船闸口门区水流结构与连接段航道范围的探讨

从水力学角度和航行条件出发,来认识船闸口门区与连接段的水流结构,探讨连接段的范围。收集概化模型与枢纽物理模型的实验资料,采用归纳、总结和分析对比的方法,对概化和枢纽工程船闸引航道出口的水流结构、形态及回流长度等规律进行总结和讨论,对口门区与连接段的水流与航行条件进行分析。结果表明:概化模型的回流长度l1=7.0b比枢纽模型l1=4.6b要长;连接段的同岸与异岸连接,实质是主航道航线与引航道轴线夹角的大小;文中连接段长度是推轮能克服水流作用于船舶(队)漂移时的长度,否则需重新确定。     

二维及彩色多普勒超声对甲状腺癌的诊断价值

目的　探讨超声对甲状腺癌的诊断价值。方法　对 2 2例甲状腺癌患者进行二维超声及彩色多普勒血流显像 (CDFI)检查 ,全部病例均经手术病理证实。结果　超声图像改变可分为“低回声”型和“混合回声”型。 CDFI显示 :瘤内有较丰富的血供 ,收缩期流速较高 ,频谱增宽 ,阻力指数升高 (RI≥ 0 .70 )。同时可发现颈淋巴结肿大征象。超声诊断符合率为 54.55%。结论　在分析肿块二维声像特征的基础上 ,依据肿块内部血流信号的多少及血流参数测定 ,对甲状腺癌的判断具有重要价值     

温州石化基地围垦工程潮流泥沙数值模拟研究

使用TK-2D软件建立了瓯江口海区潮流泥沙数学模型,通过数值计算分析了温州石化基地围垦工程对瓯江北口、中水道、黄大岙、重山、沙头、小门、黄大峡等水道,以及对瓯江泄洪排涝和附近港区、海域的影响。研究结果表明:围垦工程对附近各港区、水道影响很小,温州石化基地围垦工程建设是可行的。     

Influence of slip boundary on flow separation and drag of flow past bluff body at high Reynolds numbers北大核心CSCD

［Objectives］Flow separation increases the drag and noise of underwater vehicles, and influences the controllability of their control surfaces. Therefore, the influence of slip caused by superhydrophobic surfaces on drag reduction and flow separation is studied. ［Methods］A partial slip boundary condition is developed, and the flow around a circular cylinder and foil with a slip boundary at high Reynolds numbers are numerically simulated. ［Results］The results show that the when the slip length increases, the flow around the cylinder goes through three stages: the turbulent Kármán vortex street, laminar Kármán vortex street and non-separation Stokes flow. The drag coefficient increases first and then decreases, and the vortex shedding frequency increases. For flow around a foil, the separation position moves downstream until the separation region disappears when the slip length increases, and the drag coefficient decreases while the lift coefficient increases. ［Conclusions］The results of this study show that for flow past bluff body at high Reynolds number, the slip boundary can control flow separation and reduce drag effectively, providing technical support for the application of superhydrophobic surfaces for the flow control of underwater vehicle appendages. © 2022 Journal of Clinical Hepatology. All rights reserved.     

城市轨道交通站点数据链客流预测方法研究

城市轨道交通客流预测数据是城市轨道交通设计与运营的重要依据与基础,在总结分析我国城市轨道交通客流预测经验及研究成果的基础上,提出基于城市土地利用法的站点数据链客流预测方法,系统介绍该预测方法的理论体系,并以杭州地铁4号线为例,验证站点数据链客流预测方法的科学性与合理性,以期使该预测方法在客流预测与校核中具有指导意义。     

Platoons of connected vehicles can double throughput in urban roads

Intersections are the bottlenecks of the urban road system because an intersection’s capacity is only a fraction of the maximum flows that the roads connecting to the intersection can carry. This capacity can be increased if vehicles cross the intersections in platoons rather than one by one as they do today. Platoon formation is enabled by connected vehicle technology. This paper assesses the potential mobility benefits of platooning. It argues that saturation flow rates, and hence intersection capacity, can be doubled or tripled by platooning. The argument is supported by the analysis of three queuing models and by the simulation of a road network with 16 intersections and 73 links. The queuing analysis and the simulations reveal that a signalized network with fixed time control will support an increase in demand by a factor of (say) two or three if all saturation flows are increased by the same factor, with no change in the control. Furthermore, despite the increased demand vehicles will experience the same delay and travel time. The same scaling improvement is achieved when the fixed time control is replaced by the max pressure adaptive control. Part of the capacity increase can alternatively be used to reduce queue lengths and the associated queuing delay by decreasing the cycle time. Impediments to the control of connected vehicles to achieve platooning at intersections appear to be small.     

我国城市轨道交通网络运营盈利能力的实证分析

为从财务可持续性角度探讨城市轨道交通网络盈亏平衡问题，本文建立了以票款净收入和运营成本为基础的网络运营盈亏平衡模型，定量分析票价率、客运强度、票价优惠策略等要素对运营企业盈利能力的影响。实证研究表明：我国不同城市票价率水平差异较大，多数城市体验了初期线网扩张带来的网络化运营红利；但随着网络进一步扩大到市区边缘或郊区，多数城市网络总规模超过300 km后，全网平均客流强度呈下降态势，企业盈利能力有所下降，政府补贴压力增加。由于城市轨道交通在解决通勤出行中的公益性定位，以及不同城市居民人均可支配收入水平和城市政府财政收入的差异，应进一步研究不同城市经济发展水平下票价水平、线网规模及技术制式、不同线路功能定位的关系，以提高轨道交通网络运营盈利能力，促进我国城市轨道交通行业的可持续发展。     

Dynamic congestion pricing with day-to-day flow evolution and user heterogeneity

This paper investigates evolutionary implementation of congestion pricing schemes to minimize the system cost and time, measured in monetary and time units, respectively, with the travelers’ day-to-day route adjustment behavior and their heterogeneity. The travelers’ heterogeneity is captured by their value-of-times. First, the multi-class flow dynamical system is proposed to model the travelers’ route adjustment behavior in a tolled transportation network with multiple user classes. Then, the stability condition and properties of equilibrium is examined. We further investigate the trajectory control problem via dynamic congestion pricing scheme to derive the system cost, time optimum, and generally, Pareto optimum in the sense of simultaneous minimization of system cost and time. The trajectory control problem is modeled by a differential–algebraic system with the differential sub-system capturing the flow dynamics and the algebraic one capturing the pricing constraint. The explicit Runge–Kutta method is proposed to calculate the dynamic flow trajectories and anonymous link tolls. The method allows the link tolls to be updated with any predetermined periods and forces the system cost and/or time to approach the optimum levels. Both analytical and numerical examples are adopted to examine the efficiency of the method.     

基于PTC材料加热的柴油喷油器模拟

文章选用居里温度为60℃的陶瓷基PTC材料作为加热元件,利用流体力学计算软件Fluent模拟了两种不同燃油流量下用PTC材料加热柴油的温度场变化。仿真结果表明,利用PTC材料加热可有效提高燃油温度,改善冷启动性能,且随着燃油流量的增加,喷油器出口温度呈下降趋势。