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1.
Ｏｎｈｙｄｒａｕｌｉｃｆａｌｌｓｏｆｓｉｎｇｌｅ－ｌａｙｅｒｆｌｏｗ￥ＸｕＺｈａｏｔｉｎｇ；ＴｉａｎＪｉｗｅｉ；ＬｏｕＳｈｕｎｌｉａｎｄＳａｍｕｅｌＳｈａｎｐｎＳｈｅｎ（ＲｅｃｅｉｖｅｄＭａｒｃｈ２１，１９９５；ａｃｃｅｐｔｅｄＪｕｌｙ１０，１９９５... 相似文献
2.
根据作者导得的AfKdV方程，理论上确定了先锋孤立子生成问题的理论平均波阻，能量劈分及能量劈分比。本文的能量劈分是确定先锋孤立子生成参数的理论基础。同时，本理论确定了现有理论中的自由未知参数问题，从而使先锋孤立子生成参数得到理论预报。 相似文献
3.
The Dardanelles Strait is a remarkable example of a long, narrow, shallow, and strongly stratified strait with bidirectional exchange that is governed by both baroclinic and barotropic forcing with a wide spectrum of variability. A three-dimensional free surface primitive equation model is applied to study seasonal hydrodynamics variability in this strait. The calculated vertical structure of temperature, salinity, and velocity fields agrees well with available survey data. Seasonal monthly values of the volume exchange at the Aegean and Marmara exits are estimated. It is found that the seasonal exchange dynamics is governed by the turbulent friction and entrainment at the Nara Passage area. The mean annual water transport in the upper layer is increased by 80% after the Nara Passage. About 25% of water entering in the Dardanelles bottom layer reaches the Marmara Sea in winter, and 50% reaches it in summer. The estimate of the Dardanelles hydrodynamics according to hydraulic and viscous–advective–diffusive regime classification shows significant deviation from the two-layer hydraulic asymptotic. However, according to three-layer hydraulic theory, the flow is found to be critical in the Nara Passage area. 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.
A model for a two-layer ocean is applied to consider, in terms of the geometrical optics approximation, the effect of mean
flows propagating within the upper layer upon the dynamics of Rossby waves. The case is theoretically analysed, with the depth
of the ocean's upper layer much smaller than that of the underlying layer. In this case, the flow's impact upon the baroclinic
mode of Rossby waves is ubiquitous, with the exception of synchronicity. Depending on the parameters, four types of wave packets'
behaviour in the vicinity of synchronicity points are singled out, namely, the elimination of the peculiarity, shadowing,
and convective/absolute instability. For the mean flow profile simulating cyclonic and anticyclonic gyres, we have obtained
wave packet trajectories and have studied the wave packet's interaction with the current. Specifically, it has been demonstrated
that, given some modulus of the wave packet, vigorous energy exchange between the wave vector and the flow takes place.
Translated by Vladimir A. Puchkin. 相似文献
6.
M. Zhou 《Estuarine, Coastal and Shelf Science》1998,46(6):811-825
Baroclinic circulation in highly stratified and partially stratified estuaries is characterised by a two-layer flow: a bottom salt- water inflow and a surface brackish-water outflow. Tidal period variation of the thicknesses of a two-layer flow is observed to be associated with mixing, bottom stress and hydraulic characteristics of superposed tidal and gravity currents. Here, both analytical two-layer hydraulic equations with weak friction and a numerical model including a turbulence closure were utilised to understand the mechanism of the layer tendency within a two-layer flow under different barotropic flow conditions. It has been found that in the weak bottom friction case, a gravity current has two critical solutions at the layer thickness equal to 0·5Hand 0·292H. The layer thickness towards a particular critical solution is dependent on the sign of the bottom stress, i.e. when the bottom stress is opposite (favor) to the bottom gravity current, its layer thickness converges to 0·5H(0·292H). In the case of strong bottom stress and mixing opposing the gravity current, the solutions of the gravity current layer thickness at 0·5Hand 0·292Hwill not be valid. Both mixing and vorticity produced by bottom stress erode the halocline, and produce a high velocity core in the mid-depth, which leads to the thickness of a bottom gravity current greater than 0·5H. These internal hydraulic tendency and mixing processes, varying with time-dependent barotropic tidal current forcing, determine the tidal period variation of the gravity current structure. 相似文献
7.
Diapycnal mixing plays an important role in the ocean circulation.Internal waves are a kind of bridge relating the diapycnal mixing to external sources of mechanical energy.Difficulty in obtaining eigen solutions of internal waves over curved topography is a limitation for further theoretical study on the generation problem and scattering process.In this study,a kind of transform method is put forward to derive the eigen solutions of internal waves over subcritical topography in twodimensional and linear framework.The transform converts the curved topography in physical space to flat bottom in transform space while the governing equation of internal waves is still hyperbolic if proper transform function is selected.Thus,one can obtain eigen solutions of internal waves in the transform space.Several examples of transform functions,which convert the linear slope,the convex slope,and the concave slope to flat bottom,and the corresponding eigen solutions are illustrated.A method,using a polynomial to approximate the transform function and least squares method to estimate the undetermined coefficients in the polynomial,is introduced to calculate the approximate expression of the transform function for the given subcritical topography. 相似文献
8.
《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(1):63-78
Internal bores are a common feature of tidally modulated two-layer exchange flows through straits and over sills. Even where the forcing changes smoothly, the flow may adjust with sudden jumps in the position of the interface between the two layers. The resulting flow configuration, with a hydraulically controlled exchange flow (at the sill) coupled with a propagating internal hydraulic jump (known as a bore), is investigated with mathematical models and laboratory experiments. The study concentrates on two-dimensional flow in a rectangular channel with a sill. The parameters considered are the depth of the channel compared to the depth over the sill, the depth of the interface before the passage of the bore and the strength of the net flux through the channel.The theory is based on shallow water equations and hydraulic control theory and includes the effects of a steady net flow through the channel (driven, for example, by the tide). Once the depth of the channel is twice the depth over the sill, further changes in geometry have relatively little effect on the flow. The bore velocity and fluxes are strongly affected by the strength of any net flow. The laboratory experiments model pure exchange flows (with no net flow) and give detailed information about the bores themselves. In many cases an undular bore is produced, with a well-defined wave train on the interface behind the front of the bore. The wavelengths and amplitudes of these internal waves are quantified and a brief comparison with similar internal waves observed in the Strait of Gibraltar is presented. 相似文献
9.
The ridge and swale topography of the Middle Atlantic Bight was originally interpreted as a relict strand plain whose ridges reflect stillstands of the returning Holocene sea. However, close examination indicates that the ridges appear to be instead longitudinal bed forms, responses to a regime of intermittent, south-trending storm currents. Ridges may be initiated on the shore face and detached as the coast retreats to form fields of isolated ridges, or they may be molded into the shelf-transverse sand massifs that mark the retreat paths of littoral-drift depositional centers at estuary mouths and off cuspate forelands. The ridge and swale topography is thus a stable end configuration toward which a variety of near-shore constructional topographies have converged during the Holocene transgression.Morphologic evidence for readjustment of ridge topography to the deepening shelf flow field during the Holocene transgression is discernable. However, the extent to which the offshore topography continues to respond to hydraulic regime is unclear. The role of helical flow structure in the storm flow field remains to be documented. Resolution of these problems will require more detailed information of hydraulic process and substrate response on storm-dominated shelves. 相似文献
10.
The transformation of internal waves over the oceanic shelf of variable depth is studied analytically within a linear theory
of a two-layer flow. It is shown that, at a specific character of depth variation, the internal wave propagates without reflection
from the slope even if it is sufficiently steep. The properties of such progressive waves are studied—their form and the current
structure in the upper and lower layers. The transformation of the wave propagating from the open ocean, where the depth is
assumed to be constant, is considered. It is shown that the wave is transformed at the shelf edge and does not change its
form in the course of time during its further propagation over the shelf. The height and form of the internal wave are calculated
at the interface of the transition of the two-layer flow into the one-layer flow. Applications of the developed analytical
theory to the estimation of internal wave transformation over a real shelf are discussed. 相似文献
11.
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
12.
Results are reported herein of an open channel flow laboratory based study of the development of ripples on a fine silica sand bed, and under non-uniform turbulent subcritical flow conditions. The hydraulic model used included a diverging channel, which resulted in a variation of hydraulic and sediment transport parameters along the channel. Sediment supply limitation occurred during experimentation, impacting bed form development. The overall aim of this study was to improve the understanding and modelling capability of the development of bed forms under limited sediment supply and non-uniform flow conditions. In particular, the applicability of an existing empirical model capable of predicting ripple development was tested for the conditions of this study, using measured ripple dimensions. The ripple height and length results were extracted from detailed bed profile records, obtained using an acoustic Doppler probe traversed longitudinally over the sediment bed, at various experimentation time intervals. It was found that the non-uniform flow conditions affected the development rate of the bed forms, while sediment supply limitation impacted their steady state dimensions. The measured steady state ripple dimensions were lower, on average, than the corresponding equilibrium dimensions predicted using existing empirical equations. Non-uniform flow also caused the simultaneous occurrence of bed forms at different stages of development along the hydraulic model, where 3D and 2D ripples and incipient bed forms were recorded. Such a scenario can occur in estuarine and coastal flows, due to changing hydraulic conditions and/or a limitation of sediment supply. The ripple development model tested was verified for the conditions of this study, with its accuracy being shown to depend on an accurate determination of steady state parameters. 相似文献
13.
Within the framework of the linear theory of long waves, we study internal waves generated by a barotropic tide in a two-layer
ocean of variable depth taking into account the influence of the Coriolis force. Barotropic waves run over an extended unevenness
of the bottom at an arbitrary angle. This unevenness is regarded as a model of the continental slope and shelf. We establish
the dependences of the amplitudes of generated internal waves on the angle of incidence of the barotropic tide, topography
of the bottom, and stratification.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献
14.
Baroclinic topographic waves trapped by a sloping bottom in the case of a real stratification are considered. The dispersion properties of these waves are studied. The characteristic scales and amplitudes of trapped topographic waves observed in the Norwegian Sea are determined. The asymptotic method of multi-scale expansions is used to study nonlinear effects occurring during the propagation of these waves. The wave-induced mean flow is determined in the second order of smallness in the wave amplitude. The evolution equation for the envelope—the nonlinear Schrödinger equation—is derived. Modulation instability of these waves is examined. It is shown that trapped topographic waves are modulationally unstable. 相似文献
15.
Topographically constrained deep-water flows in the Baltic Sea 总被引：2，自引：0，他引：2
Density-driven currents have a significant impact on the deep-water characteristics of the Baltic Sea since they account for the water exchange between the deeper parts of neighbouring basins. The essential quantitative problem is to determine the flow rates in relation to a set of external parameters such as the strait topography, the stratification, and the internal circulation of the upstream basin. Using hydraulic theory it is possible to accomplish this by analysing the dynamical constraints that limit the deep-water flux between adjacent basins. On the basis of these results, the deep-water flows through the Bornholm Channel and the Irbe Strait are compared. 相似文献
16.
- The dynamic buckling of elasto-plastic cylindrical shells under axial fluid-solid impact is investigated theoretically. A simplified liquid- gas- structure model is given to approximately imitate the problem. The basic equation of the structure is derived from a minimum principle in dynamics of elasto-plastic continua at finite deformation, and the flow theory of plasticity is employed. The liquid is incompressible and the gas is compressed adiabatically. A number of numerical results are presented and the characteristics of the buckling behavior under fluid-solid impact are illustrated. 相似文献
17.
Common features of the flow behavior over mountains within the hydraulic jump model are identified based on an analysis of 36 episodes of severe winds in the regions of Novorossiysk, Pevek, and Novaya Zemlya. In all these episodes, the incoming flow is characterized by a strong inversion layer at altitudes of 0.5–1.5 km and, in the case of bora, by a critical level in the wind profile in the middle troposphere, which creates conditions for a weakened dynamic interaction between the low-level air flowing over mountains and the upper layers of the atmosphere. The wind-speed increase on the lee slope is caused by the transition of the incoming flow from the subcritical to supercritical state. In this case, the velocity amplitude increases with increasing inversion intensity. Model estimates of wind-speed increase are in good agreement with observations at lee-side weather stations for episodes with a strong elevated inversion. 相似文献
18.
Masahiro Endoh 《Journal of Oceanography》1973,29(1):16-27
A numerical experiment is made using a barotropic model for the western boundary currents. The time-dependent, non-linear vorticity equation is integrated with and without the variable of bottom topography. The inertial and frictional boundary flow is resolved with a fine grid size of 10 km. Connection of the western boundary currents with the general circulation is facilitated by giving the fixed Sverdrup transport at the eastern boundary of the model (400 km offshore).For the flat bottom topography, steady flow forRe=35 shows dynamical balance essentially of a frictional model. The transient response leading to the formation of the western boundary currents in the model seems to support theLighthill's theory (1969). ForRe=350, unsteady features revealed byBryan (1963) is re-established. A phenomenon of barotropic instability is also observed with sufficient resolution. For the model with a continental slope the steady flow is also obtained forRe=35. The boundary currents flow over the continental slope, deviating offshore as they flow northward. 相似文献
19.
Using a vertically two-dimensional, two-layer model, we have analytically examined the generation mechanism of a nonzero Eulerian
residual flow by strong tide-topography interaction in a narrow channel where the frictional effect is not included. In this
case, tidally generated baroclinic disturbances are forced non-uniformly in space and time while being advected by a strong tidal flow over the non-uniform slope of the bottom topography. Consequently, nonzero Eulerian residual flow results when averaged over one tidal period.
Although the time average of the velocity field is thus nonzero, the associated Eulerian residual transport in each layer
is compensated by a Stokes transport so that no Lagrangian residual transport results in both layers. This warns us that simple
time averaging of the velocity data obtained at a fixed mooring station might lead to a spurious material transport.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
《Marine and Petroleum Geology》2003,20(6-8):823-849
Quantifying the characteristics of the turbidity currents that are responsible for the erosion, lateral migration and filling of submarine channels maybe useful for predicting the distribution of lithofacies in channel fill and levee reservoirs. This paper uses data from a well-studied submarine channel in Amazon Fan in an attempt to reconstruct the velocity, thickness, concentration, duration, recurrence rates and vertical structure of turbidity currents in this long sinuous channel. Estimates of flow conditions are derived from the morphology of the channels and the characteristics of the deposits within them. In particular, the availability of information on the sediment distribution with respect to the channel topography at the time of deposition allows for insights into the vertical structure of the flow, a key property that has been so far poorly understood. Integration of flow constraints from well and seismic data or from detailed analysis of outcrop with numerical flow models is a critical step toward a complete understanding of the flow and associated deposits. Turbidity currents in sinuous submarine channels, exemplified by Amazon Channel, are found to last for tens of hours and occur on a regular, quasi-annual basis. Model results suggest that these flows had, on average, velocities ranging from 2 to 4 m/s in the canyon/upper fan which decreased to 0.5–1 m/s in the lower fan, travelling in excess of 800 km. The model turbidity currents were subcritical over most of the channel length, indicating a low degree of water entrainment and low rate of deceleration down the channel. The formation of such long, sinuous channels is intrinsically associated with frequent, long-duration, subcritical turbidity currents carrying a silt-dominated sediment load. 相似文献