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1.
根据高盐度湖泊水动力特征,以西北咸水湖泊艾比湖为例,建立三维水动力数学模型。选取典型风场,分析风力作用下的高盐度湖泊风生流形成过程以及风生流水动力参数的三维空间分布特征。结果表明,艾比湖风生流形成在时间上可分为湖水流向和风向一致阶段、湖水运动方向逐渐偏离风向的过渡阶段及环流形成的稳定阶段等3个阶段。当流场达到稳定状态时,表层水体除中部存在若干小尺度环流外,大部分水域流向与风向基本一致;而湖泊中心区域底层水体流向与表层水体的流向大致相反,表现为很明显的补偿流。总体上,水平方向的流速自表层向下呈现递减的变化趋势,岸边流速大于中心流速,表现出与淡水湖泊基本相似的水动力空间分布特征。水体盐度增加对湖泊环流结构无影响。 相似文献
2.
岩石复电阻率Dias模型及其参数求取方法 总被引：4，自引：0，他引：4
Dias模型是众多描述岩石复电阻率的频散特性模型中的一种,它不但参数少,且可由这些参数导出具有特定物理意义的参数。针对Dias模型参数的求取及反演解的不确定性评价,这里提出了一种模拟退火阻尼最小二乘联合反演方法。该方法首先将参数求解空间离散化,利用模拟退火找到全局最优解区间,然后利用阻尼最小二乘法在解空间进行求解。该方法有效地克服了原来两种方法的反演速度慢、反演结果依赖于初值的缺点,并实现了对反演结果多解性的评价。研究结果表明,对于岩石复电阻率数据的处理解释,Dias模型的使用比传统的Cole模型及其变形更具有潜在的优势。 相似文献
3.
在垂向二维水动力模型的基础上,叠加了泥沙模型,建立了垂向二维泥沙模型,该模型的主要特点是水动力模型采用斜压模式,可以模拟由于水库水温度分布时空变化对其水动力结构及泥沙沉降速度的影响;泥沙模型采用分步法求解,简化了计算;独立求解粘性泥沙及非粘性泥沙的沉降速度及水土界面交换通量;运用经验公式估算泥沙及水动力模型参数,弥补了资料不足的缺点。最后运用实测资料对所建泥沙模型进行了有效性验证,结果表明:悬沙模拟值与实测值相对误差较小,时空分布特征相似;同时,模型能较为准确反映由于水库出入流引起的库首与库尾水温及泥沙分布特征。 相似文献
4.
The simulation of flow in porous and fibrous permeable media is of high importance in many scientific and industrial applications. Although the finite element models at the representative elementary volume scales are used to solve a huge amount of scientific and engineering problems, they are hardly used to efficiently simulate pore-fluid flow problems at the particle scales. This encourages the development of numerical models to match the needs of such studies. In this paper, we propose a new Gray Lattice Boltzmann numerical model for simulating fluid flow in permeable media. Unlike most previous models, our proposed model has the ability to simulate multi-layers and space-variable permeability while preserving the continuity of the macroscopic velocity field. The model is verified with the available analytical solutions and a derived analytical expression for the case of variable porosity. In addition, we examine the importance of introducing a transition layer with a defined porosity function near the boundaries and interfaces. If this layer exists in practice, then the numerical results reveal that it cannot be neglected, and its impact is significant on the obtained velocity distribution. Finally, in the light of the obtained results, we can state that the proposed model has great potential to simulate complex and heterogeneous media with smoothness and accuracy, so that it may enrich the research content of the emerging computational geosciences. 相似文献
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Net-pen aquaculture results in the introduction of excess fish food and fecal matter in coastal waters. These wastes may modify the benthic environment. Mathematical models are developed in this study to simulate tidal and wind-driven currents, waves, and the resulting dispersion of fish food and fecal matter in coastal Maine, a region where limited modelling studies have been performed. Cobscook Bay and Toothacher Bay in Maine are studied in detail through the use of mathematical models and field data. We find that a systematic, site-specific, step-by-step modeling strategy involving the use of numerical models to simulate the overall hydrodynamic environment in combination with a waste-particle transport model can be an extremely powerful method of determining a priori whether aquaculture operations will cause high rates of net-pen waste accumulation at a particular site. 相似文献
7.
A two‐scale modeling of solute transport in double‐porosity (DP) media under unsaturated water flow conditions is presented. The macroscopic model was developed by applying the asymptotic homogenization method. It is based on theoretical and empirical considerations dealing with the orders of magnitude of characteristic quantities involved in the process. For this purpose a physical model that mimics the behavior of DP medium was built. The resulting two‐equation model relies on a coupling exchange term between micro‐ and macro‐porosity subdomains associated with local non‐equilibrium solute concentrations. The model was numerically implemented (Comsol Multiphysics®) to simulate the macroscopic one‐dimensional physical process taking place into the porous medium of 3D periodic microstructure. A series of dispersion experiments of NaCl solution under unsaturated steady‐state flow conditions were performed. The experimental results were used first to calibrate the dispersion coefficient of the model, and second to validate it through two other independent experiments. The excellent agreement between the numerical simulations and the measurements of the time evolution of the non‐symmetrical breakthrough curves provides a proof of predictive capacity of the developed model. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
8.
Stochastic analysis of the effect of spatial variability of diffusion parameters on radionuclide transport in a low permeability clay layer 总被引：1，自引：0，他引：1
Most studies that incorporate subsurface heterogeneity in groundwater flow and transport models only analyze and simulate the spatial variability of hydraulic conductivity. Heterogeneity of the other flow and transport parameters are usually neglected. This approach is often justified, but there are, however, cases in which disregarding the heterogeneity of the other flow and transport parameters can be questionable. In low permeability media, for instance, diffusion is often the dominant transport mechanism. It therefore seems logical to incorporate the spatial variability of the diffusion parameters in the transport model. This study therefore analyses and simulates the spatial variability of the effective diffusion coefficient and the diffusion accessible porosity with geostatistical techniques and incorporates their heterogeneity in the transport model of a low permeability formation. The formation studied was Boom clay (Belgium), a candidate host rock for the deep geological disposal of high-level radioactive waste. The calculated output radionuclide fluxes of this model are compared with the fluxes calculated with a homogeneous model and a model with a heterogeneous hydraulic conductivity distribution. This analysis shows that the heterogeneity of the diffusion parameters has a much larger effect on the calculated output radionuclide fluxes than the heterogeneity of hydraulic conductivity in the low permeability medium under study. 相似文献
9.
选取国内外常用的水动力学模型(EFDC)和典型的浅水湖泊(太湖),采用拉丁超立方取样(LHS),研究湖泊水动力模块中常用的5个重要参数(风拖曳系数、床面粗糙高度、涡粘性系数、紊流扩散系数以及风遮挡系数)对湖体水位和流速的影响。结果表明:针对大型浅水湖泊,湖泊岸线形状和湖底地形、湖泊周围地形、湖泊水面风场对模拟结果产生决定性影响。尤其是在湖湾区和周边地形比较复杂的地区,风场参数对水动力模拟结果不确定性的贡献率最大。在垂向上,表层流速受到参数不确定性的影响最大,底层次之,中层最小。床面粗糙高度对水动力模拟结果不确定性贡献率较风场参数要小,水体涡粘滞系数和扩散系数影响则更小。故在选择大型浅水湖泊水动力模型参数时,要充分考虑湖泊岸线和周围地形,着重率定风场参数以及床面粗糙高度。 相似文献
10.
针对城市河网缺乏足够的实测资料和河网水动力学模型模拟速度慢的特点,提出将河网水动力学模型与遗传算法、神经网络方法结合,建立河网智能模型。模型中,利用河网水动力学模型提供神经网络所需的信息,遗传算法用于优化神经网络的初始权重。将该模型应用于上海市浦东新区河网中,智能模拟结果与经过实测资料验证的河网水动力学模型的模拟结果吻合较好,表明河网智能模型精度与水动力学模型接近。同时实时性较好,可用来预测河网水位变化特性,也为今后类似研究提供一种模拟技术。 相似文献
11.
采用浑水控制方程,建立了基于耦合解法的一维非恒定非均匀沙数学模型,用于模拟高含沙洪水演进时的河床冲淤过程.然后采用黄河下游游荡段1977年7—8月实测高含沙洪水资料对该模型进行率定,基于水沙耦合解法的各水文断面流量、总含沙量及分组含沙量的计算过程与实测过程符合更好,计算的沿程最高水位及累计河段冲淤量与实测值也较为符合.最后还采用2004年8月高含沙洪水资料对该模型进行了验证.模型率定及验证计算结果表明,采用一维水沙耦合模型计算高含沙洪水过程,能取得较高的精度. 相似文献
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Different models were developed for evaluating the probabilistic three-dimensional (3-D) stability analysis of earth slopes and embankments under earthquake loading. The 3-D slope stability model assumed is that of a simple cylindrical failure surface. The probabilistic models evaluate the probability of failure under seismic loading considering the randomness of earthquake occurrence, and earthquake induced acceleration and uncertainties stemming from the discrepancies between laboratory-measured and in-situ values of shear strength parameters. The models also takes into consideration the spatial variabilities and correlations of soil properties. The probabilistic analysis and design approach is capable of obtaining the 2-D and 3-D static and dynamic safety factors, the probability of slope failure, the earthquake induced acceleration coefficient, the yield acceleration coefficient, the earthquake induced displacement, and the probability of allowable displacement exceedance taking into account the local site effect. The approach is applied to a well known landslide case: Congress Street Landslide in Chicago. A sensitivity analysis was conducted on the different parameters involved in the models by applying those models to the Congress Street landslide considering different levels of seismic hazard. Also, a sensitivity analysis was carried out to study the sensitivity of computed results to input parameters of undrained shear strength, and corrective factors. A comparison was made between the different models of failure. The parametric study revealed that the hypocentral distance and earthquake magnitude have major influence on the earthquake induced displacement, probability of failure and dynamic 2-D and 3-D safety factors. 相似文献
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15.
裂隙岩溶含水系统溢流泉演化过程的数值模拟 总被引：5，自引：5，他引：0
本文利用非连续裂隙网络介质模型,耦合水动力条件和碳酸盐溶蚀动力条件,建立岩溶含水系统演化的数学模型,并用数值法进行模拟分析。在已建数值模型基础上,构造了两组实例模型(降水入渗补给的裂隙岩溶含水系统和河流补给的裂隙岩溶含水系统)来研究裂隙岩溶系统中溢流泉早期演化过程。模拟发现,裂隙岩溶含水系统演化过程中,裂隙不断被溶蚀拓宽,致使系统中潜水位不断下降,许多小泉被疏干;同时不同裂隙之间存在溶蚀差异,在潜水位及优势通道附近的裂隙溶蚀速度快,而其它位置则相对慢得多,差异溶蚀促使系统形成优势溶管,优势溶管逐渐袭夺水流,形成大泉。另外对比两模型发现,降水入渗为主要补给源的裂隙岩溶含水系统,泉管道从汇向源发育;而河流入渗为主要补给源的裂隙岩溶含水系统,泉管道则由源向汇发育。 相似文献
16.
Quantification of seismic activity is one of the most challenging problems faced by earthquake engineers in probabilistic seismic hazard analysis. Currently, this problem has been attempted using empirical approaches which are based on the regional earthquake recurrence relations from the available earthquake catalogue. However, at a specified site of engineering interest, these empirical models are associated with large number of uncertainties due to lack of sufficient data. Due to these uncertainties, engineers need to develop mechanistic models to quantify seismic activity. A wide range of techniques for modeling continental plates provides useful insights on the mechanics of plates and their seismic activity. Among the different continental plates, the Indian plate experiences diffused seismicity. In India, although Himalaya is regarded as a plate boundary and active region, the seismicity database indicates that there are other regions in the Indian shield reporting sporadic seismic activity. It is expected that mechanistic models of Indian plate, based on finite element method, simulate stress fields that quantify the seismic potential of active regions in India. This article explores the development of a finite element model for Indian plate by observing the simulated stress field for various boundary conditions, geological and rheological conditions. The study observes that the magnitude and direction of stresses in the plate is sensitive to these conditions. The numerical analysis of the models shows that the simulated stress field represents the active seismic zones in India. 相似文献
17.
M. Oostrom Y. Mehmani P. Romero-Gomez Y. Tang H. Liu H. Yoon Q. Kang V. Joekar-Niasar M. T. Balhoff T. Dewers G. D. Tartakovsky E. A. Leist N. J. Hess W. A. Perkins C. L. Rakowski M. C. Richmond J. A. Serkowski C. J. Werth A. J. Valocchi T. W. Wietsma C. Zhang 《Computational Geosciences》2016,20(4):857-879
18.
Sameh A. Sakr 《Hydrogeology Journal》1999,7(2):155-160
The problem of seawater intrusion is considered for the case of a confined coastal aquifer in which there is steady seaward
flow of fresh water. Using the GWCH2O model, the problem is solved first for the case of no dispersion where a distinct interface
exists separating the fresh water from the salt water. The problem is solved next by taking into account dispersion and diffusion
of the salt-water component, along with the density effect. In this respect, a two-dimensional finite-element model, 2D-VDTRAN,
is developed to simulate density-dependent solute transport.
To investigate the limitation of the sharp-interface approach in coastal aquifers for conditions of both steady state and
unsteady state, the problem is solved twice using the two models with different parameter values. These parameters are combined
in dimensionless form, resulting in four named parameters: seepage factor (A); dispersion-to-advection ratio (B); geometry
ratio (C); and time-scale factor (T). Using the density-dependent model, the dimensionless width of the transition zone (W/L)
is determined for different values of A, B, C, and T. Steady-state simulations show that the sharp-interface approach is valid
only when the system is dominated by advection, i.e., when 0<B≤5% for all values of A and C, or when A≥65% for all values
of B and C. However, the unsteady-state analysis shows that the applicability of the sharp-interface approach is sufficiently
accurate at early times.
Received, October 1997 Revised, June 1998, October 1998 Accepted, November 1998 相似文献
19.
Optimal schemes of groundwater exploitation for prevention of seawater intrusion in the Leizhou Peninsula in southern China 总被引：1，自引：0，他引：1
The Lei-Qiong Depression Zone, near the Leizhou Peninsula in southern China, consists of unconsolidated sediments of 500-3,000 m thickness. Groundwater occurs in a multi-aquifer system in the Leizhou Peninsula. The aquifers receive recharge from precipitation, canal and reservoir infiltration, and discharge mainly through subterranean drainage into the sea. Artificial pumping for drinking and agricultural purposes is another way of groundwater discharge. Groundwater development along the coast faces the threat of seawater intrusion. A quasi-three-dimensional finite element model, containing 457 nodes and 833 elements, has been used to simulate the spatial and temporal distribution of groundwater levels in the three-aquifer system. Verification of various aquifer parameters and boundary conditions was performed with the simulation model. Linear programming models have been developed for groundwater exploitation within the two confined aquifers. The objective function of the models is to maximize the total groundwater pumpage from the confined aquifers. Control of seawater intrusion is examined by restricting the water levels at points along the coast and the withdrawal rates in coastal management cells. A response matrix approach was used in the optimization models. The response matrix was obtained from the simulation model by forecasting drawdown produced by pumping at a unit impulse discharge. Groundwater development in the Leizhou Peninsula can be primarily optimized by allocating the pumping rates of the management cells. 相似文献
20.
Giovanna De Filippis Laura Foglia Mauro Giudici Steffen Mehl Stefano Margiotta Sergio L. Negri 《Hydrogeology Journal》2017,25(7):2123-2138
The evaluation of the accuracy or reasonableness of numerical models of groundwater flow is a complex task, due to the uncertainties in hydrodynamic properties and boundary conditions and the scarcity of good-quality field data. To assess model reliability, different calibration techniques are joined to evaluate the effects of different kinds of boundary conditions on the groundwater flow in a coastal multi-layered aquifer in southern Italy. In particular, both direct and indirect approaches for inverse modeling were joined through the calibration of one of the most uncertain parameters, namely the hydraulic conductivity of the karst deep hydrostratigraphic unit. The methodology proposed here, and applied to a real case study, confirmed that the selection of boundary conditions is among the most critical and difficult aspects of the characterization of a groundwater system for conceptual analysis or numerical simulation. The practical tests conducted in this study show that incorrect specification of boundary conditions prevents an acceptable match between the model response to the hydraulic stresses and the behavior of the natural system. Such effects have a negative impact on the applicability of numerical modeling to simulate groundwater dynamics in complex hydrogeological situations. This is particularly important for management of the aquifer system investigated in this work, which represents the only available freshwater resource of the study area, and is threatened by overexploitation and saltwater intrusion. 相似文献