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121.
Avery H. Demond Paul V. Roberts 《Journal of the American Water Resources Association》1987,23(4):617-628
ABSTRACT: A key parameter in modeling two-phase flow phenomena is relative permeability. It is important to understand which variables influence relative permeability, especially since so few measurements of relative permeability have been made for typical contaminants at hazardous waste sites. This paper focuses on the effect of five variables on relative permeability: intrinsic permeability, pore-size distribution, viscosity ratio, interfacial tension, and wettability, by critically reviewing previously published relative permeability experiments. The wide variability in the functional relationship between relative permeability and saturation should be considered in attempts to model two-phase flow. 相似文献
122.
James A. Liggett 《Journal of the American Water Resources Association》1987,23(4):637-651
ABSTRACT: This paper explores some of the advances of the boundary element method, as applied to ground-water problems, during the last five years. Although the method is still somewhat limited compared to solution by finite elements, the range of solutions has increased considerably. Diffusion and advection-diffusion solutions are done efficiently. These include the incorporation of inhomogeneity, anisotropy, and nonlinear diffusion. The difficult problem of stream-aquifer interaction is an important application as it is much easier to follow a free surface with its multiple configurations. The application must be able to cycle between ground-water connection and disconnection with the stream and include seepage surfaces. Flow in fractured media is a natural application where the flow in fractures can usually be treated without a computational exception in spite of extremely high aspect ratios. The case of seawater intrusion forms a type of free surface problem and thus is a case for which the method has special advantages. For these and other applications the boundary element method provides an inexpensive technique for calculation where the data preparation and setup time is minimal. In most of these cases, programs can and have been written on microcomputers. 相似文献
123.
Scott W. Weeks Graham C. Sander Roger D. Braddock Chris J. Matthews 《Environmental Modeling and Assessment》2004,9(2):91-102
This paper considers the two-dimensional saturated and unsaturated flow of water through inclined porous media, namely a waste dump or hill slope. Since the partial differential equation governing this water flow transforms from being parabolic to elliptic as the water flow varies from unsaturated to saturated, an iterative, finite differencing scheme is used to develop a numerical solution. The model can be used to investigate the effects that hill slope angle, depth of soil cover and hilltop width have on water accumulation in the dump and the time required for saturation to occur at different areas in the dump domain. The accuracy and reliability of the computer based solution is tested for two different boundary conditions – (1) no flow on all boundaries (i.e., the internal redistribution of soil moisture to steady state) and (2) a constant rainfall flux on the dump surface. Numerical studies then show the effects of changing the hill slope angle, depth of layer, and dump geometry on the flow characteristics in the dump. 相似文献
124.
125.
Shabbir Ahmed Alauddin Khan Peter Salpas 《Journal of the American Water Resources Association》2003,39(5):1127-1142
ABSTRACT: A three‐dimensional fractured medium flow model was developed for the Bear Creek Valley (BCV) S‐3 site of the Oak Ridge Reservation (ORR) using SWIFT III. The numerical modeling for this site focused on a conceptual model established through the analysis of heterogeneous geologic units and matrix fracture properties of the subsurface in the BCV area. The SWIFT III modeling analysis was based on the previous modeling studies that used MODFLOW and MODPATH. A rigorous calibration was obtained first by comparing simulated results with the existing data on ground water levels and then by comparing pumping test results with the simulated ground water levels. A satisfactory agreement between observed and simulated results was obtained. The calibrated model was used to determine sustained yield from a ground water interceptor trench. Different withdrawal rates were used to simulate the performance of the trench for the sustained withdrawal of ground water. 相似文献
126.
127.
PROBLEM: Safety belt use rates among front seat occupants of passenger vehicles are substantially lower at night than during the day despite the fact that night driving is more dangerous. METHOD: Recent advances in night vision equipment now make it possible to enforce belt use laws in darkness. Reading, Pennsylvania conducted a night belt use publicity and enforcement campaign during September 2004 using night vision equipment. RESULTS: Front seat occupant belt use at night increased significantly from 50% prior to the campaign to 56% just after the campaign. Daylight belt use also increased though to a lesser extent (56% to 59%). Survey data indicated that motorists had heard about the campaign in newspapers and on television. Belt use increases were not seen during the same time period in a comparison community. 相似文献
128.
粒状滤料过滤理论的主要内容是过滤机理、过滤方程式和反冲洗机理。过滤机理有悬浮颗粒的迁移机理、悬浮颗粒的吸附机理和脱落机理等。过滤在水澄清的同时,滤层的水头损失增加,整个过程涉及因素多而且复杂,过滤方程式很难得到解析性的答案,所以过滤方程对过滤过程只起定性的作用。现在反冲洗机理的研究认为,悬浮颗粒从滤料表面脱落是水流剪切和颗粒碰撞综合作用的结果。 相似文献
129.
In a recent paper, it was suggested that one of the reasons behind the decline in public regard toward British Columbia's
environmental movement was an increasingly negative portrayal of them by the print media. To investigate this suggestion,
we undertook a content analysis of print media reporting of forestry and environmental activities in the province's most widely
read newspaper, the Vancouver Sun, during 1993 and 1997. We hypothesized that if the print media did contribute to the decline in public regard toward the
environmental movement, we would find increasingly negative coverage of the environmental movement over the periods studied.
We also hypothesized that this would be accompanied by a decrease in the frequency of articles dealing with issues consistent
with the agenda of the environmental movement. We were not able to provide support for our initial hypothesis, nor did we
observe a decrease in coverage emphasizing the environmental issues. We did, however, observe an increase in coverage of articles
emphasizing typically proindustry issues with many more articles written with a proforestry slant in 1997 than articles written
in 1993. This suggests that there had been an agenda shift from environmentally oriented concerns in British Columbia to those
associated with the forest industry. As an explanation for the agenda shift, we point to changes in the management and reporting
philosophy at the Vancouver Sun, the emergence of an organized, proindustry counterframing strategy by the BC Forest Alliance, and the implementation of
several government policies aimed at regulating the activities of the forest industry. 相似文献
130.
A one-dimensional transport model for simulating water flow and solute transport in homogeneous–heterogeneous, saturated–unsaturated porous media is presented. The model is composed of a combination of accurate numerical algorithms for solving the nonlinear Richard's and advection–dispersion equations (ADE). The mixed form of Richard's equation is solved using a standard finite element method (FEM) with primary variable switching. The transport equation is solved using operator splitting, with the discontinuous finite element method (DFE) for discretization of the advective term. A slope limiting procedure for DFE avoids numerical instabilities but creates very limited numerical dispersion for high Peclet numbers. An implicit finite differences scheme (FD) is used for the dispersive term.The unsaturated flow and transport model (Wamos-T) is applied to a variety of rigorous problems including transient flow, heterogeneous medium and abrupt variations of velocity in magnitude and direction due to time-varying boundary conditions. It produces accurate and mass-conservative solutions for a very large range of grid Peclet numbers. The Wamos-T model is a good and robust alternative for the simulation of mass transport in unsaturated domain. 相似文献