共查询到20条相似文献，搜索用时 399 毫秒
1.
S. V. Shagalov V. P. Reutov G. V. Rybushkina 《Izvestiya Atmospheric and Oceanic Physics》2009,45(5):629-645
The mechanisms of the large-scale vortex structures formation in zonal jet flows (atmospheric blockings, cyclonic, and anticyclonic
vortices) is investigated. Nonlinear perturbations formed during the onset of barotropic instability of a long-wave mode in
weakly-dissipative and weakly supercritical jet flows with a symmetric velocity profile are considered in the β-plane approximation.
This analysis is performed within the framework of the asymptotic theory based on the concept of a nonlinear critical layer.
The equations describing the interaction of a wave with vorticity perturbations in a critical layer are derived. The regimes
of a quasi-stationary and nonstationary nonlinear critical layer are considered separately. Combined equations of evolution
covering the principle regimes of instability development are proposed. The existence of autowave-type structures characterized
by a balance between the energy receipt to the wave and its dissipation are obtained within the framework of a numerical simulation.
The dependence of the parameters of generated autowave structures on the shape of the zonal jet profile and the flow supercriticality
level is studied. 相似文献
2.
S. V. Shagalov V. P. Reutov G. V. Rybushkina 《Izvestiya Atmospheric and Oceanic Physics》2010,46(1):95-108
The generation of narrow-band Rossby wave packets and the modulated vortex chains induced by them in a weakly-dissipative
zonal flow on the beta-plane with a velocity profile in the form of a shear layer is studied. The analysis is performed within
the framework of the asymptotic approach based on the distinguishing a thin critical layer inside of which the vortex chains
are formed. The evolution equations, describing the simultaneous development of a wave packet envelope and vorticity perturbations
in a nonlinear critical layer, are derived for a weakly supercritical flow. A transition to the complex dynamics of a wave
packet (low-mode turbulence) is studied within the framework of a numerical solution of the derived equations and its mechanism
is revealed. The onset of chaotic advection and anomalous diffusion of passive scalar in the critical layer is considered,
and the exponent of the diffusion law is calculated. 相似文献
3.
Alternating zonal flows in an idealized wind-driven double-gyre ocean circulation have been investigated using a two-layer
shallow-water eddy-permitting numerical model. While the alternating zonal flows are found almost everywhere in the time-mean
zonal velocity field, their meridional scales differ from region to region. In the subpolar western boundary region, where
the energetic eddy activity induces quasi two-dimensional turbulence, the alternating zonal flows are generated by the inverse
energy cascade and its arrest by Rossby waves, and the meridional scale of the flows corresponds well to the Rhines scale.
In the eastern part of the basin, where barotropic basin modes are dominant, the zonal structure is formed through the nonlinear
effect of the basin modes and is wider than the Rhines scale. Both effects are likely to form zonal structure between the
two regions. These results show that Rossby basin modes become an important factor in the formation of alternating zonal flows
in a closed basin in addition to the arrest of the inverse energy cascade by Rossby waves. The wind-driven general circulation
associated with eddy activities plays an essential role in determining which mechanism of the alternating zonal flows is possible
in each region. 相似文献
4.
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
5.
The equations of dynamics of eddy—wave disturbances of two-dimensional stratified flows in an ideal incompressible fluid that are written in a Hamiltonian form are used to study the resonant interaction of waves of discrete and continuous spectra. A gravity—shear wave generated at a jump of the density and vorticity of the undisturbed flow and a wave generated at a weak vorticity jump, which is similar to a wave of a continuous spectrum, participate in the interaction. The equations are written in terms of normal variables to obtain the system of evolution equations for the amplitudes of the interacting waves. The stability condition for eddy—wave disturbances is derived within the framework of the linear theory. It is shown that a cubic nonlinearity may lead to the stabilization of unstable disturbances if the coefficient of the nonlinear term is positive. 相似文献
6.
Satoshi Sakai 《Progress in Oceanography》1986,17(3-4)
Laboratory experiments with a rotating tank confirm the bifurcation character of a barotropic flow driven by an inflow and an outflow described by Sakai (1986). The model, a circular basin with a topographic β-effect, simulates a mid-latitude oceanic feature. At a low Rossby number, stationary Rossby waves are observed which are symmetrical with a line connecting the inlet and the outlet. As the Rossby number increases, a bifurcation occurs and two kinds of vortex flows are observed. In the vortex, potential vorticity is almost uniform. In addition to the two vortex flows, a jet-like inertial flow can also be observed. In general, thre results of these experiments agree well with those of a low-order model and a numerical model. 相似文献
7.
左中道 《海洋学报(英文版)》1986,5(2):195-202
The distribution of wind speed in the easterly in the tropics is not uniform. In the part with large curvature, such as lines of trough and ridge, the wind speed is small, while in the part with small curvature, the wind speed is large. In this paper, these phenomena are expounded with gradient wind equation.Considering the distribution of wind speed, we find the wave speed formula from linearized vorticity and divergence equation. The wave speed is equal to the sum of the Rossby wave speed and a harmonic function for x and t. Its period is about 3.5 days. And it is proved that the disturbance is barotropic instability. The results are caused by interaction between meriodional and zonal disturbances. 相似文献
8.
M.A.C. Teixeira 《Ocean Modelling》2011,36(1-2):149-162
The structure of turbulence in the ocean surface layer is investigated using a simplified semi-analytical model based on rapid-distortion theory. In this model, which is linear with respect to the turbulence, the flow comprises a mean Eulerian shear current, the Stokes drift of an irrotational surface wave, which accounts for the irreversible effect of the waves on the turbulence, and the turbulence itself, whose time evolution is calculated. By analysing the equations of motion used in the model, which are linearised versions of the Craik–Leibovich equations containing a ‘vortex force’, it is found that a flow including mean shear and a Stokes drift is formally equivalent to a flow including mean shear and rotation. In particular, Craik and Leibovich’s condition for the linear instability of the first kind of flow is equivalent to Bradshaw’s condition for the linear instability of the second. However, the present study goes beyond linear stability analyses by considering flow disturbances of finite amplitude, which allows calculating turbulence statistics and addressing cases where the linear stability is neutral. Results from the model show that the turbulence displays a structure with a continuous variation of the anisotropy and elongation, ranging from streaky structures, for distortion by shear only, to streamwise vortices resembling Langmuir circulations, for distortion by Stokes drift only. The TKE grows faster for distortion by a shear and a Stokes drift gradient with the same sign (a situation relevant to wind waves), but the turbulence is more isotropic in that case (which is linearly unstable to Langmuir circulations). 相似文献
9.
Gnevyshev V. G. Frolova A. V. Kubryakov A. A. Sobko Yu. V. Belonenko T. V. 《Izvestiya Atmospheric and Oceanic Physics》2019,55(5):412-422
Izvestiya, Atmospheric and Oceanic Physics - Abstract—The article focuses on the interaction of Rossby waves in the ocean with zonal jet flows. A new approach is proposed to show that... 相似文献
10.
Methods of studying the dynamics of wave disturbances in st;ratified shear flows of an ideal incompressible fluid are considered. The equations governing the motions of interest represent Hamilton equations and are derived by writing the velocity field in terms of Clebsch potentials. Equations written in terms of semi-Lagrangian variables are integrodifferential equations, which make it possible to consider both continuous and discontinuous solutions, as well as the cases where the parameters of the undisturbed medium are step functions. Two dynamic systems are presented. The first, canonical system of equations is most suitable for describing gravity waves in a shear flow in the case where the undisturbed medium is characterized by sharp gradients of density and flow velocity. The simplest model in which disturbances obey this system of equations is the well-known Kelvin-Helmholtz model. The second dynamic system describes, in particular, gravity-shear waves and, in the case of a homogeneous medium, shear waves in a two-dimensional flow. This system is most suitable for studying the dynamics of disturbances in models with sharp gradients of vorticity. On the basis of the approach developed in this study, the problem of the dynamics of disturbances in a flow with a continuous distribution of vorticity in a finite-thickness layer is solved. If the thickness of this layer is small compared to the characteristic wavelength and the gradient of the undisturbed vorticity in this layer is large, the solution has the form of a mode whose frequency is close to the frequency of the shear wave on a vorticity jump that would be obtained by letting the layer’s thickness approach zero. The results obtained allow, in particular, the estimation of the range of validity of finite-layer approximations for models with smooth profiles of flow and density. In addition, these results can be interpreted as the basis for the development of nonlinear aspects of the theory of hydrodynamic stability. 相似文献
11.
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
12.
Ponomarev V. M. Khapaev A. A. Yakushkin I. G. 《Izvestiya Atmospheric and Oceanic Physics》2008,44(1):45-52
An approximate theory is constructed to describe quasi-two-dimensional viscous incompressible flows. This theory takes into account a weak circulation in the vertical plane and the related divergence of the two-dimensional velocity field. The role of the nonlinear terms that are due to the interaction between the vortex and potential components of velocity and the possibility of taking into account the corresponding effects in the context of the concept of bottom friction are analyzed. It is shown that the nonlinear character of friction is a consequence of the three-dimensional character of flow, which results in the effective interaction of vortices with vertical and horizontal axes. An approximation of the effect of this interaction in quasi-two-dimensional equations is obtained with the use of the coefficient of nonlinear friction. The results based on this approximation are compared to the data of laboratory experiments on the excitation of a spatially periodic fluid flow. 相似文献
13.
The results of experimental studies of the interaction between the horseshoe vortices formed in nonuniform water flows and a sand surface are presented. The central part of the initial cylindrical vortex ascends, driven by the Kutta—Joukowski force. The vortex tails submerged into sand approach each other, grabbing the sand by their ends. Sharp bends are formed at the axes of the vortex tails. If the bends occlude, a ring vortex is formed above the bends. The ring approaches the surface at an angle of 40° and moves along the flow: the angle decreases, and the radius of the ring increases. When the whole vortex reaches the water surface, it breaks, loses the entrapped sand, and forms a ridge on the bottom. 相似文献
14.
Risers/pipes conveying fluid are a typical kind of slender structures commonly used in marine engineering. It is of great academic significance and application value for us to evaluate and understand the vibration characteristics and nonlinear responses of these risers under the combined action of internal and external fluid flows. In this paper, the nonplanar vibrations and multi-modal responses of pinned-pinned risers in shear cross flow are numerically studied. With this objective in mind, the van der Pol wake oscillators are used to simulate the dynamical behavior of the vortex shedding in the wake. Two nonlinear equations of motion of the riser are proposed to govern the lateral responses of the riser structure. The nonplanar nonlinear equations for the riser and wake are then discretized by employing Galerkin's method and solved by using a fourth-order Runge–Kutta integration algorithm. Theoretical results show that the coupled frequencies for cross-flow (CF) and in-line (IL) motions and the corresponding coupled damping ratio could be influenced by the external and/or internal fluid velocities. Based on extensive calculations, the dynamical behavior of the riser with various internal and external flow velocities are presented in the form of bifurcation diagrams, time traces, phase portraits, oscillation trajectories and response spectrum curves. It is shown that some interesting dynamical phenomena, such as ‘lock-in’ state, ‘figure-of-eight’ trajectory and quasi-periodic oscillation, could occur in such a fluid-structure interaction system. Our results also demonstrate that the shear parameter can significantly affect the dynamic responses of the riser. When the shear parameter of the cross flow is large, multi-modal quasi-periodic responses of the riser can be excited, showing some new features undetected in the system of fluid-conveying risers in uniform cross flow. 相似文献
15.
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
16.
A. S. Ginevsky T. V. Pogrebnaya S. D. Shipilov 《Izvestiya Atmospheric and Oceanic Physics》2006,42(5):627-631
A method is suggested for simulating axisymmetric laminar or turbulent flows formed during the motion of a vortex-ring bunch of given geometry and circulation toward a plane screen. Earlier, similar problems were simulated with the numerical solution of the Navier-Stokes equations for laminar flows. Turbulent flows have remained unconsidered until now. When a vortex ring approaches the screen, the secondary nonstationary flow is induced near the screen’s surface and this secondary flow causes the formation of the radial boundary layer (provided that air viscosity is taken into account). First, the medium spreads out from the critical point at the screen’s center with the negative pressure gradient along the radial coordinate and then detaches in the region of the positive pressure gradient. This radial wall flow and the corresponding boundary layer are considered in the quasi-stationary approximation. When the boundary layer detaches at successive instances, the flow is replenished with the radially moving secondary vortex rings whose circulations have the sign opposite to that of the circulation of the primary vortex ring. It is the interaction of the primary and secondary vortices that governs process dynamics, which differs substantially from that in the case when the formation of secondary vortices is disregarded. The suggested method is based on the method of discrete vortices (a perfect liquid) and the boundary-layer (laminar or turbulent) theory. During the development of the flow under investigation, the nonstationary ascending flow in the direction perpendicular to the screen’s plane is formed and then this flow decays and dissipates. Simulations for large Reynolds numbers corresponding to the formation of the turbulent boundary layer show that the velocity of ascending vortices in the plane of the initial vortex bunch is less than one-tenth of the initial velocity of the descending vortex ring. The boundary layer is introduced into calculations with the sole goal of determining the parameters of the secondary vortex rings formed during boundary-layer detachments. The interaction of the primary and secondary vortices is then considered within the framework of a perfect medium. Simulations for large Reynolds numbers corresponding to the formation of the turbulent boundary layer on the screen were correlated with the available data obtained in laboratory experiments for small Reynolds numbers. Qualitative agreement between the simulations and experiments is fairly satisfactory. The simulation for one combination of the circulation and vortex-ring geometry takes at most 10–15 min with the use of an average PC. 相似文献
17.
利用正压涡度方程，研究了缓变风场驱动下水平尺度1000km平底方形海盆中海洋环流的响应。结果表明，缓变风场驱动下海洋环流的响应是多涡型的，线性情形下多涡结构表现为共振受迫Rossby波；非线性情形下受迫Rossby波被扭曲，多涡结构是由受迫Rossby波和次海盆尺度的惯性再循环共同构成。无论是稳定风场还是缓变风场，非线性作用越强，环流越趋于不稳定；非线性作用强且水平耗散作用弱时，非线性不稳定过程可能完全掩盖了变化的风旋度向海盆涡度输人的影响，此时风的变化对环流型式不再重要。 相似文献
18.
Toshio Yamagata 《Journal of Oceanography》1976,32(4):155-161
The flow induced by the two-dimensional line vortex moving in a rotating fluid is discussed. The governing vorticity equation is linearized adopting the Oseen approximation.First, the problem is considered on a constantf-plane. The solution shows that the Stewartson E1/4 layer is transformed into the Oseen wake as the role of the advection becomes important.Second, the problem is considered on a-plane. When the line vortex moves westward, the solution shows a pattern of Rossby lee waves decaying downstream of the vortex and alternating flows far upstream. When the line vortex moves eastward, the inviscid solution shows definite alternating jets downstream. In a viscous case, however, the jets become less definite and identical with the above mentioned alternating flows in the far field. Far upstream, there are no disturbances because of the special propagation characteristics of Rossby waves. 相似文献
19.
Zonally propagating wave solutions of the linearized shallow water equations (LSWE) in a zonal channel on the rotating spherical earth are constructed from numerical solutions of eigenvalue equations that yield the meridional variation of the waves' amplitudes and the phase speeds of these waves. An approximate Schrödinger equation, whose potential depends on one parameter only, is derived, and this equation yields analytic expressions for the dispersion relations and for the meridional structure of the waves' amplitudes in two asymptotic cases. These analytic solutions validate the accuracy of the numerical solutions of the exact eigenvalue equation. Our results show the existence of Kelvin, Poincaré and Rossby waves that are harmonic for large radius of deformation. For small radius of deformation, the latter two waves vary as Hermite functions. In addition, our results show that the mixed mode of the planar theory (a meridional wavenumber zero mode that behaves as a Rossby wave for large zonal wavenumbers and as a Poincaré wave for small ones) does not exist on a sphere; instead, the first Rossby mode and the first westward propagating Poincaré mode are separated by the anti-Kelvin mode for all values of the zonal wavenumber. 相似文献
20.
In this study, we investigate modulational instability in the presence of wind flow in a situation where sea states crossed over water with a finite depth. It is assumed that the wind flows in a specific direction to produce angles with two directions of propagation by two wave systems with the same carrier wave number and same frequency. The evolution equations considered in this study represent a balance among the effects of wind forcing, dispersion, and nonlinearity at the lowest order. These evolution equations are used to study the stability of the uniform wave solution in crossing seas. We show that in the presence of wind flow, the uniform waves grow super-exponentially. We also demonstrate that the region of asymptotic instability in the perturbed wave number plane is larger than that in the absence of wind flow. 相似文献