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Artificial neural networks are used to predict the micro‐properties of particle flow code in three dimensions (PFC3D) models needed to reproduce macro‐properties of cylindrical rock samples in uniaxial compression tests. Data for the training and verification of the networks were obtained by running a large number of PFC3D models and observing the resulting macro‐properties. Four artificial networks based on two different architectures were used. The networks used different numbers of input parameters to predict the micro‐properties. Multi‐layer perceptron networks using Young's modulus, Poisson's ratio, uniaxial compressive strength, model particle resolution and the maximum‐to‐minimum particle ratio showed excellent performance in both training and verification. Adding one more variable—namely, minimum particle radius—showed degrading performance. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Assessment of downstream trends in channel gradient, total and specific stream power: a GIS approach
Geographic Information Systems (GIS) analyses of Digital Elevation Models (DEMs) coupled with catchment area based discharge estimation techniques provide a relatively simple means of modelling contiguous downstream trends in channel gradient, total stream power, and in riverscapes conducive to regime analysis, also specific stream power. For a small, high relief, coastal catchment in SE Australia, good agreement was obtained between channel gradients derived from a 25 m cell-size DEM and field survey equivalents over distances of several kilometres, indicating that channel gradients derived from DEMs can have a reasonable degree of absolute as well as relative accuracy over multi-kilometre reach scales. Assessment of downstream rates of change in channel gradient and specific stream power across four river systems suggests that some of the river reaches most responsive to high magnitude floods occur in zones where these variables rapidly decrease downstream. Modelling of downstream trends in channel gradient, total and specific stream power from catchment-wide DEMs has potential to provide a framework with which to investigate conceptual and empirical models between channel gradient, stream power and the form and dynamics of river systems. 相似文献
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Ivars Neretnieks 《Hydrogeology Journal》2013,21(8):1701-1716
Radon, radium and helium data from three sites in granitic rock in Sweden (Forsmark and Laxemar) and Finland (Olkiluoto) from depths greater than 1,000 m were interpreted by a model that describes how daughter nuclides, including helium from uranium and thorium decay, escape from minerals, enter the pore water in the rock matrix and diffuse to the seeping water in the fractures in the rock. The radium concentrations are on the order of <30 Bq/l of water that has recently infiltrated and then emerged from the rock. Radon concentrations are mostly several orders of magnitude larger. The model predicts values in the same range. The fair agreement between model results, field data and laboratory data over a scale spanning micrometres over meters to kilometres, and time scales of days to millions of years, shows that the micropores of the rock matrix are connected even at depths down to and beyond a kilometre. Molecular diffusion in the matrix pore water is a key migration mechanism. Laboratory-derived sorption coefficients for radium are of the same magnitude as those needed in the modelling of the in situ data to give good agreement. 相似文献
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Ivars Peterson 《Mathematical Geology》1999,31(8):1007-1009
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Ivars Gutmanis 《GeoJournal》1993,31(2):179-192
During the last few decades international diffusion of the industrial activities among the established and the newly industrialized countries has occurred. Concurrently, the United States (US) has lost some of its status as the dominant industrial power in the World's markets. These changes have forced the US Department of Defence to surrender, at least partly, one of its principal strategic tenets, that of placing the reliance for its defence goods and services almost exclusively on the supplying entities located within the boundaries of the US.To a significant extent, these developments have come about as the result of the US policies not to intervene in the nation's and world's markets, and a deliberate and comprehensive intervention via policies, laws, and regulations in such markets by the governments of the other countries, including the US allies. The significant reduction of the military threat from the former Soviet Union may already have altered the conduct of the economic policies and defence strategies by the US, by its allies and by other nations.It is reasonable to assume that the US will see the continuation of international collaboration in the development, design and production of the future weapons systems. The former US allies and the other industrial nations, on the other hand, are in quest for further expansion of these industrial bases, and show limited interest in the further collaborative effect in the development of the future weapons systems.Unless appropriate co-operative economic and strategic policies are implemented, the emerging conflicts among the US, its allied and other industrial nations, presently in their infancy, may develop into a more intense confrontation among the world's industrialized nations. If this takes place, the US will be forced to abandon its laissez-faire policies, limit access to its markets and curtail the international diffusion of its industrial entities. The ultimate result of these developments may be geoeconomic conflicts among the industrial nations.This article is adopted from chapter in a forthcoming volume,Political and Geo-economic Issues Confronting the United States, the European Community, and Japan by Ewan W. Anderson and Ivars Gutmanis. 相似文献
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Data from 10 small farm dams in SE Australia show that shoreline erosion due to farm livestock access to the dams can account for a significant proportion (up to 85%) of sediment contained in the dam. The volumes of sediment resulting from such shoreline erosion may be of the same order as the volumes produced by gully erosion in the dams' catchments, prompting caution in using farm dams to which livestock have access to determine small catchment erosion rates. Other issues, related to the trap efficiency, also mean that erosion estimates based on farm dam sedimentation should be treated with caution. © 1998 John Wiley & Sons, Ltd. 相似文献
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The solutions of advection–dispersion equation in single fractures were carefully reviewed, and their relationships were addressed. The classic solution, which represents the resident or flux concentration within the semi‐infinite fractures under constant concentration or flux boundary conditions, respectively, describes the effluent concentration for a finite fracture. In addition, it also predicts the cumulative distribution of solute particle residence time passing through a single fracture under pulse injection condition, based on which a particle tracking approach was developed to simulate the local advection–dispersion in single fractures. We applied the proposed method to investigate the influence of local dispersion in single fractures on the macrodispersion in different fracture systems with relatively high fracture density. The results show that the effects of local dispersion on macrodispersion are dependent on the heterogeneity of fracture system, but generally the local dispersion plays limited roles on marodispersion at least in dense fracture network. This trend was in agreement with the macrodispersion in heterogeneous porous media. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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The effects of stress/deformation on fluid flow and contaminant transport in fractured rocks is one of the major concerns for performance and safety assessments of many subsurface engineering problems, especially radioactive waste disposal and oil/gas reservoir fields. However, very little progress has been made to study this issue due to difficulties in both experiments and numerical modeling. The objective of this study is to systematically investigate the influence of stress on solute transport in fractured rocks for the first time, considering different stress and hydraulic pressure conditions. A hybrid approach combining discrete element method (DEM) for stress-flow simulations and a particle tracking algorithm is developed. The impact of matrix diffusion (diffusion of molecular size solutes in and out of the rock matrix, and sorption onto the surface of micropores in rock matrix) is also included. The numerical results show that stress not only significantly changes the solute residence time through the fracture networks, but also changes the solute travel paths. Matrix diffusion plays a dominant role in solute transport when the hydraulic gradient is small, which is often encountered in practice. 相似文献