A mixing-length model for predicting vertical velocity distribution in flows through emergent vegetation

Abstract

The vertical profiles of streamwise velocities are computed on flood plains vegetated with trees. The calculations were made based on a newly developed one-dimensional model, taking into account the relevant forces acting on the volumetric element surrounding the considered vegetation elements. A modified mixing length concept was used in the model. An important by-product of the model is the method for evaluating the friction velocities, and consequently bed shear stresses, in a vegetated channel. The model results were compared with the relevant experimental results obtained in a laboratory flume in which flood plains were covered by simulated vegetation.     

中国短时洪涝灾害危险性评估与验证

基于自然灾害风险理论、借助GIS空间分析功能、采用归一化和层次分析法,对中国全国范围尺度进行短时洪涝灾害危险性评估。通过对洪涝灾害危险性因子分析,分别提取当天降雨量、前三天降雨量、地形高程、地形标准差、河湖网络等因素作为评估因子,提出了各因子危险性指数计算方法,以及全国洪涝灾害危险性指数计算模型公式,根据统计分析危险指数的最小值、最大值,结合历史灾情,利用阈值分割法确定危险等级分割值为0．3、0．45及0．6,将洪涝灾害危险等级划分为高危险、中危险、低危险与无危险四个等级,从而建立类似于天气预报模式的全国洪涝灾害危险性评估模型,并以2009年9月14日为例进行了洪涝灾害危险等级评估的实际应用。最后,本文提出了基于昨日灾情的危险性评估结果验证方法,通过整理同期昨日灾情资料构建灾情数据库,对2009年汛期的洪涝灾害危险性评估结果分别从数量和面积两个角度,基于县和地市两级行政区划作为验证单元进行验证。验证结果表明,洪涝灾害危险性评估结果无论是从数量上还是从面积上看均具有较高的正确率,与实际灾情基本吻合。     

中国结在首饰设计中的传承

中国结艺术历史悠久,始于上古,兴于唐宋,盛于明清,贯穿于人类文明始终,漫长的文化积淀使得中国结渗透着中华民族特有的、纯粹的文化精髓,蕴涵着丰富的文化内容。除对中国结的定义进行了必要的阐述外,还对中国结文化进行了论述。通过研究中国结的现代造型、色彩、寓意与神韵,将其应用于现代首饰设计中,把中国结融入时尚和新的视觉语言,必将焕发其新的艺术生命力。     

Hydrological and meteorological extremes derived from taxation records: the estates of Brtnice,Třebíč and Velké Meziříčí, 1706–1849

Abstract

This paper addresses the hydrological and meteorological extremes that may be deduced from the taxation records of the estates of Brtnice, T?ebí? and Velké Mezi?í?í, all in the Moravian-Bohemian Highlands of the Czech Republic, for the years 1706–1849. At that time, damage to agricultural crops constituted grounds for tax remission for individual farmers and landowners. Where it survives, the relevant administrative documentation generally includes a statement from the applicant, a report by the official commission tasked with checking the contents of it, and any decisions made by taxation authorities at regional and “land” level (the Jihlava regional office and the Moravian Land Administration (“Gubernium”) respectively). Data extracted may include the type of event, dating, places of occurrence and damage done. The chronology of hydrological and meteorological extremes (torrential rain, flash flood, flood, hailstorm, lightning, frost) covers the period 1706–1849, but only four events are evident before 1748 and there is a gap in records between 1757 and 1789. Extremes are analysed from a spatio-temporal point of view. A total of 97 extreme events (171 extremes of particular type) were identified for the region studied. Torrential rain, hailstorm and flash flood were the major devastating phenomena, and occurred mainly from May to August. Torrential rain and hailstorm are clearly attributable to thunderstorms with very intense convection. Five outstanding events and their impacts upon individual farmers are described in detail. The results are discussed with respect to uncertainties in the basic data and in the context of the Czech Lands, because only some of the extremes disclosed are known and confirmed by other documentary data.

Editor Z.W. Kundzewicz

Citation Dolák, L., Brázdil, R., and Valá?ek, H., 2013. Hydrological and meteorological extremes derived from taxation records: the estates of Brtnice, T?ebí? and Velké Mezi?í?í, 1706–1849. Hydrological Sciences Journal, 58 (8), 1620–1634.     

坐标标注和散点高程标注功能的CAD实现

利用VBA二次开发的计算机辅助设计(computeraideddesign,CAD)实现工程需求的坐标标注和散点高程标注功能。坐标标注的开发弥补了现有软件的不足,散点标注功能满足了专项工程的应用需求,解决了开发过程中的关键技术,为进一步功能拓展提供了技术支持。     

“地物光谱测定与分析”创新实验教学改革

分析比较了遥感类相关课程的教学要求,探讨了分层次进行\"地物光谱测定与分析\"实验教学的创新建设思路。通过设置基础技能型、综合设计型和探索创新型3个实习环节,逐步拓宽实习内容和加深实习难度,分别采用教师主导、学生自主设计以及产学研相结合的方式,对学生实现由基本操作技能向综合知识应用、前沿探索创新的能力逐步提升的培养,深化了实验教学改革。     

滦河口退养还滩工程引起的径潮相互作用变化分析

围垦养殖对河口海岸的水动力和水环境带来了潜在危害,因此,在围垦区逐渐开始实施退养还滩工程以修复河口的水动力环境。但是,目前对于退养还滩工程引起的水动力变化还缺少完善的评价和研究。以滦河口退养还滩工程为研究对象,构建二维水动力数值模型,从水动力场、纳潮能力和行洪能力三个方面研究还滩工程对滦河口径潮作用特征的影响。结果表明：滦河口退养还滩工程区域面积约300 hm2,河口断面扩宽造成了河口内水动力条件的变化。径流动力明显减弱,洪季河道内下泄流速最大降幅约为61.82%;潮流动力显著增强,枯季时潮流上溯流速增加0.25 m/s;径潮作用平衡位置向上游移动。河口纳潮能力显著增强,枯季大潮期间涨潮历时延长了12.5%,涨潮周期纳潮通量增长了219.8%。河口行洪能力明显提高,河道内洪季最大水面降幅达45.8%,水力坡度逐渐减缓,主动力轴线流速明显降低。退养还滩工程有利于河口的防洪御潮及生态环境改善,建议进一步加大实施力度。     

边角同测的平面监测控制网优化设计及精度分析

讨论了多余观测值在一定条件下按设计目标函数与多余观测数之间的函数关系进行平面变形监测网优化设计的合理性和可行性。以某抽水蓄能电站平面监测控制网为例,采用COSA软件系统进行数据处理和对比分析,说明了平面监测控制网优化设计的必要性和所产生的效益。     

地铁轨道控制网网形设计及模拟计算分析

根据地铁隧道曲线段的不同曲线半径,设计了地铁轨道控制网的控制点纵向间距。以不同的观测精度,模拟生成含随机观测误差的地铁轨道控制网的观测值,采用边角网间接平差模型和方差分量估计方法进行平差计算,分析对比网的纵向间距、观测仪器的标称精度、平差后的最弱点点位中误差以及相邻点相对中误差之间的关系,确定地铁轨道控制网的合理布设网形及其精度指标。研究成果对地铁轨道控制网的布设及测量有实际参考价值。