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排序方式: 共有4115条查询结果,搜索用时 15 毫秒
981.
Michael White Daren Harmel Haw Yen Jeff Arnold Marilyn Gambone Richard Haney 《Journal of the American Water Resources Association》2015,51(3):758-775
Water quality impairment due to excessive nutrients and sediment is a major problem in the United States (U.S.). An important step in the mitigation of impairment in any given water body is determination of pollutant sources and amount. The sheer number of impaired waters and limited resources makes simplistic load estimation methods such as export coefficient (EC) methods attractive. Unfortunately ECs are typically based on small watershed monitoring data, which are very limited and/or often based on data collected from distant watersheds with drastically different conditions. In this research, we seek to improve the accuracy of these nutrient export estimation methods by developing a national database of localized EC for each ecoregion in the U.S. A stochastic sampling methodology loosely based on the Monte‐Carlo technique was used to construct a database of 45 million Soil and Water Assessment Tool (SWAT) simulations. These simulations consider a variety of climate, topography, soils, weather, land use, management, and conservation implementation conditions. SWAT model simulations were successfully validated with edge‐of‐field monitoring data. Simulated nutrient ECs compared favorably with previously published studies. These ECs may be used to rapidly estimate nutrient loading for any small catchment in the U.S. provided the location, area, and land‐use distribution are known. 相似文献
982.
京津冀地区重污染天气过程的污染气象条件数值模拟研究 总被引:8,自引:2,他引:6
通过采用全球再分析格点资料的统计分析和WRF中尺度数值模拟,从天气学和大气边界层气象学角度分析了2013年12月和2014年2月两次重污染过程中京津冀地区天气尺度大气停滞气象条件和大气污染扩散气象条件的特征及其作用,并根据WRF模式精细化模拟结果分析了太行山和燕山对京津冀地区城市大气污染形成的作用.研究结果表明,两次重污染天气过程中京津冀地区500 h Pa等压面上的平均风速均表现为明显的气候异常特征,500 h Pa平均风速较近10年同期分别下降了约30.8%和50.4%,大气停滞系数较近5年同期分别偏高10%和20%以上;京津冀地区发生严重污染时,WRF模式模拟的日平均混合层高度低于200 m,日平均地面10 m风速低于2 m·s-1,日平均通风量可降低到1000 m2·s-1以下,空气质量指数与日平均通风量成负相关,重污染期间的平均通风量比近5年同期平均通风量偏低29.3%~52.8%,这些不利于污染扩散的天气条件持续数日,导致了重污染天气的发生.此外,太行山对西风气流的阻挡是河北中南部地区大气污染加剧的一个重要原因,而当主导风向为偏南风时,偏南气流遇燕山后或转向回流、或爬坡,导致近地面风速减小,不利于污染物扩散,亦加剧了京津冀地区中南部城市的大气污染. 相似文献
983.
984.
Maintaining an adequate air flow with a desired air quality that is free from hazardous gases is among the most important actions taken toward the improvement of safety in any process plant. Due to the increased focus on the consequences of existing hazardous material on safety, health, and the environment, air quality and sufficient ventilation within a plant has been increasingly considered in the design stage. This paper investigates and analyzes methane and hydrogen sulfite dispersion and the effect of air ventilation within a CAD model of an offshore platform using computation fluids dynamics (CFD). In addition, this method and its principals could be utilized in any other hazardous environment. Simulations of possible hazardous events along with solutions for preventing or reducing their probability are presented to better assess the data. These investigations are performed by considering hypothetical hazardous scenarios which consist of gas leakages from pipes and process equipment under different conditions. After drafting a precise and highly detailed CAD model of the plant and performing CFD simulations on this model, the results of gas behaviors, dispersion, distribution, accumulation, and its possible hazards are investigated and analyzed. The larger amount of details of the actual plant model in CFD simulation are obtained by using a combination of different methods and software. These include PDMS for 3-D drawing of the plan, Rinoceros for geometrical integration of the process equipment and facilities, and Sharc Harpoon which meshes the model. Moreover, the probability of inducing ignitable or toxic concentration of gases within the atmosphere and air ventilation of the unit is considered by these investigations. 相似文献
985.
Coal dust disaster is the most serious problem in a laneway of coal mine. Dust movement regularity for comprehensive mechanized heading face is the key scientific issues for the principle and technology of dust prevention. The special topic on systematic study of the variation regularity of dust movement and dust distribution is presented with hybrid ventilation for the comprehensive mechanized heading face: Euler–Euler method was firstly established on the numerical platform for gas–solid two phase flow in a laneway. And the forces and the dynamic model of dust particles were performed in three-dimensional flow field. Then based on the visible simulations, the movement characteristics of diffusion, sedimentation and accumulation of dust particles were investigated under the action of the complex air flow, and the spatiotemporal variation of dust distribution was studied with hybrid ventilation system. Meanwhile, the obtained dust distribution regularities were compared with the obtainable experimental results. Finally, selected method on different ventilation patterns for dust control was brought out for the heading face according to the gained regularity. The research results is helpful for further understanding of the essence of dust movement with air flow, which could provide more suitable guidance for the principle of dust control and technology of ventilation. 相似文献
986.
The paper presents the results of the validation of the developed pool evaporation model using literature and our own experimental data. The proposed model was used to examine the effect of wind velocity and pool sizes on the evaporation rate of volatile liquid (hexane). Contrary to the semi-empirical evaporation model widely used in hazard assessment, stronger dependence of evaporation rate on pool size at low wind speeds is obtained. 相似文献
987.
988.
989.
990.
北京市典型绿化灌木阻滞吸附PM2.5能力研究 总被引:1,自引:0,他引:1
选取北京市典型绿化灌木物种大叶黄杨、小叶黄杨、紫叶小檗、矮紫杉,结合气室模拟与实地观测的方法,综合测定不同树种对PM2.5的吸附能力.同时,收集2012年12月~2013年5月间北京市区PM2.5浓度值,分析了北京市冬春季PM2.5污染特征.结果表明,由气室实验得到的4种植物对PM2.5阻滞吸附能力排序为:紫叶小檗>小叶黄杨>矮紫衫>大叶黄杨,其原因主要为叶片特征差异所致;室外测量结果表明,4种物种吸附能力排序为:小叶黄杨>紫叶小檗>矮紫衫>大叶黄杨.气室模拟与室外实测结果均表明,小叶黄杨和紫叶小檗具有较强的阻滞吸附PM2.5的能力;气室模拟与室外观测实验中植物阻滞吸附PM2.5能力的大小略有差异,其原因应与植物结构相关.同时,通过分析北京市PM2.5浓度的季节性变化,发现北京市冬季的PM2.5浓度值尤为高,且常绿灌木植物仍能表现出较好的阻滞吸附PM2.5的能力. 相似文献