Statistics of Extreme and Freak Waves

2006 ◽  
Author(s):  
Leonid J. Lopatoukhin ◽  
Alexander V. Boukhanovsky
Keyword(s):  
Wind Waves ◽  
Rogue Waves ◽  
Wave Climate ◽  
Multivariate Statistical ◽  
Freak Waves ◽  
Facilities Planning ◽  
Freak Wave ◽  
Port Operation ◽  
Near Shore ◽  
External Reasons

Wind waves are of the main hazards, affecting the human activity and needed for shipbuilding design, near shore facilities, planning and management of coastal and port operation, etc. Wave climate investigations, based on continuous 30-year hindcasting are performed. One of the main results of hindcasting is a set of two-dimensional spectra S(ω,θ) on selected grids and synoptic terms t, in particularly. For statistical generalization as the tools, multivariate statistical analysis is used. Special attention is drawn to point and field extremes. Specific and difference between these two statistics is crucial for solution of some applied problems. Adjusted approaches do not allow investigating phenomena known as freak (or rogue) waves. The main difference between extreme and freak waves is in their unusual form. Probability of freak wave depends from a lot of internal and external reasons. Some approaches are proposed and described in this paper.

Characteristics of the Infragravity Wave Climate

2008 ◽  
Author(s):  
Stephen Masterton ◽  
Kevin Ewans
Keyword(s):  
Oil And Gas ◽  
Wind Waves ◽  
Wave Climate ◽  
Peak Period ◽  
Infragravity Waves ◽  
Design Practices ◽  
The Us ◽  
Near Shore ◽  
Wave Models ◽  
Infragravity Wave

Infragravity waves are very long period waves below the frequency of typical wind waves. They are most significant in shallow water locations and therefore have a high impact on the response of moored vessels. For the Oil and Gas business this can be an important consideration for tanker on/offloading operations (including LNG vessels) — these larger vessels, with longer natural periods, are particularly susceptible. There are implications for both the design and operation including the calculation of extreme loading on the mooring system, extreme vessel motions, fatigue of mooring systems and the availability of on/offloading operations. There are currently limited design practices to account for the effect of infragravity waves. This may be attributed to two main factors: The development of infragravity waves is difficult to model and is sensitive to many factors, including the magnitude and shape of the incident wind and swell spectra, local bathymetry, directionality and near shore wave breaking. Secondly, very little measured data exist since the infragravity wave frequencies lie below the conventional range of commonly deployed wave measurement devices. The present paper will provide a description of the infragravity waves acting on the US coast at two locations, Duck, North Carolina, and Baja, California. The results will characterize parameters including the significant wave height, peak period, and comparison of infragravity waves through time. In addition, the relationships between the spectral shape will be examined including directionality. This type of information is needed to set design criteria for infragravity waves, and in the longer term to develop and enhance infragravity wave models e.g. Reniers 2002 (1) and ultimately contribute to establishing design practices.

Can swell increase the number of freak waves in a wind sea?

2010 ◽  
Vol 650 ◽  
pp. 57-79 ◽  
Author(s):  
ODIN GRAMSTAD ◽  
KARSTEN TRULSEN
Keyword(s):  
Nonlinear Evolution ◽  
Wind Waves ◽  
Short Wave ◽  
Freak Waves ◽  
Freak Wave ◽  
Short Waves ◽  
Term Evolution ◽  
Wind Sea ◽  
Modified Equation

The effect of a swell on the statistical distribution of a directional short-wave field is investigated. Starting from Zakharov's spectral formulation, we derive a new modified nonlinear Schrödinger equation appropriate for the nonlinear evolution of a narrow-banded spectrum of short waves influenced by a swell. The swell-modified equation is solved analytically to yield an extended version of the result of Longuet-Higgins & Stewart (J. Fluid Mech., vol. 8, no. 4, 1960, pp. 565–583) for the modulation of a short wave riding on a longer wave. Numerical Monte Carlo simulations of the long-term evolution of a spectrum of short waves in the presence of a monochromatic swell are employed to extract statistical distributions of freak waves among the short waves. We find evidence that a realistic short-crested wind sea can on average experience a small increase in freak wave probability because of a swell provided the swell is not orthogonal to the wind waves. For orthogonal swell and wind waves we find evidence that there is almost no significant change in the probability of freak waves in the wind sea. If the short waves are unrealistically long crested, such that the Benjamin–Feir index serves as indicator for freak waves (Gramstad & Trulsen, J. Fluid Mech., vol. 582, 2007, pp. 463–472), it appears that the swell has much smaller relative influence on the probability of freak waves than in the short-crested case.

scholarly journals Freak waves in 2005

2006 ◽  
Vol 6 (6) ◽  
pp. 1007-1015 ◽  
Author(s):  
I. I. Didenkulova ◽  
A. V. Slunyaev ◽  
E. N. Pelinovsky ◽  
C. Kharif
Keyword(s):  
Mass Media ◽  
Rogue Waves ◽  
Wave Impact ◽  
Freak Waves ◽  
Freak Wave ◽  
Open Sea

Abstract. Information about freak wave events in the ocean reported by mass media and derived from personal observations in 2005 is collected and analysed. Nine cases are selected as true freak wave events from a total number of 27 mentioned. Besides rogue waves in the open sea, the problem of freak wave events on the shore is emphasized. These accidents are related to unexpected wave impact upon the coast and shore constructions or to sudden intensive flooding of the coast. Of the nine events considered reliable here, three events correspond to open-sea cases, while the six others occurred nearshore.

Reconstruction and Analysis of Freak Waves Generated From Unidirectional Random Waves

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Yuxiang Ma ◽  
Changfu Yuan ◽  
Congfang Ai ◽  
Guohai Dong
Keyword(s):  
Time Series ◽  
Extreme Event ◽  
Wave Model ◽  
Rogue Waves ◽  
Random Wave ◽  
Random Waves ◽  
Long Distance ◽  
Freak Waves ◽  
Freak Wave ◽  
Wave Flume

Abstract The generation of two freak waves in a broadband and a narrowband random series registered in the experiments of Li, J. X., Li, P. F., and Liu, S. X. (2013, “Observations of Freak Waves in Random Wave Field in 2D Experimental Wave Flume,” China Ocean Eng., 27(5), pp. 659–670) is precisely reconstructed using a fully non-hydrostatic water wave model. The simulation results indicate that even when the background spectral bandwidths are different, the evolution processes of the two freak waves are similar. Both freak waves emerge quickly during the transition from normal states to extreme events. The freak waves can persist over a long distance, i.e., approximately 5 peak wavelengths. The reconstructed time series in both the backward and forward locations at which the freak waves were recorded reveal that the largest freak wave crests were not captured in the experiment. The freak waves gradually emerged from an intense wave group. The waves developed quickly during the transition from a normal state to an extreme event. Very deep troughs were also formed in the evolution process. The two freak waves were actually generated via different spectral bandwidth processes, but the generation mechanisms of the rogue waves were similar. By analyzing the time series of the freak wave groups, the formation of the freak waves is found to result from the combined effect of the dispersive focusing, the third-order resonant wave interactions, and the higher harmonics.

Freak Wave Events Within the Second Order Wave Model

2004 ◽  
Author(s):  
Elzbieta M. Bitner-Gregersen ◽  
O̸istein Hagen
Keyword(s):  
Wave Model ◽  
Wave Theory ◽  
Rogue Waves ◽  
Offshore Structures ◽  
Second Order ◽  
Short Term ◽  
Freak Waves ◽  
Freak Wave ◽  
Offshore Industry

Recently significant interest has been paid to abnormal waves, often called rogue waves or freak waves. These waves represent operational risks to ship and offshore structures, and are likely to be responsible for a number of accidents. As shown by several authors, in ‘the second order world’ the freak waves are pretty rare events. The present study focuses on statistical properties of freak waves. The analyses are based on second order time domain simulations, short term distributions for crest statistics obtained from the literature, and long term field data. Time series of wave elevations are generated using the Pierson-Moskowitz, JONSWAP and two-peak Torsethaugen frequency spectrum for long-crested seas and deep water. Effects of combined seas (swell and wind sea) on wave statistics are discussed. Assuming 2nd order wave theory, the short term and long term probability of occurrence of a freak wave is estimated. The difference between a “freak wave” and a “dangerous wave” is pointed out. Finally, 100 year and 10000 year crest events obtained by analysis procedures used in the offshore industry are discussed in relation to freak waves.

Extreme and Freak Waves: Results of Measurements and Simulation

2008 ◽  
Author(s):  
Leonid J. Lopatoukhin ◽  
Alexander V. Boukhanovsky
Keyword(s):  
Wind Waves ◽  
World Ocean ◽  
Wave Climate ◽  
Model Verification ◽  
Statistical Characteristics ◽  
Extreme Wave ◽  
Offshore Structure ◽  
Freak Wave ◽  
Advantages And Disadvantages ◽  
Wave Measurements

Main statistical characteristics of wave climate are considered in respect of offshore and ship design. Sophistication of ships and marine platforms and expansion of offshore activities to non-investigated regions means increasing of probability of being damaged by high waves. Hindcasting of wave fields, using the hydrodynamic models is main approach to wave climate investigation. Offshore wave measurements are used, mainly, for model verification. In compliance with existent regulatory documents and accepted practice applied statistical characteristics of wind waves are prescribed to operational and extreme. Operational statistics describe wind and wave conditions for the life span of a ship or an offshore structure. Extreme characteristics determine the so-called “structure survival regime”. There are a lot of approaches to calculations of extreme wave heights at a point (classical unconditional extremes). Their comparison shows the advantages and disadvantages of each of them. Freak (rogue) waves have some principal difference from extreme wave, mainly due to their form and asymmetry. In this sense freak wave is a multidimensional extreme. Contaminated distribution may be used for probability density approximation of joint extreme and freak wave. The example of recent freak wave event is the loss of ship “Aurelia” (Class of Russian Register of shipping) in February 2005 in the North Pacific. “Aurelia” sunk during passing of atmospheric front with veering wind, changing wind waves. Any wave has at least three dimensions: height, length, and crest length. The last parameter in mean is 3 times greater than wave length. Any information about three dimensional waves is of interest, as such measurements are unique. Some results of unique stereo wave measurements in the South Pacific where the wave as high as 24.9m was fixed (probably still almost the highest measured in the World Ocean), is presented and discussed.

Non-Gaussian Extreme Waves in the Central North Sea

1997 ◽  
Vol 119 (3) ◽  
pp. 146-150 ◽  
Author(s):  
J. Skourup ◽  
N.-E. O. Hansen ◽  
K. K. Andreasen
Keyword(s):  
Wave Height ◽  
North Sea ◽  
Upper Bound ◽  
Wave Crest ◽  
Extreme Waves ◽  
Freak Waves ◽  
Freak Wave ◽  
Wave Trains ◽  
Central North Sea ◽  
Crest Height

The area of the Central North Sea is notorious for the occurrence of very high waves in certain wave trains. The short-term distribution of these wave trains includes waves which are far steeper than predicted by the Rayleigh distribution. Such waves are often termed “extreme waves” or “freak waves.” An analysis of the extreme statistical properties of these waves has been made. The analysis is based on more than 12 yr of wave records from the Mærsk Olie og Gas AS operated Gorm Field which is located in the Danish sector of the Central North Sea. From the wave recordings more than 400 freak wave candidates were found. The ratio between the extreme crest height and the significant wave height (20-min value) has been found to be about 1.8, and the ratio between extreme crest height and extreme wave height has been found to be 0.69. The latter ratio is clearly outside the range of Gaussian waves, and it is higher than the maximum value for steep nonlinear long-crested waves, thus indicating that freak waves are not of a permanent form, and probably of short-crested nature. The extreme statistical distribution is represented by a Weibull distribution with an upper bound, where the upper bound is the value for a depth-limited breaking wave. Based on the measured data, a procedure for determining the freak wave crest height with a given return period is proposed. A sensitivity analysis of the extreme value of the crest height is also made.

Wave Climate Analysis for a Wave Energy Conversion Application in Brazil

2007 ◽  
Author(s):  
Eliab R. Beserra ◽  
Andre´ L. T. Mendes ◽  
Segen F. Estefen ◽  
Carlos E. Parente
Keyword(s):  
Energy Conversion ◽  
Wave Energy ◽  
Wind Waves ◽  
Energy Resource ◽  
Wave Climate ◽  
Northern Coast ◽  
Wave Energy Conversion ◽  
Annual Fluctuation ◽  
Significant Wave ◽  
Climate Analysis

A variety of ocean wave energy conversion devices have been proposed worldwide considering different technology and energy extraction methods. In order to support full-scale prototype design and performance assessments of a conversion scheme to be deployed on the northern coast of Brazil, a long-term wave climate analysis is under development. A 5-year pitch-roll buoy data series has been investigated through an adaptive technique to enhance spatial resolution and allow for accurate wave directionality evaluation. Device design most influential variables such as extreme significant wave height, peak period and directionality were considered. Temporal variability in wave energy levels was particularly investigated for energy resource assessment. The major findings of this work include the narrow directional amplitude of the incident wave and higher significant wave heights of locally generated waves. The estimated energy resource levels agreed well with literature, also showing little annual fluctuation. The wave climate demonstrated to be in full agreement with the large-scale Equatorial Atlantic atmospheric variability, dominated by either local wind waves or by distant storm swells.

Covariate Extreme Value Analysis Using Wave Spectral Partitioning

2020 ◽  
Vol 37 (5) ◽  
pp. 873-888 ◽  
Author(s):  
Jesús Portilla-Yandún ◽  
Edwin Jácome
Keyword(s):  
Extreme Values ◽  
Wind Waves ◽  
Spectral Energy Distribution ◽  
Wave Spectrum ◽  
Wave Climate ◽  
Extreme Value ◽  
Extreme Value Analysis ◽  
Spectral Energy ◽  
Value Analysis ◽  
Spectral Partitioning

AbstractAn important requirement in extreme value analysis (EVA) is for the working variable to be identically distributed. However, this is typically not the case in wind waves, because energy components with different origins belong to separate data populations, with different statistical properties. Although this information is available in the wave spectrum, the working variable in EVA is typically the total significant wave height Hs, a parameter that does not contain information of the spectral energy distribution, and therefore does not fulfill this requirement. To gain insight in this aspect, we develop here a covariate EVA application based on spectral partitioning. We observe that in general the total Hs is inappropriate for EVA, leading to potential over- or underestimation of the projected extremes. This is illustrated with three representative cases under significantly different wave climate conditions. It is shown that the covariate analysis provides a meaningful understanding of the individual behavior of the wave components, in regard to the consequences for projecting extreme values.

A Numerical Prediction on the Transient Response of a Spar-Type Floating Offshore Wind Turbine in Freak Waves

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Yan Li ◽  
Xiaoqi Qu ◽  
Liqin Liu ◽  
Peng Xie ◽  
Tianchang Yin ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Offshore Wind ◽  
Numerical Code ◽  
Modulation Method ◽  
Offshore Wind Turbine ◽  
Freak Waves ◽  
Freak Wave ◽  
Floating Offshore Wind Turbine ◽  
The Impact

Abstract Simulations are conducted in time domain to investigate the dynamic response of a spar-type floating offshore wind turbine (FOWT) under the freak wave scenarios. Toward this end, a coupled aero-hydro-mooring in-house numerical code is adopted to perform the simulations. The methodology includes a blade-element-momentum (BEM) model for simulating the aerodynamic loads, a nonlinear model for simulating the hydrodynamic loads, a nonlinear restoring model of Spar buoy, and a nonlinear algorithm for simulating the mooring cables. The OC3 Hywind spar-type FOWT is adopted as an example to study the dynamic response under the freak wave conditions, meanwhile the time series of freak waves are generated using the random frequency components selection phase modulation method. The motion of platform, the tension applied on the mooring lines, and the power generation performance are documented in several cases. According to the simulations, it is indicated that when a freak wave acts on the FOWT, the transient motion of the FOWT is induced in all degrees-of-freedom, as well as the produced power decreases rapidly. Furthermore, the impact of freak wave parameters on the motion of FOWT is discussed.

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