PN断面黑潮流速垂直分布特征及机制分析

基于全球海洋再分析模拟GLORYS2(Global Ocean Reanalysis Simulation 2)结果,分析了PN断面(126.0°E-128.2°E,1 000 m以浅)黑潮流速垂直结构的季节和年际变化,探讨了黑潮流速垂直结构形成的动力学机制。结果表明:1)PN断面黑潮夏季流量最大,春季次之,秋、冬季节最小;气候态平均的冬、夏季流速最大值都位于次表层,春、秋季节流速最大值位于表层;夏季相对流速较大、最大值深度较浅;等密线在黑潮主轴区下凹,冬季更为明显。流速最大值深度和密度水平梯度为零的深度均表现出了较大的年际差异,该年际变化甚至超过季节差异;2)流速与密度符合热成风关系。黑潮通量由太平洋大尺度风场及中尺度运动两者共同决定,但局地的热通量和环流对温盐的输运共同影响密度场,调节黑潮流速的垂直分布,影响水通量的分配及营养盐输运;3)有些年份夏季流速最大值出现在表层,可能是夏季西南季风诱导陆架水离岸输运进入黑潮上层导致的结果。非线性、非地转物理过程的影响没有考虑在本研究中,热成风关系能够解释黑潮流速垂直分布形成的部分原因。

桥测断面流速垂直分布规律分析

天然河流的流速垂直分布，一般是水面流速大于河底，且呈一定的曲线形状。由于影响流速垂直分布因素很多，如河床糙率、冰冻、水草、水深、风力、河槽形式等，故曲线形状也各不相……

非恒定流垂线流速分布规律的初探

从雷诺方程出发 ,通过对非恒定流的沿程阻力损失在垂线上分布规律的修正 ,可获得非恒定流和恒定非均匀流垂线流速分布公式。若定义均匀流垂线流速分布为A型 ,则非恒定流或恒定非均匀流垂线流速分布一般为B型和C型。B型分布在主流区 ,分布梯度大于A型 ;C型分布与A型相反 。

海岸河口水域流速分离方法初探

从海岸河口地区的水动力特征出发 ,应用潮流、风生流流速垂直分布的理论模式和最小二乘法原理 ,提出了一种从实测流速分离出潮流和风生流的方法 ,并首先对黄河口的潮流和实验室的风生流进行检验性分离计算 ,然后应用于长江口北支河段及口外实测流速的分离 ,实测流速分离后 ,不仅可获得表层的潮流速和风流速 ,而且还可从中得到底床粗糙高度并估算作用于海表面的风速数据 .初步研究表明 ,此流速分离方法原理简单、过程合理、结果可信 ,是一种适用于现场资料分析计算的有效方法 ,既可广泛应用于海岸河口实测流速的分离 ,又可为海岸河口水动力数值模拟提供合理的海底和海面边界条件 .

垂直测速定位误差的分析

用有限流速测点组合求和,是计算垂线平均流速的现行方法;而准确的特定测点相对位置,又是保证成果精度的主要条件.通过对垂直流速几种分布模式的描述,结合试验资料的分析,表明定位误差影响垂线平均流速误差的大小,与垂直流速分布有关,且随定位误差的增大而增大,并在一定的水深范围内,是随水深的变化而成反比关系。测速定位误差实质上是一种系统性的偏差,它与施测人员的素质和设备的技术改造有关。

长矩形腔体中混合流体的双局部行波

基于数值模拟,研究了分离比ψ=-0.4和长高比Γ=40的腔体内的双局部行波对流的动力学特性。结果发现,对流圈在端壁产生,向中心传播,到达一定位置对流圈消失;在矩形腔体中两端壁附近行波对流区域与中间部位无对流的传导区域同时共存,形成双局部行波对流;双局部行波对流中的行波由腔体两端向中部传播;腔体二分之一高度处的温度与垂直流速分布是谐波结构,波形比较光滑,浓度分布是台型结构;随着时间的发展,垂直流速最大值稳定在某个数值周期变化,下壁面努塞尔数基本稳定在某个数值,垂直流速最大值和下壁面努塞尔数及其达到稳定的时间随着相对瑞利数r的增加而增加;双局部行波对流稳定的存在于相对瑞利数r∈{1.52,1.57]的区间,双局部行波的对流区长度随着相对瑞利数r的增加呈良好的增加关系,并给出了双局部行波的对流区长度随着相对瑞利数r变化的拟合关系式。

明渠恒定均匀流流速垂向分布研究

恒定流是明渠水流基本原理研究的重要课题,水流的动力特性决定了泥沙的沉积和悬浮,河床底部侵蚀和沉积的演变,是水动力机理研究的重点。为了进一步讨论明渠平均流速剖面和恒定流摩阻特性,文章结合理论分析和实验研究,基于粒子图像测速仪(PIV)水槽实验系统,探究不同工况下恒定流流速剖面、紊流度和底边界层厚度等参数的变化规律。结果表明:(1)沿轴向,紊流度与平均流速成正相关,随着总水深的增加,紊流度沿垂向变化变缓。平均流速和比降的增大,都会使紊流度曲线右移。随着比降的增大,平均流速所引起的紊流度的增大幅度越小。但是,平均流速对比降引起的紊流度的增大幅度影响不大。(2)总水深较小时,平均流速对底边界层厚度的影响较大,总水深较大时,总水深对底边界层厚度的影响更明显。

Vertical distribution of the Kuroshio velocity in the Pollution Nagasaki section and its formative mechanism

The seasonal and interannual variations of the vertical distribution of the Kuroshio velocity and its formative mechanism were studied by analyzing the Global Ocean Reanalysis Simulation 2 （GLORYS2） dataset in the Pollution Nagasaki （PN） section （126.0°E-128.2°, at depths less than 1000 m）. The results indicated that： 1） the maximum transport in the PN section occurs in summer, followed by spring, and the minimum transport occurs in fall and winter; the maximum velocities are located at the subsurface in both winter and summer and velocities are relatively larger and at a shallower depth in summer; and the velocity core is located at the surface in spring and fall. The isopycnic line has a clear depression around the Kuroshio axis in winter. The depth of maximum velocity and the zero horizontal density gradients both exhibit substantial seasonal and interannual variations, and the interannual variations are larger. 2） The distributions of velocity and density are in accordance with the therma~ wind relation. Although Kuroshio transport is determined by the large-scale wind field and mesoscale motion in the Pacific Ocean; local heat flux and thermohaline circulation influence the density field, modify the vertical structure of the Kuroshio velocity, and adjust the allocation of water fluxes and nutrients transport. 3） Shelf-water offshore transport into the Kuroshio upper layer induced by southwest monsoons might contribute to the maximum velocity up to the surface in summer. Nonlinear and nongeostrophic processes are not considered in the present study, and the thermal wind relation accounts for part of the vertical structure of the Kuroshio velocity.

Single-jet Spray Mixing with a Confined Crossflow

In order to achieve uniform mixing between spray droplets and crossflow, cold-model experiment of a hollow-cone water spray in an air crossflow is investigated via a numerical simulation. The simulation cases are designed by using the orthogonal design method. The Eulerian-Lagrangian formulation is employed for modeling the droplets-crossflow two-phase flow while the realizable k-ε turbulence model is used to describe the turbulence. A new index, mixedness quality, is proposed to assess the overall mixing of the droplets in the crossflow. The simulation results demonstrate that the counter-rotating vortex pair (CVP) imposes a more significant impact on the spatial distribution than on the size distribution of the droplets. Pairs of CVP with smaller scales are preferable for achieving a better mixing. The influencing factors are listed in the following order in terms of the degree of their impact from the greatest to the least: the Sauter diameter of the initial droplets, the mixing tube diameter, the spray angle, the velocity of the inlet crossflow, and the vertical velocity of the initial droplets. A moderate droplet diameter, a smaller tube diameter, a moderate spray angle, a greater crossflow velocity and a moderate vertical velocity of the droplet are favorable for achieving a higher mixedness quality of the jet spray in a confined crossflow.

Effect of vertical overturning circulation scale and moist static energy tendency on MJO phase speed

The combined effects of vertical overturning circulation(VOC) zonal length scale and moist static energy(MSE)tendency zonal asymmetry on MJO phase speed were investigated based on diagnosis of ERA-Interim data over a 40-year period(1979-2019).In a key region(80°-100°E),128 MJO events were selected.It was found that the larger the VOC zonal length scale,the faster the MJO eastward propagation.The correlation coefficient between them was 0.52,exceeding the 99% confidence level.A significant positive correlation(0.59) was also identified between the phase speed and MSE tendency zonal asymmetry.A linear regression model based on the aforementioned two parameters was constructed,and the phase speed could be estimated based on the model.The correlation coefficient between the reconstructed phase speed and its observed counterpart was 0.73,exceeding the 99% confidence level with an F-test.A composite analysis of the fast and slow groups indicated that the VOC zonal length scale was modulated by the background state.An El Nino(La Ni?a)-like SST pattern and associated precipitation anomalies promoted a larger(smaller) VOC zonal length scale and thus a faster(slower)propagation speed.A sensitivity test with a reference point in a different longitudinal zone(120°-140°E) was conducted.Again,there were significant relationships between the MJO phase speed and the two parameters.The correlation between the reconstructed and observed phase speed was 0.67,exceeding the 99% confidence level.

Modeling the effects of mechanical parameters on the hydrodynamic behavior of vertical current classifiers

This study modeled the effects of structural and dimensional manipulations on hydrodynamic behavior of a bench vertical current classifier. Computational fluid dynamics （CFD） approach was used as modeling method, and turbulent intensity and fluid velocity were applied as system responses to predict the over- flow cut size variations. These investigations showed that cut size would decrease by increasing diameter and height of the separation column and cone section depth, due to the decrease of turbulent intensity and fluid velocity. As the size of discharge gate increases, the overflow cut-size would decrease due to freely fluid stream out of the column. The overflow cut-size was significantly increased in downward fed classifier compared to that fed by upward fluid stream. In addition, reforming the shape of angular overflow outlet＇s weir into the curved form prevented stream inside returning and consequently unselec- tire cut-size decreasing.

Experimental Studies on Critical Heat Flux in a Uniformly Heated Vertical Tube at Low Pressure and Flowrates

Investigations into critical beat flux at low flow and pressure conditions are of particular interest when predicting the nuclear reactor core behavior during Loss of Coolant accident （LOCA）. Therefore, critical heat flux （CHF） has been investigated in a uniformly heated vertical round tube at two low system pressures and six low water flowrates. The results have been compared with two correlations which have different approaches and CHF look-up table. Good agreements have been obtained for the three comparisons at the lower sets of mass fluxes. The Bowring correlation was found to be the best to correlate the experimental results with Root Mean Square Error RMSE of 0.54% and 0.56% for the 5 bar and 15 bar system pressure respectively. A comparisons with the Shim and Lee correlation yielded RMSE of 0.23% and 5.74% for the two system pressure respectively. When the look-up table of Groeneveld et al. was used, RMES of 0.55% and 25.2% was obtained for the two system pressure respectively.

Calculus of the Railway Vertical Stiffness Depending on the Base Plate Stiffness and the Ballast for High Speed Railways

The study aims to determine a mathematical formula that correlates the vertical stiffness of the principal elements of a high speed railway. To do this, beginning on the traditional formulations, a new mathematical model has been proposed, and has been verified and confirmed with the real information of high speed railways. Finally, there has been obtained a simple expression that correlates simply the vertical stiffness of the railway with the vertical stiffness of the elements that compound it, essentially with the base plate and the ballast system set. On the other hand, also the accuracy of the model has been verified to select the stiffness of the base plate and the ballast system depending on one of this stiffness and the total vertical stiffness that it is wanted. With this simplified formula, it is possible to optimize the vertical stiffness of the railway to obtain the best behavior in each zone and to reduce the final cost of the use of the via, taking in consideration the energy needed to move the trains, the maintenance cost, the useful life, etc.. The process to optimize the railway stiffness in each point depends on the vertical stiffness of the ballast and the sub-ballast, and it is possible to use different plate bases with different stiffness to obtain the optimal stiffness that has been previously obtained with a cost and maintenance analysis.

Effects of Pressure Stress Work and Viscous Dissipation in Mixed Convection Flow Along a Vertical Flat Plate

The Effects of pressure stress work and viscous dissipation in mixed convection flow along a vertical fiat plate have been investigated. The results are obtained by transforming the governing system of boundary layer equations into a system of non-dimensional equations and by applying implicit finite difference method together with Newton＇s linearization approximation. Numerical results for different values of pressure stress work parameter, viscous dissipation parameter and Prandtl number have been obtained. The velocity profiles, temperature distributions, skin friction co-efficient and the rate of heat transfer have been presented graphically for the effects of the aforementioned parameters.

Numerical investigation of particle saltation in the bed-load regime

This paper numerically investigates particle saltation in a turbulent channel flow having a rough bed consisting of 2–3 layers of densely packed spheres.In this study,we combined three the state-of-the-art technologies,i.e.,the direct numerical simulation of turbulent flow,the combined finite-discrete element modelling of the deformation,movement and collision of the particles,and the immersed boundary method for the fluid-solid interaction.Here we verify our code by comparing the flow and particle statistical features with the published data and then present the hydrodynamic forces acting on a particle together with the particle coordinates and velocities,during a typical saltation.We found strong correlation between the abruptly decreasing particle stream-wise velocity and the increasing vertical velocity at collision,which indicates that the continuous saltation of large grain-size particles is controlled by collision parameters such as particle incident angle,local rough bed packing arrangement,and particle density,etc.This physical process is different from that of particle entrainment in which turbulence coherence structures play an important role.Probability distribution functions of several important saltation parameters and the relationships between them are presented.The results show that the saltating particles hitting the windward side of the bed particles are more likely to bounce off the rough bed than those hitting the leeside.Based on the above findings,saltation mechanisms of large grain-size particles in turbulent channel flow are presented.

Modification of the land surface energy balance relationship by introducing vertical sensible heat advection and soil heat storage over the Loess Plateau

Little is known about the surface energy balance problem for a complex underlying surface.Taking data from the Loess Plateau Land-surface Processes Experiment(LOPEX) and investigating the characteristics of the surface energy balance over a complex underlying surface,this paper calculates the soil heat storage and vertical sensible heat advection,analyzes their contributions to the surface energy imbalance,and discusses the mechanism by which the vertical velocity and temperature gradient in the surface layer affect the vertical sensible heat advection transfer.We found that the vertical velocity in the surface layer provides the necessary dynamic power for vertical sensible heat advection,and a relatively strong temperature gradient is the energy source generating vertical sensible heat advection.Under an ascending condition,the effect of vertical sensible heat advection on the surface energy budget is more obvious.It is also found that when the soil heat storage term and the vertical sensible heat advection term are added to the energy balance equation,the imbalance significantly improves.The peak of average diurnal residuals decreases from 125.1 to 41.5 W m-2,the daily average absolute value of residuals falls from 59.0 to 26.4 W m-2,and the surface energy balance closure increases from 78.4% to 94.0%.

Experimental demonstration of the coupling effect of vertical velocity on latent heat flux

According to the cross coupling theorem of atmospheric turbulence, latent heat flux comprises two components, a vertical humidity gradient flux and a coupling flux of vertical velocity. In this paper, observational data are employed to demonstrate and analyze the coupling effect of vertical velocity on latent heat flux. The results highlight the presence of a coupling zero-effect height. When the observational level exceeds or underlies the coupling zero-effect height, the coupling effect suppresses or enhances the latent heat flux, respectively. Above the heterogeneous terrain in the experimental region, the overall difference between the estimated and the observed latent heat fluxes decreases from 27% to 2% (for ascending flow) and from 47% to 28% (for descending flow), after compensating for gradient flux. The coupling theorem of atmospheric turbulence is well validated by our analysis, supporting a role for experimental datasets in unraveling the mysteries of atmospheric turbulence.