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.

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.

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.

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.

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.

Influences of Structures on Urban Ventilation: A Numerical Experiment

Numerical simulations are carried out for the disturbed flow caused by three six-story buildings and a twenty-story tall tower respectively, as well as the distribution of automobile exhaust gas from a nearby road, based on the Peking University Model of Atmospheric Environment. The results show that the ventilation is better around the tall tower than around the three six-story residential buildings for the same number of households in the same urban region.

Research on an Urban Traffic Control System Based on DGPS

The basic principles of GPS (Global Positioning System) and DGPS (Differential GPS) are described. The principle and structure of vehicle navigation systems, and its application to the urban traffic flow guidance are analyzed. Then, an area coordinated adaptive control system based on DGPS and a traffic flow guidance information system based on DGPS are put forward, and their working principles and functions are researched. This is to provides a new way for the development of urban road traffic control systems.

Comparison of Three Macroinvertebrate Sampling Methods for Use in Assessment of Water Quality Changes in Flashy Urban Streams

The unique challenges associated with sampling of macroinvertebrates in flashy urban streams create a methods gap. These streams form isolated pools for much of the year, interspersed with spates that scour and deposit excessive amounts of sediment. Commonly used stream grab sampling methods, such as nets and Hess and Surber fixed-area samplers, work well in wadable streams with perennial flow. Deployed samplers (Hester-Dendy, gravel tray) can be used in waters with or without flow. We evaluated three methods which don’t require stream flow: modified Hester-Dendy (MHD), gravel tray, and bucket (a type of cylinder grab sample method), for their potential use in bioassessment of a project involving daylighting of a 180-m culvert on Congress Run, a flashy urban tributary to Mill Creek in Cincinnati, Ohio. Method efficacy was measured using three criteria: usability (level of effort and recoverability of samplers), variability, and community retrieval completeness. The bucket method required the lowest level of effort and had the highest sample recovery. The bucket sampler had the lowest variability for most metrics, including the critical metric of taxa richness, with a coefficient of variation (CV) of 20.9%. The MHD and tray samplers had taxa richness CVs of 42.9% and 53.9%, respectively. The bucket sampler also had the lowest CV (27.4%) for a multi-metric index. The bucket sampler performed best with respect to community retrieval completeness, with higher pooled and average taxa richness. The total number of taxa collected from all the replicate bucket grab samples (42) was greater than that collected by the HD and tray samplers combined (27). Multivariate analyses showed significant grouping with respect to methods and location. This study supports the bucket grab sampler method as a candidate for sampling of flashy urban streams.

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。

基于功率恒定的防饱和在线取电方法

基于厄流线圈取电装置提出了一种防止铁磁磁心饱和的方法,该方法使用旁路泄流电路将流入电流互感器过多的电流引入到旁路电路中消耗掉,将输出功率作为反馈值来调节旁路电路中开关管的关断,通过控制输出的功率大小,输电线路在宽范围电流内实现恒功率输出和防止电流互感器磁心到达饱和。根据电流互感器各方面的要求,建立电流互感器3D模型,将3D模型导入到Maxwell中对电流互感器本身进行有限元仿真分析,得到电流互感器内部各项参数,再将经过有限元分析的电流互感器模型导入到ANSYS中与外部电路组成取电电路进行联合仿真,通过仿真结果验证电流互感器的取电能力。再加入本次对电流互感器取电优化部分,通过电流互感器二次侧谐振的方式增加一次侧输电线路的等效阻抗,考虑到电流互感器磁心饱和的问题,采用旁路泄流电路将过多的电流通过旁路绕过电流互感器一次侧回到输电线路当中的方法解决。

考虑车道间差异和上下游断面关联的快速路交通流量预测方法

在现有的交通流量预测研究中,并未充分考虑断面道路内不同车道间的交通流量差异性以及上下游断面交通流量相关性。研究了结合主成分分析法(principal component analysis,PCA)与长短期记忆神经网络(long short-term memory,LSTM)的快速路交通流量预测框架,可以满足智能网联技术实时性和准确性的需求。收集城市快速路的交通流量数据,应用快速傅里叶变换方法(fast fourier transform,FFT)进行数据预处理,以提高原始数据的可预测性能;通过PCA方法对车道间的横向及纵向交通流量进行特征融合,建立车道间交通流量的关联性数据,以降低数据维度;并将关联性数据融入到LSTM模型中,进行车道级交通流量预测并汇总其预测结果,得到断面交通流量的预测值。选取武汉市三环线上的城市快速路卡口检测数据对本文方法进行验证。结果表明:考虑车道间差异和上下游断面关联的模型能够提高断面交通流量的预测精度,相较于仅考虑时间特征的断面交通流量预测结果,平均绝对误差、均方根误差和平均绝对百分比误差分别能降低6.66%,6.23%,17.51%;与单独考虑上下游断面关联性或者车道间差异的断面交通流量预测结果相比均具有更好的预测效果,在平均绝对误差、均方根误差和平均绝对百分比误差上的优化幅度,最低可降低1.53%,最高可降低12.88%;此外,所提的模型相较于支持向量机回归(support vector regression,SVR)和随机森林(random forest,RF)算法具有更高的预测精度;并且在分时段预测中,在晚高峰和平峰时段预测精度表现更佳。

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。

财政分权的供需协调效应研究

经济可持续增长是发展中面临的长期压力,供需协调是可持续增长的重要内生动力。根据耦合协调度模型对我国30个省份供需协调度进行评价,实证分析财政分权对供需耦合协调度的影响。研究表明,财政分权显著促进了供需协调,机制分析指出,财政分权通过提升政府创新偏好、城镇化水平、教育与医疗支出水平并降低城乡收入差距增强供需协调。调节效应分析表明,流动人口会弱化财政分权的协调效应,基本公共教育水平则强化其效应。门槛效应分析表明,人口密度与开放程度超过门槛值后财政分权的协调作用增强。