共查询到20条相似文献,搜索用时 15 毫秒
1.
This paper describes experiments on interfacial phenomena in a stratified shear flow having a sharp velocity shear at a density
interface. The interface was visualized in vertical cross-section using dye, and the flow pattern was traced using aluminum
powder. Two kinds of internal waves with different phase velocities and wave profiles were observed. They are here named p(positive)-waves
and n(negative)-waves, respectively. By means of a two-dimensional visualization technique, the following facts have been
confirmed regarding these waves. (1) The two kinds of waves propagate in the opposite direction relative to a system moving
with the mean velocity at the interface, and their dispersion relations approximately agree with the two solutions of interfacial
waves in a two-layer system of a linear basic shear flow. (2) The p-wave has sharp crests and flat troughs, and the n-wave
has the reverse of this. This difference in wave profile is due to the finite amplitude effect. (3) Phase velocity of each
wave lies within the range of the mean velocity profile, so that a critical layer exists and each wave has a “cat's eye” flow
pattern in the vicinity of the critical layer, when observed in a system moving with the phase velocity. Consequently, these
two waves are symmetrical with respect to the interface. The mechanisms of generation of these waves, and the entrainment
process are discussed. It is inferred that when the “cat's eye” flow pattern is distorted and a stagnation point approaches
the interface, entrainment in the form of a stretched wisp from the lower to the upper layer occurs for the p-wave, and from
the upper to the lower layer for the n-wave. 相似文献
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Asymptotic representations of solutions describing the far fields of internal gravity waves in a stratified medium of varying depth are constructed. The effect of space-frequency cutoff of the wave field for a real oceanic shelf is revealed. Depending on frequency characteristics of the wave field and bottom topography, far fields of internal waves either are located in a certain confined space domain (trapped waves) or propagate in the absence of turning points over sufficiently large distances when compared with the sea depth (progressive waves). The space domain where the progressive waves penetrate is fully determined by the presence of turning points whose locations depend on the medium stratification and inhomogeneities of bottom topography. 相似文献
4.
An experimental study of stratified mixing caused by internal solitary waves in a two-layered fluid system over variable seabed topography 总被引:4,自引:0,他引:4
Stratified mixing is observed in a wave flume on an internal solitary wave (ISW) of depression or elevation type propagating over a submarine ridge. The submarine ridges, which comprise the seabed topography, are either semicircular or triangular. Tests are performed in a series of combinations of submarine ridges with different heights and ISW in different amplitudes within a two-layer fluid system. When the thickness of the top layer is less than that of the lower layer (i.e., H1<H2), a depression-type ISW may produce a strong hydraulic jump with downwards motion and continuous eddy diffusion. During diffusion, the leading profile of the ISW transforms a wrapped vortex on the front face of the ridge, and a vortex separation at the apex of the ridge. Meanwhile, an elevation-type ISW causes a vortex in the lee of a submarine ridge, which resembles a surface solitary wave in terms of wave transmission process. The degree of wave-obstacle interaction is determined by energy loss, which is induced by submarine ridge blockage. The experiment results suggest that degree of blocking can be applied to classify various degrees of ISW-obstacle encounter in the stratified two-layer fluid system. 相似文献
5.
The plane problem on the generation of linear internal waves by a moving area of time-harmonic surface pressures in a continuously-stratified ocean of constant depth is considered. An analytical relation has been derived for forced internal waves off the site of their generation in the form of an internal wave field superposition corresponding to individual vertical modes. The possible wave regimes are determined. For the Brunt-Väisälä frequency distribution in the North Atlantic, the generation conditions and amplitudes of diverse radiated waves are numerically determined.Translated by Vladimir A. Puchkin. 相似文献
6.
S. M. Khartiev 《Physical Oceanography》1990,1(6):507-512
A stationary parallel current in a continuously stratified incompressible fluid of finite depth is considered. The instability of internal waves is studied with the assumption that the current has only a vertical velocity shear.Translated by Vladimir A. Puchkin. 相似文献
7.
《Estuarine, Coastal and Shelf Science》1986,22(2):199-214
A period of intense mixing, causing an increase in the salinity of the surface layer from 2‰ to 7‰, occurs during the ebb tide in the upper reaches of the Tees estuary. This follows the passage of internal waves of 1–2 min period. Assuming an upstream direction of propagation, the measurements indicate that the internal waves would have been released on the previous ebb tide. The waves, which would then advect with the ensuing flood, could break and cause the mixing period. However, the waves may alternatively travel downstream, and other mechanisms may be responsible for the mixing. It may be, for instance, that the mixing was generated at one of two bridges 2–3 km upstream from the observation station, and then advected downstream on the ebbing tide. Further studies are needed to clarify the situation. 相似文献
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S. V. Korsunsky 《Physical Oceanography》1995,6(5):331-341
This paper focuses on the study of linear and non-linear surface and internal waves, in a complete setting, using a two-layer model of a stratified fluid. The respective Korteweg-de Vries evolutionary equations have been obtained, analysed, and compared with the rigid lid model data. Boussinesq-type equations have been derived for the interacting modes pertaining to one type and to different types. It is shown that in addition to the known mechanisms of interaction between internal and surface waves, interaction between long non-linear baroclinic modes and barotropic modes, propagating in the same direction, is likely in such a system.Translated by Vladimir A. Puchkin. 相似文献
10.
分层流体中内孤立波在潜浮式竖直薄板上透射和反射 总被引:2,自引:0,他引:2
采用边缘层理论研究了两层流体系统中内孤立波在潜浮式竖直薄板上的透射和反射问题,提出了非线性演化方程的“初值”条件,分析了内孤立波与薄板非线性相互作用的效应。研究表明:流体层的密度比以及薄板伸入上下层的深度对于反射和透射波结构具有显著的影响,薄板伸入下层越深、密度差越小,则薄板阻碍孤立波透射的效率越高;透射波通常演化为单峰孤立波和迅速衰减的尾波,反射波演化为缓慢衰减的尾波列;对于具有小密度差的跃层结构,内孤立波在潜浮式竖直薄板上的透射及其演化近乎是无障碍的。 相似文献
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Toshio Yamagata 《Journal of Oceanography》1983,38(6):339-345
Long nonlinear topographic waves in a continuously stratified ocean with a linear bottom slope are investigated. It is shown that odd cross-channel modes are governed by the Korteweg-de Vries (K-dV) equation. The solitary waves are those of a low pressure type. The long waves are shown to be modulationally stable because of the nonlinear effect due to irrotational motion. All these results are missed if the conventional quasi-geostrophic approximation is adopted. 相似文献
15.
Ship waves generated in an exponentially stratified fluid when an axisymmetrical area of pressure of constant intensity moves over a floating ice cover are studied in a linear statement. The influence of ice rigidity on the distribution of amplitudes of the internal wave disturbances along the constant phase lines is analysed.Translated by Mikhail M. Trufanov. 相似文献
16.
K. A. Gorshkov I. A. Soustova D. A. Sergeev 《Izvestiya Atmospheric and Oceanic Physics》2007,43(6):785-793
On the basis of the perturbation theory developed previously by the authors for localized hydrodynamic vortices, the influence of a specified jet flow and of the structure of individual vortices on the stability of the Karman street is investigated. It is shown that, for a street of vortices with a power law of decrease in the azimuthal velocity, the jet flow suppresses instability only with respect to perturbations with wavelengths from a certain range determined by the parameters of the flow. At the same time, for streets formed from vortices with a Gaussian profile of the azimuthal velocity, even in the absence of a specified flow, there is a certain region of the street’s parameters in which the street is stable against perturbations of all scales. Thus, for the purposes of modeling quasi-two-dimensional flows in a stratified fluid by a sequence of localized vortices, which is discussed in this study, vortices with a Gaussian profile of the azimuthal velocity turn out to be preferable. The results of this study are consistent with numerous experiments on the structure of a quasi-two-dimensional wake behind a body in a stratified fluid at large Reynolds and Froude numbers. 相似文献
17.
Within the framework of the linear theory of long waves taking into account the action of the Coriolis force, we solve the
problem of generation of internal waves by a barotropic tide impinging on a bottom irregularity of the sea-ridge type. The
cross section of the ridge is assumed to be rectangular and the stratification of the ocean is regarded as stepwise with two
thermoclines (three-layer model). We study the dependences of the characteristics of generated waves on the parameters of
stratification and the period of the impinging barotropic tide.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献
18.
《Estuarine, Coastal and Shelf Science》1987,24(1):15-33
The results of an echo-sounding survey of the Tees estuary are presented. Intense mixing periods, characterized by a surface layer of increasing salinity and thickness, were observed on the ebb tide and were preceded by periods of internal wave activity. Previously, it had been conjectured that similar mixing periods were caused by the breaking of upstream-travelling internal waves. The present survey, however, reveals that the observed waves were travelling down-stream and indicates that the mixing was principally due to a series of bridges. The times of the onset of mixed water at various stations in the estuary were consistent with the production of mixing from about the time of high water, with subsequent advection downstream. The mixing produced in this way, and by similar structures in other estuaries, clearly needs to be quantified. 相似文献
19.
The evolution and breaking of a propagating internal wave are directly numerically simulated using a pseudo-spectral method. The mechanism of PSI ( parametric subharmonic instability) involved in the evolution is testified clearly. It dominates gradually in nonlinear resonant interactions. As a consequence, the energy cascades to a second plant wave packet which has lower frequencies and higher wavenumbers than that of the primary wave. With the growth of this wave packet, wave breaking occurs and causes strongly nonlinear regime, i.e. stratified turbulence. The strong mixing and intermittent of the turbulence can be learned from the evolution of the total energy and kurtosis of vorticity vs. time. Some statistic properties of the stratified turbulence are also analyzed, including the spectra of KE (kinetic energy) and PE (potential energy). The results show that the PE spectra display a wavenumber range scaling as 0. 2 N^4ky^-3 (N is the Brunt - Vaisala frequency, k, is the vertical wavenumber), which is called buoyancy sub-range. However, the KE spectra cannot satisfy the negative cubic law of vertical wavenumber, which have a much larger downtrend than that of the PE spectra, for the potential energy is transferred more efficiently toward small scales than the kinetic energy. The Cox number of diapycnal diffusivity is also calculated, and it shows a good consistency with the observations and deductions in the ocean interior, during the stage of the stratified turbulence maintaining a fairly active level. 相似文献
20.
Corrections to the vertical distribution of mean density and current velocity non-oscillating on the wave's time scale have been derived in the approximation, quadratic by the wave's steepness. It has been shown that the horizontal volume transport of both the induced current and the Stokesian drift, integrated over depth, equates zero in the Boussinesq approximation.Translated by V. Puchkin. 相似文献