An analysis of drag force on wind of shrubs simulated in a wind tunnel     

Ping Lv  Zhibao Dong  Qingsong Mu  Wanyin Luo  Guangqiang Qian 《Environmental Earth Sciences》2014,71(1):125-131

Shrubs that exert drag force on the wind significantly affect the air–surface interaction in arid and semiarid regions, and some coastal regions where aeolian processes are active. An understanding of the drag force on wind of shrubs provides important information on the dynamics of shrubs in reducing wind erosion, and their geomorphological significances. Thus, we analyzed the drag force and drag coefficient for model shrubs using wind measurements obtained by particle image velocimetry in a scaled wind tunnel simulation. The drag force was found to be a function of wind velocity and shrub density. Both drag force and drag coefficient revealed a critical shrub density of around 0.08. The vertical drag force changed direction when the shrub density became greater or less than the critical density. The drag coefficient increased rapidly with shrub density when the density was below 0.08, but it increased very gently when the density was increased beyond the critical value. The results have an important theoretical significance for our understanding of the dynamics of vegetated dunes and the windbreak mechanism of shrubs.  相似文献   

The response of playa and sabkha hydraulics and mineralogy to climate forcing   总被引：1，自引：0，他引：1  

Tyler SW  Muñoz JF  Wood WW 《Ground water》2006,44(3):329-338

Dry playa lakes and sabkhat often represent the terminus of large ground water flow systems and act as integrators of both upgradient (recharge) and downgradient discharge (evaporation). Ground water levels beneath playa/sabkha systems show a variety of surprising responses driven by large evaporation demands and chemical processes not typically encountered in more humid regions. When the water table is very close to the land surface, almost instantaneous rises can be observed with little observed change in either upgradient ground water recharge or potential evaporation. Conversely, when water tables are several meters below the playa surface, water table responses to interannual variability of recharge can be damped and lag significantly behind such changes. This review of the dynamics of shallow water tables in playa lakes and sabkhat discusses the pertinent hydraulic and solute processes and extracts a simple but comprehensive model based on soil physics for predicting the water table response to either upstream recharge changes or changes in potential evaporation at the playa/sabkha. Solutes and associated authigenic minerals are also shown to be important in discriminating both the causes and effects of water level fluctuations.  相似文献   

Thermal-mechanical Influences and Environmental Effects of Expressway Construction on the Qinghai-Tibet Permafrost Engineering Corridor     

Ma Wei  Mu Yanhu  Xie Shengbo  Mao Yuncheng  Chen Dun 《地球科学进展》2017,32(5):459-464

The Qinghai-Tibet Engineering Corridor (QTEC) is a strategic passage between Tibet and central China. In the past half century, several major projects have been built in this narrow corridor with vulnerable geoenvironment. Along with a new round of economic development of the Tibet autonomous region, some major linear projects including expressway, double-tracking railway, high voltage power transmission line have been incorporated into the national development planning within the corridor, and especially the expressway construction is imminent now. In the QTEC, permafrost is a controlling factor of geological environment, which will impose great restrictions on engineering construction. In turn, engineering construction will induce significant effects on permafrost geological environment. With more and more linear infrastructures crowding into the QTEC, the thermal interaction among permafrost engineering and engineering disturbance on permafrost thermal-mechanical regime will be more significant. With respect to this issue, a research program focusing on thermal-mechanical influences and environmental effects of expressway construction on the Qinghai-Tibet permafrost engineering corridor was started and supported by the National Natural Science Foundation of China. In this paper, the research significance, key scientific issues, main research contents and goals of the program are introduced so as to provide some references for related researchers and engineers.  相似文献   

扇三角洲沉积储层特征与定量评价——以辽河西部凹陷某试验区于楼油层为例     

陈欢庆  穆剑东  王珏  邓西里 《吉林大学学报(地球科学版)》2017,47(1)

随着蒸汽吞吐开采方式进入后期,储层非均质性对开发效果的影响日益凸显。以辽河西部凹陷某试验区为例,综合岩心、镜下薄片、测井、分析测试等多种资料,实现储层发育特征表征。研究区目的层属扇三角洲前缘沉积,由于水下分流河道的频繁分流改道,砂体相互切叠,储层非均质性强烈。优选充分反映储层性质影响因素的参数,基于经典的聚类分析软件平台,实现扇三角洲沉积储层定量评价。将目的层储层划分为Ⅰ类、Ⅱ类、Ⅲ类和Ⅳ类4种类型,储层分类正判率超过85%。不同类型储层发育明显受沉积相控制,Ⅰ类和Ⅱ类储层多位于水下分流河道和河口砂坝的位置,而Ⅲ类和Ⅳ类储层多位于水下分流河道间砂或前缘席状砂的位置。不同类型储层在转换热采方式时应该区别对待。  相似文献   

Monitoring the seasonal dynamics of physicochemical parameters from Atoyac River basin (Puebla), Central Mexico: multivariate approach     

E. Martinez-Tavera  P. F. Rodriguez-Espinosa  V. C. Shruti  S. B. Sujitha  S. S. Morales-Garcia  N. P. Muñoz-Sevilla 《Environmental Earth Sciences》2017,76(2):95

Spatiotemporal variations of ten physicochemical parameters in the water quality of Atoyac River basin, Central Mexico, were obtained from 22 sampling sites (66 samples in total) located all along the basin for three different seasons (dry, rainy and winter). Multivariate statistical techniques such as correlation matrix, factor analysis (FA) and cluster analysis (CA) were used as a tool to understand the process. Physicochemical parameters such as temperature (T), pH, conductivity (λ), dissolved oxygen (DO), spectral absorption coefficient (SAC), oxidation–reduction potential (ORP), turbidity, 5-day biochemical oxygen demand (BOD₅), chemical oxygen demand (COD) and total suspended solids (TSS) were analyzed. Extremely high values of pH (10.24), conductivity (1870 µS/cm) and reduced redox potential (?370.1 mV) were observed in the dry season, whereas elevated TSS of 2996 mg/L was detected during the rainy season. The results elucidated high influence from the adjoining industrial, agricultural and urban zones, making the river unsuitable for life. FA generated varifactors, which accounted for cumulative % of 75.04 (dry), 76.22 (rainy) and 79.96 (winter) clearly grouping the external factors responsible for these significant values indicating the source of contamination. Cluster analysis facilitated the ease of classifying the sampling sites based on the similarities of physicochemical parameters. This study carried out in different seasons using multivariate statistical techniques would definitely prove to be an efficient tool for the restoration and establishing the real-time monitoring stations along this important river basin of Mexico.  相似文献   

新疆楼兰地区雅丹地貌差异性侵蚀特征   总被引：2，自引：0，他引：2  

林永崇  穆桂金  秦小光  赵雪  许冰  贾红娟  张磊  阮秋荣  吴勇  魏东  王春雪  邵会秋 《中国沙漠》2017,37(1):33-39

楼兰地区雅丹地貌正处于活跃发育时期,为研究雅丹地貌侵蚀作用提供了良好的载体。对楼兰雅丹地层岩性、地貌形态特征等进行野外调查、测量,进行室内试验、分析。结果表明：楼兰雅丹地层形成于全新世时期,主要由较为坚硬的黏土粉砂层（CS）和松散的砂质粉砂层（SS）两类组成,并且CS层和SS层交替出现。这导致雅丹体出现显著的差异侵蚀现象。由于地层存在差异侵蚀,楼兰雅丹侵蚀较慢的CS层普遍出现岩层坍塌现象,CS层坍塌块体长度（L）和厚度（T）分别代表了SS岩层的相对侵蚀深度和CS层的厚度。统计结果显示楼兰雅丹CS层坍塌块体长度和厚度存在中度正相关关系（R=0.553）。但是,随着坍塌块体厚度的增加,其长度增加呈减缓趋势（L/T比值逐渐减小趋势）,直至长度和厚度相等（L/T≈1）。综合分析表明,楼兰地区雅丹地貌发育主要受风蚀作用影响,但是区域地层岩性特征、重力作用对楼兰雅丹侵蚀起着特殊重要影响。  相似文献   

激光显微探针~(40)Ar/~(39)Ar定年进入了人类历史领域——评美国伯克莱地质年代学中心最新研究成果和年轻火山岩的定年极限   总被引：1，自引：0，他引：1  

穆治国 《地质论评》1999,45(4)

美国伯克莱地质年代学中心P.R.Renne等(1997)对采自意大利维苏威火山公元79年爆发喷出物中的透长石,进行了激光显微探针~(40)Ar/~(39)Ar定年,从46个分析数据中得到了~(40)Ar/~(39)Ar等时线年龄为1925±94 a,接近于与现今使用的格里历1918年前一致。这证明激光显微探针~(40)Ar/~(39)Ar定年法的可信度已扩展到记录人类历史的时间范畴。Renne等的最新研究成果把30多年来K-Ar地质年代学者对特别年轻火山岩的定年研究带入了一个新阶段,它为与晚新生代地质年代学有关的各种研究提供了一有力工具。  相似文献   

西天山吐拉苏—也里莫墩早石炭世火山岩带地质特征     

母瑞身  田昌烈  沙德铭  贾斌  杨森  漆树基  王永新  张伟博 《地质论评》1999,45(7):1078-1087

我国西天山吐拉苏—也里莫墩早石炭世火山岩带是伊犁裂谷的北展部分,其中赋存有阿希大型金矿。火山岩带内除局部地区见底部沉积砾岩外,主体为陆相中酸性火山熔岩、火山碎屑岩以及石英角闪安山玢岩（潜火山岩）,火山岩属钙碱性—碱性系列岩石组合。火山活动受近EW向（一级）和近SN向（二级）火山构造控制,并保留了火山机构（三级）。形成的古构造环境为陆缘拉张带。火山岩带活动时限较短,只限于早石炭世早期。  相似文献   

黔中岩溶地区岩土水系统中氟的环境地球化学研究   总被引：7，自引：0，他引：7  

朱立军  李景阳  牟成刚 《中国岩溶》1999,18(2):109-115

通过对研究区碳酸盐岩— 土— 水系统中氟的系统测定和吸附实验,结合矿物表面化学和土壤化学研究,揭示了岩溶地区岩— 土— 水系统中氟的地球化学特征和迁移富集机理。黔中岩溶地区深层地下水( 100m 以下)和土层具有高氟异常特征,而浅层地下水和地表水含氟较低(大多在0. 5mg /l以下)。以含石膏碳酸盐岩为主的三叠纪海相地层是该区土水中氟的主要来源。土层中针铁矿表面对氟的专性吸附及其解吸作用是岩溶地区土水系统中氟迁移和富集的重要机理。   相似文献   

Nonlinear stability analysis of the zonal flows at middle and high latitudes   总被引：1，自引：0，他引：1  

Mu Mu  Wu Yonghui  Tang Mozhi  Liu Haiyan 《大气科学进展》1999,16(4):569-580

An attempt has been made to apply Arnol’d type nonlinear stability criteria to the diagnostic study of the persistence (stability) or breakdown (instability) of the atmospheric flows. In the case of the blocking high, the cut-off low and the zonal flow, the relationships of the geostrophic stream function versus the po-tential vorticity of the observed atmosphere are analyzed, which indicates that Arnol'd second type nonlinear stability theorem is more relevant to the observed atmosphere than the first one. For both the sta-ble and unstable zonal flows, Arnol’d second type nonlinear stability criteria are applied to the diagnosis. The primary results show that our analyses correspond well to the evolution of the atmospheric motions. The synoptically stable zonal flows satisfy Arnol'd second type nonlinear stability criteria; while the synoptically unstable ones violate the nonlinear stability criteria.  相似文献