Effects of a Building’s Density on Flow in Urban Areas

The effects of a building＇s density on urban flows are investigated using a CFD model with the RNG k - ε turbulence closure scheme. Twenty-seven cases with different building＇s density parameters （e.g., building and street-canyon aspect ratios） are numerically simulated. As the building＇s density parameters vary, different flow regimes appear. When the street canyon is relatively narrow and high, two counterrotating vortices in the vertical direction are generated. The wind speed along streets is mainly affected by the building＇s length. However, it is very difficult to find or generalize the characteristics of the street-canyon flows in terms of a single building＇s density parameter. This is because the complicated flow patterns appear due to the variation of the vortex structure and vortex number. Volume-averaged vorticity magnitude is a very good indicator to reflect the flow characteristics despite the strong dependency of flows on the variation of the building＇s density parameters. Multi-linear regression shows that the volume-averaged vorticity magnitude is a strong function of the building＇s length and the street-canyon width. The increase in the building＇s length decreases the vorticity of the street-canyon flow, while, the increase in the street- canyon width increases the vorticity.

Physical Experiments to Investigate the Effects of Street Bottom Heating and Inflow Turbulence on Urban Street-Canyon Flow

The effects of street bottom heating and inflow turbulence on urbanstreet-canyon flow are experimentally investigated using a circulating water channel. Threeexperiments are carried out for a street canyon with a street aspect ratio of 1. Results from eachexperiment with bottom heating or inflow turbulence are compared with those without bottom heatingand appreciable inflow turbulence. It is demonstrated that street bottom heating or inflowturbulence increases the intensity of the canyon vortex. A possible explanation on how street bottomheating or inflow turbulence intensifies the canyon vortex is given from a fluid dynamicalviewpoint.

Multi-Level Approach of the Ecotoxicological Impact of a Combined Sewer Overflow on a Peri-Urban Stream

In periurban zones, urban wet weather discharges have been recognized as the most significant vector of pollution in aquatic environments. The discharge of this water without treatment into the aquatic environment could present an ecotoxicological risk for biocenosis. The aim of the INVASION project is to assess the potential ecotoxicological impact of a combined sewer overflow (CSO) on a peri-urban stream. A comparative study between upstream and downstream areas of the CSO allowed observing significant effects of this overflow on the river. We studied three layers of stream: surface water, benthic layer and hyporheic layer. To characterize the potential ecotoxicological risk of water and sediments, we used a battery of 4 bioassays: Daphnia magna, Vibrio fischeri, Brachionus calyciflorus and Heterocypris incongruens. In parallel, we measured the physico-chemical parameters: ammonium (NH4+), chromium (Cr), copper (Cu) and lead (Pb). An ecological risk is greatest for the hyporheic zone in downstream river, particularly for the solid phase. These results corroborated with the physico-chemical data obtained.

Towards Urban Resource Flow Estimates in Data Scarce Environments: The Case of African Cities

Data sourcing challenges in African nations have led many African urban infrastructure developments to be implemented with minimal scientific backing to support their success. In some cases this may directly impact a city’s ability to reach service delivery, economic growth and human development goals, let alone the city’s ability to protect ecosystem services upon which it relies. As an attempt to fill this gap, this paper describes an exploratory process used to determine city-level demographic, economic and resource flow data for African nations. The approach makes use of scaling and clustering techniques to form acceptable and utilizable representations of selected African cities. Variables that may serve as the strongest predictors for resource consumption intensity in African nations and cities were explored, in particular, the aspects of the Koppen Climate Zones, estimates of average urban income and GDP, and the influence of urban primacy. It is expected that the approach examined will provide a step towards estimating and understanding African cities and their resource profiles.

Study on the Mechanism of the Integration of Urban and Rural Development from the View of Elements Flow

Fromthe enterprise,individual and government,which are the three main economic behavior subject,this paper analysis factors impact of flow behavior main body and the change of the objective function,constraint function and the impact of the change of behavior equation,and then summarizes their effects on the integration of urban and rural development,to build fromexogenous shocks to the endogenous to adapt to the economic decision-making framework,clarify elements flow affect the running mechanismof the urban-rural integration.

The Research of Urban Rail Transit Sectional Passenger Flow Prediction Method

This paper studies the short-term prediction methods of sectional passenger flow, and selects BP neural network combined with the characteristics of sectional passenger flow itself. With a case study, we design three different schemes. We use Matlab to realize the prediction of the sectional passenger flow of the Beijing subway Line 2 and make comparative analysis. The empirical research shows that combining data characteristics of sectional passenger flow with the BP neural network have good prediction accuracy.

Application of unsteady flow simulation technology to lightening urban storm waterlogged disaster

The application of unsteady simulation to lightening urban storm waterlogged disaster involves six blocks: the main program, the database of drainage networks, the abstractions and losses block, the calculating inflow of sewer block, the drainage networks routing block and the waterlogged areas calculating block. This model can be used for simulating sewer surcharge and calculating area and water depth of waterlogged areas under storm conditions. The best design of rebuilding storm sewer system or combined sewer system can be provided by simulating existing state of built drainage pipeline. The model was used for rebuilding Shenyang drainage works last year, and the good results were obtained.

Urban Forest and Tree Valuation Using Discounted Cash Flow Analysis: Impact of Economic Components

Discounted cash flow analysis is one of the standard methods used to value urban forests and trees. It involves calculating today’s value for all benefits and costs attributed to an investment;that is discounting all cash flows to today’s value using an appropriate interest rate. This requires each benefit and cost be stated in terms of its cash flow. Urban tree benefits are complex. Little notice is given to the components of these benefits. Total urban tree benefits are a summation of partial benefits, including property value increase, storm water reduction, air quality improvement, carbon sequestration, natural gas savings, and electricity savings. We discuss the nature of these partial benefits, especially the geographical, temporal, diameter size, and rate of growth differences. These differences are even reflected in nursery stock valuation. Net present value analysis is used to illustrate the impact of these differences on financial return. An understanding of these components will prove valuable to those attempting to estimate urban forest and tree benefits.

城市蔓延对生态系统服务流的影响研究进展及对长江流域的启示

全面梳理城市蔓延对生态系统服务流的影响研究现状,有利于促进区域社会经济可持续发展。综述了城市蔓延对生态系统服务流的影响研究,结果表明:城市蔓延对生态系统服务流的影响研究仍处于起步阶段。城市蔓延通过载体传递和流动路径两方面改变了生态系统服务流的流量、流速和流向,导致生态系统服务流总量的减少和空间异质性的增加;城市蔓延的单项指标变化、城市蔓延的尺度以及城市蔓延的多情景模拟是探索城市蔓延对生态系统服务流影响过程的主要切入点;城市蔓延过程中引起的生态系统服务流扩散效应主要源于土地利用类型的变化和人类居住模式的改变。已有研究在一定程度上解释了城市蔓延对生态系统服务流的影响,但在揭示影响机理、剖析影响过程、评估影响效应以及探索生态系统服务流合理分配以促进城市可持续发展等方面的研究还存在较大空白。在此前提下,未来应基于“机理揭示-影响模拟-效应评估”的研究思路,建立长江流域城市蔓延对生态系统服务流影响研究框架,探索长江流域城市可持续发展与生态系统服务流的合理分配方案,实现长江流域生态保护与社会发展的协同共进。

城际数字信息流与经济内循环动力

国内需求增量是经济内循环的主要动力,能够为全国经济循环的良好运转提供重要支撑。数字化和智能化的发展使经济循环突破了本地化和实物化的限制,为经济循环注入新的特征。运用网络爬虫技术获取城际数字信息流数据,构建数字信息传输量、信息聚合能力和信息辐射能力3个要素刻画城际数字信息流,并结合微观个体、企业和城市3个层面的数据考察城际数字信息流对经济内循环动力的影响及传递机制。研究结果表明:一是增强城际数字信息流能够提升城市的经济内循环动力,其中,城市数字信息传输量对经济内循环动力的促进作用具有边际递增特征,而城市信息聚合能力和信息辐射能力的促进作用具有边际递减特征。二是城际数字信息流更密集、城市经济内循环动力更强和人均收入更高的城市通过城际数字信息流来促进城市经济内循环动力的作用更强,城际数字信息流的发展可能会加剧数字鸿沟现象。三是城际数字信息流通过人口移动效应增加居民消费,通过新建企业效应增加企业投资,通过技术进步效应延伸产业链和供应链,从而提升城市的经济内循环动力。

基于乘客OD间路径旅行时间的城市轨道交通客流分布计算模型的适用性研究

[目的]针对目前城市轨道交通(以下简称“城轨”)线网客流分布计算模型的客流计算结果与实际客流存在偏差的现象,需基于OD间路径的实际旅行时间,对基于多路径概率分配的客流分布计算模型的适用性展开研究。[方法]基于乘客OD间路径的实际旅行时间,分析揭示了现有城轨客流分布计算模型存在的主要问题;融合AFC(自动售检票)系统和ATS(列车自动监控)系统两类数据,构建并标定了基于乘客OD间路径旅行时间的城轨客流分布计算模型;对目前国内城轨系统广泛采用的基于多路径概率分配的城轨客流分布计算模型的适用性进行了分析与评价。[结果及结论]现有城轨客流分布计算模型在路径选择集和路径选择比例上存在主要问题。通过基于多路径概率分配的城轨客流分布计算模型获取的路径分配比例,得到的旅行时间分布模拟结果均为单峰,无法重现从AFC票卡提取的实际旅行时间分布的多峰情况。当城轨线网较为简单时,基于多路径概率分配的城轨客流分布计算模型基本适用;当线网规模不断增加,线网结构进一步复杂,列车运行方式的多样性、乘客出行行为的差异性等不断加大的条件下,该模型对于路径阻抗差异小的OD可能适用,而对于路径阻抗差异大的OD不适用。

要素流动对城乡融合发展的影响机理与空间分异研究

城乡要素双向自由流动有利于提高要素配置效率和优化城乡关系,促进城乡融合发展。现有关于要素流动对城乡融合发展的研究主要围绕传统生产要素对城乡融合发展的研究展开讨论,鲜有文献将数据这一新型生产要素纳入城乡要素流动范围并探索其对城乡融合发展的影响机理。基于2010—2021年中国31个省份的面板数据,在测算要素流动、城乡融合发展水平的基础上,构建双向固定效应模型、地理加权回归模型和中介效应模型实证检验要素流动对城乡融合发展的影响效应及作用机制。研究发现:第一,全国要素流动总指数呈现出小幅度增长的态势,位于均值之上的地区中64%是城乡融合发展试验区,说明城乡融合发展政策实施具有重要的引导作用;第二,要素流动显著促进城乡融合发展,这一结论在引入城乡之间距离作为工具变量进行内生性检验、采用删除4个直辖市和缩短时间窗口的方法进行稳健性检验之后仍然成立;第三,空间异质性分析中,劳动力、土地和数据要素始终表现出促进城乡融合发展的作用,随着时间的推移,土地要素对不同地区城乡融合发展影响程度逐渐增强、影响范围逐步扩大,技术要素对城乡融合发展的促进逐渐凸现,由华东和华南地区向东北和西南地区转移;第四,在要素流动影响城乡融合发展的过程中,电商销售是要素流动影响城乡融合发展的重要途径,农业机械化和产业结构变迁并未发挥出中介变量的作用,不同于已有的研究结果。因此,今后持续深化城乡融合发展的内涵与外延、拓展深度与广度;始终以习近平新时代中国特色社会主义思想为指导,运用科学的世界观和方法论,坚持整体推进与试点示范相统一的指导原则,推广实践中形成的典型经验。研究结论为城乡要素双向合理流动的机制建立、城乡融合发展体制机制的健全提供了理论和经验上的参考。

平行式快速路出口交通组织方法研究

针对平行式快速路出口排队溢出的交通问题,本文提出平行式快速路出口在无信号控制和信号控制情况下的5种交通组织方法,根据主辅车流的车头时距分布,建立主辅车流产生延误的计算模型。从方案选择的角度,以车均延误为评价指标,研究平行式快速路不同交通流量状态下出口最适合采用的交通组织方法。结果表明:当平行式快速路主路驶出车流和辅路车流的总流量低于1500 pcu·h^(-1)时,采取无信号让行的控制方法。主路驶出交通量较高时,采用主路驶出优先控制;辅路交通量较高时,采用辅路优先控制。当总流量在[1500,2300]pcu·h^(-1)时,采用辅路信号与让行相结合的控制方法。当主路驶出交通量较大时,采用辅路信号主路优先控制;当辅路交通量较大时,采用辅路信号辅路优先控制。当总流量高于2300 pcu·h^(-1)时,采用主辅全信号的控制方法。

基于要素的城乡融合识别研究——以重庆永川南大街街道为例

科学理解城乡融合发展状态,对于实现乡村振兴、建立良性的城乡关系有着重大作用。城乡融合的实质是城乡要素的融合,本文从资源禀赋、人口、经济、文化、生态、政治6个方面构建城乡融合水平评价指标体系,并对重庆市永川区南大街街道城乡融合程度加以识别,将南大街区分为高融合度区域(中心城区、小南村)、中融合度区域(大南村、代家店村、黄瓜山村)、低融合度区域(谭家坝村、八角寺村、兴隆村),并针对不同的城乡融合度区域提出未来发展方向。研究可为我国城乡融合发展与乡村转型发展的研究与实践提供借鉴。

一维管网与二维地表双向耦合的城市暴雨内涝模拟

为快速、准确模拟城市暴雨内涝演化过程,提出一种排水管网与上覆地表动态水力交互方法,构建了一维管网模型(SWMM)与二维水动力(LISFLOOD-FP)双向耦合的模型,解决了一维管网和二维地表的双向流量交换和时间同步难题。以上海外高桥地区为例,采用两次短历时降雨过程对耦合模型进行校准和验证,比较分析了单向、双向耦合的淹没范围与水深变化。结果表明:双向耦合模拟精度较高,在研究区具有良好的适用性;对于占比80%以上的轻度(<0.2m)积水区,单向、双向耦合的模拟积水面积比为1.21;对于中等(0.2~0.3 m)和重度(>0.3 m)积水区,单向耦合模拟结果趋于严重,该比值分别增至1.88和2.1。所构建的双向耦合模型能够揭示城区内涝积水、扩散及消退的全过程,可用于城市暴雨内涝推演,为内涝治理和灾害防御提供科学依据。

考虑动态随机客流的城市轨道交通列车时刻表仿真优化

为更加精准刻画动态随机客流与列车时刻表编制间的复杂匹配过程,综合考虑乘客动态随机到达过程、列车容量限制、车内拥挤度对乘客上下车速率影响、停站时间动态调整和列车运行安全防护等重要运营特征,构建城市轨道交通列车运行离散仿真模型。在此基础上,建立以最小化乘客平均候车时间为目标的随机非线性优化模型,并设计一种基于仿真的有限差分随机逼近算法,用于优化城市轨道交通发车方案。以国内某条线路的实际运营数据为例验证仿真模型及优化方法,结果表明所构建模型及算法具有较好的优化效果和计算效率,优化后的列车实绩运行时刻能更好地适应客流需求的动态随机性,且在不增加发车频次的前提下有效降低乘客平均候车时间,提升城市轨道交通运营管理水平。

劳动力流动能够影响农地资源配置效率吗?——来自全国农村固定观察点调查的证据

农地资源配置效率直接关系到现代化农业强国目标的实现,劳动力流动在其中发挥着重要影响。基于2009—2015年全国农村固定观察点数据,运用工具变量法识别劳动力流动对农地资源配置效率的影响。结果表明,劳动力流动能提高农地资源配置效率,这主要来源于土地过度配置时农户劳动力流动,而土地配置不足时这一效应消失。机制检验证实,劳动力流动通过土地流转和农业机械化机制,提高农地资源配置效率,但未发现资本回流机制发挥作用。因此,应破除劳动力流动的体制障碍,完善土地经营权流转服务体系和加快农机装备的推广应用,以优化农村土地资源配置和推进农业现代化发展。

资本下乡如何嵌入乡村空间合作治理?——以上海市乡悦华亭项目为案例

研究目的:以上海市乡悦华亭项目为案例,探究资本下乡背景下的乡村空间合作治理机制,为提升乡村空间治理效能和实现共同富裕提供参考。研究方法:理论分析、验证性案例研究、访谈法。研究结果:(1)规划环节要基于“协商自治”的原则让资本参与村庄规划编制工作,实现空间配置权的政企共享,并以“需求前置”为导向进行规划的弹性调整;(2)整治环节要以“地位平等”为前提进行空间使用权重构,厘清多元主体之间的委托代理关系;(3)运营环节要细化空间收益权,坚持“权责一致”的收益分配,建立信任保障机制规避资本主导运营的潜在风险,实现多方共赢。研究结论:乡村空间治理是多元主体广泛参与的“规划—整治—运营”一体化行动。资本基于合作治理的理念从上述三个环节嵌入乡村空间治理体系,重构乡村空间配置权、使用权和收益权,是借助市场力量促进乡村全面振兴的可行之策。

长三角城市群入境旅游流的时空演化与空间效应研究

科学研判入境旅游流的时空分异规律和动态演化特征,对推进入境旅游一体化高质量发展大有裨益。采用探索性空间数据分析、重心—标准差椭圆模型和空间马尔科夫链模型识别2005—2020年长三角城市群入境旅游流的时空分异及其动态演化规律,并运用空间杜宾模型探析入境旅游流的溢出效应。结果表明:研究期内入境旅游流整体呈缓慢增长态势,变异系数和相对基尼系数呈小幅度波动上升趋势,表明研究区入境旅游流相对差异总体较为平稳。空间上呈显著集聚特征,但高低集聚区渐趋缩小,入境旅游流分布日益空间均衡化;入境旅游流重心轨迹呈“东南—西北”移动趋势,西部地区入境旅游流增长速度较快;标准差椭圆主要位于长三角中部偏东地区,椭圆面积样本末期大于样本初期,东部是入境旅游发展的主要区域,入境旅游流发展的溢出效应逐渐增强。入境旅游流存在显著的“状态锁定”和“俱乐部趋同”现象,整体有序向高水平方向跃迁,与高值区为邻自身向上转移的概率将增大。入境旅游流具有显著的空间溢出效应,经济发展水平、对外开放程度和旅游基础设施是推动本地及邻地入境旅游流增长的重要因素,旅游资源禀赋、区位交通条件显著促进本地入境旅游流增长,对邻地的溢出影响则显著为负。