Effects of the geometry of two‐dimensional fractures on their hydraulic aperture and on the validity of the local cubic law          下载免费PDF全文

Ahmad Hajjar  Luc Scholtès  Constantin Oltéan  Michel Antoine Buès 《水文研究》2018,32(16):2510-2525

Flow through rough fractures is investigated numerically in order to assess the validity of the local cubic law for different fracture geometries. Two‐dimensional channels with sinusoidal walls having different geometrical properties defined by the aperture, the amplitude, and the wavelength of the walls' corrugations, the corrugations asymmetry, and the phase shift between the two walls are considered to represent different fracture geometries. First, it is analytically shown that the hydraulic aperture clearly deviates from the mean aperture when the walls' roughness, the phase shift, and/or the asymmetry between the fracture walls are relatively high. The continuity and the Navier–Stokes equations are then solved by means of the finite element method and the numerical solutions compared to the theoretical predictions of the local cubic law. Reynolds numbers ranging from 0.066 to 66.66 are investigated so as to focus more particularly on the effect of flow inertial effects on the validity of the local cubic law. For low Reynolds number, typically less than 15, the local cubic law properly describes the fracture flow, especially when the fracture walls have small corrugation amplitudes. For Reynolds numbers higher than 15, the local cubic law is valid under the conditions that the fracture presents a low aspect ratio, small corrugation amplitudes, and a moderate phase lag between its walls.  相似文献   

About Darcy's law in non-Galilean frame     

C. Geindreau  E. Sawicki  J.-L. Auriault  P. Royer 《国际地质力学数值与分析法杂志》2004,28(3):229-249

This paper is aimed towards investigating the filtration law of an incompressible viscous Newtonian fluid through a rigid non-inertial porous medium (e.g. a porous medium placed in a centrifuge basket). The filtration law is obtained by upscaling the flow equations at the pore scale. The upscaling technique is the homogenization method of multiple scale expansions which rigorously gives the macroscopic behaviour and the effective properties without any prerequisite on the form of the macroscopic equations. The derived filtration law is similar to Darcy's law, but the tensor of permeability presents the following remarkable properties: it depends upon the angular velocity of the porous matrix, it verifies Hall–Onsager's relationship and it is a non-symmetric tensor. We thus deduce that, under rotation, an isotropic porous medium leads to a non-isotropic effective permeability. In this paper, we present the results of numerical simulations of the flow through rotating porous media. This allows us to highlight the deviations of the flow due to Coriolis effects at both the microscopic scale (i.e. the pore scale), and the macroscopic scale (i.e. the sample scale). The above results confirm that for an isotropic medium, phenomenological laws already proposed in the literature fails at reproducing three-dimensional Coriolis effects in all types of pores geometry. We show that Coriolis effects may lead to significant variations of the permeability measured during centrifuge tests when the inverse Ekman number Ek⁻¹ is 𝒪(1). These variations are estimated to be less than 5% if Ek⁻¹<0.2, which is the case of classical geotechnical centrifuge tests. We finally conclude by showing that available experimental data from tests carried out in centrifuges are not sufficient to determining the effective tensor of permeability of rotating porous media. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

中国北西部金矿主要类型,分布规律和成矿带划分     

程明高 《铀矿地质》1991,7(6):321-327,344

本文较系统地总结了我国北西部金矿主要类型、矿化特征和金矿时空分布规律,在此基础上划分出4个成矿区、12条成矿带、32条成矿亚带,从而指明了找矿方向,为贯彻“以铀为主,综合找矿,多种经营,搞活地质”的方针,提供了较好的参考资料。  相似文献   

Modeling on adsorption–desorption of trace metals to suspended particle matter in the Changjiang Estuary     

Y. Y. Zhang  E. R. Zhang  J. Zhang 《Environmental Geology》2008,53(8):1751-1766

The uptake and release of trace metals (Cu, Ni, Zn, Cd, and Co) in estuaries are studied using river and sea end-member waters and suspended particulate matter (SPM) collected from the Changjiang Estuary, China. The kinetics of adsorption and desorption were studied in terms of environmental factors (pH, SPM loading, and salinity) and metal concentrations. The uptake of the metals studied onto SPM occurred mostly within 10 h and reached an asymptotic value within 40 h in the Changjiang Estuary. As low pH river water flows into the high pH seawater and the water become more alkaline as it approaches to the seaside of estuary, metals adsorb more on SPM in higher pH water, thus, particulate phase transport of metal become increasingly important in the seaward side of the estuary. The percentage of adsorption recovery and the distribution coefficients for trace metals remained to be relatively invariable and a significant reduction only occurred in very high concentrations of metals (>0.1 mg L⁻¹). The general effect of salinity on metal behavior was to decrease the degree of adsorption of Cu, Zn, Cd, Co, and Ni onto SPM but to increase their adsorption equilibrium pH. The adsorption–desorption kinetics of trace metals were further investigated using Kurbatov adsorption model. The model appears to be most useful for the metals showing the conservative behavior during mixing of river and seawater in the estuary. Our work demonstrates that dissolved concentration of trace metals in estuary can be modeled based on the metal concentration in SPM, pH and salinity using a Kurbatov adsorption model assuming the natural SPM as a simple surfaced molecule.  相似文献   

Regional distribution pattern of groundwater heavy metals resulting from agricultural activities   总被引：18，自引：0，他引：18  

J. Nouri  A. H. Mahvi  G. R. Jahed  A. A. Babaei 《Environmental Geology》2008,55(6):1337-1343

Contaminations of groundwater by heavy metals due to agricultural activities are growing recently. The objective of this study was to evaluate and map regional patterns of heavy metals (Cd, Zn and Cu) in groundwater on a plain with high agricultural activities. The study was conducted to investigate the concentration of heavy metals and distribution in groundwater in regions of Shush Danial and Andimeshk aquifers in the southern part of Iran. Presently, groundwater is the only appropriate and widely used source of drinking water for rural and urban communities in this region. The region covers an area of 1,100 km² between the Dez and Karkhe rivers, which lead to the Persian Gulf. For this study, the region was divided into four sub-regions A, B, C and D. Additionally, 168 groundwater samples were collected from 42 water wells during the earlier months of 2004. The flame atomic absorption spectrometry (AAS-Flame) was used to measure the concentration of heavy metals in water samples and the Surfer software was used for determination of the contour map of metal distribution. The results demonstrated that in all of the samples, Cd and Zn concentrations were below the EPA MCLG and EPA secondary standard, respectively. However, the Cu contents of 4.8 % of all samples were higher than EPA MCL. It is also indicated that the concentrations of metals were more pronounced at the southern part of the studied region than at the others. The analysis of fertilizers applied for agricultural activities at this region also indicated that a great majority of the above-mentioned heavy metals were discharged into the environment. Absence of confining layers, proximity to land surface, excess agricultural activities in the southern part and groundwater flow direction that is generally from the north to the southern parts in this area make the southern region of the Shush plain especially vulnerable to pollution by heavy metals than by other contaminants.  相似文献   

福建海岛潮间带软体动物群落分布特征   总被引：1，自引：0，他引：1  

周时强  黄凌风  郭丰  郑怀平 《海洋科学》2001,25(8):5-8

福建海岛潮间带软体动物共鉴定248种，隶属于5纲78科161属，应用群落系数，等级聚类分析和极坐标排序研究软体动物落分布，结果表明，软体动物群落可分为3种类型，即河口型群落，近岸港湾群落和开阔海域群落，群落分布与海岛所处地理位置及其生境类型密切相关，盐度和水动力是重要的影响因子。  相似文献   

黄、渤海海岸风沙地貌类型及其分布规律和发育模式   总被引：24，自引：0，他引：24  

傅命佐  徐孝诗  徐小薇 《海洋与湖沼》1997,28(1):56-65

于１９９０－１９９４年，对黄，渤海海岸风沙地貌，风沙沉积，风沙灾害和土地沙漠化现象进行详细的外业调查，测量和填图，在此基础上，利用ＧＩＳ技术原理，对海岸岗沙地貌进行系统的分类研究，对海岸风沙地貌分布规律和发育模式进行较深入的探讨，结果表明，研究区风沙地貌，风沙灾害和土地沙漠化现象主要分布在冬，春季气候干旱，风力强而持久，砂源丰富的渤海海岸和山东半岛半岸的砂质海岸地区，海岸沙丘和风成砂地总面积达７０  相似文献   

春季东海不同水域的表层叶绿素含量   总被引：5，自引：0，他引：5  

鲁北伟  王荣  王文琪 《海洋科学》1997,21(5):53-55

利用１９９４年春季在东海及台湾海峡首次获得的表层水中绿素含量大面走航连续观测资料，结合温盐分布及以往的有关东海及台湾海峡的海流和上升流的结论，分析了春季东海表层叶绿素含量在不同水域的分布特征。结果表明，叶绿素含量分布与水文结构关系密切。叶绿素含量值随不同海流流域而变，但在各海流流域内基本不变，黑潮表层水的叶绿素含量最低，其次是台湾暖流表层水，长江冲淡水与江浙沿岸流域的叶绿素含量较高；黑潮西侧弱流剧  相似文献   

春季东海表层水叶绿素a含量分布特征   总被引：2，自引：0，他引：2  

鲁北伟  王荣 《海洋与湖沼》1996,27(5):487-492

依据“科学一号”调查船１９９４年４月在东海１０个断面上所进行的表层水连续走航观测资料，研究东海表层水叶绿素α含量在不同空间尺度上的分布特征和变化规律。结果表明，叶绿素α含量在陆架区高，在外海低；测区南部海域的含量一般高于北部海域。叶绿素α含量的分布形态变化很大，在某些外海深水区，叶绿素α含量连续百科公里没有显著变化，变化幅度小于０．２ｍｇ‘ｍ＾３；而在某些近海浅水区，叶绿素α含量在不到１公里范围内  相似文献   

外大陆架划界信息系统中数据交换方法   总被引：1，自引：0，他引：1  

刘志军  金继业  邢喆 《海洋测绘》2007,27(6):62-64

采用VB.NET作为开发工具,ArcGIS Engine作为开发平台,进行外大陆架划界的数据交换研究,所开发的程序能够实现图元和文件层次的交换。该方法的研究对于我国外大陆架的划界有着非常重要的参考作用。  相似文献