Showing papers on "Rogue wave published in 1987"

Prediction of Occurrences of Steep and High Waves in Deep Water

Abstract: Estimates for encounter probabilities of occurrence of steep and high waves in deep water for given sea states by using two different parametric models for the joint distribution of crest front steepness and wave height are presented. The parametric models are fitted to the same data set, with data from a zero‐downcross analysis of wave data obtained from measurements at sea on the Norwegian continental shelf. The probability of occurrence of waves with different crest front steepness are estimated with each parametric model for a family of JONSWAP spectra. An example is given where the probabilities of occurrence of “extreme waves,” which are considered to be critical to capsizing of smaller vessels, are estimated with one parametric model for sea states described by significant wave height and mean zero‐crossing period.

Analysis of prototype freak waves

Abstract: It is described how continuous storm wave records taken in the North Sea were used to isolate and analyze freak wave events. The analyses were performed on several levels. First, an investigation was made of whether surface profiles and horizontal orbital velocities could be explained by 2-D (long crested) wave theories up to the fifth order. Second, the phenomenon was treated as a 3-D (directional) interaction case. Velocity vectors in three levels were studied in order to reveal possible special 3-D characteristics. Low- and high-pass filters were also used as elements in the analysis of the composition of the freak waves. From the limited amount of data analyzed so far, the high frequency part of the freak waves seems to be strongly directional. To describe the character of the high frequency waves in detail, a three-dimensional second-order (higher harmonic) separation technique was used to isolate bound and free components. As a reference for the future analysis of freak waves, the wave climate producing the ones discussed was also analyzed in detail. The development over time of mean directions, directional spread and spectral density is presented.

On the behavior near the crest of waves of extreme form

Abstract: : This paper concerns waves of permanent form on the free surface of an ideal liquid which is in two-dimensional, irrotational motion under the action of gravity. We consider only extreme waves, often called 'waves of greatest height'; each of these is the end-member of a one-parameter family of waves, and is distinguished from other 'smaller' members of the family by a sharp crest. Although this corner is physically unrealistic, oceanographers have given such idealized, extreme waves a great deal of attention since Stokes postulated their existence in 1880. (One reason may be the physical importance of the smaller waves, and that scientists like to interpolate.) The present paper is a contribution to the strict mathematical theory of extreme waves, which was emerged only since 1978. We derive rigorously an asymptotic series that describes the flow near the crest. This confirms and sharpens certain earlier exploratory results due to Grant and Norman. The series should play a useful part in numerical computations of extreme waves. (Author)

The asymptotic behavior near the crest of waves of extreme form

Abstract: : This paper concerns waves of permanent form on the free surface of an ideal liquid which is in two-dimensional, irrotational motion under the action of gravity. It considers only extreme waves, often called waves of greatest heights; each of these is the end-member of a one-parameter family of waves and is distinguished from other smaller members of the family by a sharp crest. Although this corner is physically unrealistic, oceanographers have given such idealised, extreme waves a great deal of attention since Stokes postulated their existence iln 1880. This paper is a contribution to the strict mathematical theory of extreme waves, which has emerged only since 1978. An asymptotic series is known that describes the flow near the crest, but it has never been proved whether the leading term in this expansion has a non-zero coefficient or not (and so whether it is in fact the leading term or not). The author shows that the coefficient is non-zero and determines its sign. The result should play a useful part in numerical computation of extreme waves. Keywords: Nonlinear integral equations; Analytic functions; Water waves.

Extreme waves in the Agulhas - A case study in wave-current interaction

Abstract: SIR data obtained in October 1984 off the South African coast are analyzed. The analysis of the derived ocean-wave slope spectra reveals the presence of two wave systems: a swell field from the SW of about 190 m wavelength and a swell out of the SE with a wavelength of about 220 m. An observed increase in wave energy along the northern edge of the Agulhas, caused by the propagation of the 190 m wave system opposite to that of the Agulhas Current, is studied by modeling the interaction of a wave with an opposite current. The role of refraction in the energy intensification is discussed. The effects of currrent curvature on the trajectory of the wave group and of meandering on a uniform wave field are investigated. A possible mechanism for the generation of extreme waves is proposed.

Solitons, tidal bores, tsunamis, and other freak waves

Abstract: The various unusual waves named in the title of this article are defined and their causes explained.

Estimation of alongshore distribution of typhoon-generated maximum wave height around the japanese coast based on wave hindcasting

Abstract: The purpose of this paper is to estimate alongshore distribution of maximum wave height around the Japanese coast generated by long-term typhoons through wave hindcasting based on a spectral wave prediction model. First, the applicability of the model to the evaluation of typhoon-generated waves is confirmed from the comparison between hindcasted results and wave data observed during many typhoons in recent years. Second, based on the wave hindcasting for 120 typhoons which attacked Japan in the past 50 years, alongshore distribution of maximum wave heights and their occurrence probability are estimated and compared with that of design wave heights of coastal structures. It is deduced that the design wave heights in the western district of Japan seem to be slightly small for probable maximum wave heights.