Coordinate mapping of analytical contaminant transport solutions to non-uniform flow fields     

James R. Craig  Thomas Heidlauf 《Advances in water resources》2009

Existing analytical solutions to 2D and 3D contaminant transport problems are limited by the mathematically convenient assumption of uniform flow. An approximate method is developed herein for coordinate mapping of 2D (vertically-averaged) transport solutions to non-uniform steady-state irrotational and divergence-free flow fields in single-layer aquifers. The method enables existing analytical transport solutions to be applied to aquifer systems with wells, non-uniform saturated thickness, surface water features, and (to a limited degree) heterogeneous hydraulic conductivity and recharge. This mass-conservative coordinate mapping approach is inexact in its approximation of the dispersion process but is still sufficiently accurate for many simple flow systems. The degree of model error is directly proportional to the variation of velocity magnitude within the domain. These mapped analytical solutions are compared to numerical simulation results and the coordinate mapping errors are investigated. The methods described herein may be used in the traditional capacity of analytical transport models, i.e., screening and preliminary site assessment, without sacrificing accuracy by assuming locally uniform flow conditions or applying an ad-hoc coordinate transformation. The solutions benefit from the traditional advantages of analytical methods, particularly the removal of artifacts due to spatial and temporal discretization: no time-stepping or numerical discretization is required.  相似文献   

Preliminary sensitivity study of eruption source parameters for operational volcanic ash cloud transport and dispersion models — A case study of the August 1992 eruption of the Crater Peak vent, Mount Spurr, Alaska     

P.W. Webley  B.J.B. Stunder  K.G. Dean 《Journal of Volcanology and Geothermal Research》2009,186(1-2):108

Ash clouds are one of the major hazards that result from volcanic eruptions. Once an eruption is reported, volcanic ash transport and dispersion (VATD) models are used to forecast the location of the ash cloud. These models require source parameters to describe the ash column for initialization. These parameters include: eruption cloud height and vertical distribution, particle size distribution, and start and end time of the eruption. Further, if downwind concentrations are needed, the eruption mass rate and/or volume of ash need to be known. Upon notification of an eruption, few constraints are typically available on many of these source parameters. Recently, scientists have defined classes of eruption types, each with a set of pre-defined eruption source parameters (ESP). We analyze the August 18, 1992 eruption of the Crater Peak vent at Mount Spurr, Alaska, which is the example case for the Medium Silicic eruption type. We have evaluated the sensitivity of two of the ESP – the grain size distribution (GSD) and the vertical distribution of ash – on the modeled ash cloud. HYSPLIT and Puff VATD models are used to simulate the ash clouds from the different sets of source parameters. We use satellite data, processed through the reverse absorption method, as reference for computing statistics that describe the modeled-to-observed comparison. With the grain size distribution, the three options chosen, (1) an estimated distribution based on past eruption studies, (2) a distribution with finer particles and (3) the National Oceanic and Atmospheric Administration HYSPLIT GSD, have little effect on the modeled ash cloud. For the initial vertical distribution, both linear (uniform concentration throughout the vertical column) and umbrella shapes were chosen. For HYSPLIT, the defined umbrella distribution (no ash below the umbrella), apparently underestimates the lower altitude portions of the ash cloud and as a result has a worse agreement with the satellite detected ash cloud compared to that with the linear vertical distribution for this particular eruption. The Puff model, with a Poisson function to represent the umbrella cloud, gave similar results as for a linear distribution, both having reasonable agreement with the satellite detected cloud. Further sensitivity studies of this eruption, as well as studies using the other source parameters, are needed.  相似文献   

Multi-physics modeling of flow and transport in porous media using a downscaling approach     

J. Niessner  R. Helmig 《Advances in water resources》2009

Multi-phase flow and transport processes generally occur on different spatial and temporal scales. Very often also, within a physical system, they vary in space meaning that different kinds of processes might take place in different parts of the system. In order to account for the variety of processes and to take their scale-dependence into account, the development of multi-scale multi-physics techniques can be envisaged.  相似文献   

Modeling bio-geomorphological influences for offshore sandwaves     

B.W. Borsje  M.B. de Vries  T.J. Bouma  G. Besio  S.J.M.H. Hulscher  P.M.J. Herman 《Continental Shelf Research》2009

The coastal environment shows a wide range of bed patterns, for which sandwaves and sandbanks are among the most common. Less known in this context is the high benthic diversity in the coastal environment, which gives rise to the question to what extend the benthos interacts with the shape of the seabed. This paper reviews field and flume experiments on bio-geomorphological influences between benthos and sediment and tests the hypothesis that both the occurrence and the dimensions of sandwaves are dependent on the benthic diversity in the North Sea. Mathematical inclusions to account for biological activity in idealized models reveal that biota is able to influence the wavelength of sandwaves significantly, compared to the default case. More importantly, the models indicate that biota is able to induce bed patterns under conditions when the physical parameters suggest a stable flat bed and vice versa. Present model explorations indicate that future research should focus on the parameterization of subtidal biological activity on sediment dynamics and thereby on seabed patterns. Such knowledge will enable process-based modeling of the spatial and temporal variation in biological activity on seabed morphodynamics and validate the proposed modeling approach with field measurements.  相似文献   

A sensitivity analysis of Hortonian flow   总被引：6，自引：0，他引：6  

J.-O. Delfs  C.-H. Park  O. Kolditz   《Advances in water resources》2009,32(9):1386-1395

We present a sensitivity analysis for infiltration excess (Hortonian) overland flow based on a classic laboratory experiment by Smith and Woolhiser [Smith RE, Woolhiser DA. Overland flow on an infiltrating surface. Water Resour Res 1971;7(4):899–913]. The model components of the compartment approach are comprised of a diffusive wave approximation to the Saint–Venant equations for overland flow, a Richards model for flow in the variably saturated zone, and an interface coupling concept that combines the two components. In the coupling scheme a hydraulic interface is introduced to allow the definition of an exchange flux between the surface and the unsaturated zone. The effects of friction processes, soil capillarity, hydraulic interface, and vertical soil discretization on both infiltration and runoff prediction are investigated in detail. The corresponding sensitivity analysis is conducted using a small-perturbation method. As a result the importance of the hydraulic processes and related parameters are evaluated for the coupled hydrosystem.  相似文献   

A parallel mesh-free contaminant transport model based on the Analytic Element and Streamline Methods     

Karl W. Bandilla  Alan J. RabideauIgor Janković 《Advances in water resources》2009

This paper introduces a new method for simulating large-scale subsurface contaminant transport that combines an Analytic Element Method (AEM) groundwater flow solution with a split-operator Streamline Method for modeling reactive transport. The key feature of the method is the manner in which the vertically integrated AEM flow solution is used to construct three-dimensional particle tracks that define the geometry of the Streamline Method. The inherently parallel nature of the algorithm supports the development of reactive transport models for spatial domains much larger than current grid-based methods. The applicability of the new approach is verified for cases with negligible transverse dispersion through comparisons to analytic solutions and existing numerical solutions, and parallel performance is demonstrated through a realistic test problem based on the regional-scale transport of agricultural contaminants from spatially distributed sources.  相似文献   

On the role of buoyancy force in the ore genesis of SEDEX deposits: Example from Northern Australia     

JianWen Yang  ZuoHai Feng  XianRong Luo  YuanRong Chen 《中国科学D辑(英文版)》2009,52(4):452-460

Finite element modeling on a highly conceptualized 2-D model of fluid flow and heat transport is un-dertaken to simulate the paleo-hydrological system as if the Mount Isa deposits were being formed in the Mount Isa basin, Northern Australia, and to evaluate the potential of buoyancy force in driving ba-sin-scale fluid flow for the formation of sedimentary-exhalative (SEDEX) deposits. Our numerical case studies indicate that buoyancy-driven fluid flow is controlled mainly by the fault penetration depth and i...  相似文献   

低幅度构造识别技术在Carmen油田三维工区的应用   总被引：1，自引：1，他引：0       下载免费PDF全文

杨勤林  王彦春  张菊梅  苗田 《地球物理学进展》2009,24(3):965-969

近年来,随着油田勘探开发的深入,规模小,构造幅度低的油气藏所占比例逐年上升,低幅度构造也逐渐受到重视.本文分析了低幅度构造的特点及地震反射特征,结合工区实际情况,提出了在地震资料解释阶段研究低幅度构造的流程和思路,总结了针对低幅度构造的主要识别方法:地震正演模拟、井控提高分辨率处理、层位精细解释、三维速度场分析、构造图倾角校正等.通过以上技术在Carmen油田三维工区识别了12个低幅度构造,结合地质、测井资料综合分析优选了两个钻探目标,取得了较好的勘探效果.  相似文献   

复杂二维/三维大地电磁的有限单元法正演模拟策略   总被引：1，自引：0，他引：1  

童孝忠  柳建新  郭荣文 《CT理论与应用研究》2009,18(1):47-54

复杂二维和三维大地电磁模型的正演数值模拟具有一定的挑战性。对于复杂的二维和三维大地电磁正演问题,我们采用有限单元法进行求解。有限单元法最后形成一个线性方程组,系数矩阵是大型稀疏的带状对称复系数矩阵,并且其条件数远大于1,为严重病态矩阵,求解其对应方程组会遇到很多困难。不完全LU分解处理的Bi-CGSTAB迭代方法可用于该线性方程组的求解,并且具有速度快、精度高和稳定性好等优点;为了模拟无穷远边界及满足计算机的内存需求,在保证计算精度的情况下设计了非均匀网格剖分;在程序编制中,只存储有限元系数矩阵的非零元素,大大减少了正演计算的时间。通过对二维和三维模型电磁响应的计算,验证了算法的正确性。  相似文献   

An Atlas of ShakeMaps and population exposure catalog for earthquake loss modeling     

Trevor I. Allen  David J. Wald  Paul S. Earle  Kristin D. Marano  Alicia J. Hotovec  Kuowan Lin  Michael G. Hearne 《Bulletin of Earthquake Engineering》2009,7(3):701-718

We present an Atlas of ShakeMaps and a catalog of human population exposures to moderate-to-strong ground shaking (EXPO-CAT) for recent historical earthquakes (1973–2007). The common purpose of the Atlas and exposure catalog is to calibrate earthquake loss models to be used in the US Geological Survey’s Prompt Assessment of Global Earthquakes for Response (PAGER). The full ShakeMap Atlas currently comprises over 5,600 earthquakes from January 1973 through December 2007, with almost 500 of these maps constrained—to varying degrees—by instrumental ground motions, macroseismic intensity data, community internet intensity observations, and published earthquake rupture models. The catalog of human exposures is derived using current PAGER methodologies. Exposure to discrete levels of shaking intensity is obtained by correlating Atlas ShakeMaps with a global population database. Combining this population exposure dataset with historical earthquake loss data, such as PAGER-CAT, provides a useful resource for calibrating loss methodologies against a systematically-derived set of ShakeMap hazard outputs. We illustrate two example uses for EXPO-CAT; (1) simple objective ranking of country vulnerability to earthquakes, and; (2) the influence of time-of-day on earthquake mortality. In general, we observe that countries in similar geographic regions with similar construction practices tend to cluster spatially in terms of relative vulnerability. We also find little quantitative evidence to suggest that time-of-day is a significant factor in earthquake mortality. Moreover, earthquake mortality appears to be more systematically linked to the population exposed to severe ground shaking (Modified Mercalli Intensity VIII+). Finally, equipped with the full Atlas of ShakeMaps, we merge each of these maps and find the maximum estimated peak ground acceleration at any grid point in the world for the past 35 years. We subsequently compare this “composite ShakeMap” with existing global hazard models, calculating the spatial area of the existing hazard maps exceeded by the combined ShakeMap ground motions. In general, these analyses suggest that existing global, and regional, hazard maps tend to overestimate hazard. Both the Atlas of ShakeMaps and EXPO-CAT have many potential uses for examining earthquake risk and epidemiology. All of the datasets discussed herein are available for download on the PAGER Web page (). T. I. Allen and M. G. Hearne—contracted through Synergetics Incorporated.  相似文献