The influence of dunes on mixing in a migrating salt‐wedge: Fraser River estuary,Canada     

Ray Kostaschuk  Jim Best  Paul V. Villard 《地球表面变化过程与地形》2010,35(4):460-465

Dune bedforms and salt‐wedge intrusions are common features in many estuaries with sand beds, and yet little is known about the interactions between the two. Flow visualization with an echosounder and velocity measurements with an acoustic Doppler current profiler over areas of flat‐bed and sand dunes in the highly‐stratified Fraser River estuary, Canada, were used to examine the effect of dunes on interfacial mixing. As the salt‐wedge migrates upstream over the flat‐bed, mixing is restricted to the lower portion of the water column. However, as the salt‐wedge migrates into the dune field from the flat bed, there is a dramatic change in the flow, and large internal in‐phase waves develop over each of the larger dunes, with water from the salt‐wedge reaching the surface of the estuary. The friction Richardson number shows that bed friction is more important in interfacial mixing over the dunes than over the flat‐bed, and a plot of internal Froude Number versus obstacle (dune) height shows that the salt‐wedge flow over the dunes is mainly supercritical. Such bedforms can be expected to cause similar effects in interfacial mixing in other estuaries and sediment‐laden density currents, and may thus be influential in fluid mixing and sediment transport. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Topographic changes of a supply‐limited inland parabolic sand dune during the incipient phase of stabilization     

Chris H. Hugenholtz 《地球表面变化过程与地形》2010,35(14):1674-1681

Topographic surveys on an inland parabolic sand dune over a six‐year period provide insight into the effects of diminishing local sand supply on dune stabilization. During the interval (2003–2009) sparse vegetation cover (Psoralea lanceolata) increased despite drier than normal moisture conditions and steady wind power during the growing season. Whereas these climatic conditions are typically ascribed to sustaining or increasing dune activity, here they coincide with stabilization. Through the use of geographic information system (GIS) analysis of volumetric changes it is shown that the increase of P. lanceolata can be attributed to the reduction of local sand supply from two blowouts along the arms of the parabolic dune during the six‐year period. These results show that climate is not the only control on dune activity in vegetated inland dunefields. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

中国西北干旱区地-气温差变化成因分析   总被引：3，自引：1，他引：2  

符睿  韦志刚  文军  李振朝 《中国沙漠》2010,30(6):1442-1449

利用1961—2000年中国西北干旱区49个气象台站百叶箱气温、0 cm地温、降水和近地层风速月平均资料,以及NCEP/NCAR再分析月平均资料,分析了我国西北干旱区地-气温差变化的原因。结果表明,20世纪后40 a西北干旱区冬季地-气温差呈减小趋势,其可能原因是20世纪80年代后全球进一步变暖,西北干旱区对流层中层高度场升高、气温升高,风场易出现反气旋式环流距平,寒潮活动减少,近地层风速减弱使得气温增暖高于地温。而春初对流层中层高度场偏低时,气温偏低,降水偏多,风场易出现气旋式环流距平,近地层风速减弱使得气温增暖低于地温,所以春初地-气温差呈上升趋势。  相似文献   

北部湾沿海基本风压和阵风风压分析     

苏志  张瑞波  周绍毅  黄颖 《热带地理》2010,30(2)

利用北部湾沿海7个气象站建站至2008年最大风速资料,采用指数律风速廓线公式和"时次换算"方法订正最大风速,得到长年代10m高处10min平均年最大风速序列;采用极值I型分布估算北部湾沿海各地50年一遇最大风速,通过伯努利方程计算基本风压。结果表明:北部湾沿海的基本风压以涠洲岛最大,达1.13kN/m2;其次是东兴、北海,分别为0.59和0.58kN/m2;第三位是防城港和合浦,分别为0.49和0.47kN/m2;最小是防城和钦州,分别为0.39和0.33kN/m2,表明越靠近海的地方基本风压越大。利用建站至2008年的极大风速资料对北部湾沿海的阵风风压进行分析,发现阵风风压分布特点与基本风压相同,而且阵风风压比基本风压大,海岸区域的阵风风压约为基本风压的2倍,涠洲岛则是1.54倍。  相似文献   

钉形水泥土双向搅拌桩桩身强度差异原因分析与检测探讨   总被引：1，自引：0，他引：1  

和礼红  李艳  张妮娜  秦亚琼 《岩土力学》2010,31(Z1):255-260

本文简单介绍了钉形水泥土双向搅拌桩的形成及其特点,通过大量的桩身标准贯入试验和室内无侧限抗压强度试验,建立了桩身标准贯入击数与桩身无侧限抗压强度以及桩体分段深度的数学关系式,同时对钉形水泥土双向搅拌桩桩身强度不一致的现象进行了深入分析,对桩身强度检测项目和方法进行了深入探讨,并初步确定了武汉新区桩身强度检测的项目和方法。提出采用加权平均值作为桩身强度设计和检测的标准更为妥当。  相似文献   

Experimental study on the sampling efficiency of the whirl type separation sand sampler in a wind tunnel     

ManQuan Zhao  LiHong Fu  WenMing Wang  Zhi Chen  JinLian Wang  Mei Dong 《寒旱区科学》2010,2(1):0007-0014

A performance test was conducted in a wind tunnel by changing the principal configuration parameters of a sampler such as the diameter of the container, inlet width and cone height. The results show that the average sand collection rate is from 80% to 90% when any one of the configuration parameter levels is changed. However, the variation of a parameter level results in different ef-fects on the sand collection rate for each soil sample within a certain size range of sand grains. The results show that for various sand grain sized soil sample at each wind speed, the sand collection rate decreases when the diameter of the container changes from 50 mm to 40 mm, the sand collection rate increases by about 2%-3% when the inlet width changes from 10 mm to 8 mm, and the sand collection rate increases by about 3%-4% when cone height is altered from 100 mm to 125 mm. The average sand collection rate is enhanced by 2%-4% for the soil sample of different sized sand grains when the diameter of the container is 50 mm, the inlet width is 8 mm, and cone height is 125 mm.  相似文献   

栅栏绕流减速效应风洞实验模拟   总被引：12，自引：9，他引：3  

罗万银  董治宝  钱广强  袁文丽 《中国沙漠》2010,30(1):1-7

为研究阻沙栅栏的空气动力学效应,利用PIV技术对栅栏绕流的速度场进行了风洞实验模拟,并对其减速效应加以分析评价。结果表明,疏透度对栅栏绕流的平均速度场分布影响比较明显,疏透度越小栅栏后的平均水平风速衰减得越快;栅栏绕流的垂直速度分量在栅栏顶部最大,并随疏透度的增大而减小,影响了栅栏周围沙粒的跃移传输及沉积特征;栅栏后的累计减速率可以用高斯峰值函数来拟合,随疏透度的增大呈先增大后减小的趋势,疏透度η=0.2时累计减速率最大,代表了栅栏减速的理论最佳疏透度。  相似文献   

风水复合侵蚀与生态恢复研究进展   总被引：4，自引：0，他引：4  

李秋艳  蔡强国  方海燕 《地理科学进展》2010,29(1)

风水复合侵蚀是风力与水力共同或交替作用相互增强或者削弱的过程。从侵蚀区划分、驱动因素、侵蚀机理和生态恢复对策等方面论述了风水复合侵蚀的研究进展,简述了半干旱风水复合侵蚀区和海岸复合侵蚀区是两个影响最大的风水复合侵蚀区。晋陕蒙接壤区为半干旱风水复合侵蚀区的强烈侵蚀中心,在土地利用上属农牧交错区,生态环境极为脆弱。海岸复合侵蚀岸段分布广泛,侵蚀岸线在总岸线中所占比例较大。影响风水复合侵蚀的因素包括自然和人为因素,且地域差异显著。半干旱区风水复合侵蚀研究主要从侵蚀特点、土壤特性、侵蚀产沙、侵蚀能量研究等方面;海岸复合侵蚀区从侵蚀特征、风暴潮与海岸复合侵蚀关系等方面分析了取得的进展和存在的不足。总结了生物措施和工程措施对风水复合侵蚀区生态恢复的作用,展望了风水复合侵蚀与生态恢复的研究方向,并指出复合侵蚀机理与评估、生态恢复机理与评价研究是今后研究的趋势。  相似文献   

风雪共同作用下膜结构雪压分布规律的数值模拟研究     

孙芳锦  殷志祥 《地震学刊》2010,(1):83-87

对膜结构在风雪共同作用下的雪压分布规律进行了数值模拟研究。首先采用两相流原理对雪漂运动中的空气相和雪相分别进行了数值建模,然后采用CFD数值模拟技术,研究了在风雪共同作用下双坡型膜结构表面的雪荷载分布规律,分析了双坡型膜结构的重要几何参数变化时,雪漂及屋面雪荷载分布的变化规律,总结了双坡型膜屋面在风雪共同作用下的雪压分布规律。结果表明,屋面倾角和屋面宽度是影响风雪共同作用下膜结构表面雪压分布的重要因素,檐口高度和屋面长度是影响膜结构表面雪压分布的次要因素。本文研究为更安全、经济地进行膜结构的抗风雪设计、施工提供了可靠的科学依据。  相似文献   

Large-amplitude internal waves observed in the Kruzenshtern Strait of the Kuril Island Chain and possible water transport and mixing     

Tomohiro Nakamura  Yasuhiro Kawasaki  Tokihiro Kono  Toshiyuki Awaji 《Continental Shelf Research》2010

  相似文献