Characterizing the hydraulic properties of unsaturated sand considering various porosities and drying‐wetting paths of the retention curve     

Kai‐yuan Ke  Yih‐Chi Tan  Chu‐Hui Chen  Hsien‐Tsung Lin 《水文研究》2013,27(4):592-604

Previous studies have shown that water retention curve (WRC) and the hydraulic conductivity vary because of changes of the void ratio or porosity of soil. However, limited documents pointed out the change of hydraulic properties of soil when compacted to different porosities while considering both of the drying and wetting processes of the WRC. This information is sometimes necessary for research like finger flow analysis or the occurrence of wetting and drying cycles as what would be seen in the field. Therefore, this study aims to examine the change of WRC characteristics with varied porosity considering both of the drying and wetting path in WRC by conducting a sand box experiment. Results show that the same type of sand compacted to various porosities have different hydraulic parameters. Hydraulic conductivities generally decrease with reduced porosities; shape parameter α of the van Genuchten equation (1980) linearly decreases with declining porosity and shape parameter n in a reversal manner for the sands of interest whether in the drying process or wetting process. The unsaturated properties of sand are further characterized by inspecting the variations of moisture content, matric suction and vertical displacement of soil body subject to periodic changes of the water level by another sand box experiment. The outcomes suggest that the saturated water content and residual water content are changing during the wetting–drying process, which can be an implication of the changed properties of WRC. The characteristics of volumetric deformation might be varied as well because of the observation of the dissimilar patterns of the changing vertical displacements among each wetting–drying process. Infiltration patterns of the sands also are identified through numerical modelling by introducing a constant infiltration flux from the surface followed by a no‐influx condition. Results indicate that less water accumulates in the sand near the surface for the sand compacted to higher porosity, but water can move deeper. Hydraulic conductivity is found as the prime factor dominating the evolvement of wetting fronts. However, shape parameters of water retention curves also affect the infiltration pattern to some extent. In addition, different sands with similar porosities can have quite different infiltrating characteristics. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Compact and tunable mid-infrared source based on a 2 μm dual-wavelength KTiOPO₄ intracavity optical parametric oscillator     

耿优福  谭晓玲  李学金  姚建铨 《海洋学报(英文版)》2010,29(11)

Using a double resonant KTiOPO₄ (KTP) intracavity optical parametric oscillator operating at degenerated point of 2 μm, we demonstrate a unique mid-infrared source based on difference frequency generation in GaSe crystal. The output tuning range is 8.42-19.52 μm, and a peak power of 834 W for type-I phase matching scheme and 730 W for type-II phase matching scheme are achieved. Experimental results show that this oscillator is a good alternative to the generator of a compact and tabletop mid-infrared radiation with a widely tunable range.  相似文献   

天然河道一维不恒定流计算的守恒格式   总被引：2，自引：2，他引：2       下载免费PDF全文

谭维炎  胡四一 《水科学进展》1990,1(1):22-32

本文从数值计算的角度分析和讨论了天然河道一维不恒定流方程组的各种形式及其差分格式的守恒性。据此,本文总结了建立守恒差分格式的途径和应遵循的原则,并就差分格式如何达到准确或近似守恒提出了实际的处理方法。  相似文献   

焦耳效应标定高温卡尔维微量热计     

Tang Yuanjun Tan Dafang Mao Yi 《地球科学》1989,(3)

根据热流式量热计的Tian氏方程,用焦耳效应标定高温卡尔维微量热计。用偏差法得到的灵敏度值与积分法测得的值一致。用回归曲线对灵敏度实验值进行拟合,利用计算机求得灵敏度—温度回归曲线,得到了室温至700℃的全部灵敏度值,从而即可使用微量热计测量此温度范围内的未知样品热效应。  相似文献   

地震拓扑预测     

谭承业  阮圣娜 《地震研究》1989,12(3):193-200

本文对地震参数建立了地震拓扑空间并把灰色系统理论中的拓扑预测方法引入地震预测之中,研究地震长趋势的预测问题。  相似文献   

气候分析应用聚类方法的评价          下载免费PDF全文

谭冠日 《气象学报》1988,46(2):180-186

对聚类分析的华德法、重心法和平均联系法的理论分析指出:在组间距离相同的条件下,华德法优先合并小的组,最终产生大小较为均匀的组,这不能准确地反映气候的现实。在组内平方和增量相同的条件下,重心法优先合并大的组,最终产生一个很大的组和很多极小的组,背离气候的现实。平均联系法基本上避免了上述偏歧,产生凝聚、方差均匀的组,较好地反映气候现实。中国东部大陆夏季降水的分区证实了以上结论。  相似文献   

地震预报和地震对策模型体系          下载免费PDF全文

谭承业 《地震工程学报》1988,10(2):92-104

设计了一种用于地震预报和地震对策的模型体系。本文简述了建立这一模型体系的必要性,给出了模型体系的设计思想,讨论了模型体系的結构、功能和组成以及建立模型体系的数学方法。  相似文献   

地质为农业服务的初步探讨：盱眙县农业环境地质评价简介     

谭东林 《水文地质工程地质》1993,20(4):50-52

通过介绍“盱眙县农业环境地质评价”,提出了开展农业地质工作的思路、方法及成果的编制。对如何开发地质资源,控制地质灾害,以服务于农业,进行了有益地探索。  相似文献   

非均匀温度场中熔体结晶作用与科马提岩结构成因     

谭劲  赵珊茸 《地质科技情报》1994,13(4):35-40

具有重要岩石学和构造学意义的科马提岩，最吸引人同时又最令人困惑的特征之一是它的鬣刺结构和分层构造。本文从喷出地表的岩桨冷凝时温度分布、熔体性质与结晶作用的密切联系，把科马提岩浆喷发形成的岩流作为一个冷凝整体。通过与金属铸锭浇注成形和矿石冶炼生产的比较，发现它们在冷凝固结过程中温度场特征、熔体的性质、结晶能力和结晶方式都有十分相似的特点，并以此为出发点详细解析了科马提岩的鬣刺结构和岩石分层构造的形成  相似文献   

双密度重叠找气新方法     

刘舒杰  谭廷栋 《物探与化探》1994,18(4):289-296

本文根据岩石孔隙中的天然气引起介电测井孔隙度减小和密度测井孔隙度增大的原理,建立了双密度重叠找气新方法,消除了岩性的影响,提高了测井找气的分辨率,增加了评价气层的直观性。该方法用于寻找陕甘宁盆地低孔隙白云岩气藏,获得了明显的地质效果。这种方法还可以在其它储层岩性气藏中应用。  相似文献