A REVISED SOLUTION OF EQUIVALENT PERMEABILITY TENSOR FOR DISCONTINUOUS FRACTURES

The equivalent permeability tensor is essential to the application of the equivalent porous media model in the numerical seepage simulation for fractured rock masses. In this paper, a revised solution of the equivalent permeability tensor is proposed to represent the influence of the fracture connectivity in discontinuous fractures. A correction coefficient is involved to reflect the complex seepage flow type through the rock bridge. This correction coefficient is back analyzed from single-hole packer tests, based on the Artificial Neural Network (ANN) back analysis and the Finite Element Method (FEM) seepage simulation. The limitation of this back analysis algorithm is that the number of single-hole packer tests should be equal or greater than the number of fracture sets, and three is the maximum number of the fracture sets. The proposed solution and the back analysis algorithm are applied in the permeability measurement and the seepage simulation for the Xiaowan arch dam foundation.     

Application of CLEAR-VOF method to wave and flow simulations

A two-dimensional numerical model based on the Navier-Stokes equations and computational Lagrangian-Eulerian advection remap-volume of fluid (CLEAR-VOF) method was developed to simulate wave and flow problems. The Navier-Stokes equations were discretized with a three-step finite element method that has a third-order accuracy. In the CLEAR-VOF method, the VOF function F was calculated in the Lagrangian manner and allowed the complicated free surface to be accurately captured. The propagation of regular waves and solitary waves over a flat bottom, and shoaling and breaking of solitary waves on two different slopes were simulated with this model, and the numerical results agreed with experimental data and theoretical solutions. A benchmark test of dam-collapse flow was also simulated with an unstructured mesh, and the capability of the present model for wave and flow simulations with unstructured meshes, was verified. The results show that the model is effective for numerical simulation of wave and flow problems with both structured and unstructured meshes.     

NUMERICAL MODELING FOR POSITIVE AND INVERSE PROBLEMS OF 3-D SEEPAGE IN DOUBLE FRACTURED MEDIA

Three-dimensional seepage in double fractured media was modeled in this paper. The determination of hydraulic conductivity tensor of rock mass is a vital problem for the sea water intrusion or sea water encroachment and seepage of fissured medium. According to the geological and hydrogeological conditions for the Three Gorges Project (TGP),2nd stage construction of the Three Gorges Project(TGP),the physical and mathematical models for the groundwater movement through the 3D double fractured media of rock mass during construction were established in this paper. Based on discontinuity control inverse theory, some related parameters of double fractured media were inversed with flux being the known quantity and calibration of water table the objective function. Synchronously, the seepage field of the construction region was systematically analyzed and simulated, the results of which exhibit that the double fractured media model of fracture water can comprehensively and correctly describe the geological and hydrogeological conditions in the construction region.     

BASIC THEORY AND MATHEMATICAL MODELING OF URBAN RAINSTORM WATER LOGGING

In this paper, a mathematical model for the urban rainstorm water logging was established on the basis of one- and two-dimensional unsteady flow theory and the technique of non-structural irregular grid division. The continuity equation was discretized with the finite volume method. And the momentum equations were differently simplified and dis-cretized for different cases. A method of “special passage” was proposed to deal with small-scale rivers and open channels. The urban drainage system was simplified and simulated in the model. The method of “open slot” was applied to coordinate the alternate calculation of open channel flow and pressure flow in drainage pipes. The model has been applied in Tianjin City and the verification is quile satisfactory.     

NUMERICAL STUDY ON THE PURIFICATION PERFORMANCE OF RIVERBANK

During the rain time, the runoff infiltrates into the riverbank through the collecting gutter and slope surface. The city runoff is generally polluted by organic, oil, heavy metal particulates, etc. The pollutants moving with the water through the riverbank experience advection, dispersion, diffusion, adsorption, biochemical reaction and plant uptaking processes. In this article, a mathematical model was developed to simulate the performance of pollutant removal of the riverbank. The model took those main mechanisms into account. The modified Richards equation was used in simulating flow field. The mass balance law was employed in deriving the equation for pollutant transport, where the diffusion and dispersion were described with the Fick-type law, the adsorption was macroscopically expressed as form isotherm, and the bio-chemical degradation process was assumed to follow the Monod kinetics. The NH3-N and TP were considered in the present model. The mathematical model was descritized with a finite element numerical model, which was applied to two types of model riverbanks. In the model test, the hydraulic loading was assumed to have the intermittent pattern simulating the storm runoff of certain return period, and the values of the rainfall runoff and concentrations of the NH3-N and TP were taken from the model test. The computed overall removal rates for the NH3-N and TP in 6 cases are in the range of 88%-98%, 87%-97%, respectively. The differences between the computed and tested overall removal rates for the NH3-N and TP are less than 5%. The time-varying oscillation pattern of the concentrations of the NH3-N and TP were rationally simulated, which shows that the model presented in this article can be used to assess the purification performance of the riverbank constructed with sand or soil.     

STUDY OF NON-BOUSSINESQ EFFCET ON SEA SURFACE HEIGHT

A set of equations was derived for a nonBoussinesq ocean model in this paper. A new time-splitting scheme was introduced which incorporates the 4th-order Runge-Kutta explicit scheme of low-frequency mode and an implicit scheme of high-frequency mode. With this model, potential temperature, salinity fields and sea surface height were calculated simultaneously such that the numerical error of extrapolation of density field from the current time level to the next one could be reduced while using the equation of mass conservation to determine sea surface height. The non-Boussinesq effect on the density field and sea surface height was estimated by numerical experiments in the final part of this paper.     

NUMERICAL SIMULATION OF ICE CONTROL EFFECT OF SOLAR ENERGY ON TIBETAN CHANNELS

With the Tanghe Diversion Channel in Tibet as an example, the theoretical study on the ice control effect of the solar sacks was conducted based on the previous study. The numerical simulation method was adopted and a one-dimensional numerical model for ice crystal in diversion channels in high-altitude cold regions was developed in this article. The heat transfer through the air-water interface and the mass transfer between ice and water were considered in the model. The model was validated by the field observation data on the diversion channel of the Tanghe Hydropower Station. The results show that the ice control effect of the solar sacks is obvious in the channel with large mass flow rate in the high-altitude cold regions.     

QUANTITATIVE APPROACH TO INFLUENCES OF HIGH SEDIMENT LADEN INUNDATION FLOWS ON THE MORPHOLOGICAL VARIATION OF FLOODPLAINS

This article mainly aims at developing an integrated 2-D numerical simulation model on inundation, sediment transportation and the morphological variations of floodplains due to high sediment-laden inundation flows. Due to the complexity of inner and outer boundaries and the arbitrary structures within the computational domain of floodplains, an unstructured Finite-Volume Method (FVM) based on an irregular polygon mesh was worked out so that the influences of complex boundaries can be integrated into the simulation. A case study was conducted in the Lower Yellow River Basin, in which a dike-break at the Huayuankou Hydrological Station was assumed to happen when a flood scale of 1982 was suffered in the region. The simulated spatial distribution of sediment deposition and erosion can be used to reasonably explain the natural phenomena of “suspended river” of the lower part of the Yellow River. It is concluded that the inundation process of water is similar to a variable-river-bed condition during the simulation because the sediment deposition and erosion are modified by new values at the end of each time step. The mass and momentum conservation were strictly followed during the simulation. Therefore, theprediction of floodplain evolutions by the integrated simulation model, proposed in this study, can be adequately and accurately given if the real condition of an floodplain can be obtained in detail.     

VELOCITY DISTRIBUTION IN TRAPEZOID-SECTION OPEN CHANNEL FLOW WITH A NEW REYNOLDS-STRESS EXPRESSION

By considering that the coherent structure is the main cause of the Reynolds stress, a new Reynolds stress expression was given. On this basis the velocity distribution in the trapezoid-section open channel flow was worked out with the pseudo-spectral method. The results were compared with experimental data and the influence of the ratio of length to width of the cross-section and the lateral inclination on the velocity distribution was analyzed. This model can be used the large flux in rivers and open channes.     

A simplified dynamic method for field capacity estimation and its parameter analysis

This paper presents a simplified dynamic method based on the definition of field capacity. Two soil hydraulic characteristics models, the Brooks-Corey （BC） model and the van Genuchten （vG） model, and four soil data groups were used in this study. The relative drainage rate, which is a unique parameter and independent of the soil type in the simplified dynamic method, was analyzed using the pressure-based method with a matric potential of -1/3 bar and the flux-based method with a drainage flux of 0.005 cm/d. As a result, the relative drainage rate of the simplified dynamic method was determined to be 3% per day. This was verified by the similar field capacity results estimated with the three methods for most soils suitable for cultivating plants. In addition, the drainage time calculated with the simplified dynamic method was two to three days, which agrees with the classical definition of field capacity. We recommend the simplified dynamic method with a relative drainage rate of 3% per day due to its simple application and clearly physically-based concept.     

地下厂房洞室群渗流场及渗控措施效果数值分析

采用三维渗流场有限元方法,模拟地下厂房洞室群稳定渗流场。建立三维渗流场有限元分析模型,精确模拟排水孔的位置。通过多工况的计算,详细分析地下厂房洞室群渗流特性以及其中帷幕及排水幕的渗流控制效果,同时探讨坝基及消力戽排水孔间距对渗流场的影响。计算结果表明：地下厂房洞室群天然水位较高,渗流控制措施对厂房洞室群渗流场可起到很好的控制作用,排水孔的排水减压作用明显,防渗帷幕能够有效降低扬压力以及水力坡降的分布,有利于围岩稳定。另外,坝基及消力戽排水孔间距对渗流场影响并不明显。     

江口拱坝坝基渗流场有限元法分析

运用固定网格结点虚流量法及排水子结构技术，对江口拱坝坝基的防渗与排水渗控制施、两岸山体边界条件、隔水岩层阻渗及岩体成层产状等因素在影响坝基渗流场特性中的具体作用进行了计算分析。结果表明，排水子结构技术在精细求解复杂坝基渗流场中具有明显的优势，它在理论和算法上严密，完全能仿真模拟各个排水孔的几何尺寸及排水降压的真实水力行为，不仅能明显地提高计算效率，还能使渗流场的精度大大提高。     

坪头水电站地下厂房渗控措施效果研究

地下厂房洞室群渗流场中密集排水孔排水幕的处理一直是工程渗流特性和渗控研究的重点,由于排水孔(幕)众多,渗控作用大,须尽可能精确模拟,这对网格划分提出了极高的技术要求.文章采用严密的改进排水孔结构技术[1](使整体三维模拟排水孔(幕)的实际渗流行为和渗控效果成为现实),通过多方案比较对裂隙岩体中地下厂房的防渗帷幕、排水孔...     

两河口水电站地下厂房渗流控制布置方案研究

介绍两河口水电站地下厂房区的防渗排水系统布置.根据厂房区的工程地质和水文地质条件,建立三维有限元计算模型.分析了初步设计方案地下厂房区的渗流场特性以及防渗排水系统的特点,探讨了岩体的渗透性和排水孔间距变化对渗流场的影响.分析表明,该渗流控制方案是可行的,并建议幕后排水孔距为3 m.     

基于渗流应力耦合的导流洞封堵期 结构安全分析

通过建立复杂三维渗流场模型,对导流洞整体三维渗流场特性进行分析;同时基于渗流—应力耦合模型,应用空气单元模拟导流洞渗流场分析中的排水孔效应,采用三维弹塑性非线性有限元法对导流隧洞开挖、支护、下闸蓄水及封堵期的围岩稳定及结构安全性进行了全面仿真计算分析。结果表明,采用空气单元可以有效模拟排水孔的排水效果;在顶拱围岩设置排水孔可有效降低洞周围岩的外水压力水头,改善支护结构的受力状况。     

深圳抽水蓄能电站厂房洞室群优选渗控方案分析

利用求解有自由面渗流场改进的节点虚流量全域迭代法，结合精确的排水孔模拟技术，对深圳抽水蓄能电站运行期地下引水管线区及厂房洞室群围岩区三维渗流场进行了有限元仿真分析，着重研究了优选方案中高压岔管开裂时引水支管区域防渗排水系统的渗流特性．研究表明，该区域设置封闭性防渗帷幕加排水孔幕组合防渗体系，能有效控制高压引水管开裂时的高压渗水，改善该区岩体渗透比降分布，保证了下游厂房运行期的安全．     

南水北调中线挖方渠段渗控措施优化研究

南水北调中线工程中渗流调控是保障渠坡及衬砌板稳定的关键。为全面分析高地下水地区挖方渠段渗流调控措施合理性及优化的效果,针对典型渠段建立渗流模型,通过三维有限元数值模拟,研究渠道渗流场分布规律,比较不同措施的调控效果。结果表明:排水垫层结合逆止阀、排水板结合逆止阀、排水板结合衬砌板透水缝等3种排水措施都能有效降低渠底衬砌板下扬压力。最后比较了上述3种措施的差别,讨论了应用条件,提出了相应的建议,对类似工程有借鉴意义。     

渗流控制分析中密集排水孔模拟的新方法

应用叠加原理，在点汇基本解的基础上，推导出了有限元单元内排水孔的近似解表达式。然后，应用井群的叠加原理，将单个排水孔的解析理论推广到单元内多个排水孔的情况。这种排水孔的准解析方法应用于渗流控制有限元分析，具有迭代收敛速度快、精度好的特点。更为重要的是，对密集排水孔渗流控制布置方案（方位或轴线）的改变，不需要像“排水子结构法”那样重新改变有限元网格，而仅需改变排水孔极少的几个控制要素即可。因而，该方     

立洲RCC拱坝渗控方案的三维有限元优化分析

以四川木里河立洲水电枢纽工程为研究对象,对坝区的渗控措施展开研究。利用ANSYS12.1建立三维有限元渗流模型,计算分析得到了各渗控方案的渗流特征和渗透压力变化规律。对各方案中关键部位的渗透比降、渗漏量和典型剖面渗流场的渗压、地下水位等特征量进行比较分析后,得知:(1)立洲拱坝渗控措施设计方案的防渗帷幕和排水孔幕能有效降低坝后渗流浸润线,对于减小坝基、坝肩扬压力、改善坝基和坝肩受力条件起到了良好的作用;(2)加深帷幕和排水孔幕、增厚帷幕对降低坝区渗透压力作用不大;(3)适当增加f5断层附近防渗帷幕的深度,可防止f5断层形成渗漏通道,影响坝区渗透稳定;另外,取消第一层排水幕、缩短坝肩防渗帷幕延伸长度,可使渗控措施在满足渗流安全的前提下更为经济。     

空气单元法模拟渗流场分析中的排水孔

应用“空气单元”模拟渗流场分析中的排水孔。将排水孔看作是以一定的渗透系数表征其排水作用的介质单元,并将其像渗流计算域中其他岩块、土体单元一样加入到传统的有限元渗流汁算方法中。对一地下洞室中排水孔算例进行分析,给出相应的渗透系数取值范围,证明该法为含排水设施结构的渗流计算提供了较大的方便,减轻了数据前期处理的工作量、降低丁由于人为约束条件而带来的误荠,具有一定的工程应用价值。