| Low quality air has become an important factor affecting human health.Effective urban ventilation is an important way to alleviate the low quality air in the city.Therefore,the evaluation and optimization of urban ventilation by means of urban planning and design are very significant in improving the living environment and ensuring the healthy life of human beings.In this thesis,the correlations among urban planning and design,urban wind environment and urban air quality are researched.The research method with empirical research and numerical simulation combined is adopted.With the computational fluid dynamics(CFD)numerical simulations employed,the correlation model between wind environment and urban pollutant concentration is established.Then,the critical range of wind speed to dilute pollutant concentration is determined.Based on this,the correlation between design factor model system and wind environment is established,and then the goal of improving urban air quality by changing design factors is realized.Secondly,through field measurement,it is proved that the spatial distributions of wind environment are different in urban microenvironment regions,and there is a corresponding relationship between wind environment and pollutant concentration.That is,the higher the wind speed is,the lower the pollutant concentration is,and vice versa.The development of research on the correlation between urban climate and urban design,and the historical evolution of climate adaptive design are reviewed and summarized.The two-way impacts between urban planning and urban climate environment are distilled,including the specific urban climate problems brought by urban planning and construction,and also the attempts to optimize urban climate environment based on the planning level.The correlations between wind environment and urban planning are studied primarily.The existing urban ventilation designs are analyzed.The theoretical framework of improving urban wind environment and optimizing urban air quality based on urban planning is estabilshed according to the research on the disciplinary theories.Firstly,from the perspective of atmospheric physics,the processes of air pollutants diffusion and deposition with air flow are analyzed,and the importance of wind environment to alleviate urban air pollution is affirmed.Secondly,from the perspective of climatology,urban boundary layer is researched,and the important role of atmospheric turbulence movement from global scale to urban scale is determined.Especially in the local scale of the city,due to the complexity of the ground surface roughness,the movement changes more obviously.Finally,the application of CFD in urban environment is realized,and its successful experiences are the important approaches and supports of this study.The specific numerical simulation methods used in this thesis are described and discussed,including air flow control equations,numerical discretization schemes,computational grid generation,boundary condition settings and turbulence models.The whole numerical simulation processes used in the study are explained in detail.The corresponding calculation algorithm is improved,and the reliability of the calculation method is verified.The correlations between wind speed and pollutant diffusion are investigated.The wind speed threshold(critical wind speed)of effective pollutant diffusion is determined through a large amount of simulations.On this basis,it is proposed to use the static wind area on the pedestrian height(1.5m)to represent the air quality of the corresponding total area.Specifically,the static wind area is obtained from the area with the wind speed lower than the static wind speed according to the simulated results of wind speed.The ratio of this area to the total area(excluding the area of the building base)is defined as the critical wind speed ratio.The critical wind speed ratio is used as the indicator to evaluate the ventilation effect of the city.A higher critical wind speed ratio usually leads to a worse air circulation and more serious air pollution,and vice versa.The correlations between air quality and design factors are also researched.Firstly,the urban design factor system is established with all kinds of urban design elements selected.Secondly,the impacts of various factors on the urban air quality are analyzed through numerical simulation calculation using the static wind rate as the evaluation index.Finally,the correlation coefficients between various factors and air quality are calculated,and the factors with closer correlation to urban air quality are obtained,which is considered as a city setting premise of air quality optimization.The air quality evaluation and optimization design of Xinjiang Qiaziwan community,Chongqing Three Gorges Square and Urumqi Diamond City Square are performed.The selected optimization objects belong to different climatic regions in China,with both completed project and design scheme included.This optimization is not a purely numerical optimization,but an empirical design optimization based on the above conclusions.On the basis of the conclusion of Chapter 5,the corresponding design fators are extracted first and then modified.Finally,through comparing the static wind rate of the design before and after optimization,it can be seen that the optimized project achieves a significant reduction in the static wind rate,the urban ventilation effect is improved,and the urban air pollution is alleviated.Finally,particle swarm optimization algorithm is introduced to carry out the air quality optimization design of standard case model,and the optimal design scheme to achieve the goal of best air quality is obtained.This is an attempt to introduce a new intelligent algorithm in urban planning and design on the basis of empirical optimization,which lays a foundation for the application of artificial intelligence in urban planning and design.The following innovations are realized in this thesis:? The urban critical wind range is redefined.Through the study of the correlations between urban wind environment and pollutant diffusion,the critical wind speed of effective evacuation of air pollutants is determined as 1.0m/s.On this basis,a new indicator of urban air quality is proposed.? The application of CFD in urban environment is improved in some details,including:comparing the advantages and disadvantages of structured and unstructured grid,selecting the grid suitable for urban environment calculation,adjusting the boundary conditions,numerical methods,density and resolution of grid.So that it has appropriate accuracy and calculation efficiency when applied to the calculation of urban environment.?The impacts of urban design factors on air quality are investigated systematically.The results show that the wind speed and wind direction in the environmental background factors are the decisive factors affecting the air ventilation efficiency,the building density in the development intensity factors has a significant impact on the urban ventilation effect,and the air duct design and enclosure in the layout design factors also affect the urban ventilation performance.In the urban design factor system,there are both positive and negative correlation indexes to the urban ventilation efficiency.In the specific improvement strategy,the effects on the urban ventilation from each factor should be comprehensively used and considered.The overall improvement of urban air quality could be accomplished with each consideration cooperated.? The conclusion of correlation between design factors and urban air quality is applied to specific urban design projects,and its optimization results are compared to verify the conclusion.The results show that the local modification of urban design factors based on the conclusions can effectively reduce the critical wind speed ratio and achieve the optimization of urban air quality.? A simple method is proposed in this paper to determine the air quality of urban microenvironment.It links the wind speed nephogram,which can easily determine and predict the air quality of a specific place in the local area of the city.On this basis,the particle swarm optimization algorithm is introduced to lay the foundation for intelligent urban design. |
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