The response of a continental shelf to travelling pressure disturbances

1973 ◽  
Vol 24 (2) ◽  
pp. 143 ◽  
Author(s):  
VT Buchwald ◽  
RA de Szoeke
Keyword(s):  
Continental Shelf ◽  
Closed Form ◽  
Atmospheric Pressure ◽  
Step Function ◽  
Long Waves ◽  
Wave Number ◽  
Long Wave ◽  
Sinusoidal Disturbance ◽  
Speed Of Propagation ◽  
Rectangular Model

Assuming a rectangular model of a continental shelf, this paper sets out to calculate the response of the shelf and ocean regions to plane atmospheric pressure disturbances travelling with constant speed in a longshore direction. It is shown that, for a sinusoidal disturbance, there is resonance at a given speed of propagation c only if c lies between the speeds of long waves on the shelf and ocean regions, and then only if the wave number of the disturbance matches one of the possible modes of long waves trapped on the shelf. In addition, the passage of a pressure front along the shelf is modelled by a step function, and the response to such a disturbance is calculated in closed form. If the speed of the disturbance is between the speed of long waves in the shelf and ocean regions, then there is a wake of trapped long-wave modes, the amplitudes of which may be quite large compared with the change in the atmospheric pressure.

scholarly journals A NUMERICAL STUDY ON LONG-WAVE GENERATION DUE TO ATMOSPHERIC-PRESSURE VARIATION

2012 ◽  
Vol 1 (33) ◽  
pp. 17
Author(s):  
Taro Kakinuma ◽  
Kosuke Fukita
Keyword(s):  
Atmospheric Pressure ◽  
Numerical Study ◽  
Okinawa Trough ◽  
Grid Point ◽  
Pressure Profile ◽  
Pressure Variation ◽  
Long Waves ◽  
Pressure Waves ◽  
Oscillation System ◽  
Long Wave

The generation and propagation of long waves due to atmospheric-pressure variation have been numerically simulated, where the atmospheric-pressure waves are assumed to travel in the eastern direction over East Chine Sea. The wave height of long waves is larger as the moving velocity of the recovery point of water surface pressed by the atmospheric pressure is close to the long-wave celerity. Before attenuation of the harbor oscillation in Urauchi Bay, Kamikoshiki Island, the incidence of long waves can continue because of the oscillation system generated between the main island of Kyushu and Okinawa Trough. The pressure profiles of atmospheric-pressure waves supposed to have concerned the large harbor oscillation in Urauchi Bay from 2009 to 2010 are classified into four patterns based on the Grid Point Value pressure data. The incident long waves causing the largest harbor oscillation in Urauchi Bay on Feb. 25, 2009 has been simulated with the estimated pressure-profile pattern, such that the largest harbor oscillation in Urauchi Bay should occur due to the atmospheric-pressure waves.

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.

Random Vibrations of Constructions and their Damping

2009 ◽  
Vol 147-149 ◽  
pp. 345-349
Author(s):  
Danielius Gužas ◽  
A. Čiučelis
Keyword(s):  
Statistical Theory ◽  
Closed Form ◽  
Statistical Characteristic ◽  
Degrees Of Freedom ◽  
Viscous Friction ◽  
Spectral Approach ◽  
Mechanical Vibrations ◽  
Vibratory System ◽  
Long Wave ◽  
Wave Size

In the article, the equation of the equivalent movement of the oscillator with viscous friction is provided. The statistical specifications and the spectral approach for the density of intensity of the established vibrations are provided. Non-stationary vibrations in the closed form are investigated. The statistical characteristic for intensity of vibrations is obtained. The work presents a method of investigation of vibration processes of random mechanical vibrations in the equipment and apparatus. The vibratory system of a sufficiently small (as compared to vibrations of a long wave) size is described; the models with the limited number of degrees of freedom are applied. The statistical theory for discussing of vibrations at constructional damping is applied.

Continental shelf waves and their influence on the circulation around the Great Barrier Reef

1983 ◽  
Vol 34 (1) ◽  
pp. 23 ◽  
Author(s):  
E Wolanski ◽  
AF Bennett
Keyword(s):  
Continental Shelf ◽  
Great Barrier Reef ◽  
Sea Level ◽  
Atmospheric Pressure ◽  
Low Frequency ◽  
Internal Tides ◽  
Wind Component ◽  
Barrier Reef ◽  
Longshore Current ◽  
Shelf Waves

Winds and atmospheric pressure, sea level and water currents were measured at several locations over the continental shelf, both east and west of the Great Barrier Reef, between 14.5�s. and 20�S., from June to November 1980. The dominant wind direction changed from westward over the Coral Sea to north- westward (roughly parallel to the shore) over the shelf. A strong non-tidal low-frequency signal in all sea- level and longshore current data was found, highly coherent from site to site and strongly correlated with the longshore wind component over the shelf, though not with the atmospheric pressure. A model of wind- driven barotropic shelf waves is used to explain a number of observations, such as the invariance of temporal fluctuations of longshore current with distance from shore, and the northward longshore propagation of oceanic disturbances at a speed equal to twice that of the first-mode barotropic free shelf wave, a speed one order of magnitude smaller than that of the wind system. The low-frequency current fluctuations resulted in large water displacements, up and down the coast. Low-frequency cross-shelf currents were much weaker and less coherent. Two upwelling mechanisms are internal tides and internal Kelvin waves coupled to the barotropic shelf waves.

scholarly journals Upstream Propagating Long-Wave Modes at a Microtidal River Mouth

2020 ◽  
Vol 2 (1) ◽  
pp. 15
Author(s):  
Matteo Postacchini ◽  
Lorenzo Melito ◽  
Alex Sheremet ◽  
Joseph Calantoni ◽  
Giovanna Darvini ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Field Data ◽  
Tide Gauge ◽  
Low Frequency ◽  
River Mouth ◽  
Long Waves ◽  
Tidal Forcing ◽  
Long Wave ◽  
Low Frequency Waves ◽  
Wave Modes

We illustrate recent findings on the upriver propagation of long waves entering the mouth of the Misa River (Senigallia, Italy). Such a microtidal environment has been recently studied to understand river–sea interactions: it has been found that the river forcing dominates over the marine actions in winter, especially during storms. However, upriver wave propagation is not negligible with low-frequency waves propagating upriver for distances of the order of kilometers. With the aim to better understand the behavior of low-frequency waves propagating upriver, the analysis of the present work builds on field data collected by instruments installed close to the mouth and along the final reach of the Misa River: a tide gauge, two hydrometers and an acoustic Doppler sensor. It has been here observed that the tidal forcing (periods of the order of hours/days) is significantly strong at a distance of more than one kilometer from the river mouth, while shorter waves, like seiches (periods of some hours), are less important and are supposed to largely dissipate at the estuary, although their role could be of importance during relatively short events (e.g., floods).

Dynamic Response of a Circular Tunnel Embedded in a Saturated Poroelastic Medium due to a Moving Load

2006 ◽  
Vol 128 (6) ◽  
pp. 750-756 ◽  
Author(s):  
Jian-Fei Lu ◽  
Dong-Sheng Jeng
Keyword(s):  
Porous Medium ◽  
Dynamic Response ◽  
Closed Form ◽  
Pore Pressure ◽  
Fourier Transformation ◽  
Moving Load ◽  
Wave Number ◽  
Circular Tunnel ◽  
Soil Response ◽  
General Solutions

Dynamic response of a circular tunnel embedded in a porous medium and subjected to a moving axisymmetric ring load is investigated in this paper. In this study, two scalar potentials and two vectorial potentials are introduced to represent the displacements for the solid skeleton and the pore fluid. Based on Biot’s theory and applying the Fourier transformation on time variable, a set of frequency domain governing equations for the potentials are obtained. Performing the Fourier transformation on the axial coordinate, closed-form general solutions for the potentials with arbitrary constants are obtained. Using the closed-form general solutions and boundary conditions along the tunnel surface, the arbitrary constants involved in the potentials are calculated. Representations for the displacements, the stresses and the pore pressure are derived in terms of the closed-form potentials. Analytical inversion of the Fourier transformation with respect to frequency and numerical inversion of the Fourier transformation with respect to the axial wave number lead to numerical solutions for the displacements, the stresses and the pore pressure in the porous medium. Numerical results demonstrate the soil response due to a high speed load is quite different from those due to a static load or a lower speed load. These differences become more pronounced when the velocity of moving load approaches the velocities of elastic waves of a porous medium.

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.

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