scholarly journals Statistics of Extreme Waves in Coastal Waters: Large Scale Experiments and Advanced Numerical Simulations

Fluids ◽  
2019 ◽  
Vol 4 (2) ◽  
pp. 99 ◽  
Author(s):  
Jie Zhang ◽  
Michel Benoit ◽  
Olivier Kimmoun ◽  
Amin Chabchoub ◽  
Hung-Chu Hsu
Keyword(s):  
Large Scale ◽  
Numerical Models ◽  
Low Frequency ◽  
Local Maximum ◽  
Second Order ◽  
Irregular Waves ◽  
Extreme Waves ◽  
Ocean Engineering ◽  
Large Wave ◽  
Highly Nonlinear

The formation mechanism of extreme waves in the coastal areas is still an open contemporary problem in fluid mechanics and ocean engineering. Previous studies have shown that the transition of water depth from a deeper to a shallower zone increases the occurrence probability of large waves. Indeed, more efforts are required to improve the understanding of extreme wave statistics variations in such conditions. To achieve this goal, large scale experiments of unidirectional irregular waves propagating over a variable bottom profile considering different transition water depths were performed. The validation of two highly nonlinear numerical models was performed for one representative case. The collected data were examined and interpreted by using spectral or bispectral analysis as well as statistical analysis. The higher probability of occurrence of large waves was confirmed by the statistical distributions built from the measured free surface elevation time series as well as by the local maximum values of skewness and kurtosis around the end of the slope. Strong second-order nonlinear effects were highlighted as waves propagate into the shallower region. A significant amount of wave energy was transmitted to low-frequency modes. Based on the experimental data, we conclude that the formation of extreme waves is mainly related to the second-order effect, which is also responsible for the generation of long waves. It is shown that higher-order nonlinearities are negligible in these sets of experiments. Several existing models for wave height distributions were compared and analysed. It appears that the generalised Boccotti’s distribution can predict the exceedance of large wave heights with good confidence.

scholarly journals Did the Draupner wave occur in a crossing sea?

2011 ◽  
Vol 467 (2134) ◽  
pp. 3004-3021 ◽  
Author(s):  
T. A. A. Adcock ◽  
P. H. Taylor ◽  
S. Yan ◽  
Q. W. Ma ◽  
P. A. E. M. Janssen
Keyword(s):  
Low Frequency ◽  
Quality Measurement ◽  
Order Theory ◽  
Second Order ◽  
Flow Solver ◽  
The North ◽  
Highly Nonlinear ◽  
Nonlinear Potential ◽  
Wind Sea ◽  
Set Up

The ‘New Year Wave’ was recorded at the Draupner platform in the North Sea and is a rare high-quality measurement of a ‘freak’ or ‘rogue’ wave. The wave has been the subject of much interest and numerous studies. Despite this, the event has still not been satisfactorily explained. One piece of information that was not directly measured at the platform, but which is vital to understanding the nonlinear dynamics is the wave's directional spreading. This paper investigates the directionality of the Draupner wave and concludes it might have resulted from two wave-groups crossing, whose mean wave directions were separated by about 90 ° or more. This result has been deduced from a set-up of the low-frequency second-order difference waves under the giant wave, which can be explained only if two wave systems are propagating at such an angle. To check whether second-order theory is satisfactory for such a highly nonlinear event, we have run numerical simulations using a fully nonlinear potential flow solver, which confirm the conclusion deduced from the second-order theory. This is backed up by a hindcast from European Centre for Medium-Range Weather Forecasts that shows swell waves propagating at approximately 80 ° to the wind sea. Other evidence that supports our conclusion are the measured forces on the structure, the magnitude of the second-order sum waves and some other instances of freak waves occurring in crossing sea states.

Laboratory Wave Modelling for Floating Structures in Shallow Water

2006 ◽  
Author(s):  
Carl Trygve Stansberg
Keyword(s):  
Shallow Water ◽  
Low Frequency ◽  
Second Order ◽  
Wave Groups ◽  
Large Wave ◽  
Frequency Wave ◽  
Wave Modelling ◽  
Floating Structures ◽  
Wave Basin ◽  
Wave Drift Forces

The analysis of moored floating vessels in shallow water requires special attention, when compared to similar problems in deep water. In particular, low-frequency wave drift forces need to be studied. Model testing is essential in validation of numerical prediction tools for these problems. Wave-group induced low-frequency wave components is an important part of the problem. Their reproduction in laboratories needs special attention. In general, two types of low-frequency waves are present: “bound” waves following the wave groups, and “free” waves propagating with their own speed. The former is included in second-order numerical codes for floater is included in second-order numerical codes for floaters, while the latter is normally not. Therefore, identification and possible reduction of the free components is of interest. A practical way to do this in a large wave basin is described in this paper. Results from generation of bi-chromatic waves without and with correction are presented. Corrected results show a clear reduction of the free wave component.

A Note on the Second-Order Contribution to Extreme Waves Generated During Hurricanes

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Mark L. McAllister ◽  
Thomas A. A. Adcock ◽  
Paul H. Taylor ◽  
Ton S. van den Bremer
Keyword(s):  
Wind Waves ◽  
Low Frequency ◽  
Nonlinear Behavior ◽  
Wave Theory ◽  
Linear Range ◽  
Second Order ◽  
Linear Wave ◽  
Extreme Waves ◽  
Order Difference ◽  
Hurricane Wind

High wind speeds generated during hurricanes result in the formation of extreme waves. Extreme waves by nature are steep meaning that linear wave theory alone is insufficient in understanding and predicting their occurrence. The complex, highly transient nature of the direction of wind and hence of waves generated during hurricanes affects this nonlinear behavior. Herein, we examine how this directionality can affect the second-order nonlinearity of extreme waves generated during hurricanes. This is achieved through both deterministic calculations and experiments based on the observations of Young (2006, “Directional Spectra of Hurricane Wind Waves,” J. Geophys. Res. Oceans, 111(C8), epub). Our calculations show that interactions between the tail and peak of the spectrum can become significant when they travel in different directions, resulting in second-order difference components that exist in the linear range of frequencies. These calculations are generally supported by experimental observations, but we note the difficulty of generating and focusing the high-frequency tail of the spectrum experimentally. Bound second-order difference components or subharmonics typically exist as low frequency infra-gravity waves. Components that exist in the linear range of frequencies may be missed by conventional methods of processing field data where low-pass filtering is used and hence overlooked. In this note, we show that in idealized directional spreading conditions representative of a hurricane, failing to account for second-order difference components may lead to underestimation of extreme wave height.

scholarly journals Low Frequency Waves Detected in a Large Wave Flume under Irregular Waves with Different Grouping Factor and Combination of Regular Waves

Water ◽  
2018 ◽  
Vol 10 (2) ◽  
pp. 228 ◽  
Author(s):  
Luigia Riefolo ◽  
Pasquale Contestabile ◽  
Fabio Dentale ◽  
Guido Benassai
Keyword(s):  
Low Frequency ◽  
Irregular Waves ◽  
Regular Waves ◽  
Large Wave ◽  
Wave Flume ◽  
Low Frequency Waves

Nonlinear Dynamic Behaviour of the Intervertebral Disc

2013 ◽  
Author(s):  
Giacomo Marini ◽  
Gerd Huber ◽  
Stephen J. Ferguson
Keyword(s):  
Dynamic Response ◽  
Intervertebral Disc ◽  
High Frequency ◽  
Nonlinear Dynamic ◽  
Mechanical Response ◽  
Numerical Models ◽  
Low Frequency ◽  
Upper Body ◽  
Highly Nonlinear ◽  
Flexion Extension

The intervertebral disc, like many collagen-based tissues, has a mechanical response which is highly nonlinear (1). This characteristic is due to both the arrangement and composition of the tissue constituents of the disc (2). Over the past decades several studies have reported the nonlinear response of the disc for different loading scenarios. In particular, past studies were focused on the quasi-static and low frequency (< 10Hz) response to pure and combined cyclic loading, such as axial compression, shear, flexion/extension moment (3–6). The information provided by these studies has been applied in several fields, from the validation of numerical models to the development of disc prostheses. However, such loading conditions are only partially representative of the in-situ load that the intervertebral disc normally experiences. High frequency dynamics stimuli, such as that experienced while driving a car on a rough surface or driving heavy industrial machinery, are also important. It is well known that long-term exposure to vibrational loading is detrimental to normal disc metabolism (7,8). Despite its relevance only a few studies have investigated the dynamic response of the disc to high frequency vibration (9,10) with sometimes different outcomes. In particular, no study has shown an asymmetric, nonlinear dynamic behavior of the system, even though it is evident in quasi-static testing — the well-known tension / compression asymmetry. This aspect is somehow neglected when building rigid body models of the upper body for impact simulation where a Kelvin-Voigt model with linear stiffness is normally used. The aim of this experimental study was therefore to investigate the nonlinear dynamic response of the intervertebral disc to high frequency loadings, taking different pre-loads and displacement amplitude into account.

Mean- and Low-Frequency Wave Forces on Semisubmersibles

1982 ◽  
Vol 22 (04) ◽  
pp. 563-572
Author(s):  
J.A. Pinkster
Keyword(s):  
Low Frequency ◽  
Second Order ◽  
Irregular Waves ◽  
Wave Forces ◽  
Frequency Wave ◽  
First Order ◽  
Wave Drift ◽  
Frequency Components ◽  
Wave Drift Forces ◽  
Drift Forces

Abstract Mean- and low-frequency wave drift forces on moored structures are important with respect to low-frequency motions and peak mooring loads. This paper addresses prediction of these forces on semisubmersible-type structures by use of computations based on three-dimensional (3D) potential theory. The discussion includes a computational method based on direct integration of pressure on the wetted part of the hull of arbitrarily shaped structures. Results of computations of horizontal drift forces on a six-column semisubmersible are compared with model tests in regular and irregular waves. The mean vertical drift forces on a submerged horizontal cylinder obtained from model tests also are compared with results of computations. On the basis of these comparisons, we conclude that wave drift forces on semisubmersible-type structures in conditions of waves without current can be predicted with reasonable accuracy by means of computations based on potential theory. Introduction Stationary vessels floating or submerged in irregular waves are subjected to large first-order wave forces and moments that are linearly proportional to the wave height and that contain the same frequencies as the waves. They also are subjected to small second-order mean- and low- frequency wave forces and moments that are proportional to the square of the wave height. Frequencies of second-order low-frequency components are associated with the frequencies of wave groups occurring in irregular waves.First-order wave forces and moments cause the well-known first-order motions with wave frequencies. First-order wave forces and motions have been investigated for several decades. As a result of these investigations, methods have been developed to predict these forces and moments with reasonable accuracy for many different vessel shapes.For semisubmersibles, which consist of a number of relatively slender elements such as columns, floaters, and bracings, computation methods have been developed to determine the hydrodynamic loads on those elements without accounting for interaction effects between the elements. For the first-order wave loads and motion problem, these computations give accurate results.This paper deals with the mean- and low-frequency second-order wave forces acting on stationary vessels in regular and irregular waves in general and presents a method to predict these forces on the basis of computations.The importance of mean- and low-frequency wave drift forces, from the point of view of motion behavior and mooring loads on vessels moored at point of view of motion behavior and mooring loads on vessels moored at sea, has been recognized only within the last few years. Verhagen and Van Sluijs, Hsu and Blenkarn, and Remery and Hermans showed that the low-frequency components of wave drift forces in irregular waves-even though relatively small in magnitude-can excite large-amplitude low- frequency horizontal motions in moored structures. It was shown for irregular waves that the drift forces contain components with frequencies coinciding with the natural frequencies of the horizontal motions of moored vessels. Combined with minimal damping of low-frequency horizontal motions of moored structures, this leads to large-amplitude resonant behavior of the motions (Fig. 1). Remery and Hermans established that low-frequency components in drift forces are associated with the frequencies of wave groups present in an irregular wave train.The vertical components of the second-order forces sometimes are called suction forces. SPEJ p. 563

Wave Propagation in Continuous Sea Ice: An Experimental Perspective

2020 ◽  
Author(s):  
Giulio Passerotti ◽  
Alberto Alberello ◽  
Azam Dolatshah ◽  
Luke Bennetts ◽  
Otto Puolakka ◽  
...  
Keyword(s):  
Sea Ice ◽  
Wave Energy ◽  
High Frequency ◽  
Large Scale ◽  
Low Frequency ◽  
Ocean Waves ◽  
Continuous Model ◽  
Ice Cover ◽  
Irregular Waves ◽  
Ice Melt

Abstract Ocean waves penetrate hundreds of kilometres into the ice-covered ocean. Waves fracture the level ice into small floes, herd floes, introduce warm water and overwash the floes, accelerating ice melt and causing collisions, which concurrently erodes the floes and influences the large-scale deformation. Concomitantly, interactions between waves and the sea ice cause wave energy to reduce with distance travelled into the ice cover, attenuating wave driven effects. Here a pilot experiment in the ice tank at Aalto University (Finland) is presented to discuss how the properties of irregular small amplitude (linear) waves change as they propagate through continuous model sea ice. Irregular waves with a JONSWAP spectral shape were mechanically generated with a very low initial wave steepness to avoid ice break up and maintain a consistent continuous ice cover throughout the experiments. Observations show an exponential attenuation of wave energy with distance. High frequency components attenuated more rapidly than the low frequency counterparts, in agreement with a frequency-cubed power-law. The more effective attenuation in the high frequency range induced a substantial downshift of the spectral peak, stretching the dominant wave component as it propagates in ice.

Extreme waves, modulational instability and second order theory: wave flume experiments on irregular waves

2006 ◽  
Vol 25 (5) ◽  
pp. 586-601 ◽  
Author(s):  
M. Onorato ◽  
A.R. Osborne ◽  
M. Serio ◽  
L. Cavaleri ◽  
C. Brandini ◽  
...  
Keyword(s):  
Modulational Instability ◽  
Order Theory ◽  
Second Order ◽  
Irregular Waves ◽  
Extreme Waves ◽  
Flume Experiments ◽  
Wave Flume

Observations and Modeling of Linear and Nonlinear Spatio-Temporal Wave Statistics

2010 ◽  
Author(s):  
Leonel Romero ◽  
W. Kendall Melville
Keyword(s):  
Spatial Information ◽  
Second Order ◽  
Stochastic Simulations ◽  
Ocean Engineering ◽  
Engineering Applications ◽  
Large Wave ◽  
Wave Statistics ◽  
Wave Parameters ◽  
Wave Heights ◽  
Spatio Temporal

We present an analysis of airborne wave observations collected in the Gulf of Tehuantepec. The data includes LIDAR measurements of the surface displacement as a function of two horizontal dimensions and time in fetch-limited conditions, with fetches between 50 and 300 km and winds between 10 and 20 m/s. The spatio-temporal data have an advantage over the commonly used single point time-series measurements allowing direct estimates of the wavelength and wave slope, including spatial information such as the lengths of crests exceeding threshold wave heights and slopes. The statistics of these wave parameters are particularly important for risk assessment of off-shore structures and in other ocean engineering applications. We present an analysis of several statistical wind-wave parameters, including the joint probability distribution function (pdf) of wave amplitudes and wavelengths, the pdf of wave heights, wavenumber vectors, and wave slopes, including the statistics of crests lengths exceeding threshold wave heights or slopes. The empirical findings from the LIDAR data are related to the analytical work by Longuet-Higgins (1957) [1] for a linear spectrum, including the average length of contours surrounding large wave heights. The effect of second-order nonlinearities on the distribution of crest lengths is investigated with numerical stochastic simulations from computed directional wavenumber spectra. The results show that second-order nonlinearities can increase the crest length density of large waves by about a factor of two or more. The results are discussed in the context of predicting wave statistics for ocean engineering applications.

Large-Scale Model Tests With Wave Loading on Offshore Platform Deck Elements

2002 ◽  
Author(s):  
Martin J. Sterndorff
Keyword(s):  
Large Scale ◽  
Model Tests ◽  
Offshore Platform ◽  
Irregular Waves ◽  
Scale Model ◽  
Wave Forces ◽  
Wave Loading ◽  
Large Wave ◽  
Wave Channel ◽  
The Individual

The present paper concerns a detailed large-scale experimental study of wave loading on offshore platform decks. A series of model tests with wave loading on different types of deck elements have been performed in the large wave channel (GWK) at Forschungszentrum Kiiste in Hannover, Germany. The following types of deck elements have been considered: tubular elements, plate profiles, and HEB beam profiles. The tests have been performed with individual elements and arrays of elements. Tests have also been performed with an array of beam elements covered with deck plating. A large range of different wave types, air gaps, and inundation’s have been tested. Regular waves with wave height ranging from 1.4 m to 1.8 m, irregular waves and wave packages with crest heights ranging from 0.9 m to 1.6 m have been tested. During the tests the following parameters were measured: wave elevations, deck element inundation’s, wave kinematics profile, and wave forces on the individual deck elements. The model test results will be analysed to provide hydrodynamic load coefficients to a wave-in-deck load programme based on the concept of change of fluid momentum. The results will also be used to verify a CFD code based on the Volume of Fluid method.

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