Flow In Urban Environment Research Articles

Raspberry Pi Based Real Time Lane, Obstacle and Traffic Signal Detection System

The project proposes a Raspberry Pi-based system for real-time detection of lanes, obstacles, and traffic signals to improve road safety and assist drivers. The system uses computer vision algorithms and sensor data to provide situational awareness for vehicles. The lane detection module uses image processing to identify lane markings and estimate vehicle position, while the obstacle detection module uses visual and distance sensors to identify obstacles in the vehicle’s path. The traffic signal detection module uses image processing to identify and interpret traffic signals, helping drivers adhere to traffic regulations. The integration of these modules on a Raspberry Pi platform allows for compact deployment within vehicles, ensuring timely response to dynamic road conditions. This project offers a promising solution for intelligent transportation systems aimed at reducing accidents and improving traffic flow in urban environments. Key Words: Spotting,hough transform,obstascle detection,rasp cam,traffic signal detection,lane.

Space Syntax at Expression of Science on User Flows in Open and Closed Spaces Aimed at Achieving the Sustainable Development Goal: A Review

Space syntax is utilized to model flows through open and closed built environments, which enables project innovation by rethinking the design of spaces on a global scale with better flow quality. Therefore, studies focused on spatial syntax, when related to comprehensive flows in open and closed spaces, provide a holistic and valuable understanding of the dynamics of user flows in the urban environment from a perspective centered on the United Nation’s Sustainable Development Goal (SDG) 11. This goal requires urban planners and designers to use approaches that support future decisions focused on urban design and planning. The object of investigation of this bibliographic study consists of an approach to representing space syntax in open spaces and closed spaces on a global scale. This study aims to analyze the concepts of pedestrian flows (open and closed) by a space syntax-based bibliographical approach on a global scale, demonstrating the capability of improvements in SDG 11 as applied to the architecture of sustainable flows. Methodologically, bibliographic searches were carried out using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) method in databases linked to Scopus and ScienceDirect, focusing on space syntax in relation to the following terms: “open spaces” and “closed spaces”. Using the PRISMA method, 1986 manuscripts dealing with the term “open spaces” and 454 manuscripts dealing with the term “closed spaces” were identified, with the manuscripts most relevant to the topic being selected, followed by a frequency analysis based on a Content Analysis Method (CAM) to identify words with a degree of similarity, related to “spatial syntax: flow in urban environments” and “spatial syntax in closed built systems” in relation to the SDG 11. The results demonstrate the relevance of seven manuscripts in open spaces and four manuscripts in closed spaces related to space syntax. Frequency analysis identified open spaces and produced terms with frequencies such as space = 79 and shape = 46, showing a higher frequency in flows. In closed spaces, the literature has shown that the central term corresponds to space = 79 and flow = 76, making it possible to evaluate flows in circulation areas within the built environment. This study allows a better understanding of flows, highlighting the importance of the urban architecture in the functionality of user flows in sustainable environments, which is capable of contributing to the SDG 11, in the interface of architectural projects on a global scale.

A coupled multigrid solver with wall functions forthree‐dimensionalturbulent flows over urban‐like obstacles

AbstractOne of the objectives for rapid operational tools for urban atmospheric events isfastcalculation of the computational fluid dynamics (CFD) models for multiphase flows to respond to deliberate or accidental chemical, biological, and radiological (CBR) releases. This article addresses the implementation of a coupled multigrid (CMG) method in an in‐house pressure‐based low‐speed CFD solver called STREAM in detail, including its validation against several 2D/3D benchmark test problems pertinent to urban flows. It was identified that solving the advection–diffusion equation of concentration for the prediction of dispersion of CBR agents is computationally very efficient, provided that the input data of turbulence viscosity and flow fields can be supplied in a timely fashion. Since most pressure‐based solvers adopt the segregated SIMPLE algorithm, and the coupling among different (linearized) equations is established via outer iterations on a single grid, its convergence rate is generally poor, particularly for turbulent flows in urban environments involving massive flow separation. The proposed approach and main contribution here is to adopt CMG to solve turbulent flows over urban‐like obstacles efficiently in 2D and particularly 3D, in which the standard Reynolds‐averaged Navier–Stokes turbulence model in conjunction with wall functions is employed. The results presented in this paper demonstrate a speedup ratio based on work unit (WU) for 3D laminar cavity flows of roughly 100, and 25 for 3D turbulent urban flow, depending on grid sizes.

Impact of Shared Lanes on Performance of the Combined Flexible Lane Assignment and Reservation-based Intersection Control

Benefiting from opportunities offered by connected and autonomous vehicles (CAVs), a concept called Combined Alternate-Direction Lane Assignment and Reservation-based Intersection Control (CADLARIC) was proposed recently for management of directionally unrestricted traffic flows in urban environments. In CADLARIC, resolution of vehicular conflicts is distributed between links and intersections to prevent intersections from turning into traffic bottlenecks. Although CADLARIC has shown promising results, it has been observed that, once traffic volume on a certain lane reaches “physical capacity,” adding more traffic on that lane degrades performance of the entire system, as each lane is exclusively dedicated to a particular movement. To overcome this problem, Combined Flexible Lane Assignment and Reservation-based Intersection Control (CFLARIC) is proposed, which offers more flexible lane assignment possibilities. While CFLARIC allows left- and right-turning lanes to be shared with through traffic, it is unclear how much through traffic should be assigned to turning lanes. Thus, this study investigates which strategy is the most beneficial when reassigning extra through traffic to the turning lanes. This goal is divided into two objectives: 1. Identify which lanes should be shared, and 2. Find a close-to-optimal amount of through traffic that should be assigned to the identified shared lane. The proposed CFLARIC strategies are compared with Fixed-Time Control (FTC), Full Reservation-based Intersection Control (FRIC), and CADLARIC for multiple demand scenarios. The results show that the best performing CFLARIC strategies outperform FTC, FRIC, and CADLARIC for delay and number of stops, and reduce the number of conflicting situations compared with FRIC and CADLARIC.

On the Experimental, Numerical and Data-Driven Methods to Study Urban Flows

Understanding the flow in urban environments is an increasingly relevant problem due to its significant impact on air quality and thermal effects in cities worldwide. In this review we provide an overview of efforts based on experiments and simulations to gain insight into this complex physical phenomenon. We highlight the relevance of coherent structures in urban flows, which are responsible for the pollutant-dispersion and thermal fields in the city. We also suggest a more widespread use of data-driven methods to characterize flow structures as a way to further understand the dynamics of urban flows, with the aim of tackling the important sustainability challenges associated with them. Artificial intelligence and urban flows should be combined into a new research line, where classical data-driven tools and machine-learning algorithms can shed light on the physical mechanisms associated with urban pollution.

Method of measuring the acoustic characteristics of traffic flows in urban environments

When examining doctors ' workplaces, it was found that traffic noise inside the premises exceeds sanitary standards. For medical institutions, the sanitary standards are 50 dBA, and for fullscale measurements, they were 60-63 dBA. Traffic noise levels have a maximum at low frequencies (31.5 Hz) and a minimum at high frequencies (16,000 Hz).

Assessment of the influence of various tree species and their parameters on the behaviour of wind flows in urban environments (on the example of the RUDN University campus, Moscow)

Urban environments are constantly growing, as a result of which natural surface covers are replaced by artificial materials. These changes have a strong impact on the wind fields in these urban environments, changing speeds and directions of wind flows. The aim of this study is to assess the effects of various tree parameters on the behaviour of wind flows in an urban environment. The EnviMet software package is used to model wind fields. The study is conducted in the city of Moscow on the RUDN University campus. Ten different kinds of trees are identified with characteristics such as tree height, crown width, trunk height, and the LAD (Leaf Area Density) index. For these species, a similar analysis is carried out to assess their impact on the wind field. The height of the trunk has a significant effect on the wind field at the pedestrian level; depending on the parameter, the wind speed and the area of wind gusts increase. Large crowns create a protective barrier, reducing wind activity. At the same time, a high LAD index creates low wind permeability, as a result of which the wind flows are refracted, and dangerous zones arise. On the other hand, a high LAD index reduces the area of wind gusts.

Large-Eddy Simulations of Turbulent Flows around Buildings Using the Atmospheric Boundary Layer Environment–Lattice Boltzmann Model (ABLE-LBM)

ABSTRACTA three-dimensional, prognostic Atmospheric Boundary Layer Environment–Lattice Boltzmann Model (ABLE-LBM) using the multiple-relaxation-time lattice Boltzmann method was developed for large-eddy simulation of urban boundary layer atmospheric flows. In this article we describe the details of the ABLE-LBM for urban flow, its implementation of complex boundaries, and the subgrid turbulence parameterizations. As a first validation of this newly developed model, the simulation results were evaluated with two wind-tunnel datasets that were collected using particle image velocimetry and Irwin probes, respectively. The ABLE-LBM simulations use the same building layout and Reynolds numbers used in the laboratory wind tunnels. The ABLE-LBM simulations compare favorably to both laboratory studies in terms of the mean wind fields. The turbulent fluxes simulated by the model in the observational planes also agreed reasonably well with the laboratory results. The model produced urban canyon flows and vortices on the lee side and over the building tops that are similar to those of the laboratory studies in strength and location. This validation study using laboratory data indicates that our new ABLE-LBM is a viable approach for modeling atmospheric turbulent flows in urban environments. A numerical implementation using a graphics processing unit shows that real-time simulations are achieved for these two validation cases.

Impact of turbulence models and roughness height in 3D steady RANS simulations of wind flow in an urban environment

The accuracy and reliability of 3D steady RANS CFD simulations of wind flow in urban environments can be affected by numerical settings including the turbulence model and the imposed roughness heights. In that regard, various k-ε and k-ω turbulence models and roughness height (ks) values are commonly used when predicting wind flow in urban environments. However, it is insufficiently known to which extent the CFD results may be influenced by these settings when simulating wind flows in complex urban environments with large changes in surface roughness. This is the scope of the present paper, for which wind-tunnel (WT) measurements and CFD simulations were performed on a reduced-scale model (1:300) of a district of Livorno (Italy). Mean wind speed (U), turbulent kinetic energy (k) and turbulence dissipation rate (ε) profiles from WT measurements and CFD simulations were compared at 25 positions and deviations between experimental and numerical results were quantified by three metrics: fractional bias, correlation coefficient and fraction of data within a factor of 1.3. The turbulence model selection had a larger impact compared to the surface roughness selection on U, k and ε values. The best and worst performing turbulence models (e.g. for α = 240° at 0.02 m above the bottom) showed a deviation in terms of correlation (0.89 and 0.61, respectively) of about 0.28. Conversely, the best and worst performing roughness set, (e.g. for α = 240° at 0.02 m above the bottom), showed a deviation in terms of correlation (0.77 and 0.78, respectively) of only 0.01.

Modeling and Characterization of Traffic Flows in Urban Environments.

Currently, one of the main challenges faced in large metropolitan areas is traffic congestion. To address this problem, adequate traffic control could produce many benefits, including reduced pollutant emissions and reduced travel times. If it were possible to characterize the state of traffic by predicting future traffic conditions for optimizing the route of automated vehicles, and if these measures could be taken to preventively mitigate the effects of congestion with its related problems, the overall traffic flow could be improved. This paper performs an experimental study of the traffic distribution in the city of Valencia, Spain, characterizing the different streets of the city in terms of vehicle load with respect to the travel time during rush hour traffic conditions. Experimental results based on realistic vehicular traffic traces from the city of Valencia show that only some street segments fall under the general theory of vehicular flow, offering a good fit using quadratic regression, while a great number of street segments fall under other categories. Although in some cases such discrepancies are related to lack of traffic, injecting additional vehicles shows that significant mismatches still persist. Thus, in this paper we propose an equation to characterize travel times over a segment belonging to the sigmoid family; specifically, we apply logistic regression, being able to significantly improve the curve fitting results for most of the street segments under analysis. Based on our regression results, we performed a clustering analysis of the different street segments, showing that they can be classified into three well-defined categories, which evidences a predictable traffic distribution using the logistic regression throughout the city during rush hours, and allows optimizing the traffic for automated vehicles.

Street-canyon pollution with respect to urban-array complexity: The role of lateral and mean pollution fluxes

The prediction of pollution within street canyons remains challenging due to the complexity of turbulent flows in urban environments. To improve our understanding of these flows and their relation to the ventilation of street-canyons, we studied pollution fluxes through all street-canyon openings and their balance with respect to urban-array complexity using large-eddy simulations (LES). We validated the LES with wind-tunnel measurements using mean velocities and concentrations and the mean total and turbulent pollution fluxes at the top and lateral openings of the street canyons with either uniform or nonuniform heights and pitched roofs. The LES confirm and extend recent findings about the importance of mean horizontal pollution fluxes for pollutant transport within a street network. The mean fluxes have at least the same dominance as the turbulent ones in case of lateral openings. In case of top openings, the mean fluxes clearly dominate if openings at the roof eaves are selected. While pollutant removal and entrainment through lateral openings are negligible in case of uniform canyons, they are notable in case of nonuniform canyons. We demonstrate that urban roof height nonuniformity does not necessarily enhance the street-canyon ventilation because it worsens (by a factor of 1.1) or improves (by a factor of 1.5) the ventilation compared with the urban uniform height.

3D WindScanner lidar measurements of wind and turbulence around wind turbines, buildings and bridges

WindScanner is a distributed research infrastructure developed at DTU with the participation of a number of European countries. The research infrastructure consists of a mobile technically advanced facility for remote measurement of wind and turbulence in 3D. The WindScanners provide coordinated measurements of the entire wind and turbulence fields, of all three wind components scanned in 3D space. Although primarily developed for research related to on- and offshore wind turbines and wind farms, the facility is also well suited for scanning turbulent wind fields around buildings, bridges, aviation structures and of flow in urban environments. The mobile WindScanner facility enables 3D scanning of wind and turbulence fields in full scale within the atmospheric boundary layer at ranges from 10 meters to 5 (10) kilometers. Measurements of turbulent coherent structures are applied for investigation of flow pattern and dynamical loads from turbines, building structures and bridges and in relation to optimization of the location of, for example, wind farms and suspension bridges. This paper presents our achievements to date and reviews briefly the state-of-the-art of the WindScanner measurement technology with examples of uses for wind engineering applications.

Performance of Detached Eddy Simulation applied to Analysis of a University Campus Wind Environment

This paper investigates the performance of a Detached Eddy Simulation (DES) turbulence modelling approach implemented in the open-source CFD library OpenFOAM to analysis of external flows in urban environments in the context of micro wind turbine applications. For this purpose, we examine the predicted flows at the De Montfort university (DMU) campus in Leicester, UK and make comparisons with high frequency wind data recorded by three ultrasonic anemometers. We find that the CFD results using the DES model are in good agreement with the anemometer data in terms of both relative wind speeds and directions. We conclude that DES offers robustness and accuracy over a range of wind conditions and is well suited to analysis of wind energy potentials in complex urban environments.

Modelling urban airflow and natural ventilation using a GPU-based lattice-Boltzmann method

Simulation of urban airflow and ventilation potential is desirable for building design, however the complex and transient nature of flows in urban environments makes this a challenging task. This study aims to evaluate the capability of a lattice-Boltzmann method (LBM) code deployed on a graphical processing unit (GPU) using a large eddy sub-grid turbulence model for cross-flow ventilation of an idealised cubical building at wind-tunnel scale. ANSYS Fluent is used as a numerical comparison. Façade pressure and ventilation of the cube are investigated for parallel and perpendicular wind directions with the building in isolation and regular array format. Pressures, velocities and ventilation rates are compared to experimental data from wind tunnel and full-scale experiments of the Silsoe cube. Simulations compare favourably with experimental values and between each other. When the cube was surrounded by other cubes, simulations suggest that vortex shedding from up-wind buildings provides pulsating ventilation, improving airflow ingress in the parallel wind cases. A parametric study showed that doubling surrounding building height had a small negative effect on ventilation but was mitigated by high levels of downdraft and flow fluctuations in the vertical plane. Comparatively, doubling the central building height had a net positive effect but caused high internal airspeeds for both angles. The LBM code running on one GPU was several orders of magnitude faster than Fluent with similar accuracy. Simulation time using the LBM approach was several orders of magnitude lower than Fluent.

A bird\u2019s eye view: using circuit theory to study urban landscape connectivity for birds

ContextConnectivity is fundamental to understanding how landscape form influences ecological function. However, uncertainties persist due to the difficulty and expense of gathering empirical data to drive or to validate connectivity models, especially in urban areas, where relationships are multifaceted and the habitat matrix cannot be considered to be binary.ObjectivesThis research used circuit theory to model urban bird flows (i.e. ‘current’), and compared results to observed abundance. The aims were to explore the ability of this approach to predict wildlife flows and to test relationships between modelled connectivity and variation in abundance.MethodsCircuitscape was used to model functional connectivity in Bedford, Luton/Dunstable, and Milton Keynes, UK, for great tits (Parus major) and blue tits (Cyanistes caeruleus), drawing parameters from published studies of woodland bird flows in urban environments. Model performance was then tested against observed abundance data.ResultsModelled current showed a weak yet positive agreement with combined abundance for P. major and C. caeruleus. Weaker correlations were found for other woodland species, suggesting the approach may be expandable if re-parameterised.ConclusionsTrees provide suitable habitat for urban woodland bird species, but their location in large, contiguous patches and corridors along barriers also facilitates connectivity networks throughout the urban matrix. Urban connectivity studies are well-served by the advantages of circuit theory approaches, and benefit from the empirical study of wildlife flows in these landscapes to parameterise this type of modelling more explicitly. Such results can prove informative and beneficial in designing urban green space and new developments.

Crowdsourcing in ITS: The State of the Work and the Networking

In the last decade, crowdsourcing has emerged as a novel mechanism for accomplishing temporal and spatial critical tasks in transportation with the collective intelligence of individuals and organizations. This paper presents a timely literature review of crowdsourcing and its applications in intelligent transportation systems (ITS). We investigate the ITS services enabled by crowdsourcing, the keyword co-occurrence and coauthorship networks formed by ITS publications, and identify the problems and challenges that need further research. Finally, we briefly introduce our future works focusing on using geospatial tagged data to analyze real-time traffic conditions and the management of traffic flow in urban environment. This review aims to help ITS practitioners and researchers build a state-of-the-art understanding of crowdsourcing in ITS, as well as to call for more research on the application of crowdsourcing in transportation systems.

Coupled 802.11 Flows in Urban Channels: Model and Experimental Evaluation

Contending flows in multihop 802.11 wireless networks compete with two fundamental asymmetries: 1) channel asymmetry, in which one flow has a stronger signal, potentially yielding physical layer capture; and 2) topological asymmetry, in which one flow has increased channel state information, potentially yielding an advantage in winning access to the channel. Prior work has considered these asymmetries independently with a highly simplified view of the other. However, in this paper, we perform thousands of measurements on coupled flows in urban environments and build a simple yet accurate model that jointly considers information and channel asymmetries. We show that if these two asymmetries are not considered jointly, throughput predictions of even two coupled flows are vastly distorted from reality when traffic characteristics are only slightly altered (e.g., changes to modulation rate, packet size, or access mechanism). These performance modes are sensitive not only to small changes in system properties, but also small-scale link fluctuations that are common in an urban mesh network. We analyze all possible capture relationships for two-flow subtopologies and show that capture of the reverse traffic can allow a previously starving flow to compete fairly. Finally, we show how to extend and apply the model in domains such as modulation rate adaptation and understanding the interaction of control and data traffic.

Coupled urban wind flow and indoor natural ventilation modelling on a high-resolution grid: A case study for the Amsterdam ArenA stadium

Wind flow in urban environments is an important factor governing the dispersion of heat and pollutants from streets, squares and buildings. This paper presents a coupled CFD modelling approach for urban wind flow and indoor natural ventilation. A specific procedure is used to efficiently and simultaneously generate the geometry and the high-resolution body-fitted grid for both the outdoor and indoor environment. This procedure allows modelling complex geometries with full control over grid quality and grid resolution, contrary to standard semi-automatic unstructured grid generation procedures. It also provides a way to easily implement various changes in the model geometry and grid for parametric studies. As a case study, a parametric analysis of natural ventilation is performed for the geometrically complex Amsterdam ArenA stadium in the Netherlands. The turbulent wind flow and temperature distribution around and inside the stadium are solved with the 3D steady Reynolds-averaged Navier–Stokes equations. Special attention is given to CFD solution verification and validation. It is shown that small geometrical modifications can increase the ventilation rate by up to 43%. The coupled modelling approach and grid generation procedure presented in this paper can be used similarly for future studies of wind flow and related processes in complex urban environments.

Benchmarking 2D hydraulic models for urban flooding

This paper describes benchmark testing of six two-dimensional (2D) hydraulic models (DIVAST, DIVASTTVD, TUFLOW, JFLOW, TRENT and LISFLOOD-FP) in terms of their ability to simulate surface flows in a densely urbanised area. The models are applied to a 1·0 km × 0·4 km urban catchment within the city of Glasgow, Scotland, UK, and are used to simulate a flood event that occurred at this site on 30 July 2002. An identical numerical grid describing the underlying topography is constructed for each model, using a combination of airborne laser altimetry (LiDAR) fused with digital map data, and used to run a benchmark simulation. Two numerical experiments were then conducted to test the response of each model to topographic error and uncertainty over friction parameterisation. While all the models tested produce plausible results, subtle differences between particular groups of codes give considerable insight into both the practice and science of urban hydraulic modelling. In particular, the results show that the terrain data available from modern LiDAR systems are sufficiently accurate and resolved for simulating urban flows, but such data need to be fused with digital map data of building topology and land use to gain maximum benefit from the information contained therein. When such terrain data are available, uncertainty in friction parameters becomes a more dominant factor than topographic error for typical problems. The simulations also show that flows in urban environments are characterised by numerous transitions to supercritical flow and numerical shocks. However, the effects of these are localised and they do not appear to affect overall wave propagation. In contrast, inertia terms are shown to be important in this particular case, but the specific characteristics of the test site may mean that this does not hold more generally.

Interaction of Nocturnal Low-Level Jets with Urban Geometries as Seen in Joint Urban 2003 Data

Abstract Because accurate modeling of atmospheric flows in urban environments requires sophisticated representation of complex urban geometries, much work has been devoted to treatment of the urban surface. However, the importance of the larger-scale flow impinging upon the urban complex to the flow, transport, and dispersion within it and downwind has received less attention. Building-resolving computational fluid dynamics (CFD) models are commonly employed to investigate interactions between the flow and three-dimensional structures that make up the urban environment; however, such models are typically forced with simplified boundary conditions that fail to include important regional-scale phenomena that can strongly influence the flow within the urban complex and downwind. This paper investigates the interaction of an important and frequently occurring regional-scale phenomenon, the nocturnal low-level jet (LLJ), with urban-scale turbulence and dispersion in Oklahoma City, Oklahoma, using data from the Joint Urban 2003 (JU2003) field experiment. Two simulations of nocturnal tracer release experiments from JU2003 using Lawrence Livermore National Laboratory’s Finite-Element Model in 3 Dimensions and Massively Parallelized (FEM3MP) CFD model yield differing levels of agreement with the observations in wind speed, turbulence kinetic energy (TKE), and concentration profiles in the urban wake, approximately 750 m downwind of the central business district. Profiles of several observed turbulence parameters at this location indicate characteristics of both bottom-up and top-down boundary layers during each of the experiments. These data are consistent with turbulence production due to at least two sources, the complex flow structures of the urban area and the region of strong vertical wind shear occurring beneath the LLJs present each night. Strong LLJs occurred each night, but their structures varied considerably, resulting in significant differences in the magnitudes of the turbulence parameters observed during the two experiments. Because FEM3MP was forced only with an upwind velocity profile that did not adequately represent the LLJ, the downward propagation of TKE observed during the experiments was absent from the simulations. As such, the differing levels of agreement between the simulations and observations during the two experiments can, in part, be explained by their exclusion of this important larger-scale influence. The ability of the Weather Research and Forecast Model (WRF) to simulate accurate velocity fields during each night was demonstrated, and the use of regional-scale simulation data was identified as a promising approach for representing the effects of important regional-scale phenomena such as the LLJ on urban-scale simulations.