scholarly journals Nonlinear dynamics of wave-groups in random seas: unexpected walls of water in the open ocean

2015 ◽  
Vol 471 (2184) ◽  
pp. 20150660 ◽  
Author(s):  
Thomas A. A. Adcock ◽  
Paul H. Taylor ◽  
Scott Draper
Keyword(s):  
Extreme Event ◽  
Open Ocean ◽  
Extreme Waves ◽  
Wave Direction ◽  
Sea State ◽  
Wave Groups ◽  
Large Wave ◽  
Linear Evolution ◽  
Random Seas ◽  
The Waves

This paper investigates the size and structure of large waves on the open ocean. We investigate how nonlinear physics modifies waves relative to those predicted by a linear model. We run linear random simulations and extract extreme waves and the surrounding sea-state. For each extreme event, we propagate the waves back in time under linear evolution before propagating the wave-field forward using a nonlinear model. The differences between large linear and nonlinear wave-groups are then examined. The general trends are that under nonlinear evolution, relative to linear evolution, there is, on average, little or no extra amplitude in the nonlinear simulations; that there is an increase in the width of the crest of the wave-group and a contraction of large wave-groups in the mean wave direction; that large waves tend to move to the front of a wave-packet meaning that the locally largest wave is relatively bigger than the wave preceding it; and that nonlinearity can increase the duration of extreme wave events. In all these trends, there is considerable scatter, although the effects observed are clear. Our simulations show that nonlinearity does play an important part in the formation of extreme waves on deep water.

scholarly journals The Draupner Event: The Large Wave and the Emerging View

2017 ◽  
Vol 98 (4) ◽  
pp. 729-735 ◽  
Author(s):  
L. Cavaleri ◽  
A. Benetazzo ◽  
F. Barbariol ◽  
J.-R. Bidlot ◽  
P. A. E. M. Janssen
Keyword(s):  
Relevant Information ◽  
Space Time ◽  
Point Of View ◽  
Extreme Waves ◽  
Sea State ◽  
Wave Groups ◽  
Large Wave ◽  
Open Sea ◽  
Improved Model ◽  
2D Space

Abstract In a parallel paper mainly focused on the meteorological and oceanographic aspects, the conditions were described for the storm during which the iconic Draupner wave was recorded. Because of increased spatial resolution and improved model physics, the results provided new and previously unrecognized features of the storm, in particular of the wave spectra, features relevant for assessing the wave’s conditions nearby the Draupner platform. Starting from these, and after briefly summarizing the relevant information, the focus of this paper is on the nonlinear analysis of the local situation, with the main purpose of assessing if and how the conditions existed for the possible appearance of very large waves. An intensive analysis of the related probability is carried out, attacking the problem with two different statistical approaches, both briefly described: a completely new one working from the point of view of envelope heights, and a recent, though established, one based on space–time extreme waves. It is remarkable, and certainly supports this line of work, that the two different approaches lead independently to consistent results, supporting the idea, already derived from the meteo-oceanographic hindcast, that the wave conditions were indeed special at the position of the Draupner platform. This is related to a general analysis of high waves showing, also on the basis of 3D (2D space + time) measured wave data at open sea, how, given the severe sea state, the Draupner wave features represent what is expected at certain times and positions as the natural documented temporal evolution of wave groups.

Extreme Waves and Stochastic Wave Groups

2006 ◽  
Author(s):  
Francesco Fedele ◽  
M. Aziz Tayfun
Keyword(s):  
Numerical Results ◽  
Resonance Interaction ◽  
Experimental Results ◽  
Wave Crest ◽  
Extreme Waves ◽  
Zakharov Equation ◽  
Wave Groups ◽  
Probability Of Exceedance ◽  
Random Seas ◽  
Crest Height

We introduce the concept of stochastic wave groups to explain the occurrence of extreme waves in nonlinear random seas, according to the dynamics imposed by the Zakharov equation (Zakharov, 1999). As a corollary, a new probability of exceedance of the crest-to-trough height which takes in to account the quasi-resonance interaction is derived. Furthermore, a generalization of the Tayfun distribution (Tayfun, 1986) for the wave crest height is also proposed. The new analytical distributions explain qualitatively well the experimental results of Onorato et al. (2004, 2005) and the numerical results of Juglard et al. (2005).

Drifting Rogue Packets

2018 ◽  
Author(s):  
Amin Chabchoub ◽  
Norbert Hoffmann ◽  
Nail Akhmediev ◽  
Takuji Waseda
Keyword(s):  
Modulation Instability ◽  
Wave Train ◽  
Modulation Frequency ◽  
Phase Speed ◽  
Periodic Wave ◽  
Unstable Wave ◽  
Extreme Waves ◽  
Wave Groups ◽  
The Waves ◽  
Good Agreement

Modulation instability (MI) is one possible mechanism to explain the formation of extreme waves in uni-directional and narrow-banded seas. It can be triggered, when side-bands around the main frequency are excited and subsequently follow an exponential growth. In physical domain this dynamics translates to periodic pulsations of wave groups that can reach heights up to three times the initial amplitude of the wave train. It is well-known that these periodic wave groups propagate with approximately half the waves phase speed in deep-water. We report an experimental study on modulationally unstable wave groups that propagate with a velocity that is higher than the group velocity since the modulation frequency is complex. It is shown that when this additional velocity to the wave groups is small a good agreement with exact nonlinear Schrödinger (NLS) models, that describe the nonlinear stage of MI, is reached. Otherwise a significant deviation is observed that could be compensated when increasing accuracy of the water wave modeling beyond NLS.

Gyrostatic Yawing of Ships in Random Seas

1965 ◽  
Vol 9 (04) ◽  
pp. 179-182
Author(s):  
Theodore R. Goodman
Keyword(s):  
Wave Train ◽  
Wave Direction ◽  
Sea State ◽  
Single Wave ◽  
Dominant Wave ◽  
Random Seas

Based on a theory originally presented by Suyehiro for a ship being acted upon by a single wave train, it is shown that all ships at zero speed, when acted upon by a fully developed random sea up to sea state 5 will tend to turn so that they lie parallel to the dominant wave direction. For higher sea states, the ultimate heading is found by reference to a graph within this paper. For the highest sea states the ship tends to turn beam to the dominant wave direction.

On the Sequence of Large Waves From Field Data

2018 ◽  
Author(s):  
Anita Santoro ◽  
Felice Arena ◽  
Carlos Guedes Soares
Keyword(s):  
Field Data ◽  
Energy Content ◽  
Wave Group ◽  
Wave Groups ◽  
Large Wave ◽  
Dominant Component ◽  
Average Profile ◽  
Wind Sea ◽  
The Waves

The present work focuses on large wave groups, in particular the succession of three waves, i.e. the largest one and the preceding and following ones, in presence of bimodal spectra. Results highlight that the profile is influenced by the dominant component, in the case of swell or wind sea dominated fields. In general, troughs amplitudes attain larger values than crests amplitudes when considering the waves preceding and following the largest crest. Moreover, the average profile of the three largest waves is generally symmetric about the central crest. The spectrum influences the largest waves in a wave group, in particular the greater the wind sea energy, compared to the swells energy content, the bigger the crests and troughs amplitudes of the preceding and following wave.

scholarly journals The nonlinear evolution and approximate scaling of directionally spread wave groups on deep water

2012 ◽  
Vol 468 (2145) ◽  
pp. 2704-2721 ◽  
Author(s):  
Thomas A. A. Adcock ◽  
Richard H. Gibbs ◽  
Paul H. Taylor
Keyword(s):  
Water Wave ◽  
Wave Equations ◽  
Scaling Laws ◽  
Large Change ◽  
Analytical Relationship ◽  
Wave Group ◽  
Wave Direction ◽  
Wave Groups ◽  
Linear Evolution ◽  
Steep Waves

The evolution of steep waves in the open ocean is nonlinear. In narrow-banded but directionally spread seas, this nonlinearity does not produce significant extra elevation but does lead to a large change in the shape of the wave group, causing, relative to linear evolution, contraction in the mean wave direction and lateral expansion. We use the nonlinear Schrödinger equation (NLSE) to derive an approximate analytical relationship for these changes in group shape. This shows excellent agreement with the numerical results both for the NLSE and for the full water wave equations. We also consider the application of scaling laws from the NLSE in terms of wave steepness and bandwidth to solutions of the full water wave equations. We investigate these numerically. While some aspects of water wave evolution do not scale, the major changes that a wave group undergoes as it evolves scale very well.

Cyclic recurrence in nonlinear unidirectional ocean waves

1988 ◽  
Vol 192 ◽  
pp. 329-337 ◽  
Author(s):  
Peter J. Bryant
Keyword(s):  
Wave Breaking ◽  
Ocean Surface ◽  
Ocean Waves ◽  
Open Ocean ◽  
Nonlinear Interactions ◽  
Slow Time ◽  
Wave Groups ◽  
Stokes Waves ◽  
Local Wave ◽  
The Waves

A fully nonlinear model is developed for the unidirectional propagation of periodic gravity wave groups in deep water, in which the shape of the group envelopes changes cyclically. It is intended to describe the slow-time evolution of wave groups on the open ocean surface, and to generalize the cyclic recurrence that can occur during the sideband modulation of Stokes waves and Schrödinger wave groups. The weak nonlinear interactions are shown to concentrate the wave energy at the centre of each group at regular intervals, causing the waves there to be of greater height locally in space and time. This is suggested as one mechanism for the local wave breaking that is observed on the open ocean surface. The cyclically recurring wave groups may be interpreted as the limit-cycle stage in a progression from uniform wave groups to chaos on the forced, damped, ocean surface.

scholarly journals EXTREME WAVE PRESSURES AND LOADS ON A PILE-SUPPORTED WHARF DECK - INFLUENCES OF AIR GAP AND WAVE DIRECTION

2018 ◽  
pp. 5
Author(s):  
Andrew Cornett
Keyword(s):  
Offshore Structures ◽  
Model Tests ◽  
Scale Model ◽  
Extreme Waves ◽  
Wave Direction ◽  
Coastal Structures ◽  
Extreme Wave ◽  
Wave Impact ◽  
The Past ◽  
Water Depths

Many deck-on-pile structures are located in shallow water depths at elevations low enough to be inundated by large waves during intense storms or tsunami. Many researchers have studied wave-in-deck loads over the past decade using a variety of theoretical, experimental, and numerical methods. Wave-in-deck loads on various pile supported coastal structures such as jetties, piers, wharves and bridges have been studied by Tirindelli et al. (2003), Cuomo et al. (2007, 2009), Murali et al. (2009), and Meng et al. (2010). All these authors analyzed data from scale model tests to investigate the pressures and loads on beam and deck elements subject to wave impact under various conditions. Wavein- deck loads on fixed offshore structures have been studied by Murray et al. (1997), Finnigan et al. (1997), Bea et al. (1999, 2001), Baarholm et al. (2004, 2009), and Raaij et al. (2007). These authors have studied both simplified and realistic deck structures using a mixture of theoretical analysis and model tests. Other researchers, including Kendon et al. (2010), Schellin et al. (2009), Lande et al. (2011) and Wemmenhove et al. (2011) have demonstrated that various CFD methods can be used to simulate the interaction of extreme waves with both simple and more realistic deck structures, and predict wave-in-deck pressures and loads.

Numerical Study of Two Vessels Seakeeping in Waves

2014 ◽  
Author(s):  
Dexin Zhan ◽  
Don Bass ◽  
David Molyneux
Keyword(s):  
Objective Function ◽  
Degrees Of Freedom ◽  
Numerical Study ◽  
Wave Direction ◽  
Small Motion ◽  
Head Waves ◽  
Close Proximity ◽  
Connection Line ◽  
Sheltering Effect ◽  
The Waves

This paper presents a numerical study of seakeeping in regular waves for two vessels in close proximity using commercial seakeeping software HydroStar and an in-house code MOTSIM. The objective was to study the possible sheltering effect of the larger vessel (FPSO) on the smaller one (OSV) during personnel transfer between the two vessels, where one vessel was at some angle relative to the other vessel and there was no connection line between them. The study mainly focused on the OSV motion resulting from the interaction of the FPSO when the OSV was at different headings and wave directions. Initially the OSV motions close to the FPSO (and parallel) were compared with those for the OSV alone. For an un-parallel position of the two vessels, an objective function based on the OSV RAOs motion in roll, pitch and heave directions was used to optimize the OSV position. Finally comparisons between HydroStar and MOTSIM results are provided. The main conclusions are: 1) When the FPSO and OSV are located in parallel, the OSV motions in sway, roll and yaw are larger than the single OSV motions in head waves while surge, heave and pitch are almost the same. The OSV motions in most of the six degrees of freedom are smaller than the single OSV motions when the waves are from other directions (always on the port side of the FPSO), which means that there is a sheltering effect. 2) The simulation results from different OSV rotation angles show that the hydrodynamic interaction between the FPSO and OSV e.g. the sheltering effect is related to the OSV angle and the wave heading. The objective function in roll, pitch and heave RAOs indicates that the OSV should maintain a close to parallel position with the FPSO to minimize motion when the waves come from the port side of the FPSO from 180 to 240 degrees. When the wave direction is around 240 degrees the OSV should have relatively small motion in waves for any OSV rotation angle. 3) A comparison of HydroStar and MOTSIM results shows that the MOTSIM results of a single vessel seakeeping simulation is in a good agreement with HydroStar. In two vessels situation more validation work needs to be done.

scholarly journals Control-Influenced Layout Optimization of Arrays of Wave Energy Converters

2014 ◽  
Author(s):  
Philip Balitsky ◽  
Giorgio Bacelli ◽  
John V. Ringwood
Keyword(s):  
Wave Climate ◽  
Radiative Properties ◽  
Optimal Layout ◽  
Wave Direction ◽  
Sea State ◽  
Wave Energy Converters ◽  
Control Schemes ◽  
And Control ◽  
Tuning Scheme ◽  
Optimal Configurations

In this paper we compare the optimal configurations for an array of WECs given two control schemes, a real-time global control and a passive sea-state based tuning scheme. In a particular wave climate and array orientation with its axis normal to the prevailing wave direction, closely-spaced symmetrical arrays of 2, 3, 4, 5, and 6 cylinders of different radiative properties are simulated for varying inter-device separation distances. For each device and control type, we focus on the factors that influence the optimal layout, including number of devices, separating distance and angular spreading. The average annual power output is calculated for each optimal configuration.

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