Dynamic processes of a simple linear dune—a study in the Taklimakan Sand Sea, China   总被引：1，自引：0，他引：1  

Xunming Wang  Zhibao Dong  Jianjun Qu  Jiawu Zhang  Aiguo Zhao 《Geomorphology》2003,52(3-4):233-241

Samples of dune sands, surveys of the morphology and field measurements of wind velocity and direction of a simple linear dune in Taklimakan Sand Sea show that the airflow and sand flux vary with the change of wind direction on the dune surface. Decrease of the airflow stress on the lee flank does not result in much decrease of the sand flux because of the low threshold shear velocities and the airflow conditions. There are no significant relations between the sand flux on the lee flank and the angle of incidence of the airflow. The low threshold shear velocities and the maintenance of the sand flux at the lee flank are the main mechanisms keeping the linear shape of the dunes. Measurements of the sand flux shows that it reaches a maximum on the crest of the dune. The grain size of the transported sands has some differences compared to that of the dune surface. The sands transported are finer than that on the dune surface, but better sorted under the influence of the medium to low wind activity. The field experiment results exhibit that it is possible for the dunes to be shaped as linear dunes during the processes of accumulation and elongation.  相似文献   

Wind velocity and sand transport on a barchan dune   总被引：2，自引：0，他引：2  

G. Sauermann  J. S. Andrade  Jr.  L. P. Maia  U. M. S. Costa  A. D. Araújo  H. J. Herrmann 《Geomorphology》2003,54(3-4):245-255

We present measurements of wind velocity and sand flux performed on the windward side of a large barchan dune in Jericoacoara, northeastern Brazil. From the measured profile, we calculate the air shear stress using an analytical approximation and treat the problem of flow separation by an heuristic model. We find that the results from this approach agree well with our field data. Moreover, using the calculated shear velocity, we predict the sand flux according to well-known equilibrium relations and with a phenomenological continuum saltation model that includes saturation transients and thus allows for nonequilibrium conditions. Based on the field data and theoretical predicted results, we indicate the principal differences between saturated and nonsaturated sand flux models. Finally, we show that the measured dune moves with invariant shape and predict its velocity from our data and calculations.  相似文献   

A critical state interpretation for the cyclic liquefaction resistance of silty sands   总被引：1，自引：0，他引：1  

George D. Bouckovalas  Konstantinos I. Andrianopoulos  Achilleas G. Papadimitriou 《Soil Dynamics and Earthquake Engineering》2003,23(2):115-125

Contrary to many laboratory investigations, common empirical correlations from in situ tests consider that the increase in the percentage of fines leads to an increase of the cyclic liquefaction resistance of sands. This paper draws upon the integrated Critical State Soil Mechanics framework in order to study this seemingly not univocal effect. Firstly the effect of fines on the Critical State Line (CSL) is studied through a statistical analysis of a large data set of published monotonic triaxial tests. The results show that increasing the content of non-plastic fines practically leads to a clockwise rotation of the CSL in (e–ln p) space. The implication of this effect on cyclic liquefaction resistance is subsequently evaluated with the aid of a properly calibrated critical state elasto-plastic constitutive model, as well as a large number of published experimental results and in situ empirical correlations. Both sets of data show clearly that a fines content, less than about 30% by weight, may prove beneficial at relatively small effective stresses (p₀<50–70 kPa), such as the in situ stresses prevailing in most liquefaction case studies, and detrimental at larger confining stresses, i.e. the stresses usually considered in laboratory tests. To the extent of these findings, a correction factor is proposed for the practical evaluation of liquefaction resistance in terms of the fines content and the mean effective confining stress.  相似文献   

激光测速粒子对复杂流动的响应研究——Ⅱ典型流场中粒子跟随性的数值分析   总被引：4，自引：0，他引：4       下载免费PDF全文

黄社华  魏庆鼎 《水科学进展》2003,14(1):28-35

以修正后适用于高颗粒雷诺数的粒子非恒定运动方程为基础,将该方程无量纲化,定义了一般流场中粒子跟随性的概念,给出了粒子跟随性的数学表述。据此对典型流场中粒子的运动进行了数值计算,并定量分析了粒径、密度等参数对不同流动中示踪粒子跟随特性的影响。  相似文献   

固体粒子的稳泡机理          下载免费PDF全文

吴飞 《探矿工程》1997,(1):50-52

固体粒子是良好的稳泡剂，其稳泡作用实质是在气－水界面产生吸附，形成固态膜，固态膜致密性强，机械强度高，表面粘度大。固体粒子的润湿性能，粒子大小及形状对固态膜的牢固程度有很大影响。  相似文献   

中国西北部“4.5”沙尘暴过程中尺度低压的数值模拟   总被引：3，自引：9，他引：3  

陈伟民  王强  牛志敏  徐建芬  高风荣 《中国沙漠》1996,16(2):140-144

利用改进型ＰＳＵ／ＮＣＡＲ中尺度数值模式（ＭＭ４标准版），取模式水平格距４０ｋｍ，４６×６１网格，垂直方向ａ取１５层，即从地面到模式顶（１００ｈＰａ），σ＝０．０、０．１、０．２、０．３、０．４、０．５、０．６、０．７、０．７８、０．８４、０．８９、０．９３、０．９６、０．９８、０．９９、１．００，采用ＮＣＡＲ的３０＇×３０＇地形资料，以常规观测资料作为初始场，较好地模拟了此次沙尘暴过程的海平面气压的演变和分布，特别是张掖、柴达本盆地以及敦煌附近的三个中低压。同时，模拟了张掖中低压与蒙古冷高压之间的甘肃河西沙尘暴东大风。敏感性试验表明，沙尘暴中低压的形成发展主要是受于物理过程制约；沙尘暴中尺度系统的研究与暴雨中尺度系统的研究是有区别的，积云对流参数化并不是特别重要，在设计研究沙尘暴的数值模式中，应当合理地处理其他的热力、动力过程及大气外强迫源的作用。模式水平格距、地形真实程度对模拟中低压的位置、中心强度有重要贡献；下垫面变化中低压强度有一定影响。张掖热低压的形成发展主要是在有利的环境形势下，特殊地势起了重要作用，表现为直接动力强迫和间接热力强迫。  相似文献   

陕西直罗油田长_2油层组储层特征     

刘勇  孙冬胜 《陕西地质》1996,(2)

直罗油田主力产层为三叠系延长组长2油层组，储层以三角洲分支河道砂体为主，岩性主要为长石细砂岩，大量的自生矿物对原生孔隙产生了很大程度的破坏。较强的成岩后生作用使得储层以粒间溶孔及原生粒间余孔为主要储集空间。储层孔隙结构表现为以小孔隙、小喉道为主要特征，非均质性较强。物性分布主要与其在砂体中的分布部位有关。  相似文献   

Evolution of sand waves in the Messina Strait, Italy   总被引：1，自引：0，他引：1  

V. C. Santoro  E. Amore  L. Cavallaro  M. De Lauro 《Ocean Dynamics》2004,54(3-4):392-398

In the present paper the morphodynamics of sand waves in the Messina Strait, Italy, is analysed by comparing data gathered during two different surveys carried out in 1991 and 2001, respectively. In particular, a morphometric analysis on the most recent data and a qualitative analysis of the differences between bottom bedform patterns, are carried out. At locations characterised by greater depths, only minor changes to the planimetric configuration of the field, i.e. crest orientation (which is seen to be orthogonal to the direction of net gross sand transport) and wave length are observed, while differences in wave length and crest direction are more evident in more shallow areas. On the other hand, wave height has significantly increased in the whole field. A possible explanation of such a change, based on the previsions of a theory which relates sand-wave growth and migration to the main components of the tidal ellipse, is provided.Responsible Editor: Jens Kappenberg  相似文献   

沈阳地区沙尘天气分析   总被引：5，自引：1，他引：5       下载免费PDF全文

路爽  张菁  孙凤华 《气象科学》2004,24(1):112-119

本文总结了沈阳地区沙尘天气的时空分布特点，从天气条件、地表自然条件(沙源)两方面分析了沈阳地区沙尘天气的成因，总结了沈阳地区预报沙尘天气时应参考的5个因素。  相似文献   

塔河油田卡拉沙依组砂组沉积相与储层研究     

樊怀阳  陈文  刘百春 《新疆地质》2004,22(4):417-421

卡拉沙依组砂岩是塔河油田石炭系重要储层，从上到下分为4个砂组，即Ⅰ砂组、Ⅱ砂组、Ⅲ砂组及Ⅳ砂组，根据岩石组合特征、岩石粒度、分选性、以及沉积构造等特征，可得出Ⅰ砂组为较典型的扇三角洲沉积环境；Ⅱ-Ⅳ砂组为潮坪环境，其中Ⅲ砂组沉积时的古环境水动力相对最强，以潮间带下部为主，储层砂体最发育，单个砂体的厚度也最大，为纵向上最好储层段。  相似文献