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 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.

Multi-Focused Wave Groups in Wave Flume

2019 ◽  
Author(s):  
Qinghe Fang ◽  
Cunbao Zhao ◽  
Anxin Guo
Keyword(s):  
Irregular Waves ◽  
Frequency Resolution ◽  
Random Wave ◽  
Wave Group ◽  
Wave Groups ◽  
Large Wave ◽  
Wave Flume ◽  
Space And Time ◽  
Focused Wave ◽  
Focused Wave Group

Abstract People can simulate extreme hydrodynamic conditions in a laboratory facility by interfering a numbers of regular waves at a certain point in space and time, which is focused wave. It is obviously higher and steeper than any other wave, e.g. regular or irregular waves, within the propagating wave group. The focused wave occurs at a designed point both in space and time. It represents an event with a large return period which would take a long time to reproduce within a random wave sequence. The focused wave, representing of a large wave occurring in a random sea, is quite frequently used to investigate wave loading on marine or coastal structures. However, most research only employ one single focused wave group. Taking the randomness of the wave-structure interaction, repeated tests would be suggested by some textbooks or codes to eliminate the odd results. However, it would take more time to conduct those tests no matter in the laboratory or in the numerical simulations. In our present work, we use a novel method to experimentally generate several focused wave group with different focus time but same focus point at the same time to obtain multi-focused wave groups. The wave elevation and water particle kinematics are measured. The influence of peak frequency, frequency resolution and period of focused wave group are checked and discussed. The results show that present method can generate stable and repeatable focused wave groups in the wave flume.

scholarly journals VERIFICATION OF KIMURA's THEORY FOR WAVE GROUP STATISTICS

1984 ◽  
Vol 1 (19) ◽  
pp. 43 ◽  
Author(s):  
J.A. Battjes ◽  
G.Ph. Van Vledder
Keyword(s):  
Wave Motion ◽  
Random Phase ◽  
Wave Generation ◽  
Original Form ◽  
Wave Group ◽  
Sea Waves ◽  
Wave Groups ◽  
Wave Groupiness ◽  
Active Wave ◽  
Sea Wave

North Sea wave records, obtained in conditions of active wave generation, have been analyzed with respect to the distribution of the length of wave groups. The results are compared to a theory by Kimura, in its original form as well as with the addition of a new spectral wave groupiness parameter, based on the theory of Gaussian processes. The results lend support to the validity of Kimura's theory, this in turn implies further evidence that the phenomenon of wave groups in sea waves can by and large be explained, both qualitatively and quantitatively, in terms of the linear, random phase model for the wave motion, even in conditions of active wave generation.

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.

The Effect of Directional Spreading on Interaction of Focused Wave Groups With a Cylinder

2004 ◽  
Author(s):  
Eugeny V. Buldakov ◽  
Rodney Eatock Taylor ◽  
Paul H. Taylor
Keyword(s):  
Numerical Solutions ◽  
Amplitude Spectrum ◽  
Wave Group ◽  
Helmholtz Equations ◽  
Incoming Wave ◽  
Wave Groups ◽  
Practical Applications ◽  
Amplitude Spectra ◽  
Focused Wave ◽  
Focused Wave Group

The problem of diffraction of a directionally spread focused wave group by a bottom-seated circular cylinder is considered from the view point of second-order perturbation theory. After applying the time Fourier transform and separation of vertical variable the resulting two-dimensional non-homogeneous Helmholtz equations are solved numerically using finite differences. Numerical solutions of the problem are obtained for JONSWAP amplitude spectra for the incoming wave group with various types of directional spreading. The results are compared with the corresponding results for a unidirectional wave group of the same amplitude spectrum. Finally we discuss the applicability of the averaged spreading angle concept for practical applications.

Ocean Wave Non-Linearity and Wind Input in Directional Seas: Energy Input During Wave-Group Focussing

2018 ◽  
Author(s):  
Thomas A. A. Adcock ◽  
Paul H. Taylor
Keyword(s):  
Energy Input ◽  
Wind Waves ◽  
Rogue Waves ◽  
Wave Group ◽  
Spectral Evolution ◽  
Wave Groups ◽  
Small Influence ◽  
Non Linear ◽  
Linear Effects ◽  
Wind Input

There has been speculation that energy input (wind) can play an important role in the formation of rogue waves in the open ocean. Here we examine the role energy input can play by adding energy to the modified non-linear Schrödinger equation. We consider NewWave type wave-groups with spectra which are realistic for wind waves. We examine the case where energy input is added to the group as the wave-group focuses. We consider whether this energy input can cause significant non-linear effects to the subsequent spatial and spectral evolution. For the parameters considered here we find this to have only a small influence.

CFD Analysis of Deck Impact in Irregular Waves: Wave Representation by Transient Wave Groups

2011 ◽  
Author(s):  
O̸ystein Lande ◽  
Thomas B. Johannessen
Keyword(s):  
Wave Field ◽  
Irregular Waves ◽  
Computational Domain ◽  
Cfd Analysis ◽  
Wave Group ◽  
Regular Waves ◽  
Transient Wave ◽  
Wave Groups ◽  
Wave Induced ◽  
Random Background

Analysis of wave structure interaction problems are increasingly handled by employing CFD methods such as the well known Volume-of-Fluid (VoF) method. In particular for the problem of deck impact on fixed structures with slender substructures, CFD methods have been used extensively in the last few years. For this case, the initial conditions have usually been treated as regular waves in an undisturbed wave field which may be given accurately as input. As CFD analyses become more widely available and are used for more complex problems it is also necessary to consider the problem of irregular waves in a CFD context. Irregular waves provide a closer description of the sea surface than regular waves and are also the chief source of statistical variability in the wave induced loading level. In general, it is not feasible to run a long simulation of an irregular seastate in a CFD analysis today since this would require very long simulation times and also a very large computational domain and sophisticated absorbing boundary conditions to avoid build-up of reflections in the domain. The present paper is concerned with the use of a single transient wave group to represent a large event in an irregular wave group. It is well known that the autocovariance function of the wave spectrum is proportional to the mean shape of a large wave in a Gaussian wave field. The transient nature of such a wave ensures that a relatively small wave is generated at the upwave boundary and dissipated at the downwave boundary compared with the wave in the centre of the domain. Furthermore, a transient wave may be embedded in a random background if it is believed that the random background is important for the load level. The present paper describes the method of generating transient wave groups in a CFD analysis of wave in deck impact. The evolution of transient wave groups is first studied and compared with experimental measurements in order to verify that nonlinear transient waves can be calculated accurately using the present CFD code. Vertical wave induced loads on a large deck is then investigated for different undisturbed wave velocities and deck inundations.

Observed Variability of Ocean Wave Stokes Drift, and the Eulerian Response to Passing Groups

2006 ◽  
Vol 36 (7) ◽  
pp. 1381-1402 ◽  
Author(s):  
Jerome A. Smith
Keyword(s):  
Surface Waves ◽  
Current Theory ◽  
Surface Flow ◽  
Stokes Drift ◽  
Wave Group ◽  
Lagrangian Surface ◽  
Wave Groups ◽  
Wide Range ◽  
Momentum Fluxes ◽  
Waves And Currents

Abstract Waves and currents interact via exchanges of mass and momentum. The mass and momentum fluxes associated with surface waves are closely linked to their Stokes drift. Both the variability of the Stokes drift and the corresponding response of the underlying flow are important in a wide range of contexts. Three methods are developed and implemented to evaluate Stokes drift from a recently gathered oceanic dataset, involving surface velocities measured continually over an area 1.5 km in radius by 45°. The estimated Stokes drift varies significantly, in line with the occurrence of compact wave groups, resulting in highly intermittent maxima. One method also provides currents at a fixed level (Eulerian velocities). It is found that Eulerian counterflows occur that completely cancel the Stokes drift variations at the surface. Thus, the estimated Lagrangian surface flow has no discernable mean response to wave group passage. This response is larger than anticipated and is hard to reconcile with current theory.

The effect of multiple splay fault rupture on tsunamis

2020 ◽  
Author(s):  
Iris van Zelst ◽  
Leonhard Rannabauer ◽  
Alice-Agnes Gabriel ◽  
Ylona van Dinther
Keyword(s):  
Vertical Surface ◽  
Tsunami Hazard ◽  
Fault Rupture ◽  
Geophysical Research ◽  
Large Wave ◽  
Surface Displacements ◽  
Seismic Cycles ◽  
Splay Faults ◽  
Splay Fault ◽  
The Waves

<p>Earthquake rupture on splay faults in subduction zones could pose a significant tsunami hazard, as they could accommodate more vertical displacement and are situated closer to the coast. To better understand this tsunami hazard, we model splay fault rupture dynamics and tsunami propagation and inundation constrained by a geodynamic seismic cycle (SC) model; building on work presented in Van Zelst et al. (2019). This two-dimensional modelling framework considers geodynamics, seismic cycles, dynamic ruptures, and tsunamis together for the first time. The SC model provides six blind splay fault geometries, self-consistent stress and strength conditions, and heterogeneous material properties in the domain. We find that all six splay faults are activated when the megathrust ruptures. The largest splay fault closest to the nucleation region ruptures immediately when the main rupture front passes the branching point. The other splay faults are activated through dynamic stress transfer from the main megathrust rupture or reflected waves from the surface. Splay fault rupture results in distinct peaks in the vertical surface displacements with a smaller wavelength and larger amplitudes. The effect of the vertical surface displacements also translates into the resulting tsunami, which consists of one large wave for the megathrust-only model and seven waves for the model including splay faults. Here, six of the waves can be attributed to the splay faults and the seventh wave results from the shallow tip of the megathrust. The waves from the rupture including splay faults have larger amplitudes and result in two episodes of coastal flooding. The first episode is due to the large wave caused by rupture on the largest splay fault nearest to the coast. The second flooding episode results from the combination and interference of the waves caused by the rest of the splay faults and the shallow megathrust tip. In contrast, the tsunami caused by rupture on only the megathrust has only one episode of flooding. Our results suggest that larger-than-expected tsunamis could be attributed to rupture on large splay faults. When multiple smaller splay faults rupture their effect on the tsunami might be hard to distinguish from a pure megathrust rupture. Considering the significant effects splay fault rupture can have on a tsunami, it is important to understand splay fault activation and to consider them in hazard assessment.</p><p>References:</p><p>Van Zelst, I., Wollherr, S., Madden, E. H. , Gabriel, A.-A., and Van Dinther, Y. (2019). Modeling megathrust earthquakes across scales: one-way coupling from geodynamics and seismic cycles to dynamic rupture. Journal of Geophysical Research: Solid Earth, 124, https://doi.org/10.1029/2019JB017539</p><p></p>

The energy and action of small waves riding on large waves

1988 ◽  
Vol 189 ◽  
pp. 443-462 ◽  
Author(s):  
Frank S. Henyey ◽  
Dennis B. Creamer ◽  
Kristian B. Dysthe ◽  
Roy L. Schult ◽  
Jon A. Wright
Keyword(s):  
Coordinate System ◽  
Hamiltonian Formulation ◽  
Capillary Waves ◽  
Two Dimensional ◽  
Scale Separation ◽  
Large Wave ◽  
Action Density ◽  
Lagrangian Equations ◽  
Small Wave ◽  
The Waves

We derive the dynamics of small waves riding on larger waves using a canonical, Hamiltonian formulation. The small waves are treated linearly and their energy is derived to all orders in the scale separation between the waves. Our results are similar to those of Longuet-Higgins (1987), but we have extended his calculations to include gravity-capillary waves and to allow for a more general, two-dimensional, large-wave field. Our result for the small-wave Hamiltonian is expressed in both Eulerian (horizontal) coordinate system and a non-inertial system determined by the large wave's surface. On further assuming scale separation between the small and large waves the averaged Lagrangian equations and the action density are derived. Action conservation is explicitly demonstrated.

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