Numerical Simulation of Dam-Break Flows Using Radial Basis Functions: Application to Urban Flood Inundation

Dam-break flows pose significant threats to urban areas due to their potential for causing rapid and extensive flooding. Traditional numerical methods for simulating these events struggle with complex urban landscapes. This paper presents an alternative approach using Radial Basis Functions to simulate dam-break flows and their impact on urban flood inundation. The proposed method adapts a new strategy based on Particle Swarm Optimization for variable shape parameter selection on meshfree formulation to enhance the numerical stability and convergence of the simulation. The method’s accuracy and efficiency are demonstrated through numerical experiments, including well-known partial and circular dam-break problems and an idealized city with a single building, highlighting its potential as a valuable tool for urban flood risk management.

Urban Dynamics and Emergence of New Centers in the Dakar Region (Senegal)

Due to the status of the Dakar region as the former capital of AOF (French West Africa) and current capital of the Republic of Senegal, it is home to a very large part of the population and most of the socio-economic, administrative and cultural activities on a very small area of the country (0.28%). This situation makes it a very attractive region and subject to strong land pressure. The objective of this article is to study past and current urban dynamics as well as changes in natural spaces, in order to identify new urban centers. The methodological approach consists in analyzing satellite images to understand the evolution of different forms of spatial occupation in the Dakar region, and to study population movement flows and urban forms in order to reveal new urban centers. The results of the study show that the Dakar urban space is characterized by diverse forms which express a heterogeneous set of spaces. They also revealed the emergence of new clusters between 1986 and 2016, notably Ngor, Grand Yoff, Parcelles Assainies in the North-West, and Keur Massar and the North of the communes of Rufisque in the eastern part of the Dakar region.

Model construction of urban agglomeration expansion simulation considering urban flow and hierarchical characteristics

Since the launch of China’s reform and opening up policy,the process of urbanization in China has accelerated significantly.With the development of cities,inter-city interactions have become increasingly close,forming urban agglomerations that tend to be integrated.Urban agglomerations are regional spaces with network relationships and hierarchies,and have always been the main units for China to promote urbanization and regional coordinated development.In this paper,we comprehensively consider the network and hierarchical characteristics of an urban agglomeration,while using urban flow to describe the interactions of the inter-city networks and the hierarchical generalized linear model(HGLM)to reveal the hierarchical driving mechanism of the urban agglomeration.By coupling the HGLM with a cellular automata(CA)model,we introduced the HGLM-CA model for the simulation of the spatial expansion of an urban agglomeration,and compared the simulation results with those of the logistic-CA model and the biogeography-based optimization CA(BBO-CA)model.According to the results,we further analyzed the advantages and disadvantages of the proposed HGLM-CA model.We selected the middle reaches of the Yangtze River in China as the research area to conduct this empirical research,and simulated the spatial expansion of the urban agglomeration in 2017 on the basis of urban land-use data from 2007 and 2012.The results indicate that the spatial expansion of the urban agglomeration can be attributed to various driving factors.As a driving factor at the urban level,urban flow promotes the evolution of land use in the urban agglomeration,and also plays an important role in regulating cell-level factors,making the cell-level factors of different cities show different driving effects.The HGLM-CA model is able to obtain a higher simulation accuracy than the logistic-CA model,which indicates that the simulation results for urban agglomeration expansion considering urban flow and hierarchical characteristics are more accurate.When compared with the intelligent algorithm model,i.e.,BBO-CA,the HGLM-CA model obtains a lower simulation accuracy,but it can analyze the interaction of the various driving factors from a hierarchical perspective.It also has a strong explanatory effect for the spatial expansion mechanism of urban agglomerations.

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.

A Laboratory Model for the Flow in Urban Street Canyons Induced by Bottom Heating

Water tank experiments are carried out to investigate the convection flow induced by bottom heating and the effects of the ambient wind on the flow in non-symmetrical urban street canyons based on the PIV (Particle Image Visualization) technique. Fluid experiments show that with calm ambient wind, the flows in the street canyon are completely driven by thermal force, and the convection can reach the upper atmosphere of the street canyon. Horizontal and vertical motions also appear above the roofs of the buildings. These are the conditions which favor the exchange of momentum and air mass between the street canyon and its environment. More than two vortices are induced by the convection, and the complex circulation pattern will vary with time in a wider street canyon. However, in a narrow street canyon, just one vortex appears. With a light ambient wind, the bottom heating and the associated convection result in just one main vortex. As the ambient wind speed increases, the vortex becomes more organized and its center shifts closer to the leeward building.

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.

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。

数字经济要素流动与城市创新差距

为探讨数字经济对城市创新差距的影响,文章基于2011—2022年我国273个地级及以上城市的面板数据,测算城市数字经济指数和城市创新差距,并以数据要素流动环境为调节变量,同时选取人才要素流动和资本要素流动为中介变量,在此基础上进行计量分析。研究发现:数字经济发展扩大了本地城市创新差距,而对邻近地区表现出缩小城市创新差距的溢出效应;中介效应检验结果表明,数字经济发展能够促进人才和资本要素流动,但是扩大了城市创新差距;门槛效应检验结果表明,数字经济对城市创新差距的影响存在以数据要素流动环境为门槛变量的双重门槛效应,在第一个门槛值前后表现为扩大城市创新差距,在跨越第二个门槛值后,则表现为缩小城市创新差距;以数字经济为门槛变量时,则为单门槛效应,低于门槛值时表现为扩大城市差距,高于门槛值时则表现为缩小城市差距;在数据要素流动环境的调节作用下,数字经济缩小本地和邻近区的城市创新差距的能力显著增强。

地理学视角的乡村吸引力研究框架与重要议题

乡村吸引力是表征流动情境的乡村地域系统功能的重要指标,是乡村地理学理论研究的前沿领域。基于对乡村吸引力的研究进展与理论基础的回溯,从地理学视角建构乡村吸引力的理论框架,阐释其重要议题。①乡村吸引力研究从对吸引力乡村的零散阐述和乡村吸引力的单维分析,转向城乡交互作用的乡村吸引力概念、机制与评价体系的探索。人地关系地域系统理论、引力定律与引力模型、人口迁移理论与吸引物权理论,可为乡村吸引力研究提供理论支撑与观点启发。②围绕乡村吸引力“是何—如何—因何—能何”等科学问题,朝向“理论发展—服务实践—方法指导”的框架目标,以乡村地理学时空综合理论范式及其方法体系为支撑,建构乡村吸引力的理论框架。③从时空过程视角,解析基于乡村地域系统本底的、空间交互作用的乡村吸引力概念内涵;依据乡村吸引力的概念内涵与测评原理,建构乡村吸引力的测度框架;从空间关联和尺度转换的视角,识别乡村吸引力的地域类型与空间结构;遵循系统思维思维和尺度思想,探究乡村吸引力的内生发展机理和外源嵌入机制;考量历史过程和空间异质性,探讨乡村吸引力的提升路径与政策建议。研究旨在推进乡村吸引力的“时—空—人—地”综合分析,为乡村振兴战略实施与宜居宜业和美乡村建设提供理论借鉴与政策启示。

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.

短时疾增客流下的轨道交通换乘空间应变研究

伴随着以通勤为目的的城市轨道公共交通使用人数的增加,高峰期轨道交通站点内出现的快速变化的、大流量的短时疾增客流使得换乘站点难以安全、稳定、有效地承载客流并满足客流换乘需要。本研究通过实地调研与借助Anylogic平台的仿真来剖析短时疾增客流的特点及其对站内空间的作用效果,将现有的预制式、组装式、折叠式等应变技术或设备作为基础,提出建筑空间层面与站内设备设施层面的分类应变思路。建立应变应用场景与应变技术及措施的对应关系,并探究空间可变在动态优化地下轨道交通站内换乘空间方面的应用。研究成果可为未来既有轨道交通站点的优化设计提供参考。

人口纵向流动与城市高质量发展互动机制及政策研究

人口流动与产业发展密切配合,带来了改革开放以来的巨大人口红利等经济利益.随着我国城镇化率的不断提高,人口纵向流动将会成为城市经济高质量发展的重要推动力量,也成为城市高质量发展的重要体现和人口特征.在中国社会现代化进程中,人口纵向流动和城市高质量发展的互动机制显著增强,城镇高质量发展首先要推进人口的纵向流动,畅通社会向上流动通道、提高市民劳动者的平均受教育年限、推进城市整体职业化教育、促进人力资本与产业的匹配,不断调整优化人口纵向流动所需的制度支持.通过城市人口纵向流动促进中等收入群体的大范围扩展和经济社会地位的显著提升,实现人人向上的人口纵向流动下的城市高质量发展的共同富裕.

职业教育赋能县域城乡融合发展:逻辑理路、现实梗阻与实践路向

职业教育与县域城乡融合发展以人的全面发展为共同逻辑基点,职业教育依托技能人才培养、科教融汇发展、公共服务供给、教化育人实践和开放合作办学等赋能县域城乡要素流动、产业融合、社会公平、文化交融与治理协同。在加快构建新发展格局的时代背景下,发挥职业教育在县域城乡融合发展中的赋能作用,需要聚焦当前职业教育在人才培养、科技创新、资源配置、文化传播、开放合作领域的现实梗阻,以育人体系完善、科教融汇深化、资源配置优化、文化场域构建、开放格局打造为路向,推动县域城乡人才、产业、服务、文化和治理的多维融合。

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。