首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 344 毫秒
1.
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   

2.
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   

3.
Intense atmospheric vortices are characterized by a regime of cyclostrophic balance, i.e., the balance between the pressure gradient and centrifugal force. To describe motions in the core of an axisymmetrical vortex, a class of exact solutions to the equations of gas dynamics with a linear dependence on radius is derived for the velocity components and with a quadratic dependence for temperature. It is shown that small deviations from the balance state give rise to oscillations of the hydrothermodynamic fields in the vortex core with a frequency proportional to the angular velocity of the rotation of the core. For fairly large initial deviations, oscillations are clearly anharmonic and, under the conditions of the prevailing centrifugal force, result in a significant temperature decrease on the vortex axis. The application of this class of solutions to describing the Ranque vortex effect (the intense cooling of gas during rapid rotations) and the acoustic radiation from tornadoes is discussed.  相似文献   

4.
The dependence that the structure and intensity of turbulent and large-scale quasiordered eddies in the atmospheric boundary layer (ABL) have on the direction of geostrophic wind has been studied on the basis of a series of numerical experiments with a three-dimensional nonstationary model of high spatial resolution. The presence of the meridional component of the angular velocity of the Earth’s rotation results in a significant intensification of velocity fluctuations in a neutrally stratified turbulent flow during the easterly and northeasterly winds and in their decay during the westerly and southwesterly winds. This, in turn, results in significant variations in the mean velocity profile. It is shown that these variations are associated with the largest scale fluctuations and are comparable (in scale) to the depth of Ekman’s turbulent layer. It is found that, in the neutrally stratified ABL bounded in height and under stable stratification inside the ABL, the wind-direction dependence significantly decreases. The possibilities of parameterizing these effects in locally one-dimensional ABL models are discussed.  相似文献   

5.
We consider quasi-two-dimensional rapidly dissipating mesoscale atmospheric vortices generated over the Black Sea near the Crimean and Caucasian coasts. Based on the results of numerical modeling for a characteristic example of the Crimean eddy, we determine its structure and parameters and estimate the rate of decay of kinetic energy and enstrophy. In addition to the large-scale secondary circulation in the vortex, we also consider a small-scale secondary circulation induced by Raleigh-Bénard convection.  相似文献   

6.
通过构建中尺度涡的数学模型,利用射线-简正波-抛物方程(RMPE)声学模型进行传播损失计算,进而分析在深海声道、深海会聚区、海底反射3种传播模式下,中尺度涡对深海声效应的影响。数值仿真结果显示,暖涡对深海声道、会聚区产生下压效果,使会聚区水平距离变大,深海声道深度方向上变宽;冷涡使会聚区上抬,距离变短,对声场散射现象明显。研究结果表明,涡旋环境条件下,声场特征会产生显著变化。试验结果揭示了中尺度涡对深海声场效应的影响,对指导海上运用中尺度涡现象开展的科学研究、工程实践、军事运用具有积极的指导意义。  相似文献   

7.
A scheme of a periodic assimilation of climatic temperature and salinity data into a model is proposed. In accordance with the criteria chosen on the basis of numerical experiments, an optimum assimilation period of three hours is set. The proposed method allows a hydrodynamic adaptation of the fields of temperature, salinity, and flow velocity that are close to the climatic ones within the framework of the proposed criteria. The main feature of the adapted fields of vertical flows in the layer 0–700 m is their smooth character and an almost complete absence of small-scale noise. The extreme values of vertical velocity in this layer decrease by almost an order of magnitude as compared to analogous values calculated for the variant of data assimilation with a weak adjustment of fields.  相似文献   

8.
《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   

9.
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   

10.
《Coastal Engineering》2006,53(5-6):441-462
The structure of large-scale turbulence under a broken solitary wave on a 1 in 50 plane slope was studied. Three-component velocity measurements were taken at different heights above a smooth bed in the middle surf zone using an acoustic Doppler velocimeter. The measured data showed that turbulent velocity components were well correlated in the middle part of the water column. The velocity correlations could be produced by an oblique vortex similar to the obliquely descending eddy observed previously by other investigators. The vertical distributions of the relative values of the components of the Reynolds stress tensor showed that the structure of turbulence evolved continuously between the free surface and the bottom. The evolution was related to transition from two-dimensional to three-dimensional flow structures and the effect of the solid bottom on flow structures. Time histories of measured turbulent kinetic energy and turbulence stresses showed episodic turbulent events near the free surface but more sporadic turbulence in the lower layer. Large or intense turbulent events were found to have short duration and time lag relative to the wave crest point. These events also maintained good correlations between the turbulence velocity components close to the bottom.Instantaneous turbulent velocity fields were measured near the bottom at the same cross-shore location by using a stereoscopic particle image velocimetry system. These measurements showed that the near-bed flow field was characterized by large-scale, coherent flow structures that were the sources of most of the turbulent kinetic energy and turbulence stresses. The types of organized flow structures observed included vortices and downbursts of turbulence descending directly from above, lateral spreading of turbulent fluid along the bed, and formation of vortices in shear layers between fluid streams. A common feature of the organized flow structures near the bed was the large turbulence velocities in the longitudinal and transverse directions, which reflected the influence of a solid bottom on the breaking-wave-generated turbulence arriving at the bed.  相似文献   

11.
Laboratory experiments have been carried out to investigate conditions for the generation of a large-scale spiral vortex from a localized heat source in a rotating fluid. It is shown that there is a threshold for the excitation of a vortex rotating much more rapidly than the cuvette. The influence of the intensities of convection and background rotation on the excitation threshold of a spiral vortex has been investigated for various liquids in cuvettes of different geometry. In all experiments, the threshold of vortex excitation corresponds to turbulent convection states and a relatively slow background rotation and practically does not depend on the Prandtl number. The influence of the spatial distribution of temperature in the heating area on the threshold of vortex generation has been revealed.  相似文献   

12.
本文以21世纪初渤海湾大规模的围填海工程为背景,对2000-2015年典型年份的卫星遥感影像资料进行了岸线提取,并分析了其时空演变规律.以此为基础,建立了不同岸线及地形条件下的渤海湾水动力数值模型,计算结果与塘沽、黄骅港和东风港三个潮位观测站的实测数据吻合良好.模拟结果显示:渤海湾大规模围填海工程的建设使得三个主要工程区(曹妃甸工业区、天津港及黄骅港)附近的潮流运动更加剧烈,但对于渤海湾离岸潮流场的影响不大.M2分潮流速及流向变化明显,其最大流速方向与建筑物布置、深水航道航线方向一致.黄骅港挡沙堤的建设使其附近流场出现局部涡旋,导致潮流以旋转流的形式运动.  相似文献   

13.
An unstructured grid, Finite Volume Coastal Ocean Model (FVCOM) is used to study hydrodynamics and large-scale structure impacts in Changjiang Estuary. Field measurements conducted after the construction of the large-scale channel-jetty system are used to assess numerical results. The agreements between simulated and measured water levels, depth-averaged current velocities and tidally averaged longitudinal salinity distributions are excellent, as indicated by predictive skills higher than 0.94. The predictive skills for time series of salinity show a large range, from 0.97 to 0.62, in different measurement locations. The impacts of two 50 km long jetties and tens of spurs on the estuarine circulations as well as salinity distribution are investigated using comparisons of numerical results with and without jetty structures. Results reveal that the jetty structures intensify currents in the navigation channel and generate strong shear and vortices in jetty-spur blocks, which enhance turbulent mixing and degrade salinity stratification in the channel. The large-scale structures not only affect the flow field in the northern passage, but also play an important role in redistributing freshwater runoff in the multi-channel system, resulting in estuary-scale adjustments of circulations and salinity distribution.  相似文献   

14.
人工鱼礁单体按不同的数量和排列方式组合投放会产生不同的流场效应。圆管型礁为目前黄渤海区增殖礁的重要礁体型式,为优化该礁体的投放数量与排列方式,选择了3种不同叠放个数(1个、3个和6个)的圆管礁,设定了5个流速梯度(4.5、9.0、13.5、18.0和22.5cm/s),利用PIV粒子图像测速技术和Fluent数值模拟软件对圆管型人工鱼礁的流场进行水槽模型试验和数值模拟。结果表明,数值模拟结果与水槽试验结果基本吻合,误差在20%以下,表明数值模拟能够反映人工鱼礁的流场效应;当礁体叠放个数一定时,最大上升流流速、上升流高度和上升流面积均随来流速度的增加而增大,背涡流面积呈现不规则的变化;当来流速度一定时,最大上升流流速、上升流面积、上升流高度和背涡流面积均随礁体叠放个数的增加而增大。  相似文献   

15.
A series of fully three-dimensional(3 D) numerical simulations of flow past a free-to-oscillate curved flexible riser in shear flow were conducted at Reynolds number of 185–1015. The numerical results obtained by the two-way fluid–structure interaction(FSI) simulations are in good agreement with the experimental results reported in the earlier study. It is further found that the frequency transition is out of phase not only in the inline(IL) and crossflow(CF) directions but also along the span direction. The mode competition leads to the non-zero nodes of the rootmean-square(RMS) amplitude and the relatively chaotic trajectories. The fluid–structure interaction is to some extent reflected by the transverse velocity of the ambient fluid, which reaches the maximum value when the riser reaches the equilibrium position. Moreover, the local maximum transverse velocities occur at the peak CF amplitudes, and the values are relatively large when the vibration is in the resonance regions. The 3 D vortex columns are shed nearly parallel to the axis of the curved flexible riser. As the local Reynolds number increases from 0 at the bottom of the riser to the maximum value at the top, the wake undergoes a transition from a two-dimensional structure to a 3 D one. More irregular small-scale vortices appeared at the wake region of the riser, undergoing large amplitude responses.  相似文献   

16.
为了助力海洋牧场减流防护工程, 研究Savonius型转轮阵列减流性能。作者建立Savonius型转轮三角阵列尾流场数值模型, 并通过水池实验验证准确性, 基于可靠数值模型探究转轮阵列尾涡减流机理, 研究三角阵列结构参数LX、LY, 以及动力参数TSR、初始流速、旋向对整体减流性能的影响规律。结果表明,下游转轮产生的涡流呈现非对称分布, 并且产生更多涡流的转轮拥有更好的减流效果。另外, LX为3D和LY为2D时减流性能最佳。最后对比发现, 在叶尖速比为0.9~1.1减流效果更好; 初始流速大小不影响减流效果; 下游转子对称分布时, 随着上游转子改变旋转方向, 减流效果出现明显差异。  相似文献   

17.
Submarine channels are major morphological features of the sea floor and are important in the transport of sediment to the deep ocean. Although much is known concerning the large-scale distribution of sediment within and surrounding submarine channels, there is little understanding of the fluid dynamic processes that control this sedimentation. Direct measurement of flow velocities and concentrations has proved to be extremely difficult within submarine channels, with the resultant paucity of direct observations making physical laboratory modelling a critical technique for examining the processes that operate in, and control, submarine channel development.Recent experimental and numerical studies have proposed a new model of secondary circulation within submarine channel bends, characterised by a reversal in the orientation of the secondary circulation cell relative to that found in meandering rivers. This new paradigm for submarine channels thus predicts basal flow from the inside to the outside of the bend at a bend apex, with an upper return flow directed towards the inner bend. The reversal in orientation of the secondary flow cell has been linked to the vertical distribution of downstream velocity and associated changes in centrifugal and pressure gradient forces. However, previous work has additionally proposed that shearing of the within-channel flow by overbank flow may also generate secondary flow reversal.This study assesses the applicability of the proposed submarine bend flow model against a range of key channel parameters. We demonstrate that the sense of secondary circulation is the same for all experimental conditions, strongly supporting the new model of secondary flow in submarine channels. Furthermore, investigation of overbank shear induced secondary circulation confirms for the first time that this mechanism can occur, and identifies the channel styles most likely to exhibit this effect. Such shear-induced circulation is, however, shown to be a secondary mechanism, with the vertical distribution of downstream velocity the principal mechanism. In certain channel configurations, the two mechanisms may act to augment one another.  相似文献   

18.
The purpose of the present work is <!–<query>The highlights are in an incorrect format. Hence they have been deleted. Please refer the online instructions: http://www.elsevier.com/highlights and provide 3-5 bullet points.</query>–>to study the effect of the Reynolds number on the near-wake structure and separating shear layers behind a circular cylinder. Three-dimensional unsteady large-eddy simulation is carried out and two different subgrid scale models are applied in order to evaluate the turbulent wake reasonably. The Reynolds number based on the free-stream velocity and the cylinder diameter is ranging from Re = 5500–41,300, corresponding to the full development of the shear-layer instability in the intermediate subcritical flow regime. For a complete validation of this numerical study, hydrodynamic bulk coefficients are computed and compared to experimental measurements and numerical studies in the literature. Special focus is made on the variations of both the large-scale near-wake structure and the small-scale shear-layer instability with increasing Reynolds numbers. The present numerical study clearly shows the broadband nature of the shear-layer instability as well as the dependence of the shear-layer frequency especially on the high Reynolds numbers.  相似文献   

19.
Turbulent vortical structures under broken solitary waves are studied using three-dimensional smoothed particle hydrodynamics (SPH) method. The numerical model predicts water surface evolution and horizontal velocity very well in comparison with the experimental results. The numerical results detect organized coherent structures characterized as reversed horseshoe (hairpin) vortices being generated at the back of the broken spilling wave and traveling downward. The counter rotating legs of the reversed horseshoe structures appear to be a continuous form of the previously found obliquely descending eddies. The reversed horseshoe structures are associated with the turbulence motion of sweep events (downwelling motion) and transport momentum and turbulent kinetic energy downward into the water column. Vortex turning play an important role on the generation and evolution of three dimensional reversed horseshoe structures from the spanwise breaking wave rollers.  相似文献   

20.
A laboratory system was used to test the effect of water flow on the resuspension of mud and sand sediments and, specifically, benthic diatoms from the Ems estuary, The Netherlands. Current velocities generated by two rotating cylinders in a cylindrical tank were determined by a small float and a laser Doppler velocimeter. At low angular velocities, the amount of suspended matter increased linearly with angular velocity and the float current velocity. However, at higher angular velocities, the increase in current velocity was less because of the strong turbulence: concomitantly, the current velocity boundary layer (δ) became thinner and the suspended matter concentration increased rapidly. The dominant diatom species from the sandy sediment were suspended in two distinct groups, one of which consisted of the species Navicula aequorea, Navicula salinicola, Ophephora martyi and Opephora pacifica, and was more exclusively bound to sand grains than the other. The benthic diatom species inhabiting the silty sediment did not show this difference. The most important shortcoming in the experiments was the inability to determine the radial and vertical velocity components. This precluded reliable calculations of the shear stress. The data presented emphasize the importance of finding a method to determine the shear stress under experiments and field conditions so that direct comparisons can be made. Despite this it is assumed that, just as under the experimental conditions discussed, under natural conditions in shallow waters resuspension starts at current velocities as low as ca. 10 cm s−1.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号