西南低涡东移对华南暴雨增幅的动力机制分析

对1996年6月13~14日华南大暴雨发生过程的天气形势和物理量场进行分析,并从中尺度能量方面探讨了西南低涡对华南暴雨增幅的动力机制。结果表明:暴雨的发生与西南低涡及850hPa孟湾地区的水汽通量有着密切的联系;而500hPa较强的负螺旋度有利于低层低涡的发展加强;暴雨发生前,华南上空维持一支反气旋性的西南急流,当西南涡东南移时,造成本地重力惯性波能量增加,从而对华南暴雨有正贡献,即对暴雨有一定的增幅作用。     

2015年台风“彩虹”过境后下山冷急流引起的南海北部海域异常海面降温

This study deals with a unusual cooling event after Typhoon Mujigea passed over the northern South China Sea(SCS) in October 2015. We analyze the satellite sea surface temperature(SST) time series from October 3 to 18,2015 and find that the cooling process in the coastal ocean had two different stages. The first stage occurred immediately after typhoon passage on October 3, and reached a maximum SST drop of –2℃ on October 7 as the usual cold wake after typhoon. The second stage or the unusual extended cooling event occurred after 7d of the typhoon passage, and lasted for 5d from October 10 to 15. The maximum SST cooling was –4℃ and occurred after 12d of typhoon passage. The mechanism analysis results indicate that after landing and moving northwestward to the Yunnan-Guizhou Plateau(YGP), Typhoon Mujigea(2015) met the westerly wind front on October 5. The lowpressure and positive-vorticity disturbances to the front triggered meridional air flow and low-pressure trough,thus induced a katabatic cold jet downward from the Qinghai-Tibet Plateau(QTP) passing through the YGP to the northwestern SCS. The second cooling reached the maximum SST drop 4d later after the maximum air temperature drop of –9℃ on October 11. The simultaneous air temperature and SST observations at three coastal stations reveal that it is this katabatic cold jet intrusion to lead the unusual SST cooling event.     

Numerical flow and performance analysis of a water-jet axial flow pump

The purpose of the present study is to investigate the performance and three-dimensional flow fields in a water-jet pump. TASCflow is employed to simulate the rotator-stator coupling flow field. A standard k-ε turbulence model combined with standard wall functions is used. In order to investigate the effect of a rear stator on flow fields, the flows in two water-jet pumps with and without a rear stator are studied. Computational fluid dynamics (CFD)-predicted overall performances are in good agreement with the experimental results. Then the flow fields, such as the pressure distribution on the blade surfaces, and the axial and tangential velocity distribution, especially the radial loading distribution, are investigated at different flow rates. In addition, the effects of a rear stator and different spacings between the rotor and the stator on the overall performance and the flow fields of the water-jet pump are also investigated.     

Theoretical Analysis of A Buoyant Jet Interacting with Small Amplitude Waves

A new theoretical solution is presented here for the dynamic characteristics of a buoyant jet due to opposing small amplitude waves.The conservation equations of mass,tangential momentum and vertical momentum are solved by the integral method which encompasses the Gaussian profiles of velocity and density.The action of waves is incorporated into the equations of motion as an external force and a new exact solution is obtained to predict the trajectory,velocity distribution and boundary thickness of the buoyant jet over an arbitrary lateral cross section.It is found that the velocity along the centerline is inversely proportional to the ratio of the momentum of the wave to the buoyant jet.The averaged boundary width varies with the fluctuation of the boundary width,the distance from the orifice and the velocity correction function.Owing to the motion d waves,the fluctuation of the boundary width is proportional to the wave steepness.     

2011年春夏长江中下游旱涝急转特征及原因分析

利用NCEP再分析资料,分析了影响2011年春夏季长江南部中下游地区发生旱涝急转的异常大气环流特征及影响因素。发现:长江南部中下游地区旱涝急转发生与西北太平洋副热带高压的变化有密切关系。副热带高压由弱到强的变化为降水提供了水汽条件,高空急流的变化则为降水提供了上升运动条件。进一步分析表明,西太平洋副热带高压西伸加强的原因与副热带高压加强前一候时间内孟加拉湾地区的异常对流加强有密切的关系。急流的变化则与陆地气温的季节变化和中纬度西太平洋强经向海表面温度(SST)梯度异常存在密切的联系。本文的研究表明:2011春夏季长江中下游地区旱涝急转现象的发生,是局地大气环流变化,南北半球大气相互影响以及海洋对大气环流影响的共同作用造成。     

Numerical study of sand scour with a modified Eulerian model based on incipient motion theory

Application of the standard Eulerian model to simulations of sand scour results in unrealistic phenomena. Therefore, the present work develops a modified Eulerian model based on sand incipient motion theory. The modified model is applied for simulating a two-dimensional single vertical jet and a moving planar jet. The simulation results generally demonstrate fairly good agreement with published results of scour profiles and the velocity contours of the water and sand phases. In addition, equations to describe self-similar scour profiles for the moving planar jet cases are given. The results demonstrate that the modified model efficiently and accurately simulates the two-dimensional sand scour produced by jets, particularly for the moving jet cases.     

雷诺数对圆形渐缩喷嘴湍流射流的影响

The present study systematically investigates by experiment the influence of Reynolds number (Re) on a turbulent jet issuing from a smoothly-contracting round nozzle. Measurements were performed for seven Reynolds numbers varying from Re = 4,050 to Re = 20,100 using single hot-wire anemometry and over an axial distance of 30 nozzle exit diameters. Although all the exit velocity profiles are of "top-hat" shape, these measurements reveal significant dependence on Re of the exit and downstream flows. The effect of Re on both the mean and turbulent fields is substantial for Re ＜ 10,000 and becomes weak beyond Re = 10,000. The length of the jet’s potential core and the far-field rates of decay and spread all depend significantly on Re.     

TRAJECTORY DIAGNOSIS OF AIR PARCELS IN HIGH-AND LOW-LEVEL JETS FOR A HEAVY RAINFALL CASE DURING MEIYU SEASON OF 1991

Trajectory diagnostic methods were used to analyze air parcels of high-and low-level jets during the heavy rainfall of 4-6 July 1991.It is found that air parcels above rainfall area travelled from the entrance of the high-level jet,passing through the jet center and reached the exit region.Upper tropospheric divergence over rainfall area resulted from decelerative motion of the jet flow.Warm and moist southwest flow converged and ascended ahead of the low-level jet.The decreasing of low-level pressure as a result of high-level divergence that caused the low-level jet became unexpectedly strong.     

9216号热带风暴的初步分析

对9216号热带风暴在9月1日02时中心分裂的原因,作了初步探讨,认为东南低空急流使热带风暴倒槽区的气旋性环流加强,以及低涡的吸引合并,是产生新中心的原因。青岛产生大暴雨的条件,是充沛的水汽,强烈的上升运动和长波槽东移影响。     

高压喷射注浆在上海鱼品厂污水处理工程中的应用

上海鱼品厂污水处理工程地基采用高压喷射注浆法加固,並作为深基坑的围护结构,用于大面积建筑工程和水工构筑物的尚不多见。经过高压旋喷工艺施工和充水予压试验以及运行的实践,业已证明应用新崛起的高压旋喷工艺成桩技术具有良好的技术效果和经济效益,加固软基和围护的综合功能是成功的。