scholarly journals Occurrence of extreme waves in three-dimensional mechanically generated wave fields propagating over an oblique current

2011 ◽  
Vol 11 (3) ◽  
pp. 895-903 ◽  
Author(s):  
A. Toffoli ◽  
L. Cavaleri ◽  
A. V. Babanin ◽  
M. Benoit ◽  
E. M. Bitner-Gregersen ◽  
...  
Keyword(s):  
Modulational Instability ◽  
Three Dimensional ◽  
Wave Direction ◽  
Subsequent Increase ◽  
Wave Fields ◽  
Wave Trains ◽  
Directional Wave ◽  
The Mean ◽  
Wave Maker ◽  
Non Gaussian

Abstract. Laboratory experiments were performed to study the dynamics of three- dimensional mechanically generated waves propagating over an oblique current in partial opposition. The flow velocity varied along the mean wave direction of propagation with an increasing trend between the wave-maker and the centre of the tank. Tests with regular wave packets traversing the area of positive current gradient showed that the concurrent increase of wave steepness triggered modulational instability on otherwise stable wave trains and hence induced the development of very large amplitude waves. In random directional wave fields, the presence of the oblique current resulted in a weak reinforcement of wave instability with a subsequent increase of the probability of occurrence of extreme events. This seems to partially compensate the suppression of strongly non-Gaussian properties due to directional energy distribution.

Modulational Instability in Directional Wave Fields, and Extreme Wave Events

2011 ◽  
Author(s):  
Alexander V. Babanin ◽  
Takuji Waseda ◽  
Igor Shugan ◽  
Hwung-Hweng Hwung
Keyword(s):  
Modulational Instability ◽  
Wave Train ◽  
Three Dimensional ◽  
Breaking Waves ◽  
Two Dimensional ◽  
Wave Fields ◽  
Linear Evolution ◽  
Individual Wave ◽  
Wave Trains ◽  
Directional Wave

The paper is based on review of research articles by the authors, with the purpose to demonstrate that the modulational-instability mechanism is active in typical directional wave fields. If so, possible limits for the wave height due to such mechanism can be outlined. The modulational instability can lead to occurrence of very high waves, which either proceed to the breaking or appear as rogue events, but it was derived for and is usually associated with two-dimensional wave trains. There exists argument, both analytical and experimental, that this kind of instability is impaired or even suppressed in three-dimensional (directional) wave systems. The first part of the paper demonstrates indirect experimental evidences which relate the wave breaking in oceanic conditions to features of two-dimensional breaking waves due to modulational instability. The second section is dedicated to direct measurements of such instability-caused breaking in a directional wave tank with directional spread and mean steepness typical of those in the field. The last section provides conclusions on what is maximal height of an individual wave, depending on the mean wave steepness in a wave train/field, that can be achieved due to such non-linear evolution of wave trains.

Freak Wave Generation in a Wave Basin With HOSM-WG Method

2015 ◽  
Author(s):  
Hidetaka Houtani ◽  
Takuji Waseda ◽  
Wataru Fujimoto ◽  
Keiji Kiyomatsu ◽  
Katsuji Tanizawa
Keyword(s):  
Control Method ◽  
Irregular Waves ◽  
Frequency Bandwidth ◽  
Freak Waves ◽  
Freak Wave ◽  
Wave Basin ◽  
Wave Trains ◽  
Directional Wave ◽  
Wave Maker ◽  
The Difference

A method to produce freak waves with arbitrary spectrum in a fully directional wave basin is presented here. This is an extension of Waseda, Houtani and Tanizawa at OMAE 2013[1], which used “HOSM-WG” based on the higher-order spectral method (HOSM). We used the following three methods to improve the HOSM-WG in [1]: “separation of free waves from bound waves,” “using Biesel’s transfer function in wavenumber space” and “using Schaffer’s 2nd-order wave maker control method.” Modulational wave trains, freak waves in unidirectional irregular waves and freak waves in short-crested irregular waves were generated in a wave basin. The experimental results using the improved HOSM-WG were compared to the HOSM simulation, and good agreements were found. The effectiveness of the improved HOSM-WG was ascertained. We showed that the difference between HOSM-WG and HOSM simulations became larger as wave steepness, frequency bandwidth of the spectrum or directional spreading became larger.

Diffraction and Instability of Short-Crested Limited-Length One-Dimensional Coherent Wave Trains

2015 ◽  
Author(s):  
Alexander V. Babanin ◽  
Takuji Waseda
Keyword(s):  
Modulational Instability ◽  
Three Dimensional ◽  
Lateral Spread ◽  
Wave Tank ◽  
One Dimensional ◽  
Coherent Wave ◽  
Limited Length ◽  
Lateral Extent ◽  
Wave Trains ◽  
The University

Alternative representations of the wave field (as opposed to superposition of Fourier components) are possible. In this paper, behaviour of short-crested limited-length one-dimensional coherent wave trains is investigated. Experiments were conducted in the three-dimensional wave tank of the University of Tokyo. Description of the directional wave tank and its capacity to generate short-crested coherent wave trains, including those concurrent, superposed and directionally-superposed is provided. If the crest is shorter than the lateral extent of the wave tank, diffraction tends to redistribute the wave energy into clear surfaces, and thus energy of the wave trains is reduced and the modulational instability bandwidth changes correspondingly. Rates of such nonlinear lateral spread are estimated, and they are proportional to mean wave steepness. To avoid the diffraction, in further tests concurrent trains were mechanically generated, each of which occupied half of the lateral width of the wave tank and had the same energy as another half. The trains had the same frequency, and in order to keep them separate phase shift of 180 degrees was used. Sideband growth was significantly impaired by comparison with the long-crested evolution of the train with the same steepness.

Modulational instability and non-Gaussian statistics in experimental random water-wave trains

2005 ◽  
Vol 17 (7) ◽  
pp. 078101 ◽  
Author(s):  
M. Onorato ◽  
A. R. Osborne ◽  
M. Serio ◽  
L. Cavaleri
Keyword(s):  
Water Wave ◽  
Modulational Instability ◽  
Wave Trains ◽  
Gaussian Statistics ◽  
Non Gaussian

scholarly journals A Method to Estimate Reflection and Directional Spread Using Rotary Spectra from Accelerometers on Large Ice Floes

2017 ◽  
Vol 34 (5) ◽  
pp. 1125-1137 ◽  
Author(s):  
Graig Sutherland ◽  
Jean Rabault ◽  
Atle Jensen
Keyword(s):  
Sea Ice ◽  
Length Scale ◽  
Wave Spectra ◽  
Robust Method ◽  
Wave Direction ◽  
Wave Dissipation ◽  
Model Free ◽  
Directional Wave ◽  
The Mean ◽  
Ice Floes

AbstractThe directional wave spectra in sea ice are an important aspect of wave evolution and can provide insights into the dominant components of wave dissipation, that is, dissipation due to scattering or dissipation due to viscous processes under the ice. A robust method for the measurement of directional wave spectra parameters in sea ice from a three-axis accelerometer—or a heave, pitch, and roll sensor—is proposed. The method takes advantage of certain aspects of sea ice and makes use of rotary spectra techniques to provide model-free estimates for the mean wave direction, directional spread, and reflection coefficient. The method is ideally suited for large ice floes—that is, where the ice floe length scale is much greater than the wavelength—but a framework is provided to expand the parameter space where the method may be effective.

Wave Breaking in Directional Fields

2011 ◽  
Vol 41 (1) ◽  
pp. 145-156 ◽  
Author(s):  
A. V. Babanin ◽  
T. Waseda ◽  
T. Kinoshita ◽  
A. Toffoli
Keyword(s):  
Wave Breaking ◽  
Modulational Instability ◽  
Primary Wave ◽  
Angular Domain ◽  
Instability Mechanism ◽  
Wave Fields ◽  
Directional Distribution ◽  
Directional Wave ◽  
Directional Distributions ◽  
The University

Abstract Wave breaking is observed in a laboratory experiment with waves of realistic average steepness and directional spread. It is shown that a modulational-instability mechanism is active in such circumstances and can lead to the breaking. Experiments were conducted in the directional wave tank of the University of Tokyo, and the mechanically generated wave fields consisted of a primary wave with sidebands in the frequency domain, with continuous directional distribution in the angular domain. Initial steepness of the primary wave and sidebands, as well as the width of directional distributions varied in a broad range to determine the combination of steepness/directional-spread properties that separates modulational-instability breaking from the linear-focusing breaking.

Probability of Occurrence of Extreme Waves in Three Dimensional Mechanically Generated Random Wave Fields: A Comparison With Numerical Simulations

2011 ◽  
Author(s):  
A. Toffoli ◽  
S. Chai ◽  
E. M. Bitner-Gregersen ◽  
F. Pistani
Keyword(s):  
Numerical Simulations ◽  
Quantitative Estimate ◽  
Numerical Models ◽  
Modulational Instability ◽  
Three Dimensional ◽  
Random Wave ◽  
Extreme Waves ◽  
Wave Fields ◽  
Numerical Investigations ◽  
Probability Of Occurrence

Experimental and numerical investigations reveal that nonlinear modulational instability can significantly affect the probability of occurrence of extreme waves, especially if waves are sufficiently steep and narrow banded both in the frequency and directional domain. However, it is not yet completely clear whether numerical simulations can provide an accurate quantitative estimate of experimental results. Here the potential Euler equations are used to assess the ability of numerical models to describe the evolution of statistical properties of mechanically generated directional, random wave fields and in particular the evolution of the kurtosis. Results show that simulations provide a good quantitative estimate of experimental observations within a broad range of wave directional width.

Non-Gaussian Wave Groups Generated in an Offshore Wave Basin and Their Statistics

2011 ◽  
Author(s):  
Zhivelina Cherneva ◽  
C. Guedes Soares
Keyword(s):  
Wave Groups ◽  
Wave Basin ◽  
Lower Envelopes ◽  
The Mean ◽  
Wave Maker ◽  
Using Data ◽  
Non Gaussian ◽  
Offshore Wave ◽  
The Hilbert Transform ◽  
Theoretical Results

The main goal of this work is to investigate the wave groups using data from a deep water basin. Available data are for unidirectional waves measured at several fixed points situated in different distances from the wave maker. Previous works of many authors show that such series describe a process which differs significantly from the Gaussian one. Omitting the usual envelope definition by the Hilbert transform an upper and lower envelopes are introduced. Then the mean high run, mean group length and their distributions are found and compared with the theoretical results for Gaussian process.

The Effect of Aircushion Division on the Motions of Large Floating Structures

2007 ◽  
Author(s):  
J. L. F. van Kessel ◽  
J. A. Pinkster
Keyword(s):  
Water Surface ◽  
Three Dimensional ◽  
Potential Method ◽  
Wave Fields ◽  
Floating Structures ◽  
Different Types ◽  
The Mean ◽  
Motion Characteristics ◽  
The Stability ◽  
Drift Forces

The effect of aircushion division on the motions of large floating structures is studied by means of calculations based on a linear three-dimensional potential method. A linear adiabatic law is used to describe the air pressures inside the cushions. The water surface within the aircushions and the mean wetted surface are modelled by panel distributions representing oscillating sources. The behaviour of different types of aircushion supported structures is described and compared with that of a rectangular barge having the same dimensions. Successively, the aircushion theory, motion characteristics, wave frequency forces and moments, mean second order drift forces and surrounding wave fields are discussed. The results show that aircushions significantly influence the stability and behaviour of large floating structures.

Electron Holographic Nano-Characterization of Gold Catalyst at Interface

2002 ◽  
Vol 727 ◽  
Author(s):  
S. Ichikawa ◽  
T. Akita ◽  
M. Okumura ◽  
M. Haruta ◽  
K. Tanaka
Keyword(s):  
Contact Angle ◽  
Titanium Oxide ◽  
Gold Catalyst ◽  
Three Dimensional ◽  
High Resolution Electron Microscopy ◽  
Electron Holography ◽  
Gold Particles ◽  
Oxide Support ◽  
The Mean ◽  
A Charge

AbstractThe catalytic properties of nanostructured gold catalyst are known to depend on the size of the gold particles and to be activated when the size decreases to a few nanometers. We investigated the size dependence of the three-dimensional nanostructure on the mean inner potential of gold catalysts supported on titanium oxide using electron holography and high-resolution electron microscopy (HREM). The contact angle of the gold particles on the titanium oxide tended to be over 90° for gold particles with a size of over 5 nm, and below 90° for a size of below 2 nm. This decreasing change in the contact angle (morphology) acts to increase the perimeter and hence the area of the interface between the gold and titanium oxide support, which is considered to be an active site for CO oxidation. The mean inner potential of the gold particles also changed as their size decreased. The value of the inner potential of gold, which is approximately 25 V in bulk state, rose to over 40 V when the size of the gold particles was less than 2 nm. This phenomenon indicates the existence of a charge transfer at the interface between gold and titanium oxide. The 3-D structure change and the inner potential change should be attributed to the specific electronic structure at the interface, owing to both the “nano size effect” and the “hetero-interface effect.”

Sign in / Sign up

Export Citation Format

Share Document