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.

Some Effects of Non-Linearity for High Wave Groups in Front of a Vertical Wall

2007 ◽  
Author(s):  
Alessandra Romolo ◽  
Felice Arena
Keyword(s):  
Velocity Potential ◽  
Vertical Wall ◽  
Surface Displacement ◽  
Wave Crest ◽  
Sea Waves ◽  
Wave Groups ◽  
Large Wave ◽  
High Wave ◽  
Free Surface Displacement ◽  
Sea Wave

The upright fully reflective wall-types breakwaters have been widely adopted for development of harbours. The design of these structures depends on the characteristic wave field resulting from the interaction of the sea waves with the reflective structure, which is strongly irregular and nonlinear. This paper deals with the mechanics of long-crested wave groups in front of a vertical wall. For this purpose the ‘Quasi Determinism’ theory, particularized for the reflection of sea wave groups, is extended up to the second-order. The nonlinear processes free surface displacement and velocity potential, when a large wave crest occurs on the vertical wall or in front of it, are obtained. In the application some properties of nonlinear wave groups in reflection, when a high wave crest occurs on the wall or in front of it, are investigated.

scholarly journals A New Solution for Sea Wave Energy Harvesting, the Proposal of an Ironless Linear Generator

2020 ◽  
Vol 8 (2) ◽  
pp. 93 ◽  
Author(s):  
Domenico Curto ◽  
Alessia Viola ◽  
Vincenzo Franzitta ◽  
Marco Trapanese ◽  
Fabio Cardona
Keyword(s):  
Wave Energy ◽  
Magnetic Force ◽  
Vertical Motion ◽  
Small Islands ◽  
Sea Waves ◽  
Energy Converter ◽  
Energy Potential ◽  
Linear Generator ◽  
Three Phase ◽  
Sea Wave

The paper investigates an innovative ironless linear generator, installable inside a wave energy converter, in order to produce electricity from sea waves. This energy source is considered strategic for the future, especially in small islands; however, this technology is still far from the commercial phase. Considering the wave energy potential of the Mediterranean Sea, a first prototype of the electrical linear generator was realized at the Department of Engineering of Palermo University. This machine can be run by a two-floating buoys system, able to produce a linear vertical motion. The main goal of this paper is the investigation of the advantages and the disadvantages of the utilization of steel materials to realize the stator of linear generators. Thus, starting from the prototype, the authors analyzed the effects produced by the replacement of steel in the stator with a non-magnetic material. For comparison, the authors evaluated the amplitude of no-load voltages, using a three-phase connection scheme, and the amplitude of the magnetic force produced by the interaction of magnets with the stator. Both aspects were evaluated through numerical simulations and mathematical models.

Tadpole: A Design Problem in the Mechanics of the Use of Sea Wave Energy

1996 ◽  
Vol 210 (4) ◽  
pp. 273-277 ◽  
Author(s):  
M J French
Keyword(s):  
Wave Energy ◽  
Special Interest ◽  
Reaction Force ◽  
Electrical Energy ◽  
Wave Forces ◽  
Sea Waves ◽  
Small Machine ◽  
Clear Insight ◽  
Insight Into ◽  
Sea Wave

A study is made of a device for obtaining electrical energy from sea waves, in which the problem of providing a reaction against the wave forces is met by a combination of a pendulum and gyroscopes. The mechanics is developed in a logical manner which gives a clear insight into the function, the pendulum providing the reaction force, which leaves an unbalanced moment to be countered by the gyroscopes, which also constitute the power take-off. The result is a relatively small machine with no external moving parts. The treatment requires no understanding of wave hydrodynamics. It is felt this paper may be of special interest as a design study, in which the relation between the mechanics and the development of the concept is peculiarly cogent.

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.

scholarly journals A COMPARISON OF NATURE WAVES AND MODEL WAVES WITH SPECIAL REFERENCE TO WAVE GROUPING

1980 ◽  
Vol 1 (17) ◽  
pp. 177 ◽  
Author(s):  
Hans F. Burcharth
Keyword(s):  
Phase Distribution ◽  
Random Phase ◽  
Power Spectra ◽  
Height Distribution ◽  
Wave Group ◽  
Storm Waves ◽  
Wave Height Distribution ◽  
Storm Wave ◽  
Wave Heights ◽  
The Impact

This paper represents a comparative analysis of the occurrence of wave grouping in field storm waves and laboratory waves with similar power spectra and wave height distribution. Two wave patterns - runs of waves and jumps in wave heights - which have significant influence on the impact on coastal structures were included in the analysis of storm wave records off the coasts of Cornwall, U.K. and Jutland, Denmark. Two different laboratory wave generator systems, based on random phase distribution of component waves, were used. Within the limitations given by the relatively small number of analysed records it is shown that wave group statistics can be satisfactorily reproduced by random phase generators that are not based on a limited number of component waves, but for example based on filtering of white noise. It is also shown that the statistics of large waves and wave groups containing large waves depend on whether the waves are defined from zero-upcrossings or zero-downcrossings. Although very similar seas were chosen for the analysis it was found that significant differences in the wave group statistics from the two locations existed. Also a considerable scatter in the wave group statistics throughout the storms was found.

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 Track and Accompanying Sea Wave Forecasts of the Supertyphoon Mangkhut (2018) by a Real-Time Regional Forecast System

2020 ◽  
Vol 37 (11) ◽  
pp. 2075-2084
Author(s):  
Yuhang Zhu ◽  
Yineng Li ◽  
Shiqiu Peng
Keyword(s):  
Real Time ◽  
Large Scale ◽  
Negative Impact ◽  
Wave Model ◽  
Forecast Skill ◽  
Track Forecast ◽  
Sea Waves ◽  
Mean Error ◽  
Forecasting System ◽  
Sea Wave

AbstractThe track and accompanying sea wave forecasts of Typhoon Mangkhut (2018) by a real-time regional forecasting system are assessed in this study. The real-time regional forecasting system shows a good track forecast skill with a mean error of 69.9 km for the forecast period of 1–72 h. In particular, it predicted well the landfall location on the coastal island of South China with distance (time) biases of 76.89 km (3 h) averaging over all forecasting made during 1–72 h and only 3.55 km (1 h) for the forecasting initialized 27 h ahead of the landfall. The sea waves induced by Mangkhut (2018) were also predicted well by the wave model of the forecasting system with a mean error of 0.54 m and a mean correlation coefficient up to 0.94 for significant wave height. Results from sensitivity experiments show that the improvement of track forecasting skill for Mangkhut (2018) are mainly attributed to application of a scale-selective data assimilation scheme in the atmosphere model that helps to maintain a more realistic large-scale flow obtained from the GFS forecasts, whereas the air–sea coupling has slightly negative impact on the track forecast skill.

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