scholarly journals Effect of Street Canyon Shape and Tree Layout on Pollutant Diffusion under Real Tree Model

2020 ◽  
Vol 12 (5) ◽  
pp. 2105 ◽  
Author(s):  
Le Wang ◽  
Junwei Su ◽  
Zhaolin Gu ◽  
Qingxiang Shui
Keyword(s):  
Street Canyon ◽  
Source Model ◽  
Pollutant Concentration ◽  
Leeward Side ◽  
Low Velocity ◽  
Tree Model ◽  
Real Tree ◽  
Tree Models ◽  
Small Change ◽  
Pollutant Diffusion

Trees have a significant impact on the airflow and pollutant diffusion in the street canyon and are directly related to the comfort and health of residents. In this paper, OpenFOAM is used for simulating the airflow and pollutant diffusion in the street canyon at different height–width ratios and tree layouts. Different from the drag source model in the previous numerical simulation, this study focuses on the characterization of the blocking effect of tree branches on airflow by using more precise and real tree models. It is found that the airflow is blocked by the tree branches in the canopy, resulting in slower airflow and varying velocity direction; the air flows in the pore area between trees more easily, and the vortex centers are different in cases where the street canyon shape and tree layout are different. Low-velocity airflow distributes around and between two tree canopies, especially under the influence of two trees with different spacing. At the height of the pedestrian, the tree branches change the vortex structure of airflow, and thereby high pollutant concentration distribution on both sides of the bottom of the leeward side of the street canyon changes constantly. In the street canyon, the small change in tree spacing has a very limited influence on the pollutant concentration. The street canyon has the lowest average pollutant concentration at the largest y-axis direction spacing between two trees.

A Comparative Study of Various Turbulence Models for Simulating Pollutant Dispersion within an Isolated Street Canyon

2011 ◽  
Vol 356-360 ◽  
pp. 766-770
Author(s):  
Yuan Dong Huang ◽  
Yue Jiao Peng ◽  
Jian Wei Jiang ◽  
Zhong Hua Zhou ◽  
Jing Gu
Keyword(s):  
Wind Tunnel ◽  
Street Canyon ◽  
Vector Fields ◽  
Turbulence Models ◽  
Pollutant Dispersion ◽  
Pollutant Concentration ◽  
Leeward Side ◽  
Perfect Agreement ◽  
Pollutant Concentrations ◽  
Wind Tunnel Data

CFD calculations are carried out using the standard, RNG and realizable κ-ε turbulence models to simulate the airflow and pollutant dispersion inside an isolated street canyon. The computed air velocity vector fields and pollutant concentration contours show that all the three studied κ-ε models produce a very similar clockwise vortex structure that carries the pollutants released from the line source on the street floor towards the leeward side of the canyon. The calculated non-dimensional pollutant concentration distributions on both the leeward and windward walls of the canyon are compared with the wind tunnel measured data. It is revealed that (1) on the windward wall of the canyon, the calculated pollutant concentrations using the standard, RNG and realizable κ-ε models are all in perfect agreement with the experimental observations, (2) the RNG and realizable κ-ε models provide almost the same results for pollutant concentration distributions on the leeward wall of the canyon, (3) the RNG and realizable κ-ε models overestimate greatly the pollutant concentration values on the leeward wall of the canyon, whereas the concentration distributions predicted by the standard κ-ε model on the leeward wall are in reasonable agreement with the wind tunnel data.

scholarly journals The Numerical Simulation of Uplifted Street Canyon On Flow Field Structure And Pollutant Diffusion

2021 ◽  
Author(s):  
Mengru Sun ◽  
Yuqing Song ◽  
Changfa Tao ◽  
Xiaoping Liu ◽  
Quanli Wang ◽  
...  
Keyword(s):  
Flow Field ◽  
Street Canyon ◽  
Concentration Distribution ◽  
Field Structure ◽  
Pollutant Concentration ◽  
Windward Side ◽  
Leeward Side ◽  
Building Height ◽  
Lift Height ◽  
Pollutant Concentration Distribution

Abstract The flow field structure, pollutant concentration distribution and dimensionless concentration evolution of uplifted street canyon has been analyzed in this study. Different from the ideal street canyon, the pollutant concentration distribution of the uplifting street canyon is higher at the bottom, lower at the top, higher at the windward side and lower at the leeward side. The total pollutant concentration (TPC) generally decreases with the increase of leeward building lifting height while the lift height increases with the same total building height or the total building height increases with increase in the lifting height. It is beneficial to the pollutant emission of in street canyon. On the contrary, the TPC increases when the total building height increases with the same lift height. The main reason is that the vertical length of the vortex increases, which is more difficult for pollutants to be discharged from the street canyon.

Pollutant Effect on the Pedestrians and Bicyclists for the Different Setting of Bus Lanes in Urban Street Canyons

2012 ◽  
Vol 518-523 ◽  
pp. 3038-3044
Author(s):  
Li Lei ◽  
Jian Zhang Wang ◽  
Heng Zhang
Keyword(s):  
Emission Intensity ◽  
Street Canyon ◽  
Pollutant Dispersion ◽  
Pollutant Concentration ◽  
Windward Side ◽  
Leeward Side ◽  
Urban Street ◽  
Pollutant Concentrations ◽  
Bus Lane ◽  
Bicycle Lane

In order to study the pollutant effect on the pedestrians and bicyclists for the different setting of bus lanes, the numerical simulation of pollutant dispersion for isolated street canyon was conducted based on a two dimensional k-ε turbulence model and species transport equation. The simulation results fit well with the corresponding wind tunnel tests. The analysis result shows that the pollutant concentration at the leeward side is evidently higher than that of the windward side in the isolated street canyon. The pollutant concentration for the bicycle lane is obviously higher than that of the sidewalk near the ground at the leeward side. As the height increases, the pollutant concentration for the sidewalk is higher than that of the bicycle lane instead. The pollutant concentrations for the sidewalk and the bicycle lane are nearly the same, and almost no change with the height increases at the windward side. When the density of bus lane is low, the emission intensity of the bus lanes is lower than that of the vehicle lanes, and setting of outside bus lanes will have less pollution to the pedestrians and bicyclists. And when the density of bus lane is high, the emission intensity of the bus lanes is higher than that of the vehicle lanes, and setting of inside bus lanes will have less pollution to the pedestrians and bicyclists.

scholarly journals Interactive Modeling of 3D Tree with Ball B-Spline Curves

2009 ◽  
Vol 8 (2) ◽  
pp. 101-107 ◽  
Author(s):  
Zhongke Wu ◽  
Mingquan Zhou ◽  
Xingce Wang
Keyword(s):  
Iterated Function Systems ◽  
Interactive Methods ◽  
Tree Model ◽  
B Spline ◽  
Spline Curves ◽  
Novel Approach ◽  
Iterated Function ◽  
Tree Models ◽  
Generating Tree ◽  
L Systems

A novel approach to modeling realistic tree easily through interactive methods based on ball B-Spline Curves (BBSCs) and an efficient graph based data structure of tree model is proposed in the paper. As BBSCs are flexible for modifying, deforming and editing, these methods provide intuitive interaction and more freedom for users to model trees. If conjuncted with other methods like generating tree models through L-systems or iterated function systems (IFS), the models are more realistic and natural through modifying and editing. The method can be applied to the design of bonsai tree models.

scholarly journals Estonian traces in the tree of life concept and in the language family tree theory

2012 ◽  
Vol 3 (1) ◽  
pp. 297-326
Author(s):  
Urmas Sutrop
Keyword(s):  
Charles Darwin ◽  
Tree Of Life ◽  
Family Tree ◽  
Language Family ◽  
Animal Life ◽  
Tree Model ◽  
Tree Models

In this paper the tree model – a well-formed tree is shortly described. After that the language family tree model by August Schleicher is treated and compared with the Charles Darwin’s tree of life diagram and metaphor. The development of the idea of the linguistic trees and the tree of life is considered historically. Earlier models – scala naturae – and tree models, both well-formed and not-well-formed are introduced. Special attention is paid to the scholars connected to Estonia who developed the idea of tree models: Georg Stiernhielm was the first who pictured a language tree already in 1671; Karl Eduard Eichwald published an early tree of animal life in 1829; and Karl Ernst von Baer influenced the tree of  life models and diagrams of Charles Darwin.

scholarly journals Developing and Applying IR-Tree Models: Guidelines, Caveats, and an Extension to Multiple Groups

2020 ◽  
pp. 109442812091109
Author(s):  
Hansjörg Plieninger
Keyword(s):  
Response Styles ◽  
Model Specification ◽  
Sequential Order ◽  
Tree Model ◽  
Multiple Group ◽  
Tree Diagram ◽  
Tree Models ◽  
Item Responses ◽  
Model Equations ◽  
The Relationship

IR-tree models assume that categorical item responses can best be explained by multiple response processes. In the present article, guidelines are provided for the development and interpretation of IR-tree models. In more detail, the relationship between a tree diagram, the model equations, and the analysis on the basis of pseudo-items is described. Moreover, it is shown that IR-tree models do not allow conclusions about the sequential order of the processes, and that mistakes in the model specification can have serious consequences. Furthermore, multiple-group IR-tree models are presented as a novel extension of IR-tree models to data from heterogeneous units. This allows, for example, to investigate differences across countries or organizations with respect to core parameters of the IR-tree model. Finally, an empirical example on organizational commitment and response styles is presented.

scholarly journals Surface rupture in stochastic slip models

2020 ◽  
Vol 221 (2) ◽  
pp. 1081-1089 ◽  
Author(s):  
S Murphy ◽  
A Herrero
Keyword(s):  
Probability Density Function ◽  
Probability Density ◽  
Density Function ◽  
Source Model ◽  
Surface Rupture ◽  
Size Frequency Distribution ◽  
Fault Surface ◽  
Planar Fault ◽  
Small Change ◽  
Composite Source Model

SUMMARY As an alternative to spectral methods, stochastic self-similar slip can be produced through a composite source model by placing a power-law scaling size-frequency distribution of circular slip dislocations on a fault surface. However these models do not accurately account for observed surface rupture behaviour. We propose a modification to the composite source model that corrects this issue. The advantage of this technique is that it accommodates the use of fractal slip distributions on non-planar fault surfaces. However to mimic a surface rupture using this technique, releasing the boundary condition at the top of the fault, we observed a systematic decrease in slip at shallow depths. We propose a new strategy whereby the surface is treated like a reflector with the slip being folded back onto the fault. Two different techniques based on this principal are presented: the first is the method of images. It requires a small change to pre-existing codes and works for planar faults. The second involves the use of a multistage trilateration technique. It is applied to non-planar faults described by an unstructured mesh. The reflected slip calculated using the two techniques is near identical on a planar fault, suggesting they are equivalent. Applying this correction, where reflected slip is accounted for in the composite source model, the lack of slip at shallow depths is not observed any more and there is no systematic trend with depth. However, there are other parameters which may affect the spatial distribution of slip across the fault plane. For example, the type of probability density function used in the placement of the subevent is also important. In the case where the location of maximum slip is known to a first order, a Gaussian may be appropriate to describe the probability function. For hazard assessment studies a uniform probability density function is more suitable as it provides no underlying systematic spatial trend.

scholarly journals Latent Tree Models and Approximate Inference in Bayesian Networks

2008 ◽  
Vol 32 ◽  
pp. 879-900 ◽  
Author(s):  
Y. Wang ◽  
N. L. Zhang ◽  
T. Chen
Keyword(s):  
Bayesian Networks ◽  
Linear Time ◽  
Computational Cost ◽  
Approximate Inference ◽  
Tree Model ◽  
Approximation Accuracy ◽  
Latent Tree Models ◽  
Tree Models ◽  
Novel Method ◽  
Latent Tree Model

We propose a novel method for approximate inference in Bayesian networks (BNs). The idea is to sample data from a BN, learn a latent tree model (LTM) from the data offline, and when online, make inference with the LTM instead of the original BN. Because LTMs are tree-structured, inference takes linear time. In the meantime, they can represent complex relationship among leaf nodes and hence the approximation accuracy is often good. Empirical evidence shows that our method can achieve good approximation accuracy at low online computational cost.

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