Grid resolution study of ground water flow and transport     

Bower KM  Gable CW  Zyvoloski GA 《Ground water》2005,43(1):122-132

Three-dimensional grids representing a heterogeneous, ground water system are generated at 10 different resolutions in support of a site-scale flow and transport modeling effort. These grids represent hydrostratigraphy near Yucca Mountain, Nevada, consisting of 18 stratigraphic units with contrasting fluid flow and transport properties. The grid generation method allows the stratigraphy to be modeled by numerical grids of different resolution so that comparison studies can be performed to test for grid quality and determine the resolution required to resolve geologic structure and physical processes such as fluid flow and solute transport. The process of generating numerical grids with appropriate property distributions from geologic conceptual models is automated, thus making the entire process easy to implement with fewer user-induced errors. The series of grids of various resolutions are used to assess the level at which increasing resolution no longer influences the flow and solute transport results. Grid resolution is found to be a critical issue for ground water flow and solute transport. The resolution required in a particular instance is a function of the feature size of the model, the intrinsic properties of materials, the specific physics of the problem, and boundary conditions. The asymptotic nature of results related to flow and transport indicate that for a hydrologic model of the heterogeneous hydrostratigraphy under Yucca Mountain, a horizontal grid spacing of 600 m and vertical grid spacing of 40 m resolve the hydrostratigraphic model with sufficient precision to accurately model the hypothetical flow and solute transport to within 5% of the value that would be obtained with much higher resolution.  相似文献   

An investigation of numerical grid effects in parameter estimation     

Zyvoloski GA  Vesselinov VV 《Ground water》2006,44(6):814-825

Modern ground water characterization and remediation projects routinely require calibration and inverse analysis of large three-dimensional numerical models of complex hydrogeological systems. Hydrogeologic complexity can be prompted by various aquifer characteristics including complicated spatial hydrostratigraphy and aquifer recharge from infiltration through an unsaturated zone. To keep the numerical models computationally efficient, compromises are frequently made in the model development, particularly, about resolution of the computational grid and numerical representation of the governing flow equation. The compromise is required so that the model can be used in calibration, parameter estimation, performance assessment, and analysis of sensitivity and uncertainty in model predictions. However, grid properties and resolution as well as applied computational schemes can have large effects on forward-model predictions and on inverse parameter estimates. We investigate these effects for a series of one- and two-dimensional synthetic cases representing saturated and variably saturated flow problems. We show that "conformable" grids, despite neglecting terms in the numerical formulation, can lead to accurate solutions of problems with complex hydrostratigraphy. Our analysis also demonstrates that, despite slower computer run times and higher memory requirements for a given problem size, the control volume finite-element method showed an advantage over finite-difference techniques in accuracy of parameter estimation for a given grid resolution for most of the test problems.  相似文献   

双层软土非线性固结理论研究     

冶小平  万龙  赵杰伟  王志春  周舟 《煤田地质与勘探》2010,38(2):28-31

对固结系数的非线性变化进行了理论分析,推导了固结系数的非线性控制方程,指出了γ因子对固结系数非线性变化的影响。考虑到固结系数、渗透系数、压缩系数整体变化以及双层软土一维非线性固结方程求解困难,建立了差分格式的双层软土一维非线性固结差分方程,利用差分法对该方程进行了求解,为工程中复杂方程的计算提供了一种新的方法。研究表明:固结系数并不是决定双层软土非线性固结性状的唯一指标,须综合考虑各种因素的影响。   相似文献   

Design and application of a direct-push vadose zone gravel permeameter     

Miller RB  Heeren DM  Fox GA  Storm DE  Halihan T 《Ground water》2011,49(6):920-925

A borehole permeameter is well suited for testing saturated hydraulic conductivity (K(sat)) at specific depths in the vadose zone. Most applications of the method involve fine-grained soils that allow hand auguring of test holes and require a small water reservoir to maintain a constant head. In non-cohesive gravels, hand-dug test holes are difficult to excavate, holes are prone to collapse, and large volumes of water are necessary to maintain a constant head for the duration of the test. For coarse alluvial gravels, a direct-push steel permeameter was designed to place a slotted pipe at a specific sampling depth. Measurements can be made at successive depths at the same location. A 3790 L (1000 gallons) trailer-mounted water tank maintained a constant head in the permeameter. Head in the portable tank was measured with a pressure transducer and flow was calculated based on a volumetric rating curve. A U.S. Bureau of Reclamation analytical method was utilized to calculate K(sat). Measurements with the permeameter at a field site were similar to those reported from falling-head tests.  相似文献   

Effects of two sediment types on the fluorescence yield of two Hawaiian scleractinian corals     

Piniak GA 《Marine environmental research》2007,64(4):456-468

This study used non-invasive pulse-amplitude modulated (PAM) fluorometry to measure the maximum fluorescence yield (F(v)/F(m)) of two Hawaiian scleractinian coral species exposed to short-term sedimentation stress. Beach sand or harbor mud was applied to coral fragments in a flow-through aquarium system for 0-45 h, and changes in F(v)/F(m) were measured as a function of sediment type and length of exposure. Corals were monitored for up to 90 h to document recovery after sediment removal. Sediment deposition significantly decreased F(v)/F(m) in both species and was a function of sediment type and time. Corals that received sediment for 30 h or more had the greatest reduction in yield and exhibited little recovery over the course of the experiment. Harbor mud caused a greater reduction in Porites lobata yield than beach sand, whereas both sediment types had equally deleterious effects on Montipora capitata. Colony morphology and sediment type were important factors in determining yield reduction--P. lobata minimized damage from coarse sand grains by passive sediment rejection or accumulation in depressions in the skeleton, and fluorescence yield decreased most in corals exposed to sticky harbor mud or in colonies with flattened morphologies. Species-specific differences could not be tested due to differences in colony morphology and surface area.  相似文献   

不充足数据的三维电磁反演     

Newm.  GA 郑世雄 《物探化探译丛》1993,(6):24-28

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简评VAN地震预报方法     

Tsel.  GA 高伟 《世界地震译丛》1997,(2):58-60

评估一种地震预报方法预报准确与否的标准，不应仅仅依赖于应用抽象而严格的统计定律的方法，而忽视的地震现象的具体特点。断层破裂过程与掷股子不能相拼并论的。本文的结论是如何我们采用Ｍｕｌａｒｇｉａ，Ｇａｓｐｅｒｉｎｉ（１９９２）在评估ＶＡＮ方法时所提出的方法，那么，即使是一种理想的地震方法，也会在前兆和震间表现出某种“不确定”的联系，每次ＶＡＮ预报需单独评估，同时必须考虑所有具体情况和信息，震中位置预报  相似文献   

边界层扩散问题的相似理论与经验推导     

Ethr.  GA  杨建忠 《山西气象》1989,(1):42-48

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GPS在尼日利亚基本测量控制网中的应用     

Oyen.  GA 段贻民 《测绘译丛》1993,(1):11-16,10

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Comparison of velocity-log data collected using impeller and electromagnetic flowmeters     

Newhouse MW  Izbicki JA  Smith GA 《Ground water》2005,43(3):434-438

Previous studies have used flowmeters in environments that are within the expectations of their published ranges. Electromagnetic flowmeters have a published range from 0.1 to 79.0 m/min, and impeller flowmeters have a published range from 1.2 to 61.0 m/min. Velocity-log data collected in five long-screened production wells in the Pleasant Valley area of southern California showed that (1) electromagnetic flowmeter results were comparable within +/-2% to results obtained using an impeller flowmeter for comparable depths; (2) the measured velocities from the electromagnetic flowmeter were up to 36% greater than the published maximum range; and (3) both data sets, collected without the use of centralizers or flow diverters, produced comparable and interpretable results. Although either method is acceptable for measuring wellbore velocities and the distribution of flow, the electromagnetic flowmeter enables collection of data over a now greater range of flows. In addition, changes in fluid temperature and fluid resistivity, collected as part of the electromagnetic flowmeter log, are useful in the identification of flow and hydrogeologic interpretation.  相似文献