scholarly journals DUNE EROSION ABOVE REVETMENTS

2012 ◽  
Vol 1 (33) ◽  
pp. 95 ◽  
Author(s):  
Jaap Van Thiel de Vries
Keyword(s):  
Incident Wave ◽  
Extreme Events ◽  
Long Waves ◽  
Impact Model ◽  
Dune Erosion ◽  
Short Waves ◽  
Long Wave ◽  
Storm Impact ◽  
Wave Groupiness

In a situation with a narrow dune, the dune base can be protected with a revetment to reduce dune erosion during extreme events. To quantify the effects of a revetment on storm impact, the functionality of the numerical storm impact model XBeach (Roelvink et al., 2009) is extended to account for the complex morphodynamics around revetments. Here the focus is on dune erosion above revetments, which is simulated with a simple avalanching algorithm that is triggered by the combined runup of short waves and long waves. The simulated runup statistics depend on the incident wave groupiness and associated long wave variance.

A nonlinear mechanism for the generation of sea waves

1969 ◽  
Vol 311 (1506) ◽  
pp. 371-389 ◽  
Keyword(s):  
Wave Propagation ◽  
Surface Waves ◽  
Orbital Motion ◽  
Long Waves ◽  
Shear Instability ◽  
Sea Waves ◽  
Short Waves ◽  
Long Wave ◽  
Nonlinear Mechanism ◽  
Surrounding Fluid

Recent observations of the growth of sea waves under the action of wind have established that the rate of growth is several times greater than has yet been accounted for. In this paper a new mechanism of wave generation is proposed, based on the idea of a maser-like action of the short waves on the longer waves. It is shown that when surface waves decay they impart their momentum to the surrounding fluid. Short waves are readily regenerated by shear instability. But a longer wave passing through shorter waves causes the short waves to steepen on the long-wave crests. Hence the short waves impart more of their momentum to the crests of the long waves, where the orbital motion of the long waves is in the direction of wave propagation. If the short waves are decaying only weakly (under the action of viscosity), the effect on the long waves is slight. But when the short waves are forced to decay strongly by breaking on the forward slopes of the long waves the gain of energy by the latter is greatly increased. Calculations suggest that the mechanism is capable of imparting energy to sea waves at the rate observed.

A stochastic model of sea-surface roughness. II

1991 ◽  
Vol 435 (1894) ◽  
pp. 405-422 ◽  
Keyword(s):  
Wave Energy ◽  
Short Wave ◽  
Long Waves ◽  
Scale Model ◽  
Short Waves ◽  
Long Wave ◽  
Proportional Rate ◽  
The Mean ◽  
Sheltering Effect ◽  
Increasing Function

A two-scale model of a wind-ruffled surface is developed which includes (1) modulation of the short waves by orbital straining in the long waves, (2) dissipation of short-wave energy by breaking, and (3) regeneration of the short-wave energy by the wind. For simplicity the long waves are at first assumed to be uniform. It is shown that the character of the surface is governed by the parameter Ω = (β/σγKA ), where β is the proportional rate of short-wave growth due to the wind, σ , K and A are the long-wave frequency wavenumber and amplitude, and γ = 2.08. When Ω < 1 the short waves break over only part of the long-wave surface. When Ω ≽ 1 they break everywhere. The mean-square steepness s 2 ¯ of the short waves is an increasing function of β/σ , but a decreasing function of the long-wave steepness AK . The phase angle between s 2 ¯ and the long-wave elevation η is an increasing function of Ω . The correlation between s 2 ¯ and η is largest when Ω ≪1, but tends to 0 as Ω → 1. The simple model is extended to the case when the long-wave amplitude A has a Rayleigh probability density. To take account of the ‘sheltering ’ effect of high waves we compute the case when any two successive waves have a bivariate Rayleigh density. The application of the model to laboratory and field data is discussed.

Excitation of long internal waves by groups of short surface waves incident on a barrier

1988 ◽  
Vol 192 ◽  
pp. 17-31 ◽  
Author(s):  
Yehuda Agnon ◽  
Chiang C. Mei
Keyword(s):  
Surface Waves ◽  
Group Velocity ◽  
Internal Waves ◽  
Long Waves ◽  
Baroclinic Wave ◽  
Short Waves ◽  
Phase Velocities ◽  
Long Wave ◽  
Incident Waves ◽  
Model Ocean

The effects of diffraction by a long barrier on second-order long waves forced by sinusoidally modulated short incident waves are examined for a two-layered model ocean. When the group velocity of the short waves lies between the phase velocities of the longest baroclinic and barotropic modes, long internal waves of the frequency equal to twice the modulational frequency of the short waves are found to radiate away from the edge ray which divides the geometrical shadow and the illuminated region. In particular the baroclinic wave can penetrate the shadow. This penetration occurs when the internal long wave is not resonated by short surface waves.

scholarly journals LONG WAVES IN A SPANISH HARBOUR

1988 ◽  
Vol 1 (21) ◽  
pp. 73 ◽  
Author(s):  
Jose C. Santos Lopez ◽  
Gregorio Gomez Pina
Keyword(s):  
Physical Model ◽  
Model Test ◽  
Long Waves ◽  
Port Authority ◽  
Short Waves ◽  
Wave Data ◽  
Long Wave ◽  
Other Hand ◽  
The One

Short and Long Wave data recorded in Bilbao Harbour < Spain ) have been analyzed in order to study water movements at the inner basins under storms conditions . Some of the trends obtained in prototype have been correlated with model test (regular long wave and irregular short waves ) . This harbour has been chosen for this research on the one hand because of tha availability of the physical model and on thge other hand because of the means provided by the Bilbao Port Authority.

scholarly journals EROSION AROUND A PILE DUE TO CURRENT AND BREAKING WAVES

1988 ◽  
Vol 1 (21) ◽  
pp. 102 ◽  
Author(s):  
E.W. Bijker ◽  
C.A. De Bruyn
Keyword(s):  
Shear Stress ◽  
Breaking Waves ◽  
Velocity Profiles ◽  
Long Waves ◽  
Orbital Velocity ◽  
Bottom Shear Stress ◽  
Normal Waves ◽  
Short Waves ◽  
A Current

Tests have been performed on a vertical pile subject to current only and to a combination of current with normal waves and current with breaking waves. The scour around the pile produced by current only is decreased by normal short waves superimposed upon that current and increased when breaking waves are superimposed upon the current. After analysis of the velocity profiles in the undisturbed area upstream of the pile and next to the pile, the following explanation is found for this phenomenon. When normal short waves are superimposed upon a current, the bottom shear stress of the combination of current with waves is increased more in the undisturbed area than next to the pile in the scour area. This results in a decrease of the scour around the pile. Due to the large values of the orbital velocity under breaking waves this effect is reversed for the combination of a current with breaking and relatively long waves. This results in an increase of the scour around the pile.

Wave breaking in the presence of wind drift and swell

1974 ◽  
Vol 66 (4) ◽  
pp. 625-640 ◽  
Author(s):  
O. M. Phillips ◽  
M. L. Banner
Keyword(s):  
Wind Speed ◽  
Wave Breaking ◽  
Wind Wave ◽  
Maximum Amplitude ◽  
Velocity Difference ◽  
Wind Drift ◽  
Short Waves ◽  
Long Wave ◽  
Molecular Viscosity ◽  
Surface Drift

Wind, blowing over a water surface, induces a thin layer of high vorticity in which the wind stress is supported by molecular viscosity; the magnitude of the surface drift, the velocity difference across the layer, being of the order of 3% of the wind speed. When long waves move across the surface, there is a nonlinear augmentation of the surface drift near the long-wave crests, so that short waves, superimposed on the longer ones, experience an augmented drift in these regions. This is shown to reduce the maximum amplitude that the short waves can attain when they are at the point of incipient breaking.Theoretical estimates of the reduction are compared with measurements in wind-wave tanks by the authors and by Mitsuyasu (1966) in which long mechanically generated waves are superimposed on short wind-generated waves. The reductions measured in the energy density of the short waves by increasing the slope of the longer ones at constant wind speed are generally consistent with the predictions of the theory in a variety of cases.

The Propagation of Compressional Waves in a Dispersive Elastic Rod: Part II—Experimental Results and Comparison With Theory

1957 ◽  
Vol 24 (2) ◽  
pp. 240-244
Author(s):  
Julius Miklowitz ◽  
C. R. Nisewanger
Keyword(s):  
Shock Tube ◽  
Longitudinal Mode ◽  
Long Waves ◽  
Experimental Results ◽  
Radial Mode ◽  
Approximate Representation ◽  
Elastic Rod ◽  
Compressional Waves ◽  
Short Waves

Abstract Experimental results, obtained by employing an aerodynamic shock tube for rod excitation, are presented. Comparison of these results with the theoretical information presented in Part I is made. It is shown that the Mindlin-Herrmann theory, through its upper mode (radial), offers a good approximate representation of the moderately short waves that predominate at the later times at a random station of the rod. The very short waves of this same radial mode, however, govern the early disturbance, thus precluding the possibility of representing this portion of the disturbance, which the experiment shows to be composed of relatively long waves, by the longitudinal mode of the theory.

5. Long Waves and Conjunctures of Democratization

2018 ◽  
pp. 67-81
Author(s):  
Dirk Berg-Schlosser
Keyword(s):  
Eighteenth Century ◽  
Long Waves ◽  
Political Equality ◽  
Short Term ◽  
Late Eighteenth Century ◽  
Long Wave ◽  
Late Eighteenth ◽  
The Future ◽  
History Of

This chapter focuses on the history of democratization since the late eighteenth century. It introduces the concepts of ‘waves’ (trends) and ‘conjunctures’ (briefer turmoils) and delineates the major developments in this respect. In this way, the major long-term and short-term factors leading to the emergence and breakdowns of democracies are also highlighted. The first long wave occurred during the period 1776–1914, followed by the first positive conjuncture in 1918–19, the second long wave (with some intermittent turbulences) in 1945–88, and the latest conjuncture in 1989–90. The chapter identifies the main ingredients to democratization throughout history, namely: republicanism, representation, and political equality. It concludes by considering some of the current perspectives and dangers for the future of democracy.

Radiation of short waves from the resonantly excited capillary–gravity waves

2016 ◽  
Vol 810 ◽  
pp. 5-24 ◽  
Author(s):  
M. Hirata ◽  
S. Okino ◽  
H. Hanazaki
Keyword(s):  
Solitary Wave ◽  
Solitary Waves ◽  
Gravity Waves ◽  
Wave Pattern ◽  
Short Wave ◽  
Bond Number ◽  
Linear Wave ◽  
Cnoidal Wave ◽  
Short Waves ◽  
Long Wave

Capillary–gravity waves resonantly excited by an obstacle (Froude number: $Fr=1$) are investigated by the numerical solution of the Euler equations. The radiation of short waves from the long nonlinear waves is observed when the capillary effects are weak (Bond number: $Bo<1/3$). The upstream-advancing solitary wave radiates a short linear wave whose phase velocity is equal to the solitary waves and group velocity is faster than the solitary wave (soliton radiation). Therefore, the short wave is observed upstream of the foremost solitary wave. The downstream cnoidal wave also radiates a short wave which propagates upstream in the depression region between the obstacle and the cnoidal wave. The short wave interacts with the long wave above the obstacle, and generates a second short wave which propagates downstream. These generation processes will be repeated, and the number of wavenumber components in the depression region increases with time to generate a complicated wave pattern. The upstream soliton radiation can be predicted qualitatively by the fifth-order forced Korteweg–de Vries equation, but the equation overestimates the wavelength since it is based on a long-wave approximation. At a large Bond number of $Bo=2/3$, the wave pattern has the rotation symmetry against the pattern at $Bo=0$, and the depression solitary waves propagate downstream.

ICOAST – DID THE COAST CHANGE?: STORM-IMPACT MODEL VERIFICATION USING CITIZEN SCIENTISTS

2019 ◽  
Author(s):  
KAREN L.M. MORGAN ◽  
NATHANIEL G. PLANT ◽  
HILARY STOCKDON ◽  
RICHARD J. SNELL
Keyword(s):  
Model Verification ◽  
Impact Model ◽  
Storm Impact
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