Shape asymmetry of rogue waves

2020 ◽  
Author(s):  
Anna Kokorina ◽  
Alexey Slunyaev
Keyword(s):  
Spectral Characteristics ◽  
Rogue Waves ◽  
Engineering Management ◽  
Wave Crest ◽  
Extreme Wave ◽  
Linear Waves ◽  
Stokes Waves ◽  
Wave Nonlinearity ◽  
The Waves ◽  
Management And Conservation

<p>Direct numerical simulations of the directional sea surface gravity waves are carried out within the framework of the primitive potential equations of hydrodynamics using the High Order Spectral Method. The data obtained for conditions of deep water, the JONSWAP spectrum, and various wave intensities are processed and the results are discussed. The statistical and spectral characteristics of the waves evolve over a long period. The particular asymmetry of the profiles of rogue waves is highlighted. We show that besides the conventional crest-to-trough asymmetry of nonlinear Stokes waves, the extreme events are characterized by a specific combination of the troughs adjacent to the large crest, so that the trough behind the crest is typically deeper than the preceding trough. Surprisingly, the extreme wave crest-to-trough asymmetry and the discrimination between the extreme wave troughs exhibit the tendency to grow when the angle spectrum broadens. This effect contradicts the expectation based on the Benjamin – Feir Index that broad-banded waves should behave similar to linear waves, and hence the asymmetries should diminish.</p><p>                                                                 </p><p>The research is supported by the RSF grant No. 19-12-00253.</p><p> </p><p>A. Kokorina, A. Slunyaev, The effect of wave nonlinearity on the rogue wave lifetimes and shapes. Proc. 14th Int. MEDCOAST Congress on Coastal and Marine Sciences, Engineering, Management and Conservation (Ed. E. Ozhan), Vol. 2, 711-721 (2019).</p>

scholarly journals Numerical modelling of extreme waves by Smoothed Particle Hydrodynamics

2011 ◽  
Vol 11 (2) ◽  
pp. 419-429 ◽  
Author(s):  
M. H. Dao ◽  
H. Xu ◽  
E. S. Chan ◽  
P. Tkalich
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Rogue Waves ◽  
Offshore Structures ◽  
Wave Crest ◽  
Extreme Waves ◽  
Coastal Structures ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
The Impact ◽  
The Waves

Abstract. The impact of extreme/rogue waves can lead to serious damage of vessels as well as marine and coastal structures. Such extreme waves in deep water are characterized by steep wave fronts and an energetic wave crest. The process of wave breaking is highly complex and, apart from the general knowledge that impact loadings are highly impulsive, the dynamics of the breaking and impact are still poorly understood. Using an advanced numerical method, the Smoothed Particle Hydrodynamics enhanced with parallel computing is able to reproduce well the extreme waves and their breaking process. Once the waves and their breaking process are modelled successfully, the dynamics of the breaking and the characteristics of their impact on offshore structures could be studied. The computational methodology and numerical results are presented in this paper.

scholarly journals Dynamical and statistical explanations of observed occurrence rates of rogue waves

2011 ◽  
Vol 11 (5) ◽  
pp. 1437-1446 ◽  
Author(s):  
J. Gemmrich ◽  
C. Garrett
Keyword(s):  
Standard Model ◽  
Water Waves ◽  
Rogue Waves ◽  
Value Theory ◽  
Occurrence Rate ◽  
Exceedance Probability ◽  
Extreme Wave ◽  
Straight Line ◽  
The Standard Model ◽  
The Waves

Abstract. Extreme surface waves occur in the tail of the probability distribution. Their occurrence rate can be displayed effectively by plotting ln(–ln P), where P is the probability of the wave or crest height exceeding a particular value, against the logarithm of that value. A Weibull distribution of the exceedance probability, as proposed in a standard model, then becomes a straight line. Earlier North Sea data from an oil platform suggest a curved plot, with a higher occurrence rate of extreme wave and crest heights than predicted by the standard model. The curvature is not accounted for by second order corrections, non-stationarity, or Benjamin-Feir instability, though all of these do lead to an increase in the exceedance probability. Simulations for deep water waves suggest that, if the waves are steep, the curvature may be explained by including up to fourth order Stokes corrections. Finally, the use of extreme value theory in fitting exceedance probabilities is shown to be inappropriate, as its application requires that not just N, but also lnN, be large, where N is the number of waves in a data block. This is unlikely to be adequately satisfied.

Impact of Sampling Variability on Sea Surface Characteristics of Nonlinear Waves

2018 ◽  
Author(s):  
Elzbieta M. Bitner-Gregersen ◽  
Odin Gramstad
Keyword(s):  
Wave Model ◽  
Surface Characteristics ◽  
Rogue Waves ◽  
Sea Surface ◽  
Wave Crest ◽  
Linear Wave ◽  
Extreme Wave ◽  
Sampling Variability ◽  
Wave Forecasting ◽  
Jonswap Spectrum

The restricted duration of wave records, usually 20 or 30 minutes, introduces sampling variability, the statistical uncertainty due to limited number of observations, in estimates of sea surface characteristics. This uncertainty may have significant impact on derived wave parameters commonly used in design and marine operations, and quantifying it is also of importance for wave forecasting purposes as well as for investigations of extreme wave events such as rogue waves. The study shows, using numerical simulations, effects of sampling variability on the measures of wave field nonlinearity, the skewness and kurtosis coefficients of sea surface elevation, and on the wave crest. Wave data are simulated by the nonlinear wave model HOSM (Higher Order Spectral Method). The Pierson-Moskowitz and the JONSWAP spectrum with different gamma parameters and different directional energy spreading functions are used in the analysis and their effect on sampling variability estimates is demonstrated. Sea states where rogue waves were recorded in nature are considered. The results are compared with the ones obtained from linear wave model simulations. Consequences of sampling variability on description of sea surface nonlinearity are discussed.

Wavelet Analysis of an Extreme Wave in a Model Basin

2008 ◽  
Author(s):  
Kevin Ewans ◽  
Bas Buchner
Keyword(s):  
Phase Locking ◽  
Spectral Characteristics ◽  
Nonlinear Effects ◽  
Wave Crest ◽  
Order Effects ◽  
Extreme Wave ◽  
Average Spectrum ◽  
Propagating Waves ◽  
Wave Event ◽  
High Frequency Waves

Analyses of laboratory wave records including extreme crests, based on the continuous wavelet transform, are reported. The analyses have provided further insight into the spectral characteristics of these extreme events. During the period of the extreme wave crest, spectral levels over all frequencies are substantially elevated by comparison with average spectrum for the complete wave record. This was also observed in a similar analysis of the famous New Year wave event that occurred at the Draupner platform. The analyses also indicate that nonlinear effects are active during the crest event, second-order effects being particular strong and indicating phase-locking of high frequency waves to freely-propagating waves with frequencies close to the spectral peak. These nonlinear effects appear to be strong only in the vicinity of the extreme.

Effect of Short-Crestedness on Extreme Wave Impact: A Summary of Findings From the Joint Industry Project “ShorTCresT”

2015 ◽  
Author(s):  
Janou Hennig ◽  
Jule Scharnke ◽  
Chris Swan ◽  
Øistein Hagen ◽  
Kevin Ewans ◽  
...  
Keyword(s):  
Wave Breaking ◽  
Good Description ◽  
Spectral Characteristics ◽  
Offshore Structures ◽  
Wave Crest ◽  
Extreme Waves ◽  
Extreme Wave ◽  
Wave Impact ◽  
Directional Model

Long-crested waves are typically used in the design of offshore structures. However, the corresponding statistics, kinematics and loading are significantly different in short-crested waves and up to date, there is no state-of-the-art methodology to apply short-crested models instead. The objective of the “ShortCresT” Joint Industry Project was to take into account short-crestedness in the design of offshore structures against extreme waves based on a good description of their spectral characteristics, statistics, kinematics, breaking and loading and to deliver (empirical) design recommendations and methods. This paper gives an overview of the findings of ShorTCresT regarding wave crest and height distributions, a comparison of basin and field data, the role of wave breaking, the most realistic directional model, hindcast models as well as the related platform loading.

scholarly journals Multi-year satellite observations of instability waves in the Tropical Atlantic Ocean

2005 ◽  
Vol 2 (1) ◽  
pp. 1-35 ◽  
Author(s):  
A. C. V. Caltabiano ◽  
I. S. Robinson ◽  
L. P. Pezzi
Keyword(s):  
Atlantic Ocean ◽  
Spectral Characteristics ◽  
Coupling Mechanism ◽  
Tropical Atlantic ◽  
Atlantic Region ◽  
Instability Waves ◽  
Tropical Atlantic Ocean ◽  
Zonal Winds ◽  
Meridional Winds ◽  
The Waves

Abstract. Instability waves in the tropical Atlantic Ocean are analysed by microwave satellite-based data spanning from 1998 to 2001. This is the first multi-year observational study of these waves in the region. Sea surface temperature (SST) data were used to show that the waves spectral characteristics vary from year-to-year. They also vary on each latitude north of the equator, with the region of 1° N, 15° W concentrating the largest variability when the time series is averaged along the years. Analyses of wind components show that meridional winds are more affected near the equator and 1° N, while zonal winds are more affected further north at around 3° N and 4° N. Concurrent observations of SST, wind, atmospheric water vapour, liquid cloud water, precipitation rates and wind were used to demonstrate the possible influence of these waves on the Intertropical Convergence Zone (ITCZ). It seems that these instabilities have a large impact on the ITCZ due to its proximity of the equator, compared to its Pacific counterpart, and the geography of the tropical Atlantic basin. These analyses also suggest that the air-sea coupling mechanism suggested by Wallace can also be applied to the tropical Atlantic region.

scholarly journals Statistical properties of nonlinear one-dimensional wave fields

2005 ◽  
Vol 12 (5) ◽  
pp. 671-689 ◽  
Author(s):  
D. Chalikov
Keyword(s):  
Surface Waves ◽  
Nonlinear Wave ◽  
High Accuracy ◽  
Statistical Properties ◽  
Statistical Characteristics ◽  
Small Scale ◽  
Sea Waves ◽  
Wave Fields ◽  
Linear Waves ◽  
Stokes Waves

Abstract. A numerical model for long-term simulation of gravity surface waves is described. The model is designed as a component of a coupled Wave Boundary Layer/Sea Waves model, for investigation of small-scale dynamic and thermodynamic interactions between the ocean and atmosphere. Statistical properties of nonlinear wave fields are investigated on a basis of direct hydrodynamical modeling of 1-D potential periodic surface waves. The method is based on a nonstationary conformal surface-following coordinate transformation; this approach reduces the principal equations of potential waves to two simple evolutionary equations for the elevation and the velocity potential on the surface. The numerical scheme is based on a Fourier transform method. High accuracy was confirmed by validation of the nonstationary model against known solutions, and by comparison between the results obtained with different resolutions in the horizontal. The scheme allows reproduction of the propagation of steep Stokes waves for thousands of periods with very high accuracy. The method here developed is applied to simulation of the evolution of wave fields with large number of modes for many periods of dominant waves. The statistical characteristics of nonlinear wave fields for waves of different steepness were investigated: spectra, curtosis and skewness, dispersion relation, life time. The prime result is that wave field may be presented as a superposition of linear waves is valid only for small amplitudes. It is shown as well, that nonlinear wave fields are rather a superposition of Stokes waves not linear waves. Potential flow, free surface, conformal mapping, numerical modeling of waves, gravity waves, Stokes waves, breaking waves, freak waves, wind-wave interaction.

scholarly journals On the Spectra of Gravity Waves Generated by Two Typical Convective Systems

Atmosphere ◽  
2019 ◽  
Vol 10 (7) ◽  
pp. 405
Author(s):  
Yuan Wang ◽  
Lifeng Zhang ◽  
Jun Peng ◽  
Yun Zhang ◽  
Tongfeng Wei
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
Gravity Waves ◽  
Spectral Characteristics ◽  
Wave Source ◽  
Convective Systems ◽  
Spectral Distributions ◽  
The Waves

Spectral characteristics of lower-stratospheric gravity waves generated in idealized mei-yu front and tropical cyclone (TC) are compared by performing high-resolution simulations. The results suggest that the systems which organize convection in different forms can generate waves with distinctly different presentation. The mei-yu front appears as a linear zonal wave source and gravity waves are dominated by cross-frontal (meridional) propagating components. The northward (southward) components have dominant meridional wavelengths of 125–333 km (>250 km), periods of 100–200 min (83–143 min), and phase speeds of 0–15 m s−1 (15–20 m s−1). The TC appears as a point wave source and gravity waves propagate equally in various horizontal directions. The waves exhibit greater power and broader spectral distributions compared with those in the mei-yu front, with dominant horizontal wavelengths longer than 62.5 km, periods of 33–600 min, and phase speeds slower than ~40 m s−1.

Reliability Assessment of TLP Air-Gap in Nonlinear Waves

2011 ◽  
Author(s):  
Elzbieta M. Bitner-Gregersen
Keyword(s):  
Sea Water ◽  
Vertical Displacement ◽  
Rogue Waves ◽  
Future Research ◽  
Diffraction Radiation ◽  
Cooperative Research ◽  
Structure Reliability ◽  
Sensitivity Studies ◽  
Water Level Variations ◽  
Wave Nonlinearity

The present study demonstrates effects of the CresT JIP (Cooperative Research on Extreme Seas and their impacT) findings regarding extreme and rogue waves through a simplified structure reliability analysis of a generic TLP structure defined by the project. The study demonstrates effects of wave nonlinearity beyond the second order, diffraction-radiation of incoming waves with the structure, spatial variations of crest statistics, a vertical displacement of the TLP system at the deck location as well as sea water level variations due to surge and tide. In order to account for these effects a stochastic model is suggested. Sensitivity studies are carried out to identify importance of analysed parameters and their stochastic behaviour to the failure probability. Uncertainties related to the analysis are identified and ranked given special attention to the effect of wave nonlinearities beyond the 2nd order. Recommendations for future research needs are suggested.

Extreme Load-Response Mechanisms of a Tension Leg Platform due to Larger Wave Crests: Some Results of the ‘CresT’ JIP

2011 ◽  
Author(s):  
Janou Hennig ◽  
Jule Scharnke ◽  
Bas Buchner ◽  
Joris van den Berg
Keyword(s):  
Gulf Of Mexico ◽  
Extreme Event ◽  
Offshore Structures ◽  
Wave Load ◽  
Extreme Wave ◽  
Response Process ◽  
Load Response ◽  
Extreme Load ◽  
The Waves ◽  
Crest Height

For the design of ships and offshore structures the largest crest height which can be expected in their lifetime is of key importance. This was confirmed by several incidences e.g. in hurricanes in the Gulf of Mexico during the recent years. This is why MARIN started up the CresT JIP with a number of partners. The CresT JIP is now completed and some results of the extreme wave load and response mechanisms observed during model tests with a TLP will be presented in this paper. First an overview is given of the loading and response process during the most extreme event observed. As a next step the loading and response is related to the time and spatial characteristics of the waves, as it is not per definition the highest local crest or wave height that results in the most extreme dynamic response. Furthermore, the effect of different TLP design variations and short-crestedness will be discussed.

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