Chaotic Behavior and Pollution Dispersion Characteristics in Engineered Tidal Embayments: A Numerical Investigation1

Abstract: This paper presents a numerical investigation of approaches to enhance the mixing and dispersion processes in tidal areas by effecting changes in the natural estuary system. It compares the impact of various estuary modifications stemming from human intervention to pollutant dispersion and chaotic flow within the estuary including the implications of alteration of the original channel shape, change of the channel bathymetry, and modification of the tidal signal. Our findings indicate that chaotic flow analysis is similar in many regards, but not all, to conventional dispersion analysis. Specifically, we conclude that (1) simplification of the flow regime reduces chaotic flow patterns and tracer particle dispersion, (2) creation of extensively protruding barriers and/or installation of barriers on opposite sides of the main stem of the estuary enhances particle dispersion and chaotic mixing, (3) installation of underwater berms has relatively minor beneficial, but highly localized, effects on chaotic regime and particle dispersion, and (4) increasing the tidal signal amplitude was shown to increase chaotic and dispersion properties of the estuarine system. A parametric study investigating the effect of several geometrical configurations and tidal signals on characteristics of chaotic flows concludes the paper.     

井喷硫化氢扩散分析

井喷有毒气体扩散对周围居民的危害很大[1],由于井场所位于的山区地形下垫面特殊,气体扩散的过程比较复杂,无法用普通的烟羽模式进行模拟,本文采用大涡模型以及贴体网格技术、卫星遥感技术,对某地区发生泄漏进行研究并进行三维数值模拟,模拟结果显示了气体扩散的时空分布以及对人员的危害,通过模拟结果,可以对井场地区的安全情况作出评价,能够对应急人员疏散策略及安全区域规划的制定提供帮助。     

SEWAGE DISCHARGES FROM SHIPS TRANSITING COASTAL SALT WATERS1

ABSTRACT: A number of aspects of the discharging of non-oily wastewaters by transiting ships are treated in this overview paper. In the introduction, options to discharging (the use of holding tank, on board treatment) and the impact of changing regulations are discussed. Assessment of the effects of sewage discharges on coastal waters required that data, at first not available, be generated. An account is given of the characterization of Navy shipboard wastewaters and of experiments involving sewage discharges at sea, measurements of water quality before, during and after an amphibious operation, and fore and aft of transitting Navy ships. A better understanding of sewage dilution after discharge led to the verification of a method for controlled discharging of sewage (and other wastewaters). This method permits limiting the coliform bacteria count in the ship's wake to values below acceptable limits. The final sections contain information on long range effects of ships’sewage discharges, obtained in studies by the U.S. Navy and others, as well as public health considerations.     

Measurements of Traffic-Induced Turbulence within a Street Canyon during the Nantes'99 Experiment

A full scale experiment has been performed in a streetcanyon, the Rue de Strasbourg in Nantes (France). Thiscampaign, the Nantes'99 experiment, provided a detaileddata base documenting, amongst others, the production ofturbulent kinetic energy (TKE) by vehicles within thestreet. Airflow and CO concentration measurements have beenanalysed during days with low wind perpendicular to thestreet axis, i.e. for conditions expected to greatly favourthe enhancement of the turbulence produced by traffic onflow and dispersion within the street canyon. It is shownthat traffic is associated with an increase in turbulentkinetic energy at the lowest levels of the street,especially at the leeward side of the street. It issuggested that turbulent kinetic energy increases with thenumber of vehicles up to a threshold value and thendecreases when vehicles form a `block' shape that limitsthe additional production of turbulence. Moreover, it issuggested that traffic-produced turbulence affectspollutant dispersion reducing CO concentration at the lowerlevels of the leeward side of the street from a thresholdvalue of TKE equal to about 0.15 m² s^-2. On the other hand, high traffic density generates less turbulencewhich in turn leads to a lower pollutant dispersion.     

基于健康风险的危险废物智能化分级分类研究

在分析国内外危险废物分级管理经验的基础上,结合健康风险的评估步骤,提出了基于全过程危险废物污染物释放情景的精细化-动态健康风险评价方法。充分考虑处理利用工艺、企业管理水平等因素对于危险废物中污染物释放概率和能力的影响,并基于污染物向环境介质的迁移转化,定量评估危险废物的健康风险。基于危险废物污染特性数据库和事故情景数据库,结合全过程信息采集技术,构建危险废物分级分类管理平台,进行涉废企业的风险级别划分,实施差异化管理,形成更加科学有效的危险废物全过程精细化管理体系。     

基于GIS的城市最小生态用地空间分析模型研究——以深圳市为例

21世纪,全球范围内城市化已经成为人类社会发展的必然趋势,城市扩张不可避免地将大量的森林、农田、草地、湿地和水域等发挥着重要生态服务功能的生态用地转化为城市建设用地,对城市、区域乃至全球的生态系统造成较大的影响。在未来快速城市化过程中,保护必需的生态用地对于维持城市自身生态系统健康、改善城市居民生活质量和城市可持续发展有着重要意义。研究以中国经济特区深圳市为例,将景观生态概念模型与生态系统服务功能价值评估方法结合起来,在GIS技术的支持下,构建了城市最小生态用地空间分析模型,并分别按照保留城市面积30%、40%、50%和60%生态用地的4种情景,分析最小生态用地空间分布的合理性,结果表明论文所构建的最小生态用地模型能够很好地将城市当中具有重要生态系统服务功能的土地提取出来。     

Study on convection and dispersion characteristics of dense gases in urban environment considering trees

Although several studies on the dispersion of heavy toxic gas released from ruptured tanks on vehicles during transportation have considered complex terrain such as urban buildings, the influence of trees on the flow field in urban areas during gas dispersion tends to be ignored. In this study, a Computational Fluid Dynamics (CFD) model was proposed to investigate the characteristics of gas release and dispersion from loaded vehicle in the urban environment. In this model, the tree crown was treated as a porous medium, and the influence of drag due to the crown was incorporated into the model by a momentum source term through a user-defined function. In this study, the dynamic characteristics of chlorine (Cl₂) dispersion under the conditions of building distribution, tree species and porosities were comprehensively analysed, to cover the influence of urban complexity, leaf density, and tree planting configuration. The results show that compared with flat terrain, the presence of urban buildings will prolong the dense gas retention time and increase the dangerous distance. It is found that the horizontal dispersion distance can increase by 63% and the isosurface of 25 ppm hazardous gas can increase by 130% with the introduction of buildings. Compared with the terrain with only buildings, the introduction of arbors or shrubs can result in a 147% or 359% increase in the maximum concentration. Also, trees will prolong the dispersion duration. It is also found that the higher the porosity, the less the wind blocking effect, and the weaker the ability of capturing gas. The wind field affected by arbores and shrubs are different in height, and arbores capture more Cl₂. Planting short shrubs around buildings can effectively reduce the spread of harmful gases.     

Process analysis of an industrial waste-to-energy plant: Theory and experiments

Thermal conversion is fundamental in an integrated waste management system due to the capability of reducing mass and volume of waste and recovering energy content from unrecyclable materials. Indeed, power generation from industrial solid wastes (ISW) is a topic of great interest for its appeal in the field of renewable energy production as well as for an increasing public concern related to its emissions. This paper is based on the process engineering and optimization analysis, commissioned to the University Campus-Biomedico of Rome by the MIDA Tecnologie Ambientali S.r.l. enterprise, ended up in the construction of an ISW thermo-conversion plant in Crotone (Southern Italy), where it is nowadays operating. The scientific approach to the process analysis is founded on a novel cascade numerical simulation of each plant section and it has been used initially in the process design step and after to simulate the performances of the industrial plant. In this paper, the plant process scheme is described together with the values of main operating parameters monitored during the experimental test runs. The thermodynamic and kinetic basics of the mathematical model for the simulation of the energy recovery and flue gas treatment sections are presented. Moreover, the simulation results, together with the implemented parameters, are given and compared to the experimental data for 10 specific plant test runs. It was found that the model is capable to predict the process performances in the energy production as well as in the gas treatment sections with high accuracy by knowing a set of measurable input variables. In the paper fundamental plant variables have been considered such as steam temperature, steam flow rate, power generated as well as temperature, flow rate and composition of the resulting flue gas; therefore, the mathematical model can be simply implemented as a reliable and efficient tool for management optimization of this kind of plants.     

Effects of the support material addition on the hydrodynamic behavior of an anaerobic expanded granular sludge bed reactor

As a support material, zeolite can be used to promote the granulation process due to its high settable property and the ability to retain biomass on its surface. The present paper reports on the influence of zeolite addition on the hydrodynamic behavior of an expanded granular sludge bed reactor (EGSB). Different models were applied to fit the flow pattern and to compare EGSB hydrodynamic performance with and without the addition of zeolite. The experimental data fit the tanks in a series model for zeolite bed height of 5 cm and upflow velocity of 6 m/hr. Higher axial dispersion degree (D/uL) was obtained at lower heights of zeolite. The real hydraulic retention time (HRTr) was increased with both increased zeolite bed height and increased upflow velocity. The short-circuit results for 5 cm of zeolite bed and 6, 8 and 10 m/hr upflow velocity were 0.3, 0.24 and 0.19 respectively, demonstrating the feasibility of using zeolite for a proper hydrodynamic environment to operate the EGSB reactor. The presence of zeolite resulted in the higher percentage values of dead zones, ranging from 12% to 24%. Zeolite addition exerted a positive effect on the hydrodynamics pattern for this technology being advantageous for the anaerobic process because of its possible contribution to better biofilm agglomeration, granule formation and substrate-microorganism contact.