共查询到20条相似文献，搜索用时 78 毫秒
1.
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
2.
M. V. Kalashnik 《Izvestiya Atmospheric and Oceanic Physics》2011,47(4):439-444
Cyclone-anticyclone asymmetry in a rotating fluid results in vortices with cyclonic rotation being attenuated more rapidly than vortices with anticyclonic rotation due to the Ekman bottom friction. To explain this effect, some authors invoked rather complex integral (averaged along the vertical) models with the parametrization of nonlinear friction. A simple analytical model, free of the procedure of formal averaging and based on a separate consideration of the equations for external flow in the nonviscous region and internal flow in the boundary layer, is investigated in this work. The corresponding equations are written in the so-called geostrophic momentum approximation, which makes it possible to take into account the nonlinear advective mass transport in the boundary layer at small Rossby numbers. The nonlinear equation of the hyperbolic type for the tangential velocity, which describes the process of attenuation of an axisymmetric vortex, is obtained from the condition of total mass conservation. Based on the solutions to this equation, it was shown that distinctions in the character of vortex attenuation are caused by deviations from the geostrophic regime in the nonviscous region. It was established that the concentration (compression) of anticyclonic vortices and the extension of cyclonic ones take place in the process of attenuation. 相似文献
3.
Jean-Michel Baey Dominique Renouard Gabriel Chabert D'hieres 《Deep Sea Research Part I: Oceanographic Research Papers》1995,42(11-12)
Experiments were run on a 14 m diameter rotating platform to study the stability conditions for a constant volume flow rate current of intermediate water. The flow was introduced in a two-layer system initially at rest in solid body rotation, along the sidewall of the tank, and allowed freely to evolve. A sink collected the intermediate water and thus ensured that the free surface height was constant. Thus the upstream conditions were the rotation rate, the volume flow rate, the density and the initial width of the intermediate current, which was in geostrophic equilibrium when it left the source; i.e. its thickness along the wall at the source was fixed by this condition. The relevant parameters appear to be the Ekman and the Burger numbers. The data collected from the experiments are very consistent, and it appears that there were five typical flow regimes: (1) a stable current along the whole basin; (2) a series of cyclonic vortices attached to the outer edge of the current, with an upstream stable current; (3) a large cyclonic vortex attached to an anticyclonic instability; (4) dipoles shed from the current into the interior fluid; and (5) generation of lenses of intermediate water, similar to meddies. This last result shows that no topographical effect is required to generate such long-lived lenses, which then drift slowly upstream as the dipoles do. 相似文献
4.
A. E. Gledzer E. B. Gledzer A. A. Khapaev O. G. Chkhetiani 《Izvestiya Atmospheric and Oceanic Physics》2017,53(6):579-591
This paper presents the results of experiments in a circular stationary and rotating channels with thin layers of conductive fluid for configurations consisting of a large number of permanent magnets and providing the MHD generation of small-scale velocity fields. The alternating radial configurations of magnets were chosen in such a way as to ensure the conservation of a discrete symmetry of their mutual arrangement relative to rotations of the circular channel around a central axis and were formed on the basis of numerical calculations with the shallow-water equations. Both in numerical and laboratory experiments, large-scale nearly circular vortices were obtained as a result of the energy transfer from the system of externally generated small-scale vortices to large-scale velocity fields (inverse cascade) under the influence of the Coriolis force in the rotating case. Single large-scale vortices and wide jet streams appear in subrotation and superrotation modes relative to external rotation, depending on its angular velocity. Rotation in a nearly circular vortex has a differential character with a decrease in the angular velocity of rotation with the radius in most area of the channel. 相似文献
5.
《Coastal Engineering》2001,44(1):13-36
Interactions between a solitary wave and a submerged rectangular obstacle are investigated both experimentally and numerically. The Particle Image Velocimetry (PIV) technique is used to measure the velocity field in the vicinity of the obstacle. The generation and evolution of vortices due to flow separation at the corners of the obstacle are recorded and analyzed. It is found that although the size of the vortex at the weatherside of the obstacle is smaller than that at the leeside, the turbulence intensity is, however, stronger. A numerical model, based on the Reynolds Averaged Navier–Stokes (RANS) equations with a k–ϵ turbulence model, is first verified with the measurements. Overall, the agreement between the numerical results and laboratory velocity measurements is good. Using the RANS model, a series of additional numerical experiments with different wave heights and different heights of the rectangular obstacle are then performed to test the importance of the energy dissipation due to the generation of vortices. The corresponding wave transmission coefficient, the wave reflection coefficient and the energy dissipation coefficient are calculated and compared with solutions based on the potential flow theory. As the height of the obstacle increases to D/h=0.7, the energy dissipation inside the vortices can reach nearly 15% of the incoming wave energy. 相似文献
6.
Seok Lee Heung-Jae Lie Cheol-Ho Cho Sok Kuh Kang William J. Teague Kyung-Il Chang Kyu-Min Song Kyung-Hee Oh 《Ocean Science Journal》2011,46(2):73-84
The vertical structure of the M2 tidal current in the Yellow Sea is analyzed from data acquired using an acoustic Doppler current profiler. The observed vertical
profiles of the M2 tidal current are decomposed into two rotating components of counter-clockwise and clockwise, and restructured using a simple
one-point model with a constant vertical eddy viscosity. The analyzed results show that the internal fictional effect dominates
the vertical structure of the tidal current in the bottom boundary layer. In the Yellow Sea, the effect of the bottom friction
reduces the current speed by about 20–40% and induces the bottom phase advance by about 15–50 minutes. In the shallower coastal
regions, the effects of bottom topography are more prominent on the vertical structure of tidal currents. The vertical profile
of the tidal current in summer, when the water column is strongly stratified, is disturbed near the pycnocline layer. The
stratification significantly influences the vertical shear and distinct seasonal variation of the tidal current. 相似文献
7.
Norihisa Imasato Shinzou Fujio Qian Zhang Toshiyuki Awaji Kazunori Akitomo 《Journal of Oceanography》1994,50(2):119-139
We have investigated the three-dimensional Lagrangian motion of water particles related with tidal exchange between two basins with a constant depth connected through a narrow strait and the effects of density stratification on the exchange processes by tracking a number of the labeled particles. Tide-induced transient eddies (TITEs), which are similar to those in two-dimensional basin, are generated behind the headlands. Upwelling appears around the center of the eddy and sinking around the boundary. When the basins are filled with homogeneous water, a pair of vortices are produced in the vertical cross section of the strait due to bottom stress, with upwellings along the side walls of the strait and sinking in the center of the strait. These circulations form the horizontally convergent field in the cross-strait direction in the upper layers while the horizontal divergence takes place in the bottom layer. These vertical water-motions produce the three-dimensional distribution of velocity shear and phase lag of the tidal current around the strait, and the Lagrangian drifts of water particles become large. As a result, water exchange through the strait is greatly enhanced: The water exchange rate reaches 94.1% which is much larger than that obtained in the vertically integrated two-dimensional model. When the basins are stratified, the stable stratification suppresses the vertical motion so that a pair of vertical vortices are confined in the lower layers. This leads to a decrease in the exchange rate, down to 88.6%. Our numerical results show that the three-dimensional structure of tidal currents should be taken into account in tidal exchange through a narrow strait. 相似文献
8.
Analysis of suspended matter collected in the lower St. Lawrence estuary indicated short-term variabilities in both the structure and dynamics of the particles. Variations with time and depth were ascribed to fluctuation of particle concentrations within the size ranges of the major peaks of concentration. A deterministic pattern was found for the temporal succession of the spectra when total particle concentrations were high. This was due to combinations of three factors that act in one of two ways, either (i) high current velocity—spring tide—stratified waters, or (ii) lower current velocity—neap tide—mixed waters. In the first case, the current effect prevailed, while the tide effect was dominant in the second one. A random pattern occurred in the succession of the spectra when lower particle concentrations and patches of smaller dimensions were present in well mixed water bodies. Successions of spectra were not always in phase at different depths within the water column. 相似文献
9.
通过对海洋中长生命反气旋涡在Ｇａｕｓｓ型孤立地形上演变的研究,发现地形对长生命反气旋涡的发展和传播有相当重要的影响。在无地形作用的情况下,仅有反气旋涡能够存在于向西的均匀基流中,这个涡是长生命的,并且在西移过程中有明显的向西倾斜。然而当其上游存在一个孤立地形时,可以发现这个涡有一个向东的倾斜,它的强度将增强且向西的移速会增加,其规迹象陀螺的运动。另一方面,当两个强度相同的反气旋涡同时存在时,这两个 相似文献
10.
A. E. Gledzer 《Izvestiya Atmospheric and Oceanic Physics》2014,50(3):292-303
This paper presents the results of numerical calculations using shallow water equations for the currents in the laboratory experiments with a rotating circular channel. An axial symmetric function of mass source is introduced into the equations for the depth of the layer to model experimental sources and sinks of fluid, which induces opposing zonal flows together with the Coriolis force. Different configurations and amplitudes of mass sources lead to the appearance of vortex motions in the channel with different circular motions in the vortices and azimuthal displacements of their centers along the channel. Diagrams of regimes are presented in the parameters of relative angular velocities of the mean zonal flow and vortex transport around the axis of the system rotation. The differences of the theory and real experiments with currents of finite depth in a channel are discussed. 相似文献
11.
A. E. Gledzer E. B. Gledzer A. A. Khapaev Yu. L. Chernous’ko 《Izvestiya Atmospheric and Oceanic Physics》2014,50(2):122-133
Results of experiments are considered for flows generated by different sources-sinks of mass in the rotating annular channel with beta-effect simulation using the inclined bottom. Diagrams of regimes are presented in parameters of the dimensionless angular velocity of the zonal flow averaged over the channel width and the dimensionless angular velocity of transport of vortex perturbations of cyclonic and anticyclonic types. In experiments and the simplest linear theories, most attention is paid to diagram regions with a slow motion of vortices relative to the rotating coordinate system near the parameters for stationary Rossby waves. 相似文献
12.
A three-dimensional numerical model is developed in this study to investigate the problem of wave–current–body interaction. The model solves the spatially averaged Navier–Stokes equations. Turbulence effects are modeled by a subgrid-scale (SGS) model using the concept of large eddy simulation (LES). The model is employed to study the wave–current interaction with a square cylinder that is mounted on the bottom and vertically pierces the free surface. The force analysis demonstrates that the presence of waves can reduce both the strength and frequency of vortex shedding induced by a uniform current due to the nonlinear wave–current interaction. The free surface elevation, strain rates of the mean flow, and eddy viscosity are found to closely correlate with the mechanism of vortex shedding. It is also shown that when the vortex shedding is neglected in the calculation such as by the potential flow approach, one may significantly underestimate the magnitude of in-line force. The energy spectral analysis reveals that there exist initiating, growing, and decaying regions for shedding vortices around the cylinder. In the vortex initiating region, both coherent and turbulent structures are nearly two-dimensional that become three-dimensional in the vortex growing region. The kinetic energy of both coherent and turbulent motions is dissipated in the vortex decaying region, within which the mean flow gradually returns back to two-dimensional. 相似文献
13.
In this article, the authors study the influence of a constant wind on the displacement of a vortex. The well known Ekman current develops in the surface layer and is responsible for a transport perpendicular to the wind: the Ekman drift.An additional process is, however, evidenced, whose importance is as strong as the Ekman drift. There indeed exists a curl of the wind-driven acceleration along isopycnic surfaces when they are spatially variable (they enter and leave the depth where the wind stress acts), which generates potential vorticity anomalies. This diabatic effect is shown to generate potential vorticity anomalies which acts on the propagation of vortical waves and non linear vortices.It is shown that this effect drastically reduces the effect of the Ekman drift for linear waves and surface intensified vortices, while extending its effect to subsurface vortices. It also generates along wind propagation, whose sign depends on the vortex characteristics. 相似文献
14.
Moving-Particle Semi-Implicit Method for Vortex Patterns and Roll Damping of 2D Ship Sections 总被引：2，自引：1，他引：1
A meshless method, Moving-Particle Semi-hnplicit Method （MPS） is presented in this paper to simulate the rolling of different 2D ship sections. Sections S. S. 0.5, S.S. 5.0 and S. S. 7.0 of series 60 with CB = 0.6 are chosen for the simulation. It shows that the result of MPS is very close to results of experiments or mesh-numerical simulations. In the simulation of MPS, vortices are found periodically in bilges of ship sections. In section S. S. 5.0 and section S. S. 7.0, which are close to the middle ship, two little vortices are found at different bilges of the section, in section S. S. 0.5, which is close to the bow, only one big vortex is found at the bottom of the section, these vortices patterns are consistent with the theory of Ikeda. The distribution of shear stress and pressure on the rolling hull of ship section is calculated. When vortices are in bilges of the section, the sign clmnge of pressure can be found, but in section S. S. 0.5, there is no sign change of pressure because only one vortex in the bottom of the section. With shear stress distribution, it can be found the shear stress in bilges is bigger than that at other part of the ship section. As the free surface is considered, the shear stress of both sides near the free surface is close to zero and even sign changed. 相似文献
15.
For the first time, the concepts of the theory of helical vortices have been applied to the Lofoten vortex of the Norwegian Sea. The estimates for azimuthal and vertical velocities have been obtained from the Massachusetts Institute of Technology general circulation model (MITgcm) for 1992–2012. The columnar vortex model with helical vorticity lines and distributions has been adapted to Scully and Rayleigh vortices. It has been shown that the vortex parameters can be determined simply from mass balance equations. The parameters of the helical vortex simulating the structure of the Lofoten vortex have been found and the radial distributions of azimuthal and vertical velocity components have been constructed. The resulting data can be interesting for an analysis of the three-dimensional structure of mesoscale vortices in the ocean. 相似文献
16.
M. S. Permyakov V. I. Semykin N. P. Malikova 《Izvestiya Atmospheric and Oceanic Physics》2018,54(5):423-429
The generalized two-dimensional vortex equation is derived for an incompressible viscous fluid in a rotating system for a vertically averaged flow taking into account the variability of the boundary layer characteristics. The resulting equation contains parameters and their spatial derivatives determined by the second moments of functions describing the vertical profiles of the flow components. Numerical experiments demonstrate the influence of the boundary-layer horizontal inhomogeneity on the evolution of the vorticity field of a pair of atmospheric vortices. 相似文献
17.
18.
Numerical modeling of a semienclosed narrow channel demonstrates the dynamical dependency of an estuarine residual circulation
(ERC) on tidal amplitudes. The ERC is defined by tidally-averaged current field. The tidally-averaged fields show that the
ERC-strength variation is classified into highly stratified, partially stratified and weakly stratified ranges, respectively.
The ERC becomes weaker as the tidal amplitude (and hence vertical mixing) increases in the highly and weakly stratified ranges.
However, the ERC becomes stronger oppositely in the partially stratified range. The nonlinear forces induced by tides significantly
affect the ERC as well as the pressure gradient force due to the freshwater flux and the vertical stress divergence (vertical
eddy viscous force). In particular, the tidal stress and tidally-oscillating component of vertical stress divergence are quite
important in ERC dynamics. The latter causes the enhancement of ERC in proportion to the vertical mixing in the partially
stratified range. 相似文献
19.
G. M. Reznik 《Izvestiya Atmospheric and Oceanic Physics》2010,46(6):784-797
This paper studies the joint influence that rotation and the earth’s sphericity have on the dynamics of localized synoptic
scale vortices within the quasi-geostrophic barotropic model in the beta-plane approximation. Rossby solitons (two-dimensional
vortices exponentially localized in space which propagate without changing their form along the latitude circles) are considered
in the first part of the article. The general properties of such solutions are discussed. The simplest examples are presented,
and a brief review of the main results is given. The second part is dedicated to the theory of nonstationary monopoles. The
physical mechanisms governing the evolution of such vortices are described; different stages of this evolution are determined
for intense vortices. Analytical and numerical results are used to confirm the qualitative explanations. 相似文献
20.
Hidekazu Yasuda 《Journal of Oceanography》2009,65(4):455-476
Time-dependent wind drift currents in a basin with finite depth have been solved analytically in order to understand their
fundamental behavior in coastal waters. The drift currents due to the land/sea breeze, as a typical example of time-dependent
winds, have been examined with attention to the manner of their oscillation in their vertical profiles. The theoretical analysis
indicates that the drift current due to the land/sea breeze might be amplified effectively around the southern part of Japan,
where the oscillating period of the wind is near to the inertial period. The analysis of the physical process of the drift
current reveals the following two important aspects: the Ekman boundary layer in a rotating frame is physically consistent
with the Stokes boundary layer due to oscillating currents in an inertial frame, and so the inertial motion due to the wind
is dispersed to the deeper level by the vertical viscosity in a rotating frame. The harmonic analysis was performed for the
residual data after removal of the four main tidal constituents, M2, S2, K1 and O1, from the raw data observed in Suonada
sound, the Seto Inland Sea. The feature of the analytically solved drift currents corresponded well to the observed picture.
The vertical viscosity in this field has been estimated at 10−3 m2/s by adjusting the harmonically analytical result of the observed data to the vertical profile of the analytically solved
drift current. 相似文献