Influence of liquid bridges on the mechanical behaviour of polydisperse granular materials   总被引：1，自引：0，他引：1  

F. Souli  F. Cherblanc  M.S. El Youssoufi  C. Saix 《国际地质力学数值与分析法杂志》2006,30(3):213-228

We investigate a polydisperse granular material in which the particle interactions are governed by a capillary force law. The cohesion force for a grain‐pair with unequal diameters is expressed as an explicit function of the inter‐particle distance and the volume of the liquid bridge. This analytical relation is validated by experiments on a reference material. Then, it is completed by a rupture criterion and cast in the form of a force law that accounts for solid contact, capillary force and rupture characteristics of a grain‐pair. Finally, in order to evaluate the influence of capillary cohesion on the macroscopic behaviour, radial and axial compression tests on cylindrical assemblies of wet particles are simulated using a 3D distinct element method. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Interactive effects of the type of milling media and copper sulphate addition on the flotation performance of sulphide minerals from Merensky ore Part I: Pulp chemistry     

D.J. Bradshaw  A.M. Buswell  P.J. Harris  Z. Ekmekci 《International Journal of Mineral Processing》2006

It is well known that the chemical environment determines the success of the flotation process, however its characterisation and control is difficult to achieve. This paper, as two parts, Part I and Part II, evaluates the use of various measurements and their interpretation to gain an understanding of the influence of varying parameters such as the type of milling media and copper sulphate addition on the flotation performance of sulphide minerals from a platinum group mineral (PGM) bearing Merensky ore. It shows the complexity of interpretation and the importance of analysing flotation performance holistically. Part I focuses on the pulp chemistry and mineral potential measurements have been used to show the differences in the response of the various mineral electrodes to different conditions. The final flotation recoveries of the sulphide minerals in the ore followed the same trend as the decrease in mineral potential due to collector addition viz. chalcopyrite > pentlandite > pyrrhotite. Type of milling media and copper sulphate addition slightly affected the mineral electrode potential and flotation recovery of chalcopyrite. Addition of copper sulphate increased the recovery of pentlandite and particularly pyrrhotite due to activation by copper (II) ions. The copper activation mechanism was likely to be in the form of initial adsorption of copper hydroxide followed by reduction to Cu⁺ at the surface. However, the changes in flotation performance of the different minerals in the ore could not be completely described by the electrochemical changes, demonstrating the limitations of these measurements. Part II addresses the effect of froth stability as demonstrated by the variations in the mass and water recovery data resulting from the different milling conditions and addition of copper sulphate which emphasised the importance of considering the froth phase in the evaluation of flotation data.  相似文献   

Bringing it all back home: The extensification and ‘overflowing’ of work: The case of San Francisco’s new media households     

Helen Jarvis  Andy C. Pratt 《Geoforum》2006,37(3):331-339

This paper explores the extensification of work—that is the distribution or exporting of work across different spaces/scales and times—and its impact on individual workers and households. We argue that contracting out and the work life balance debates might be developed more usefully within the holistic framework of extensification. The key process that we follow can be described as overflowing. We contrast the universally positive representations of spillovers and embedding that we are familiar with in economic geographies with the more negatively characterised overflowing of work into and out of the household. The paper is built around a case study of those involved in the new media industry in San Francisco: households, workers and companies.  相似文献   

空间信息格网框架体系和关键技术分析   总被引：17，自引：1，他引：16  

夏曙东李琦  承继成 《地球信息科学学报》2002,4(4):30-35

空间信息格网 (SIG)是格网 (Grid)技术在数字城市等地球信息应用服务领域中的具体应用。本文首先分析了格网兴起的背景以及国内外在格网领域的研究进展 ,然后建立了格网三层体系结构 ,提出了格网操作系统中基于 XML 的格网资源描述语言的资源管理方法和多层格网节点分治式格网任务调度管理方法 ,最后提出了基于空间智能体的空间信息格网的体系结构 ,并且探讨了空间信息格网中空间信息连通性和一致性、空间信息格网的智能化等一系列重点问题。  相似文献   

Chemically induced deformation of a porous layer coupled with advective–dispersive transport. Analytical solutions     

Mariusz Kaczmarek 《国际地质力学数值与分析法杂志》2001,25(8):757-770

In this paper a chemically induced deformation of porous material taking place during advective–dispersive transport of a chemical is considered. Linearized governing equations are derived and analytical solutions of 2 one‐dimensional problems for a homogeneous layer with drained boundaries are developed. Numerical results for a particular clayey material and a chemical migrating through the layer showing distributions of concentration of chemical, changes in porosity of the material and pore fluid pressure, and evolution of settlement of the layer as functions of time are discussed. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

基于双相介质理论的AVO属性交汇图识别天然气水合物     

张聿文  刘学伟  姚长利 《应用地球物理》2005,2(1):7-13

天然气水合物(gas hydrates)作为一种新的潜在能源 是目前世界范围内研究的热点和难点之一。目前 普遍认为拟海底反射(简称BSR)是天然气水合物存 在的重要标志之一,但有关水合物的识别仍有很 多问题需要解决。例如世界各地已发现水合物的 例证表明在没有BSR的情况下仍然存在水合物,在 没有BSR的情况下如何识别水合物仍是没有解决 的研究课题。本文以天然气水合物的识别为研究 目的,以AVO属性交汇图为研究手段,通过双相介 质正演理论模型研究了当地层含有天然气水合物 或游离气时的AVO属性特征,并与由双相介质的 交错网格有限差分法得到的合成地震记录所反演 得出的AVO交汇图进行了对比,得到高度一致的 对比结果,表明利用AVO属性交汇图是识别天然 气水合物和游离气并能估测其含量的有效技术。  相似文献   

Modeling Hysteresis in Porous Media Flow via Relaxation     

B. Plohr  D. Marchesin  P. Bedrikovetsky  P. Krause 《Computational Geosciences》2001,5(3):225-256

Two-phase flow in a porous medium can be modeled, using Darcy's law, in terms of the relative permeability functions of the two fluids (say, oil and water). The relative permeabilities generally depend not only on the fluid saturations but also on the direction in which the saturations are changing. During water injection, for example, the relative oil permeability k _ro falls gradually until a threshold is reached, at which stage the k _ro begins to decrease sharply. The latter stage is termed imbibition. If oil is subsequently injected, then k _ro does not recover along the imbibition path, but rather increases only gradually until another threshold is reached, whereupon it rises sharply. This second stage is called drainage, and the type of flow that occurs between the imbibition and drainage stages is called scanning flow. Changes in permeability during scanning flow are approximately reversible, whereas changes during drainage and imbibition are irreversible. Thus there is hysteresis, or memory, exhibited by the two-phase flow in the porous medium. In this work, we describe two models of permeability hysteresis. Common to both models is that the scanning flow regime is modeled with a family of curves along which the flow is reversible. In the Scanning Hysteresis Model (SHM), the scanning curves are bounded by two curves, the drainage and imbibition curves, where the flow can only occur in a specific direction. The SHM is a heuristic model consistent with experiments, but it does not have a nice mathematical specification. For instance, the algorithm for constructing solutions of Riemann problems involves several ad hoc assumptions. The Scanning Hysteresis Model with Relaxation (SHMR) augments the SHM by (a) allowing the scanning flow to extend beyond the drainage and imbibition curves and (b) treating these two curves merely as attractors of states outside the scanning region. The attraction, or relaxation, occurs on a time scale that corresponds to the redistribution of phases within the pores of the medium driven by capillary forces. By means of a formal Chapman–Enskog expansion, we show that the SHM with additional viscosity arises from the SHMR in the limit of vanishing relaxation time, provided that the diffusion associated with capillarity exceeds that induced by relaxation. Moreover, through a rigorous study of traveling waves in the SHMR, we show that the shock waves used to solve Riemann problems in the SHM are precisely those that have diffusive profiles. Thus the analysis of the SHMR justifies the SHM model. Simulations based on a simple numerical method for the simulation of flow with hysteresis confirm our analysis.  相似文献   

A mathematical and numerical model for reactive fluid flow systems     

Astrid Holstad 《Computational Geosciences》2000,4(2):103-139

We formulate mathematical and numerical models for multispecies, multi-phase and non-isothermal reactive fluid flow in porous media focusing on the chemical reactions and the transport of solutes. Mass conservation and stability in the time integration are emphasized. We use cell-centered finite volume differencing in space and an implicit Runge-Kutta method in time. Assuming two space dimensions, we introduce flux approximation for arbitrarily shaped convex quadrilaterals. On equidistant and variable sized rectangular grids we choose limited κ= related schemes to approximate the advective flux and the central difference scheme for the diffusive flux. On non-rectangular grids we recommend the VF9 scheme for the estimation of the diffusive flux. Our model exists as a code. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

随机介质热弹性力学模型球坐标问题的解析解   总被引：2，自引：0，他引：2  

康健  梁冰 《水文地质工程地质》2005,32(6):49-51

针对随机介质热弹性力学模型,在随机韦泊分布和指数分布下,提出了一种解决随机概率分布用连续函数表示的方法,并推导出该模型球坐标问题的解析解。通过算例,对随机模型与均质模型热应力的区别做了详细研究,结果表明随机概率分布参数m对随机模型的热应力有重要影响。  相似文献   

A viscoelastic damage rheology and rate- and state-dependent friction   总被引：1，自引：0，他引：1  

Vladimir Lyakhovsky  Yehuda Ben-Zion  Amotz Agnon 《Geophysical Journal International》2005,161(1):179-190

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