水质大涡模拟数学模型研究   总被引：2，自引：0，他引：2       下载免费PDF全文

张昌兵  熊朝坤  桂林  刘华  莫政宇 《水科学进展》2004,15(4):431-435

建立了基于弱可压缩流基础上的水质大涡模拟数学模型及污染物质扩散系数与平均运动的关系。数值计算采用有限体积法和预测校正法,固壁边界条件采用"部分滑移条件"。并应用该模型对重庆嘉陵江、长江两江交汇段的流场,污染物质浓度分布进行了计算,计算结果与实测值比较吻合。研究表明,横向扩散与流动状态有关,当支流流量相对较小时,横向扩散较弱,形成岸边污染带,当支流流量相对较大时,横向扩散较强,污染带向江心移动。  相似文献   

西藏纳木错和藏北高原古大湖晚更新世以来的湖泊演化与气候变迁   总被引：10，自引：5，他引：10       下载免费PDF全文

朱大岗孟宪刚  赵希涛邵兆刚杨朝斌  马志邦吴中海 王建平 《中国地质》2004,31(3):269-277

根据野外水准测量与室内实验分析，本文探讨了西藏纳木错和藏北高原古大湖晚更新世以来的湖泊演化和气候变迁。在纳木错沿岸拔湖48m以下，发育了6级湖岸阶地，拔湖48-139．2m发育有高位湖相沉积。研究表明，纳木错湖泊发育与藏北高原东南部古大湖演化可划分为3个阶段：①116-37ka B．P．间的古大湖期；②37-30ka B．P．间的外流湖期；③30kaB．P．以来的纳木错期。在古大湖阶段，包括纳木错、色林错和扎日南木错、当惹雍错等藏北高原东南部的一大批现代大、中、小型湖泊，都是互相连通的一个古大湖，其范围可能超过了现代的藏北内、外流(怒江)水系的分水岭。它或许还与藏北高原南部和西部的其他古湖相连，成为统一的藏北高原“古大湖”。通过对纳木错湖相沉积形成时代与深海氧同位素对比，易溶盐、pH值、地球化学、介形类和孢粉分析等的综合研究发现，湖相沉积记录了自晚更新世以来的湖泊演化和气候变迁信息。资料显示古大湖期湖面最高，气候温和清爽；外流湖期湖面急剧下降，气温和湿度较现今略高；纳木错期以来气候经历了全新世最宜期的暖湿后日益干旱化，气温波动，湖面持续下降。表明自晚更新世以来该区气候在逐渐变干的总趋势的基础上，经历了多次明显的冷暖与干湿波动。  相似文献   

金丽温高速公路K81高边坡变形动态数值分析     

汪会帮  陆锡铭  吕庆  许建聪 《岩土力学》2004,25(Z2):479-481

对金丽温高速公路K81高边坡进行接触大变形有限元动态数值分析.结果表明,路堑边坡开挖,导致滑面的法向应力减小、抗滑力下降,是引起古滑坡复活的根本原因.研究结果也说明了接触大变形有限元分析方法可以较好地分析潜在滑面的力学作用,是研究滑坡的滑动机理的有效方法.  相似文献   

A furrow runs through it: An example of sustainable traditional irrigation in Western Cape Province,South Africa     

H. A. P. Smit  J. A. Jacobs 《GeoJournal》2004,61(2):191-196

Water and water related matters are important issues in water scarce countries like the Republic of South Africa. This is especially true for the agricultural sector that relies heavily on the availability of water for irrigation to ensure a secure food supply. In South Africa, present day irrigation projects rely on government subsidies and are usually large undertakings beyond the reach of individuals or small communities. The sustainability of such large irrigation projects is still a matter of debate. A 100 years ago a different set of rules applied. Irrigation could only be achieved by hand-dug furrows that supplied water in relatively small quantities to small farming communities. This paper investigated such a small community, the Leeukloof farming community in the Western Cape Province of the Republic of South Africa. For the past 93 years this community has maintained a furrow that supplies water not only to farms bordering the Perdeberg River, which supplies the furrow with water, but also to farms not bordering the river. The authors try to reconstruct the changes in agricultural practices brought about by the furrow, methods of water extraction during each phase, as well as the development and role of the furrow system. The perception by the community of the necessity of this method of water extraction from the river system is also investigated. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Weathering: Toward a Fractal Quantifying   总被引：1，自引：0，他引：1  

Klaudia Oleschko  Jean-Francois Parrot  Gerardo Ronquillo  Sergey Shoba  Georges Stoops  Vera Marcelino 《Mathematical Geology》2004,36(5):607-627

Weathering occurs over a wide range of scales. To link features through these scales is a major challenge for interdisciplinary weathering studies. Fractal approach seems to be specially useful for this purpose. We introduce a multistep fractal weathering assessment scheme devoted to extract fractal weathering classifiers from texture analysis of the mineral's image. Our scheme enables to quantitatively estimate the global and local information about the geometry of the weathering pattern. This information is basic to develop geometrical indices of weathering, which can significantly enrich the common qualitative and semiquantitative weathering assessment schemes. To justify the fractal approach, a strong statistical self-similarity has been documented for both the weathering and fresh features of two common silica minerals: quartz and biogenic A-opal (phytolith) over four orders of length scales. The procedure is fast, drastically reduces thresholding bias, promises to be universal, it is valid for genetically different minerals and rock types, scale independent, and specially useful for monitoring the changes in the mineral's roughness during the alteration. Two of the proposed classifiers seem to be potentially useful for direct application in the field and be used by nonspecialist.  相似文献   

温州世贸中心大厦超深大直径钻孔灌注桩施工技术          下载免费PDF全文

徐辉雄  张涛  晏军  杨建林  鄢泰宁  蒋国盛 《探矿工程》2004,31(9):35-37

介绍了超深大直径钻孔灌注桩在温州世贸中心大厦桩基工程中的应用情况，对其施工中出现的主要问题进行了分析和处理，并提出了解决措施。  相似文献   

利用现有重力场模型求定CHAMP卫星加速度计修正参数   总被引：3，自引：0，他引：3  

徐天河  杨元喜 《测绘学报》2004,33(3):200-204

CHAMP卫星加速度计数据的标定是通过确定其尺度因子和偏差参数来完成的.本文基于能量守恒方程,给出利用现有重力场模型标定CHAMP卫星加速度数据的基本原理和数学模型;提出相邻历元间差分算法,大大简化了观测方程,同时避免积分常量的计算.该算法既能同时解算尺度因子和偏差参数,也可任意求解其中之一.基于实测的CHAMP卫星加速度数据,利用EGM96模型和最新公布的EIGEN-2模型进行计算与比较,验证该方法的有效性.  相似文献   

Magma flow in the East Greenland dyke swarm inferred from study of anisotropy of magnetic susceptibility: magmatic growth of a volcanic margin   总被引：2，自引：0，他引：2  

Jean-Paul Callot  Laurent Geoffroy 《Geophysical Journal International》2004,159(2):816-830

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中国大陆地区中强地震前加卸载响应比异常时间尺度的统计研究   总被引：4，自引：2，他引：4  

张晖辉  尹祥础  梁乃刚 《中国地震》2005,21(4):486-495

加卸载响应比理论是近年来提出的地震预测方法。本文进行了加卸载响应比异常时间尺度的统计研究，其中包括中国大陆地区5．0～8．1级的部分中强地震共30个震例，并得出加卸载响应比异常的时间尺度与未来地震震级之间的拟合函数。结果表明，地震前加卸载响应比异常的时间尺度与未来地震的震级具有正变关系，即震级越高，地震前加卸载响应比异常的时间尺度越长。根据加卸载响应比异常的时间尺度与震级之间的关系可以估计未来地震的发震时间，同时，可以确定加卸载响应比时空扫描过程中时问长度的大小。  相似文献   

Wood storage in a wide mountain river: case study of the Czarny Dunajec,Polish Carpathians     

Bart&#x;omiej Wyga  Joanna Zawiejska 《地球表面变化过程与地形》2005,30(12):1475-1494

Storage of large woody debris in the wide, mountain, Czarny Dunajec River, southern Poland, was investigated following two floods of June and July 2001 with a seven‐year frequency. Within a reach, to which wood was delivered only by bank erosion and transport from upstream, wood quantities were estimated for eighty‐nine, 100 m long, channel segments grouped into nine sections of similar morphology. Results from regression analysis indicated the quantity of stored wood to be directly related to the length of eroded, wooded banks and river width, and inversely related to unit stream power at the flood peak. The largest quantities of wood (up to 33 t ha^?1) were stored in wide, multi‐thread river sections. Here, the relatively low transporting ability of the river facilitated deposition of transported wood while a considerable length of eroded channel and island banks resulted in a large number of trees delivered from the local riparian forest. In these sections, a few morphological and ecological situations led to the accumulation of especially large quantities of wood within a small river area. Very low amounts of wood were stored in narrow, single‐thread sections of regulated or bedrock channel. High stream power facilitated transport of wood through these sections while the high strength of the banks and low channel sinuosity prevented bank retreat and delivery of trees to the channel. Considerable differences in the character of deposited wood existed between wide, multi‐thread channel sections located at different distances below a narrow, 7 km long, channellized reach of the river. Wood deposited close to the downstream end of the channellized reach was highly disintegrated and structured into jams, whereas further downstream well preserved shrubs and trees prevailed. This apparently reflects differences in the distance of wood transport and shows that in a mountain river wider than the height of trees growing on its banks, wood can be transported long distances along relatively narrow, single‐thread reaches but is preferentially deposited in wide, multi‐thread reaches. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献