共查询到20条相似文献，搜索用时 31 毫秒
1.
Vic Kelson 《Ground water》2012,50(6):918-926
Groundwater flow models are commonly used to design new wells and wellfields. As the spatial scale of the problem is large and much local‐scale detail is not needed, modelers often utilize two‐dimensional (2D) or quasi three‐dimensional models based on the Dupuit‐Forchheimer assumption. Dupuit models offer a robust set of tools for simulating regional groundwater flow including interactions with surface waters, the potential for well interference, and varying aquifer properties and recharge rates. However, given an assumed operating water level or drawdown at a well screen, Dupuit models systematically overpredict well yields. For design purposes, this discrepancy is unacceptable, and a method for predicting accurate well yields is needed. While published methods exist for vertical wells, little guidance is available for predicting yields in horizontal screens or collector wells. In plan view, a horizontal screen has a linear geometry, and will likely extend over several neighboring cells that may not align with rows or columns in a numerical model. Furthermore, the model must account for the effects of converging three‐dimensional (3D) flow to the well screens and hydraulic interference among the well screens; these all depend on the design of a specific well. This paper presents a new method for simulating the yield of angled or horizontal well screens in numerical groundwater flow models, specifically using the USGS code MODFLOW. The new method is compared to a detailed, 3D analytic element model of a collector well in a field of uniform flow. 相似文献
2.
Stepwise use of GFLOW and MODFLOW to determine relative importance of shallow and deep receptors 总被引：1，自引：0，他引：1
A stepwise modeling approach is implemented in which a regional one-layer analytic element model is used to simulate the flow system and to furnish boundary conditions for an extracted local three-dimensional model. In this case study the stepwise approach is used to evaluate the fate of recharge in the Menomonee Valley adjacent to Lake Michigan. Two major receptors exist for recharge that flows through contaminated valley fill: the surface water estuary and a tunnel system constructed approximately 75 to 110 m below land surface to store storm runoff. The primary objective of the modeling is to delineate the contributing areas of recharge to each receptor. Of interest is the ability of the one-layer regional model to furnish flux boundary conditions to the local three-dimensional model despite the presence of vertical flow conditions at the boundaries of the local model. Sensitivity analysis suggests that the local model was insensitive to the vertical distribution of the flux. Each step of the modeling approach demonstrates that both receptors play an important role in capturing valley recharge. The pattern of capture of the one-layer model differed in shape from that delineated by the multi-layer local model in the presence of a flow system with pronounced vertical anisotropy and with sinks drawing water from different elevations. 相似文献
3.
Charles R. Fitts Joshua Godwin Kathleen Feiner Charles McLane Seth Mullendore 《Ground water》2015,53(3):432-439
This paper presents the analytic element modeling approach implemented in the software AnAqSim for simulating steady groundwater flow with a sharp fresh‐salt interface in multilayer (three‐dimensional) aquifer systems. Compared with numerical methods for variable‐density interface modeling, this approach allows quick model construction and can yield useful guidance about the three‐dimensional configuration of an interface even at a large scale. The approach employs subdomains and multiple layers as outlined by Fitts (2010) with the addition of discharge potentials for shallow interface flow (Strack 1989). The following simplifying assumptions are made: steady flow, a sharp interface between fresh‐ and salt water, static salt water, and no resistance to vertical flow and hydrostatic heads within each fresh water layer. A key component of this approach is a transition to a thin fixed minimum fresh water thickness mode when the fresh water thickness approaches zero. This allows the solution to converge and determine the steady interface position without a long transient simulation. The approach is checked against the widely used numerical codes SEAWAT and SWI/MODFLOW and a hypothetical application of the method to a coastal wellfield is presented. 相似文献
4.
Two new approaches are presented for the accurate computation of the potential due to line elements that satisfy the modified Helmholtz equation with complex parameters. The first approach is based on fundamental solutions in elliptical coordinates and results in products of Mathieu functions. The second approach is based on the integration of modified Bessel functions. Both approaches allow evaluation of the potential at any distance from the element. The computational approaches are applied to model transient flow with the Laplace transform analytic element method. The Laplace domain solution is computed using a combination of point elements and the presented line elements. The time domain solution is obtained through a numerical inversion. Two applications are presented to transient flow fields, which could not be modeled with the Laplace transform analytic element method prior to this work. The first application concerns transient single-aquifer flow to wells near impermeable walls modeled with line-doublets. The second application concerns transient two-aquifer flow to a well near a stream modeled with line-sinks. 相似文献
5.
Multilayer shallow water flow using lattice Boltzmann method with high performance computing 总被引：1，自引：0，他引：1
A multilayer lattice Boltzmann (LB) model is introduced to solve three-dimensional wind-driven shallow water flow problems. The multilayer LB model avoids the expensive Navier–Stokes equations and obtains stratified horizontal flow velocities as vertical velocities are relatively small and the flow is still within the shallow water regime. A single relaxation time BGK method is used to solve each layer coupled by the vertical viscosity forcing term. To increase solution stability, an implicit step is suggested to obtain flow velocities. The main advantage of using the LBM is that after selecting appropriate equilibrium distribution functions, the LB algorithm is only slightly modified for each layer and retains all the simplicities of the LBM within the high performance computing (HPC) environment. The performance of the parallel LB model for the multilayer shallow water equations is investigated on CPU-based HPC environments using OpenMP. We found that the explicit loop control with cache optimization in LBM gives better performance on execution time, speedup and efficiency than the implicit loop control as the number of processors increases. Numerical examples are presented to verify the multilayer LB model against analytical solutions. We demonstrate the model’s capability of calculating lateral and vertical distributions of velocities for wind-driven circulation over non-uniform bathymetry. 相似文献
6.
We present results of a design study performed for the Saylorville Wellfield in Iowa, which is owned and operated by the Des Moines Water Works. The purpose of this study was to estimate wellfield capacity and provide a preliminary design for two radial collector wells to be constructed in the outwash aquifer along the Des Moines River near Saylorville, Iowa. After a field investigation to characterize the aquifer, regional two-dimensional and local three-dimensional, steady-state groundwater flow modeling was performed to locate and design the wells. This modeling was the foundation for design recommendations based on the relative performance of 12 collector well designs with varying lateral numbers, elevations, screen lengths, and orientations. For each site, alternate designs were evaluated based on model estimates of the capacity, the percent of surface water captured, and the production per unit length of screen. Many of our results are consistent with current design practices based on experience and intuition, but our methods allow for a quantitative approach for comparing alternate designs. Although the results are site-specific, the framework for evaluating the hydraulic design of the Saylorville radial collector wells is broadly applicable and could be used at other riverbank filtration sites. In addition, many of the conclusions from this design study may apply at other sites where construction of radial collector wells is being considered. 相似文献
7.
Writing Analytic Element Programs in Python 总被引：1，自引：0，他引：1
The analytic element method is a mesh-free approach for modeling ground water flow at both the local and the regional scale. With the advent of the Python object-oriented programming language, it has become relatively easy to write analytic element programs. In this article, an introduction is given of the basic principles of the analytic element method and of the Python programming language. A simple, yet flexible, object-oriented design is presented for analytic element codes using multiple inheritance. New types of analytic elements may be added without the need for any changes in the existing part of the code. The presented code may be used to model flow to wells (with either a specified discharge or drawdown) and streams (with a specified head). The code may be extended by any hydrogeologist with a healthy appetite for writing computer code to solve more complicated ground water flow problems. 相似文献
8.
An approach to characterization of multilayer aquifer systems using open well borehole dilution is described. The approach involves measuring observation well flow velocities while a nearby extraction well is pumped by introducing a saline tracer into observation wells and collecting dilution vs. depth profiles. Inspection of tracer profile evolution allows discrete permeable layers within the aquifer to be identified. Dilution profiles for well sections between permeable layers are then converted into vertical borehole flow velocities and their evolution, using an analytic solution to the advection-dispersion equation applied to borehole flow. The dilution approach is potentially able to measure much smaller flow velocities that would be detectable using flowmeters. Vertical flow velocity data from the observation wells are then matched to those generated using a hydraulic model of the aquifer system, "shorted" by the observation wells, to yield the hydraulic properties of the constituent layers. Observation well flow monitoring of pumping tests represents a cost-effective alternative or preliminary approach to pump testing each layer of a multilayer aquifer system separately using straddle packers or screened wells and requires no prior knowledge of permeable layer depths and thicknesses. The modification described here, of using tracer dilution rather than flowmeter logging to obtain well flow velocities, allows the approach to be extended to greater well separations, thus characterizing a larger volume of the aquifer. An example of the application of this approach to a multilayer Chalk Aquifer in Yorkshire, Northeast England, is presented. 相似文献
9.
10.
实际工程场地中的断层通常具有三维尺寸,应进行三维分析。本文考虑均匀弹性半空间内存在不同长度、深度的三维断层,由下向上垂直入射一个脉冲波,主要采用三维时域显式有限元结合透射人工边界的方法及相应编写的三维显示有限元波动程序DSI3,计算断层附近地震地面运动的时程反应,研究含有三维断层场地地面运动的一些特点,并与自由场反应对比,以说明三维竖向断层对地震波传播的特点和对断层附近地面运动的影响。 相似文献
11.
本文对板采用四结点分层板弯曲单元,对柱采用八结六面体等参单元,建立了钢筋混凝土板柱节点有限元非线性计算模型,编制了反复荷载下钢筋混凝土非线性有限元计算程序。文中介绍了作者进行的板柱节点在反复荷载作用下的试验结果,用试验数据合流验证了所建立的有限元程序的可靠性。文反柱中节点和边节 竖向剪力和低周反复水平茶叶工共同作用下的受力性能进行了全过程计算分析。 相似文献
12.
The simplified hydraulic two-layer model for a katabatic flow is analysed using the outputs from a high-resolution mesoscale
simulation. A stably stratified night is simulated for the Duero basin, a complex terrain area located in the northern Spanish
plateau, with large vertical and horizontal spatial resolution. Well-defined katabatic flows on the basin slopes are generated
by the simulation, that are relatively stationary and quasi-bidimensional for some areas in the central part of the night.
The bulk quantities used in the two-layer approach as well as the different terms in the equations are computed from the three-dimensional
information provided by the mesoscale simulation. This method allows to inspect how well the simplified approach represents
the katabatic flow generated by the mesoscale model. The study shows that the hydraulic model allows for a comprehensive analysis
of the basic mechanisms of the slope flows but is not able to close the budget equations, since the residuals are large. 相似文献
13.
Charles R. Fitts 《Ground water》2018,56(4):557-561
This proposed technique allows sensible and numerically stable behavior in multilayer analytic element models when layers dewater. When saturated thickness approaches zero in an unconfined or fresh/salt interface domain, the domain transitions to a very thin confined domain with a minimum saturated thickness M. M is an adjustable input parameter, so you can make the horizontal flow in dewatered domains negligibly small by making the minimum saturated thickness very small. Vertical flows can pass through a dewatered domain, whether it is near the surface or at depth. For example, recharge may pass through a shallow dewatered layer to a deeper layer that is not dewatered. This approach is examined in detail in an example multilayer model of mine dewatering. 相似文献
14.
《Journal of Atmospheric and Solar》1999,61(16):1227-1236
Dual-frequency transmissions from the Global Positioning System satellites can be used to measure and map ionospheric total electron content (TEC) on global scales. Using data exclusively from ground-based GPS networks, global ionosphere mapping has been successfully applied using either two- or three-dimensional techniques. Two-dimensional TEC maps retrieve a horizontally-varying distribution of total electron content, assuming a fixed vertical electron density profile. In three-dimensional mapping, both the horizontal and vertical distribution density are adjusted to fit the data. We describe a three-dimensional TEC mapping algorithm that uses three independent constant-density slabs stacked vertically to model the electron density, and compare with a more conventional two-dimensional approach using a single slab. One apparent benefit of the new method is reduction in a level error of the TEC maps, which decreased by 1.7 TECU using the three-dimensional retrieval on simulated data (1 TEC Unit corresponds to 1016 electrons/m2). Another benefit of the multilayer approach is improved slant TEC modeling. Using actual data from an equatorial site at Cocos Islands (96.8E, 12.2 S), three slab modeling improved estimates of slant TEC by a factor of 2 for elevation angles between 10 and 20° (9 versus 4.4 TECU, root-mean-square). However, the global structure of the vertical TEC retrievals we analyzed did not improve using three-dimensional modeling. This may be due to a critical approximation shared by both techniques that TEC persists unchanged at a given local time. This assumption is required to produce global maps from observations acquired from widely scattered ground receivers. Further improving the retrieval of global TEC structure with ground-based data probably requires improved dynamical models of TEC behavior. New data available from GPS receivers in low Earth orbit is also promising. 相似文献
15.
参考青藏高原东缘松潘-甘孜地块至四川盆地陡变地形起伏和地壳密度结构的横向差异,本文建立了二维牛顿黏性流体有限元模型,计算分析构造加载、陡变地形和重力效应控制下青藏高原东缘岩石圈变形特征,探讨横向不均匀的地壳密度结构、陡变地形和岩石圈流变性质对区域现今垂向运动的影响.计算结果显示：在构造加载作用下,松潘-甘孜地块至四川盆地地表抬升微弱.区域横向不均匀的地壳密度结构驱使松潘-甘孜地块地壳整体抬升,速率高达2 mm·a-1,四川盆地整体下沉,速率约1 mm·a-1,与龙门山两侧现今观测到的地表垂向变形模式相近.龙门山地区陡变地形驱使柔性地壳流动,调整区域地壳局部变形;岩石圈流变结构影响重力驱动作用下的模型变形量值和岩石圈变形耦合程度,松潘-甘孜地块较低的中地壳黏滞系数引起上、下地壳的变形解耦;模型较高的岩石圈地幔黏滞系数使重力驱动作用下区域垂向变形量降低.因此,青藏高原东缘地壳密度结构差异、地形起伏和岩石圈流变性质是现今区域垂向变形的重要动力学控制因素. 相似文献
16.
An analytic approach is presented for the simulation of variations in the groundwater level due to temporal variations of recharge in surficial aquifers. Such variations, called groundwater dynamics, are computed through convolution of the response function due to an impulse of recharge with a measured time series of recharge. It is proposed to approximate the impulse response function with an exponential function of time which has two parameters that are functions of space only. These parameters are computed by setting the zeroth and first temporal moments of the approximate impulse response function equal to the corresponding moments of the true impulse response function. The zeroth and first moments are modeled with the analytic element method. The zeroth moment may be modeled with existing analytic elements, while new analytic elements are derived for the modeling of the first moment. Moment matching may be applied in the same fashion with other approximate impulse response functions. It is shown that the proposed approach gives accurate results for a circular island through comparison with an exact solution; both a step recharge function and a measured series of 10 years of recharge were used. The presented approach is specifically useful for modeling groundwater dynamics in aquifers with shallow groundwater tables as is demonstrated in a practical application. The analytic element method is a gridless method that allows for the precise placement of ditches and streams that regulate groundwater levels in such aquifers; heads may be computed analytically at any point and at any time. The presented approach may be extended to simulate the effect of other transient stresses (such as fluctuating surface water levels or pumping rates), and to simulate transient effects in multi-aquifer systems. 相似文献
17.
There are few studies on the hydrogeology of sedimentary rock aquitards although they are important controls in regional ground water flow systems. We formulate and test a three-dimensional (3D) conceptual model of ground water flow and hydrochemistry in a fractured sedimentary rock aquitard to show that flow dynamics within the aquitard are more complex than previously believed. Similar conceptual models, based on regional observations and recently emerging principles of mechanical stratigraphy in heterogeneous sedimentary rocks, have previously been applied only to aquifers, but we show that they are potentially applicable to aquitards. The major elements of this conceptual model, which is based on detailed information from two sites in the Maquoketa Formation in southeastern Wisconsin, include orders of magnitude contrast between hydraulic diffusivity (K/S(s)) of fractured zones and relatively intact aquitard rock matrix, laterally extensive bedding-plane fracture zones extending over distances of over 10 km, very low vertical hydraulic conductivity of thick shale-rich intervals of the aquitard, and a vertical hydraulic head profile controlled by a lateral boundary at the aquitard subcrop, where numerous surface water bodies dominate the shallow aquifer system. Results from a 3D numerical flow model based on this conceptual model are consistent with field observations, which did not fit the typical conceptual model of strictly vertical flow through an aquitard. The 3D flow through an aquitard has implications for predicting ground water flow and for planning and protecting water supplies. 相似文献
18.
A new computer program, FLASH (Flow-Log Analysis of Single Holes), is presented for the analysis of borehole vertical flow logs. The code is based on an analytical solution for steady-state multilayer radial flow to a borehole. The code includes options for (1) discrete fractures and (2) multilayer aquifers. Given vertical flow profiles collected under both ambient and stressed (pumping or injection) conditions, the user can estimate fracture (or layer) transmissivities and far-field hydraulic heads. FLASH is coded in Microsoft Excel(5) with Visual Basic for Applications routines. The code supports manual and automated model calibration. 相似文献
19.
A new analytic solution approach is presented for the modeling of steady flow to pumping wells near rivers in strip aquifers; all boundaries of the river and strip aquifer may be curved. The river penetrates the aquifer only partially and has a leaky stream bed. The water level in the river may vary spatially. Flow in the aquifer below the river is semi-confined while flow in the aquifer adjacent to the river is confined or unconfined and may be subject to areal recharge. Analytic solutions are obtained through superposition of analytic elements and Fourier series. Boundary conditions are specified at collocation points along the boundaries. The number of collocation points is larger than the number of coefficients in the Fourier series and a solution is obtained in the least squares sense. The solution is analytic while boundary conditions are met approximately. Very accurate solutions are obtained when enough terms are used in the series. Several examples are presented for domains with straight and curved boundaries, including a well pumping near a meandering river with a varying water level. The area of the river bottom where water infiltrates into the aquifer is delineated and the fraction of river water in the well water is computed for several cases. 相似文献
20.
利用卫星观测的长波磁异常，用等效偶极源方法推导了中国地区的视磁化强度分布．因卫星的高度远大于磁性地壳的厚度，将视磁化强度转换成磁化强度的垂直积分，它代表地壳内磁性物质的区域变化，利用视磁化强度与地表热流相应关系，计算了中国的新疆和东部一些地区居里等温面的深度．新疆地区的居里面深度为35-50km，其分布形态与塔里木盆地和准噶尔盆地的地貌比较相似；中国东部一些地区居里面深度在20-40km之间，与一些作者用航磁等数据得到的居里深度十分接近． 相似文献