such a highly nonlinear event, we have run numerical simulations using a fully nonlinear potential flow solver, which confirm the conclusion deduced from the second-order theory. This is backed up by a hindcast from European Centre for Medium-Range Weather Forecasts that shows swell waves propagating at approximately 80• to the wind sea. Other evidence that supports our conclusion are the measured forces on the structure, the magnitude of the second-order sum waves and some other instances of freak waves occurring in crossing sea states.

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“…Other properties of the individual wave are given in Guedes Soares et al (2004). Despite being very steep, there is no obvious sign in the data that the wave was breaking.…”

Section: Introductionmentioning

confidence: 99%

Did the Draupner wave occur in a crossing sea?

et al. 2011

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“…As often these waves are asymmetric, it is useful to define also the coefficient of front steepness [ Guedes Soares et al , 2004]:

where T fr is the time interval between the lowest and the highest point of the down‐crossing wave and H d is the height of the wave defined between the down‐crossing points.…”

Section: Characteristics Of Individual Wavesmentioning

confidence: 99%

“…The coefficient of crest back steepness is given by

where T bc is the time interval between the highest and the lowest point of the upcrossing wave and H u the height of the wave between upcrossing points [ Guedes Soares et al , 2004].…”

Section: Characteristics Of Individual Wavesmentioning

confidence: 99%

“… Guedes Soares et al [2004] have discussed this topic and stressed that the coefficients of skewness and kurtosis of sea states could be used to characterize their degree of nonlinearity. For processes of any type which are nonlinear of second and third order at the same time it is impossible to choose the coefficients of skewness and kurtosis independently from each other and there is a range of possible values.…”

Section: Criteria To Identify Abnormal Wavesmentioning

confidence: 99%

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Abnormal waves during Hurricane Camille

2004

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[1] A reanalysis is reported of the wave time series recorded during Hurricane Camille having as objective the identification of individual waves that satisfy current criteria defining abnormal or freak waves. It is shown that during the hurricane development, a very nonstationary situation has occurred during which the second-order sea state parameters changed significantly with time. The parameters of the largest individual waves in sea states which identify abnormal waves did not show any clear trend, and such waves occurred during the development stage and not when the significant wave height was the largest. It is argued that the present criteria of identification of abnormal waves are not satisfactory, as they do not take into account the nature of the sea states in which the waves occur.

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“…Time-domain measurements are used to investigate wave dynamics and to gain insight into processes such as wave breaking and freak wave formation (Holthuijsen and Herbers 1986; Guedes Soares et al 2004;Waseda et al 2014;Whittaker et al 2016). In such studies, the two types of measurement are often used interchangeably.…”

Section: Introductionmentioning

confidence: 99%

Lagrangian Measurement of Steep Directionally Spread Ocean Waves: Second-Order Motion of a Wave-Following Measurement Buoy

McAllister

Bremer

2019

Journal of Physical Oceanography

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The notion that wave-following buoys provide less accurate measurements of extreme waves than their Eulerian counterparts is a perception commonly held by oceanographers and engineers (Forristall 2000, J. Phys. Oceanogr., 30, 1931–1943, https://doi.org/10.1175/1520-0485(2000)030<1931:WCDOAS>2.0.CO;2 ). By performing a direct comparison between the two types of measurement under laboratory conditions, we examine one of the hypotheses underlying this perception and establish whether wave measurement buoys in extreme ocean waves correctly follow steep crests and behave in a purely Lagrangian manner. We present a direct comparison between Eulerian gauge and Lagrangian buoy measurements of steep directionally spread and crossing wave groups on deep water. Our experimental measurements are compared with exact (Herbers and Janssen 2016, J. Phys. Oceanogr., 46, 1009–1021, https://doi.org/10.1175/JPO-D-15-0129.1 ) and new approximate expressions for Lagrangian second-order theory derived herein. We derive simple closed-form expressions for the second-order contribution to crest height representative of extreme ocean waves—namely, for a single narrowly spread wave group, two narrowly spread crossing wave groups, and a single strongly spread wave group. In the limit of large spreading or head-on crossing, Eulerian and Lagrangian measurements become equivalent. For the range of conditions that we test, we find that our buoy behaves in a Lagrangian manner, and our experimental observations compare extremely well to predictions made using second-order theory. In general, Eulerian and Lagrangian measurements of crest height are not significantly different for all degrees of directional spreading and crossing. However, second-order bound-wave energy is redistributed from superharmonics in Eulerian measurements to subharmonics in Lagrangian measurement, which affects the “apparent” steepness inferred from time histories and poses a potential issue for wave buoys that measure acceleration.

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Steepness and asymmetry of the largest waves in storm sea states

Cited by 72 publications

References 13 publications

Did the Draupner wave occur in a crossing sea?

Did the Draupner wave occur in a crossing sea?

Abnormal waves during Hurricane Camille

Lagrangian Measurement of Steep Directionally Spread Ocean Waves: Second-Order Motion of a Wave-Following Measurement Buoy

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