共查询到20条相似文献，搜索用时 31 毫秒
1.
The shelfbreak wintertime thermal front in the Northeastern Gulf of Mexico often exhibits meandering, eddy formation and warm-water
intrusion. A high level of frontal variability plays an essential role in exchange processes across the shelf. This study
examines the impacts of local frontal instability and bottom topography on turbulent heat exchange across the front using
the results of two numerical models. Analysis of a series of numerical experiments reveals that the flow is baroclinically
unstable. Predicted frontal instability contributes significantly to cross-frontal exchange and accounts for about 35% of
the total eddy heat flux. Onshore eddy heat flux has the highest intensity at the frontal position. In addition, eddy activity
and heat flux are sensitive to variation of bottom topography. For topographic features and frontal characteristics that are
typical of the area, bottom steepness enhances the flux and is nearly proportional to the cross-frontal heat exchange. The
study attempts to explain physical mechanisms that drive frontal circulation in the area and to quantify heat transport across
the shelf. Estimated heat fluxes can provide important information for climate and ecosystem modeling of the Mississippi Bight. 相似文献
2.
In light of the pressing need for development of parameterizations of gravity current entrainment in ocean general circulation models, the behavior of turbulent gravity currents in the presence of ambient stratification is studied via numerical simulation, for cases in which equilibrated product water masses are formed. The main objective is to explore how the ambient stratification impacts entrainment and the properties of product water masses, which are of ultimate interest to ocean and climate modelers. Numerical experiments are conducted by employing the high-order nonhydrostatic spectral element model Nek5000. It is investigated how the separation level of the current from the bottom, the propagation speed, the salinity of the product water masses, and the transport and entrainment of the gravity current are affected as a function of the strength of the ambient stratification and the slope angle. Results show that, for the case of constant slope angle and linear ambient stratification, the gravity current separates from the bottom such that the entrained mass flux is independent of the slope angle. The entrainment mass transport, product mass transport, and product salinity then depend only on the ambient stratification, and these quantities are approximated as simple algebraic functions of the ambient stratification parameter that modify the source properties. 相似文献
3.
B.R. Sutherland M.R. Flynn K. Dohan 《Deep Sea Research Part II: Topical Studies in Oceanography》2004,51(25-26):2889
The collapse of a uniform density fluid (a “mixed region”) into a surrounding ambient fluid with complex stratification is examined by way of laboratory experiments and fully nonlinear numerical simulations. The analysis focuses upon the consequent generation of internal gravity waves and their influence upon the evolution of the collapsing mixed region. In experiments and simulations for which the ambient fluid has uniform density over the vertical extent of the mixed region and is stratified below, we find the mixed region collapses to form an intrusive gravity current and internal waves are excited in the underlying stratified fluid. The amplitude of the waves is weak in the sense that the intrusion is not significantly affected by the waves. However, scaling the results to the surface mixed layer of the ocean we find that the momentum flux associated with the waves can be as large as 1 N/m2. In simulations for which the ambient fluid is stratified everywhere, including over the vertical extent of the mixed region, we find that internal waves are excited with such large amplitude that the collapsing mixed region is distorted through strong interactions with the waves. 相似文献
4.
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
5.
This paper describes a numerical approach to model the dynamic response of a pneumatic floating platform, and the laboratory experiments and parametric study to verify the numerical results. The pneumatic platform is composed of an array of open-bottom vertical cylinders trapping pressurized air that displaces the water. The cylinder diameter is assumed to be small compared to the wavelength and the water inside each cylinder oscillates as a piston. These assumptions simplify the mathematical formulation in that the bottom of the platform can be treated as a continuous surface on which the source distribution method can be applied. In the laboratory experiments, the compressibility and displacement of the trapped air are modeled by a spring and float assembly. The comparison between the numerical and experimental results indicates favorable agreement. The oscillation of the water columns and the overall dynamic characteristics of the platform are illustrated and discussed in the parametric study. 相似文献
6.
基于非静压单相流模型NHWAVE建立了高精度数值波浪水槽。通过设计不同的计算工况,系统研究了非淹没刚性植物对海啸作用下海堤周围水动力特性的影响。着重分析了不同入射波高、不同植物分布密度以及不同植物分布宽度条件下海啸波沿程波形特征以及海堤堤顶越浪流空间分布特征。结果表明:不同入射波高、植物分布密度以及植物宽度条件下,堤顶流厚度和水体流速具有明显单调的变化趋势,并且随着植物分布密度和宽度增大,波能衰减增大;随着入射波非线性增强,植物分布密度和分布宽度对堤顶前段水流厚度的影响也随之增强,而对堤顶后段水流厚度的影响则减弱,且堤顶后缘水流厚度约为堤顶前缘厚度的二分之一;在波浪非线性较大情况下,植物的存在对堤顶流速度的空间分布趋势几乎没有影响,但相对堤顶流速度增加程度均大于无植物情况,且堤顶后缘水流速度约为堤顶前缘的1.6倍。 相似文献
7.
When pycnocline thickness of ocean density is relatively small, density stratification can be well represented as a two-layer system. In this article, a depth integrated model of the two-layer fluid with constant density is considered,and a variant of the edge-based non-hydrostatic numerical scheme is formulated. The resulting scheme is very efficient since it resolves the vertical fluid depth only in two layers. Despite using just two layers, the numerical dispersion is shown to agree with the analytical dispersion curves over a wide range of kd, where k is the wave number and d the water depth. The scheme was tested by simulating an interfacial solitary wave propagating over a flat bottom, as well as over a bottom step. On a laboratory scale, the formation of an interfacial wave is simulated,which also shows the interaction of wave with a triangular bathymetry. Then, a case study using the Lombok Strait topography is discussed, and the results show the development of an interfacial wave due to a strong current passing through a sill. 相似文献
8.
In the last decade, offshore pipeline engineering extended its action field to very deep waters and continental slopes. This implied the necessity to deal with continental slope instability and mass gravity flows. Mass gravity flows are rare and have random occurrence; therefore, considering also the technical difficulties, the direct measurement of the phenomena is practically impossible. This has encouraged the development of physical and numerical models for investigating the characteristics and intensity of the phenomena (Proc. OTC Conf., Houston, TX (2000); Proc. 19th OMAE Conference, New Orleans, LA (2000)). In order to provide design activities with reliable predictive tools, two numerical models, one for debris flows and the other for turbidity currents, have been developed. The two models are coupled by the bottom boundary conditions of the turbidity current model that depends on the instantaneous velocity of the debris flow model. The two models used together provide a tool for the evaluation of a mass gravity flow event starting as a debris flow and evolving into a turbidity current. 相似文献
9.
Understanding of sea bottom boundary layer characteristics, especially bottom shear stress acting on the sea bed, is an important step needed in sediment transport modeling for practical application purposes. In the present study, a new generation system for bottom boundary layer under solitary wave is proposed. Applicability of this system is examined by comparing measured and numerical solution velocities. Moreover, transitional behavior from laminar to turbulence was investigated. It is concluded that the critical Reynolds number in the experiments shows good agreement with DNS result of Vittori and Blondeaux (2008) and laboratory data of Sumer et al. (2010), indicating validity of the generation system. Since the present generation system enables continuous measurement to obtain ensemble averaged quantities, it can be effectively utilized for future experimental studies on solitary wave boundary layers, including sediment transport experiments with movable bed. 相似文献
10.
S. V. Anisimov S. V. Galichenko N. M. Shikhova K. V. Afinogenov 《Izvestiya Atmospheric and Oceanic Physics》2014,50(4):390-398
The electric state of the middle-latitude convective atmospheric boundary layer (ABL) is investigated during a point in time when it is not disturbed by clouds, precipitation, mist, or industrial aerosols. A numerical model is developed that estimates the electroaerodynamic state of the convective ABL. The model is parameterized using results of field observations and laboratory experiments. According to the model, vertical profiles of atmospheric electric field strength, space charge density, electric conductivity, and atmospheric electric current density are calculated in the horizontally homogeneous approximation with a high space-time resolution. 相似文献
11.
A thermohaline front is located at the southeastern entrance of the Yellow Sea in winter, and it is generated by the intrusion of warm saline water into the Yellow Sea caused by a strong northerly wind. Recently, a westward transversal current traveling away from the west coast of Korea toward the open sea area along the front was reported. The westward transversal current is dominant in the surface layer during the temperature inversion period. The formation and structure of this current are examined using a numerical vertical ocean-slice model. When two different water masses meet, a front is formed and adjusted geostrophically. In this frontal zone, a horizontal pressure gradient flow by the vertically inclined isopycnal occurs under the thermal wind process in a baroclinic effect, and the cold fresh coastal water moves westward along the front in the upper layer. The barotropic effect across the front and the bottom friction effect strengthen the westward component of the velocity. The velocity of the bottom layer decreases remarkably in the increase of the bottom drag coefficient. This means that the bottom friction with the strong background tidal current causes a reduction in the current in the bottom layer. 相似文献
12.
Laboratory modeling of the structure of a thermal bar and related circulation in a basin with a sloping bottom 总被引：1，自引：0，他引：1
Development of a thermal bar in a laboratory flume with an inclined bottom (3.7°–12°) under the conditions of cooling/heating of the water with a temperature close to that of the maximal density is studied. The structure of the temperature field and currents during different stages of the circulation is examined: (i) formation of an along-slope gravity current, (ii) generation of a subsurface jet, and (iii) transformation of one type of the circulation into another at passing the temperature of the maximum density. The “fall” and “spring” types of the thermal bar are shown to be dynamically equivalent: the transport of the near-shore waters to the deepwater part, which is driven by the buoyancy flux rather than by the heat flux across the surface, transforms stage (i) into stage (ii), while the opposite (on-shore) flow is generated in the intermediate layers. A comparison of the results with the field and laboratory data published allows us to suggest that the propagation of the thermal bar front in the “fast” stage can be considered as the development of a convective jet with its velocity U ～ h 3/4, which is proportional to the growing thickness of the upper layer h affected by the heating/cooling processes 相似文献
13.
水下溢油数值模拟研究 总被引：1，自引：0，他引：1
基于Lagrange积分法和Lagrange粒子追踪法建立了一个水下溢油数值模型。该溢油模型由两个子模型组成:羽流动力模型和对流扩散模型,其中羽流动力模型用以模拟溢油的喷发阶段和浮力羽流阶段;对流扩散模型用以模拟溢油的对流扩散阶段。通过数值实验,结合实验室水槽实验和水下溢油现场实验的观测资料进行模型验证。实验结果表明,模拟结果与观测资料一致性较好,从而验证了本文溢油模型的合理性和准确性;羽流动力模型为对流扩散模型提供源,海流、海水的垂向密度结构和油滴的直径分布是影响溢油在对流扩散阶段运动和分布的主要因素。 相似文献
14.
Masahiro Endoh 《Journal of Oceanography》1973,29(4):140-147
Investigated is a possibility of two-dimensional model in the study of the dynamics of the western boundary current by a numerical experiment. Emphasis is laid on the effect of bottom barrier corresponding to the Izu Ridge.The western boundary current in the model is formed by source and sink of the water prescribed at an artificial eastern wall (600 km offshore). The bottom topographyconsists of a continental slope parallel to the straight western coast, and a ridge protruding from the western coast to 500 km offshore (1,500 m deep and 400 km wide). The grid size of 12 km× 25 km (offshore and longshore directions, respectively) resolves both the western boundary current and the bottom topography.The assumption of homogeneity of the water density makes the western boundary current detour along the isobath of the ridge.A steady state solution is obtained under the assumptions that the horizontal velocity does not change direction vertically (equivalent barotropic), and that the geostrophic relationship holds at the bottom. Homogeneity of the water density is not assumed. The solution shows that most of the volume transport of the western boundary current cross the ridge and the current has cyclonic vorticity near the summit of the ridge. It seems to suggest that the investigation by three-dimensional models is neccesary in order to study the complete dynamics of the western boundary current crossing the ridge. 相似文献
15.
黄海冷水团的环流结构 总被引：1，自引：2，他引：1
运用定性分析和数值模拟，对黄海冷水团的环流结构进行了探讨，结果表明黄海冷水团的垂向环流结构为双环结构：跃层以上区为中心上升，边缘下降的弱环流;跃层以下区为中心下降，边缘上升的强环流；在冷水团的中心区域，流动很弱，且无穿越温跃层的垂向流动。同时也对以往有关黄海冷水团垂向环流结构的工作进行了讨论。 相似文献
16.
The paper presents a simple approach to estimate the bottom shear stress in the swash zone by coupling the Non Linear Shallow Water Equations with the momentum integral equation for the bottom boundary layer. The approach allows not only the computation of the frictional dissipation term in the equations but also to have an insight into the flow structure in the water column during a swash event. The numerical results have been compared with a new set of experiments involving a single dam-break generated swash event. Three different grain sizes, ranging from coarse sand to gravel, have been tested in the laboratory. 相似文献
17.
内孤立波与海脊相互作用的模拟研究 总被引：1，自引：0，他引：1
A nonhydrostatic numerical model was developed and numerical experiments performed on the interaction of an internal solitary wave(ISW) with a sill, for a two-layer fluid with a diffusive interface. Based on the blocking parameter(Br), the flow was classified into three cases:(1) when bottom topography has little influence on the propagation and spatial structure of the ISW(Br0.5),(2) where the ISW is distorted significantly by the blocking effect of the topography(though no wave breaking occurs,(0.5Br0.7), and(3) where the ISW is broken as it encounters and passes over the bottom topography(0.7Br). The numerical results obtained here are consistent with those obtained in laboratory experiments. The breaking process of the incident ISW when Br≈0.7 was completely reproduced. Dissipation rate was linearly related to the blocking parameter when Br0.7, and the maximum dissipation rate could reach about 34% as Br raised to about 1.0. After that, instead of breaking, more reflection happened. Similarly, breaking induced mixing was also most effective during Br around 1.0, and can be up to 0.16. 相似文献
18.
Numerical simulation of the influences of sinker weight on the deformation and load of net of gravity sea cage in uniform flow 总被引：11，自引：0，他引：11
1IntroductionThe fish farming and aquaculture industry areexpanding and the demand for suitable locations forfish farms is increasing.In the future,more of thefish farms will be located offshore,as the number ofsuitable nearshore locations is limited.Futu… 相似文献
19.
基于中国近海浪-流耦合业务化预报系统（OFS-C）和Lagrangian粒子追踪方法,本文首次建立了辽东湾海蜇增殖放流模型。模型中,海蜇用虚拟的粒子表示,具有昼夜垂直运动（DVM）特性。海蜇运动由海流和次网格参数化引起的随机运动驱动。利用航次调查数据对模型结果进行了验证,模式结果可以很好的模拟放流海蜇分布的主要结构。模型分析了物理过程对辽东湾放流海蜇的输运和分布的影响,结果显示海蜇运动主要受海流和间接的风应力的影响。放流地和捕捞地的连通性分析表明,辽东湾海蜇的主要捕捞地集中于湾顶。另外,连通性矩阵表明,瓦房店放流的部分海蜇不能到达捕捞地,因此,相对于其它放流地来说,瓦房店不是理想的放流地。敏感性实验表明了随机游走的重要性,但是对于游走格式并不敏感。海蜇栖息的深度会影响海蜇最终的分布,若海蜇栖息于海底,则在低层环流的影响下,最终分布于辽东湾中部,部分会流出辽东湾,而不能到达湾顶。 相似文献
20.
Laboratory experiments on the dynamics of a downwelling coastal current over a sloping bottom were conducted in a tank on a rotating platform. The current was generated by a source of stable water flow of the same density (barotropic case) or of lesser density (baroclinic case) compared with the surrounding water in the tank. It was found that even in the case of the baroclinic current, a less dense water downflow in the bottom Ekman layer was formed under certain conditions. At some moment, this downflow undergoes convective instability. Taking into account the results of the experiment, the parameters of the bottom Ekman layer on the continental shelf/slope of the Black Sea were preliminarily estimated and the possible sinking depth of less dense water was calculated. 相似文献