scholarly journals NOTES ON THE GENERATION AND GROWTH OF OCEAN WAVES UNDER WIND ACTION

2000 ◽  
Vol 1 (3) ◽  
pp. 7
Author(s):  
Gerhard Neumann
Keyword(s):  
Energy Dissipation ◽  
Energy Supply ◽  
Basic Problem ◽  
Ocean Waves ◽  
Wind Action ◽  
Wave Development ◽  
Component Wave ◽  
Wave Trains ◽  
Physical Laws ◽  
The Waves

The basic problem of forecasting wind-generated waves is the development of equations which express the energy budget between wind and waves, and the derivation of physical laws governing the growth of the component wave trains. The waves can grow only in the case where the supply of energy by wind exceeds the loss of energy by friction and turbulence. Thus any attempt to calculate the growth of ocean waves under wind action requires a knowledge of the energy supply and the energy dissipation in every phase of wave development.

The generation of waves by wind

1952 ◽  
Vol 215 (1122) ◽  
pp. 299-328 ◽  
Keyword(s):  
Ocean Waves ◽  
Irish Sea ◽  
North Coast ◽  
Empirical Relationships ◽  
The North ◽  
Component Wave ◽  
Wave Trains ◽  
The Irish Sea ◽  
The Waves ◽  
Group Velocities

This paper describes an investigation of the height and length of ocean waves and swell in relation to the strength, extent and duration of the wind in the generating area, and the subsequent travel of the swell through calm and disturbed water. The investigation is based on records of waves made on the north coast of Cornwall, in the Irish Sea and in Lough Neagh. It is a practical continuation of the work of Barber & Ursell (1948), who showed that the waves leaving the generating area behave as a continuous spectrum of component wave trains which travel independently with the group velocities appropriate to their periods. The spectral distribution of energy in the storm area is considered, and the relative amplitudes of the different components are deduced empirically under various wind conditions. The results indicate that the wave characteristics become practically independent of fetch after 200 to 300 miles, and that in the equilibrium condition the steepness of the highest waves is inversely proportional to the square root of the wind speed. Some theoretical foundation can be found for the form of the empirical relationships if it is assumed that the wind acts on each wave component independently, and that the sheltering coefficient used by Jeffreys is proportional to the wave steepness. The results provide a basis for making reasonably accurate predictions of waves and swell from meteorological charts and forecasts.

scholarly journals An Analysis of West African Dynamics Using a Linearized GCM*

2008 ◽  
Vol 65 (4) ◽  
pp. 1182-1203 ◽  
Author(s):  
S. E. Nicholson ◽  
A. I. Barcilon ◽  
M. Challa
Keyword(s):  
Interannual Variability ◽  
Spherical Model ◽  
Planetary Scale ◽  
Wave Disturbances ◽  
Easterly Wave ◽  
Key Factor ◽  
Wave Development ◽  
Basic States ◽  
Vertical Development ◽  
The Waves

Abstract This study utilizes a linear, primitive equation spherical model to study the development and propagation of easterly wave disturbances over West Africa. Perturbations are started from an initial disturbance consisting of a barotropic vortex and the governing equations are integrated forward in time. The perturbations are introduced into basic states corresponding to the observed dynamical and thermodynamical characteristics of two wet years in the Sahel and two dry years. The model simulations show consistent contrasts in wave activity between the wet and dry years. The waves are markedly stronger in the wet years and show a barotropic structure throughout the troposphere. The waves tend to extend throughout the troposphere to the level of the tropical easterly jet (TEJ) in the wet years, but not in the dry years. The upper-tropospheric shear, which is stronger in wet years, appears to be a key factor in wave development. This shear is dependent on the intensity of the TEJ, suggesting that the TEJ is an important factor in interannual variability in the Sahel. When the overall shear is weak, vertical development is suppressed. Another contrast is that in the dry years the growth rates show a single maximum around 3000–4000 km, but in the wet years there is a second, around 6000–7000 km. This suggests that both synoptic-scale and planetary-scale waves are active in the rainy season of some wet years. Imposing considerations of potential vorticity, the generation of planetary-scale waves implies a strong link between the surface and the TEJ in wet years. Such a link is absent in the dry years. This is likely a major factor in the interannual variability of rainfall in the Sahel.

Studies of Extreme Energy Localizations With Smoothed Particle Hydrodynamics

2015 ◽  
Author(s):  
Ayan Moitra ◽  
Christopher Chabalko ◽  
Balakumar Balachandran
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Ocean Waves ◽  
Breaking Wave ◽  
Wave Focusing ◽  
Wave Interference ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Wave Heights ◽  
The Waves ◽  
Wave Phenomena

Smoothed particle hydrodynamics (SPH) is used to simulate hydrodynamic waves and wave phenomena including focusing from wave interference. This Lagrangian based method can be used to naturally simulate hydrodynamic free surfaces, including the free surface of a breaking wave. A virtual wave tank is simulated where wave motions can be excited from either side. Wave focusing is observed at the tank center, where the waves interfere. As a measure of the interference, the wave heights that result from focusing are presented. Certain types of wave focusing are thought to lead to large ocean waves. The efficacy of SPH in modeling wave focusing is critical to further understanding and predicting extreme wave phenomena with SPH.

Experimental investigation on the evolution of the modulation instability with dissipation

2012 ◽  
Vol 711 ◽  
pp. 101-121 ◽  
Author(s):  
Y. Ma ◽  
G. Dong ◽  
M. Perlin ◽  
X. Ma ◽  
G. Wang
Keyword(s):  
Experimental Investigation ◽  
Modulational Instability ◽  
Experimental Results ◽  
Damping Term ◽  
Wave Flume ◽  
Perturbation Frequency ◽  
Linear Damping ◽  
Wave Trains ◽  
Momentum Integral ◽  
The Waves

AbstractAn experimental investigation focusing on the effect of dissipation on the evolution of the Benjamin–Feir instability is reported. A series of wave trains with added sidebands, and varying initial steepness, perturbed amplitudes and frequencies, are physically generated in a long wave flume. The experimental results directly confirm the stabilization theory of Segur et al. (J. Fluid Mech., vol. 539, 2005, pp. 229–271), i.e. dissipation can stabilize the Benjamin–Feir instability. Furthermore, the experiments reveal that the effect of dissipation on modulational instability depends strongly on the perturbation frequency. It is found that the effect of dissipation on the growth rates of the sidebands for the waves with higher perturbation frequencies is more evident than on those of waves with lower perturbation frequencies. In addition, numerical simulations based on Dysthe’s equation with a linear damping term included, which is estimated from the experimental data, can predict the experimental results well if the momentum integral of the wave trains is conserved during evolution.

Wave-Coherent Airflow and Critical Layers over Ocean Waves

2013 ◽  
Vol 43 (10) ◽  
pp. 2156-2172 ◽  
Author(s):  
Laurent Grare ◽  
Luc Lenain ◽  
W. Kendall Melville
Keyword(s):  
Momentum Flux ◽  
Wave Spectrum ◽  
Phase Speed ◽  
Ocean Waves ◽  
Naval Research ◽  
Critical Height ◽  
Office Of Naval Research ◽  
Mean Wind Speed ◽  
Wave Induced ◽  
The Waves

Abstract An analysis of coherent measurements of winds and waves from data collected during the Office of Naval Research (ONR) High-Resolution air–sea interaction (HiRes) program, from the Floating Instrument Platform (R/P FLIP), off the coast of northern California in June 2010 is presented. A suite of wind and wave measuring systems was deployed to resolve the modulation of the marine atmospheric boundary layer by waves. Spectral analysis of the data provided the wave-induced components of the wind velocity for various wind–wave conditions. The power spectral density, the amplitude, and the phase (relative to the waves) of these wave-induced components are computed and bin averaged over spectral wave age c/U(z) or c/u*, where c is the linear phase speed of the waves, U(z) is the mean wind speed measured at the height z of the anemometer, and u* is the friction velocity in the air. Results are qualitatively consistent with the critical layer theory of Miles. Across the critical height zc, defined such that U(zc) = c, the wave-induced vertical and horizontal velocities change significantly in both amplitude and phase. The measured wave-induced momentum flux shows that, for growing waves, less than 10% of the momentum flux at z ≈ 10 m is supported by waves longer than approximately 15 m. For older sea states, these waves are able to generate upward wave-induced momentum flux opposed to the overall downward momentum flux. The measured amplitude of this upward wave-induced momentum flux was up to 20% of the value of the total wind stress when Cp/u* > 60, where Cp is the phase speed at the peak of the wave spectrum.

scholarly journals NATURAL WAVE TRAINS: DESCRIPTION AND REPRODUCTION

1978 ◽  
Vol 1 (16) ◽  
pp. 16 ◽  
Author(s):  
H. Lundgren ◽  
S.E. Sand
Keyword(s):  
Numerical Models ◽  
Wave Train ◽  
Three Dimensional ◽  
Correct Description ◽  
Linear Superposition ◽  
Natural Wave ◽  
Wave Trains ◽  
Steep Waves ◽  
Deterministic Description ◽  
The Waves

In many applications there is a great need for a correct description of the natural, irregular three-dimensional sea and its reproduction in physical and numerical models. Because of the tremendous difficulties inherent in the nonlinearities, the science of coastal engineering is still very far from this ultimate goal. Indeed, the scope of this paper is comparatively very modest: To describe and reproduce natural, irregular two-dimensional waves, i.e. waves propagating in one direction in a flume. In addition, this scope is fulfilled only by assuming linear superposition of Fourier terms. As opposed to the usual spectral description, the deterministic description presented here does not eliminate the phase information in the wave train recorded. Because of the nonlinearities, however, the linear deterministic description invariably degenerates with the distance travelled by the waves. It appears though from the present paper that the degeneration is fairly slow even for rather steep waves.

On the interaction of wind and waves

1989 ◽  
Vol 329 (1604) ◽  
pp. 289-301 ◽  
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Wind Profile ◽  
Air Flow ◽  
Ocean Waves ◽  
Wave Age ◽  
Mean Flow ◽  
Layer Model ◽  
Wind Sea ◽  
The Waves

We discuss the effect of wind-generated, gravity waves on the air flow. We study this example of resonant wave mean flow interaction using the quasi-linear theory of wind-wave generation (A. L. Fabrikant Izv. atmos. ocean. Phys. 12, 524 (1976); P. Janssen J. Fluid Mech . 117, 493-506 (1982)). In this theory both the effects of the waves and the effect of air turbulence on the mean wind profile is taken into account. For a given wave spectrum, results of the numerical calculation of the steady-state wind profile are presented. The main result is that for young wind sea most of the stress in the boundary layer is determined by the transfer of momentum from wind to waves, therefore resulting in a strong coupling between air flow and waves. For old wind sea there is, however, hardly any coupling. As a consequence, a sensitive dependence of the aerodynamic drag on the wave age is found, explaining the scatter in plots of the experimentally observed drag as a function of the wind speed at 10 m. Also, the growth rate of waves by wind is found to depend on wave age, reflecting the effect of the waves on the wind profile. All this suggests that a proper description of the physics of the momentum transfer from atmosphere to the ocean waves can only be given by coupling an atmospheric boundary-layer model with an ocean-wave prediction model. Here, we present the first results of the coupling of a simple surface-layer model with the third-generation wave model. The wave-induced stress is found to have a significant impact on the results for the wave height and the stress in the surface layer.

scholarly journals Thermoelastic waves without energy dissipation in an unbounded body with a spherical cavity

2000 ◽  
Vol 23 (8) ◽  
pp. 555-562 ◽  
Author(s):  
D. S. Chandrasekharaiah ◽  
K. S. Srinath
Keyword(s):  
Energy Dissipation ◽  
Spherical Cavity ◽  
Small Time ◽  
Laplace Transform Technique ◽  
The Laplace Transform ◽  
Thermoelastic Body ◽  
Without Energy Dissipation ◽  
The Waves ◽  
Thermoelastic Waves ◽  
Stress Free Boundary

The linear theory of thermoelasticity without energy dissipation is employed to study waves emanating from the boundary of a spherical cavity in a homogeneous and isotropic unbounded thermoelastic body. The waves are supposed to be spherically symmetric and caused by a constant step in temperature applied to the stress-free boundary of the cavity. Small-time solutions for the displacement, temperature, and stress fields are obtained by using the Laplace transform technique. It is found that there exist two coupled waves, of which one is predominantly elastic and the other is predominantly thermal, both propagating with finite speeds but with no exponential attenuation. Exact expressions for discontinuities in the field functions that occur at the wavefronts are computed and analysed. The results are compared with those obtained earlier in the contexts of some other models of thermoelasticity.

Two Variational Stereo Methods for Space-Time Measurements of Ocean Waves

2013 ◽  
Author(s):  
Guillermo Gallego ◽  
Anthony Yezzi ◽  
Francesco Fedele ◽  
Alvise Benetazzo
Keyword(s):  
Spatial Scales ◽  
Ocean Surface ◽  
Ocean Waves ◽  
Video Data ◽  
The Black Sea ◽  
Intermediate Step ◽  
Surface Displacements ◽  
Pros And Cons ◽  
Variational Approaches ◽  
The Waves

In recent years, the study of the dynamics of ocean waves via stereo vision systems has focused on investigating sea states with wavelengths in the range of 0.01 m to 1 m. In this work, we present two modern stereo variational approaches, viz. the disparity and graph methods, for the estimation of the ocean surface displacements over larger spatial scales of 10 to 100 m. The disparity method estimates the disparity between images as an intermediate step toward retrieving the depth of the waves with respect to the cameras, and the graph method estimates the ocean surface displacements directly in 3-D space. The pros and cons of both methods are compared and their performance is evaluated using experimental video data collected at an offshore platform in the Black Sea.

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