狭长通道内风幕挡烟效果的数值分析

研究利用风幕阻挡通道内烟气蔓延的可能性及其效果,结合一小型狭长通道,采用数值模拟计算方法进行了初步分析.重点考察了风幕前倾角、风幕出口风速和回风口位置三个主要因素对风幕在狭长通道内挡烟效果的影响.结果表明,适当增大风幕前倾角、逐渐提高出口风速、适当前移回风口位置均有助于加强风幕在狭长通道内的挡烟效果.而当火源功率较大而风幕出口风速过小时,将不能很好地阻挡烟气的蔓延.数值分析结果表明,综合考虑上述三种因素,就可以使用风幕有效地阻挡烟气在狭长通道内的蔓延.     

不确定性信息下河道型水库纳污能力计算初探

基于河流水文、水质条件等因素的实际变化,并在考虑了参量取值可信度的基础上,运用未确知数学理论对河道型水库闭闸期间滞流水体纳污能力计算问题进行了初步探讨.研究表明,依据未确知数学计算不确定性信息下水体纳污能力,理论上是可行的,计算结果是可信的.      

石墨炉原子吸收分光光度法测定城市交通干道空气中的铅

用超细玻璃纤维滤膜收集城市交通干道空气中的铅,硝化后使用石墨 炉原子吸收分光光度法测定。本方法具有灵敏度高,精密度和准确度较好等优点。铅平均浓度在10.57-69.67ug/L时,其相对偏差在0.47%-5.7%,标准差在0.185-0.33%之间,CV在0.47%-3.03%之间,标准曲线的相关系数为0.998.     

TIMBER HARVEST IMPACTS ON SMALL HEADWATER STREAM CHANNELS IN THE COAST RANGES OF WASHINGTON1

ABSTRACT: We evaluated changes in channel habitat distributions, particle‐size distributions of bed material, and stream temperatures in a total of 15 first‐or second‐order streams within and nearby four planned commercial timber harvest units prior to and following timber harvest. Four of the 15 stream basins were not harvested, and these streams served as references. Three streams were cut with unthinned riparian buffers; one was cut with a partial buffer; one was cut with a buffer of non‐merchantable trees; and the remaining six basins were clearcut to the channel edge. In the clearcut streams, logging debris covered or buried 98 percent of the channel length to an average depth of 0.94 meters. The slash trapped fine sediment in the channel by inhibiting fluvial transport, and the average percentage of fines increased from 12 percent to 44 percent. The trees along buffered streams served as a fence to keep out logging debris during the first summer following timber harvest. Particle size distributions and habitat distributions in the buffered and reference streams were largely unchanged from the pre‐harvest to post‐harvest surveys. The debris that buried the clearcut streams effectively shaded most of these streams and protected them from temperature increases. These surveys have documented immediate channel changes due to timber harvest, but channel conditions will evolve over time as the slash decays and becomes redistributed and as new vegetation develops on the channel margins.     

CHANGING NEAR‐STREAM LAND USE AND RWER CHANNEL MORPHOLOGY IN THE VENEZUELAN ANDES1

ABSTRACT: The shape of a river channel is linked to surrounding land use through interacting hydrologic and geologic processes. This study analyzes the relationship between the change in near‐stream land use and the shape of the adjacent river channel over time. Three watersheds in the foothills of the Venezuelan Andes that have experienced differing degrees of development were studied to determine river channel width, sinuosity, and position relative to surrounding land use. Change in land use over time was obtained from multiple‐date aerial photographs (1946 and 1980) referenced to 1996 Landsat Thematic Mapper (TM) satellite imagery, and verified by field inspection. Measurements of land‐use type and amount and river channel morphology from the two dates were made using geographic information system (GIS) methods. The three watersheds differed in the extent of deforestation, the location of remaining forested land, and how much land‐use change had already occurred by 1946. Change in river channel morphology was greatest at the most deforested sites. Valley shape and channel constraint also had a discernible effect on change in channel morphology. This study introduces a method for analyzing change in coupled terrestrial‐aquatic systems based on multiple‐date, remotely sensed data and GIS analysis of spatial properties. The results document human impacts on river channels through a comparison of multiple watersheds over a 35‐year time interval.     

河道生态环境分区需水量的计算方法与实例分析

为真实反映流域各区间的河道生态环境需水量差异 ,同时解决流域上下游河道生态环境需水量的重复计算问题 ,提出了河道生态环境分区需水量的概念 ,对流域分区、河道功能确定和河道生态环境分区需水量计算方法进行了研究 .以黄河流域为例进行了实证分析 .结果表明 ,黄河流域的河道需水分区需水量差异显著 ,黄河下游区间的河道分区需水量最大 ,为 14 8 93× 10 8m3·a- 1 ,上游兰州—河口干流区间最小 ,为-5 0 12× 10 8m3·a- 1 ,龙羊峡—兰州干流区间和黄河下游区间河道分区需水量超过区间的自产水资源量 ,需要其它区间的水量补充 ,才能维持其河道的生态环境功能 .黄河流域的河道分区需水量之和为 2 3 0 6× 10 8m3·a- 1 ,约为流域地表水资源量的 3 9% ,说明黄河流域地表水资源的最大利用率应低于 61% .     

基于气候调节的城市通风道探析

近年来,夏季炎热的气候和愈来愈强的热岛效应使城市饱受因挠,而城市设计策略中缺乏有效的生态规划方法来解决目前存在的问题,城市对炎热气候的适应性不足。论文在利用CFD(计算流体动力学)技术进行实例模拟分析的基础上,重点介绍了一种在城市尺度进行节能设计的新方法:在城市中建立多种形式的通风道,提高城市的通风和排热能力,以达到利用自然资源和有效的规划方式降低夏季城市“热岛”温度、节约能源的目的。文中详细论述了通风道的可行性和必要性、营建方式、注意原则等问题,并进行了一系列的计算机风场模拟研究。     

基于注意力机制的人群计数方法

为准确预测固定场景中的人群计数,在人群分析领域,采用一种融合注意力机制的卷积神经网络(CNN)进行人群计数,该模块结合空间域注意力和通道域注意力,空间域注意力可以编码整个图像的像素级上下文信息,以更准确地表达像素级别的密度图,而通道域注意力可以在不同的通道中提取更多的区分特征使网络显著表达人群的局部区域,并在多个公开数...     

长距离人工输水渠道水质时空演变规律研究——以南水北调中线总干渠为例

以南水北调中线工程通水6年来沿线30个常规水质监测断面逐月的水质监测数据为基础,基于斯皮尔曼秩次相关检验,系统分析总干渠水质时空变化趋势.结果表明,总干渠水质总体良好,主要指标能够达到Ⅱ类及以上水平.空间尺度上,总干渠水温(r=-0.897,p＜0.01)、总磷(r=-0.820,p＜0.01)、生化需氧量(r=-0....     

CHANNEL STABILITY DOWNSTREAM FROM A DAM ASSESSED USING AERIAL PHOTOGRAPHS AND STREAM‐GAGE INFORMATION1

ABSTRACT: The stability of the Neosho River channel downstream from John Redmond Dam, in southeast Kansas, was investigated using multiple‐date aerial photographs and stream‐gage information. Bankfull channel width was used as the primary indicator variable to assess pre‐ and post‐dam channel change. Five sin‐mile river reaches and four stream gages were used in the analysis. Results indicated that, aside from some localized channel widening, the overall channel change has been minor with little post‐dam change in bankfull channel width. The lack of a pronounced post‐dam channel change may be attributed to a substantial reduction in the magnitude of the post‐dam annual peak discharges in combination with the resistance to erosion of the bed and bank materials. Also, the channel may have been overwidened by a series of large floods that predated construction of the dam, including one with an estimated 500‐year recurrence interval.