Showing papers on "Rogue wave published in 2004"

The Interaction of Ocean Waves and Wind

Abstract: This book was published in 2004. The Interaction of Ocean Waves and Wind describes in detail the two-way interaction between wind and ocean waves and shows how ocean waves affect weather forecasting on timescales of 5 to 90 days. Winds generate ocean waves, but at the same time airflow is modified due to the loss of energy and momentum to the waves; thus, momentum loss from the atmosphere to the ocean depends on the state of the waves. This volume discusses ocean wave evolution according to the energy balance equation. An extensive overview of nonlinear transfer is given, and as a by-product the role of four-wave interactions in the generation of extreme events, such as freak waves, is discussed. Effects on ocean circulation are described. Coupled ocean-wave, atmosphere modelling gives improved weather and wave forecasts. This volume will interest ocean wave modellers, physicists and applied mathematicians, and engineers interested in shipping and coastal protection.

A possible freak wave event measured at the draupner jacket January 1 1995

Abstract: A brief informal description of the weather conditions at the Draupner platform January 1. 1995 is given. During this day a wave with a majestic crest height, often referred to as the New Year Wave or the Draupner Wave, was measured by a down-looking laser. The crest height is clearly an outlier in view of what is expected for that sea state and is considered as a possible freak wave event.

Laboratory measurements of limiting freak waves on currents

Abstract: [1] The results of laboratory measurements on limiting freak waves in the presence of currents are reported. Both dispersive spatial-temporal focusing and wave-current interaction are used to generate freak waves in a partial random wave field in the presence of currents. Wave group structure, for example, spectral slope and frequency bandwidth, is found to be critical to the formation and the geometric properties of freak waves. A nondimensional spectral bandwidth is shown to well represent wave group structure and proves to be a good indicator in determining limiting freak wave characteristics. The role of a co-existing current in the freak wave formation is recognized. Experimental results confirm that a random wave field does not prevent freak wave formation due to dispersive focusing. Strong opposing currents inducing partial wave blocking significantly elevate the limiting steepness and asymmetry of freak waves. At the location where a freak wave occurs, the Fourier spectrum exhibits local energy transfer to high-frequency waves. The Hilbert-Huang spectrum, a time-frequency-amplitude spectrum, depicts both the temporal and spectral evolution of freak waves. A strong correlation between the magnitude of interwave instantaneous frequency modulation and the freak wave nonlinearity (steepness) is observed. The experimental results provide an explanation to address the occurrence and characteristic of freak waves in consideration of the onset of wave breaking.

Abnormal waves during Hurricane Camille

Abstract: [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.

Spatial Extreme Value Analysis of Nonlinear Simulations of Random Surface Waves

Abstract: The paper first recalls the Slepian Model Representation and a theorem of V. I. Piterbarg as generic tools for analyzing the spatial characteristic of ocean waves. We then consider numerical simulations of random surface gravity waves carried out in space and time by means of the modified nonlinear Schrodinger equation. It is shown that the extreme waves in the simulations are steeper and more asymmetric than predicted by the Gaussian theory. Moreover, the reconstructed wave fields shows extreme crest heights well in excess of what is expected from the Gaussian theory.Copyright © 2004 by ASME

Bending Moments of an FPSO in Rogue Waves

Abstract: The increasing numbers of reported rogue waves with extreme crest and wave heights and unusual group pattern with the consequence of severe damages raise the question if such exceptional events have to be considered routinely for the design of ships and offshore structures. For the investigation of the effects of rogue wave impacts time domain simulation methods are required in addition to traditional frequency domain methods which may not be sufficient to consider these extreme events. In this paper the vertical bending moments at the midship section of an FPSO are investigated using state of the art numerical simulation tools in combination with experiments. For the seakeeping tests the extremely high New Year Wave (registered in the North Sea) is generated in the wave tank, and motions and structural forces are analyzed at model scale. For validation the results are evaluated deterministically and compared to numerical simulations. The time domain calculation allows to artificially change local wave characteristics. The steepness of the selected rogue wave is varied and the influence on wave induced loads is studied. A comparison with standard procedures of seakeeping analysis and classification rules closes the paper.Copyright © 2004 by ASME

Freak Waves at Campos Basin, Brazil

Abstract: Freak waves occur abundantly in Campos Basin, located on the northeast coast of Rio de Janeiro, Brazil in the South Atlantic Ocean. This surprising and unexpected discovery was made from a search of the time-series data of wave measurements recorded in the Campos Basin from 1991 to 1995. In a study on the occurrence of freak waves and their relevant properties, we have also found that freak waves are not of rare occurrence as conventionally presumed, and they occur not only during storm conditions but also during fair weather states as well. While the conventional approach of spectrum analysis provides some weak inference of freak wave effects, the basically stationary random process approach is clearly incapable of contending with the localized non-stationary process of freak wave occurrences.

Freak waves - more frequent than rare!

Abstract: Contrary to the widely held notion that consid- ers the occurrence of freak waves in the ocean as being rare, from an examination of five years of wave measurements made in the South Atlantic Ocean, we found the occurrence of freak waves is actually more frequent than rare.

A discrete wavelet analysis of freak waves in the ocean

Abstract: A freak wave is a wave of very considerable height, ahead of which there is a deep trough. A case study examines some basic properties developed by performing wavelet analysis on a freak wave. We demonstrate several applications of wavelets and discrete and continuous wavelet transforms on the study of a freak wave. A modeling setting for freak waves will also be mentioned.

Measurements of freak waves in Norway and related ship accidents

Abstract: This paper describes establisment of a world data bank related to ship and platform accidents caused by freak waves and rogue waves. It was found that many of these accidents follow a certain pattern. It was not the highest waves but violent breaking waves that gave the largest responses on the structures. Force models that predict drag- lift- and impact forces on superstructures of ships and platforms are developed. Some of the coefficients used in the force models are obtained from measurements on platforms at sea. Here impact forces were measured in asymmetric wind waves. Others are obtained from laboratory experiments some of them performed in a wind-wave flume with asymmetric wind waves. Thus a large data bank was established, and valuable information might be available for future designs. Accidents related to freak waves are not randomly distributed but are concentrated in 21 specific sea areas worldwide. Further a forecast of freak waves were established in one of these exposed areas.

Extreme events in field data and in a second order wave model

Abstract: The analysis is based on North Sea field data and on second order time domain simulations. Statistical properties of extreme waves are presented. Particular focus is given to the wave crest. Wave parameters obtained from the field data are compared with the values derived from the second order time domain simulations. Limitations of the 2 n d order wave model to predict extreme events are shown. Uncertainties related to the field and numerically generated data are discussed.

Experiments on extreme wave generation using the soliton on finite background

Abstract: Freak waves are very large water waves whose heights exceed the significant wave height of a measured wave train by a factor of more than 2.2. However, this in itself is not a well established definition of a freak wave. The mechanism of freak wave generation in reality as well as modeling it in a wave basin has become an issue of great importance. Recently one is aware of the generation of freak wave through the Benjamin–Feir type of instability or self–focussing. Consequently the Non–Linear–Schrodinger (NLS) equation forms a good basis for understanding the formation of freak waves. However, the complex generation of a freak wave in nature within a sea condition is still not well understood, when the non-linearity of the carrier wave is not small. In our study we will focus on the Soliton on Finite Background, an exact solution of the NLS equation, as a generating mechanism for extreme waves. Apart from a numerical investigation into the evolution of a soliton on a finite background also extensive detailed model tests have been performed for validation purposes in the hydrodynamic laboratories of the Maritime Research Institute Netherlands (marin). Furthermore, a numerical wave tank [12] is used to model the complete non-linear non-breaking wave evolution in the basin.

Experimental study of the wind effect on the focusing of transient wave groups

Abstract: One of the popular mechanisms of the freak waves phenomenon is the dispersive focusing of transient wave groups. In all published theoretical and experimental papers the surface gravity waves are considered as an ensembleof free waves. This paper reports on a series of experiments conducted in the large wind-wave tank of IRPHE (Marseille - Luminy) to study the wind effect on the generation of freak waves. A suitable theory is presented to explain and discuss the experimental results.

Wave impacts due to steep fronted waves

Abstract: It is the question whether ‘Rogue waves’ can only be identified and characterized by their extreme heights. The results presented in this abstract and related papers [1,2,4,5,6] show for instance that an extreme wave front steepness can induce large impact pressures on the hull of a moored ship-type offshore structure. As part of the ‘SAFE-FLOW’ Joint Industry Project these loads were investigated with a dedicated series of model tests.

Deterministic analysis of extreme roll motions and subsequent evaluation of capsizing risk

Abstract: Encountering a freak wave remains one of the most horrible visions for a ship master. Until now the mechanisms which underlie large rolling and subsequent capsizing due to a rogue wave are only partly disclosed. In the framework of the German research project ROLL-S which is funded by the German Federal Ministry of Research and Education (BMBF) nine partners are cooperating on the investigation of large rolling and capsizing mechanisms covering fields like numerical analysis and simulation, validation, and evaluation of capsizing risk. The project part presented here deals with the validation of numerical tools for the analysis of large rolling and capsizing. The main goal is the implementation of a sophisticated capsizing test procedure. For providing useful data for the analysis of the capsizing process as well as for the validation of numerical methods, exact correlation of wave excitation and ship rolling is indispensable. All wave trains are tailored for the specific purpose of each capsizing test and generated in the model tank. Unusual wave trains like regular waves followed by a freak wave and special wave groups within a defined random sea as well as realistic wave scenarios have been generated. The parameters of the model seas are systematically varied to investigate the ship model response with regard to metacentric height, model velocity, and course angle for different ship types. The wave elevation at the position of the ship model in time and space is calculated (and controlled by registrations during model tests) in order to relate wave excitation to the resulting roll motion.

Freak wave generation and their probability

Abstract: The problem of extreme wave estimation is crucial at last 25-30 years due to active using of ocean resources. Mainly the attention paid to estimation of extreme waves in the fixed spatial point of the sea. But for ship navigations, transport operations, offshore supplying etc. estimates of the spatial occurrences of extreme waves are required. In these cases spatiotemporal variability of wave fields is of special interest. One of the most interesting extreme phenomena is freak (or rogue) waves. These one are anomaly steep and high waves. The probability of freak waves generation depends from a lot of internal (modulation, nonlinearities, etc.) and external (metocean) factors. Spatial dimensions of the sea region increase the probability of ship encounter with a freak wave. Classical statistical analysis of time series do not allows estimating the probabilities of freak waves occurrence and associated weather conditions. Main definitions of freak waves, reasons of appearance, possibility of generation in the sea and approach to estimation is presented.

Rogue wave impact on offshore structures

Abstract: must contain conspicuous acknowledgement of where and by whom the paper was presented. Write Librarian, OTC, P.O. Box 833868, Richardson, TX 75083-3868, U.S.A., fax

Freak Wave Events Within the Second Order Wave Model

Abstract: 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.Copyright © 2004 by ASME

Wave Amplification and Possible Deck Impact on Gravity Based Structure in 10-4 Probability Extreme Crest Heights

Abstract: Model tests with a Gravity-Based Structure (GBS) platform in extreme waves are presented. First, the background for the experiments is given, based on the analysis of a possible late life production scenario in the Statfjord field. The statistical approach applied in the specification of the wave conditions, and the laboratory reproduction is then described. This is focused on the generation of a statistical ensemble of 50 extreme crests sampled from random wave realisations. The model test set-up and instrumentation is described. Finally, results on deck impact loads and nonlinear wave amplification effects are presented and discussed.Copyright © 2004 by ASME

Wave energy focusing in a three-dimensional numerical wave tank

Abstract: Extreme waves are obtained from the motion of a snake wavemaker in a numerical wave tank. Spatial focusing is one of the mechanisms which may take part in the generation of a rogue wave. In particular, directional focusing is only a three-dimensional phenomenon, that we want to isolate in this study. The numerical model solves incompressible free-surface Euler equations for potential flow, with a Boundary Element Method and a mixed Eulerian-Lagrangian time updating. Its more recent improvement has consisted in the insertion of the Fast Multipole Algorithm in order to reduce the computational complexity of the spatial solver. A typical case of a near breaking rogue wave is presented. A description of the particular geometry of such a wave is discussed, as well as the kinematics at the surface.

Extreme wave statistics from radar data sets

Abstract: The objective of this paper is the identification of areas of extreme wave events, in which rogue waves of exceptional height and shape do occur. These extreme waves are dangerous for navigation safety, as well as the operability on board offshore platforms. An explanation for the existence of groups of high waves based on the superposition of wave systems that form a solution of the linear wave equation is given. Synthetic Aperture Radar wave mode images from the ERS an ENVISAT satellites are investigated. These images are acquired every 200 to 100 km along the satellite orbit and thus yield global coverage. For ERS these images had to be specially reprocessed from radar raw data, for ENVISAT the imagettes are now available as a standard ESA product. High wave groups were found in situations of storm systems moving with the group speed of the ocean waves. The highest waves occurred near the center of the lows in the region of high wind speed

Exploring rogue waves from observations in South Indian Ocean

Abstract: Amidst all the enticing advancements on rogue waves in recent years, the conspicuous scarcity of actual, in situ, rogue wave measurements still represents an inevitable hindrance shadowing over the horizon of rogue wave studies. In this paper we wish to present an exploratory observational study of rogue waves based on wave measurement made in South Indian Ocean. As there have been significant theoretical advancements in numerical simulation of rogue waves, the need for actual field observations of rogue waves should certainly be commensurably supplemented. We hope our efforts in this study can be ventured toward further understanding of rogue waves in reality.

Coupling freak wave events with green water simulations

Abstract: In this paper a VoF method will be presented together with a coupling to a non-linear potential flow solver. The non-linear flow input is generated using a FEM/FD method described by Westhuis [8]. The generation of a freak wave event is based on the description of the freak wave as a realization of a soliton on a finite background (see Andonowati [1]) The VoF method has shown to represent most of the non-linear characteristics of waves as will be demonstrated by a soliton splitting example. The use of the non-linear inflow conditions has shown to be relevant when computing green water incidents. The pressure calculations on a fixed object in waves do show a high frequency noise behaviour due to the simulation of the body boundary conditions.

Statistics of Wave Crests in Storms

Abstract: The least-upper-bound (lub) theory recently proposed by Tayfun and Al-Humoud as a model for the statistical distribution of nonlinear wave crests is explored further. The theoretical distribution of the lub to the largest crest in N waves is also considered, deriving expressions for the associated mode, mean, and standard deviation. These provide a rational basis for describing the nature and occurrence of freak waves and outliers in observational data. The lub distribution and related statistics are then checked with additional measurements gathered during the peaks of two severe storms in the North Sea. The data comprise two hourly records and coincide with the extremes of more extensive measurements discussed by Forristall. Analyses of both records yield crest height distributions and statistics that compare with the lub model predictions quite well, thus confirming the validity of the lub theory convincingly. The theoretical expressions describing the statistics of the largest crest in N waves are then used to examine the nature of two exceptionally large waves recorded within the two hourly measurements. Although these waves display characteristics in apparent conformity with freak-wave occurrences, they are shown to be simple outliers that can be predicted well within the context of the extreme-value statistics derived here.

Predicting rogue waves in random oceanic sea states

Abstract: Using the inverse spectral theory of the nonlinear Schrodinger (NLS) equation we correlate the development of rogue waves in oceanic sea states characterized by the JONSWAP spectrum with the proximity to homoclinic solutions of the NLS equation. We find in numerical simulations of the NLS equation that rogue waves develop for JONSWAP initial data that is ``near'' NLS homoclinic data, while rogue waves do not occur for JONSWAP data that is ``far'' from NLS homoclinic data. We show the nonlinear spectral decomposition provides a simple criterium for predicting the occurrence and strength of rogue waves (PACS: 92.10.Hm, 47.20.Ky, 47.35+i).