Evaluation of Various Surface Irrigation Numerical Simulation Models

In this study, a zero-inertia model (ZIMOD) is presented to simulate all phases of border and furrow irrigation systems. The governing equations were discretized using a control volume of moving cells, by procedures reported in the literature for borders and for furrows. Later, the discretized equations were linearized by applying a Taylor series expansion according to the Newton-Raphson procedure, and then the algebraic linearized equations were iteratively solved using the Gaussian elimination technique. The ZIMOD was verified against several field experimental data and output of various numerical models in the SIRMOD package. Computational times, errors in predicting advance and recession trajectories, and estimated runoff and infiltrated volumes were compared. All models used in the comparative analysis predicted the advance and recession times and the infiltrated and runoff volumes satisfactory. However, models in the SIRMOD package were computationally faster than ZIMOD.     

Evaluating Safety of Concrete Gravity Dam on Weak Rock: Scott Dam

Scott Dam is owned and operated by Pacific Gas & Electric Co. (PG&E) as part of the Potter Valley Project. Although it is an unimpressive concrete gravity dam [233 m (765 ft) long with maximum water surface 33.4 m (110 ft) above tailwater], the dam has unusually complex and weak foundation rocks; this condition caused design changes during construction, numerous subsequent special investigations, and several corrections and additions. A main stumbling block to clarification of the dam safety issue for Scott Dam has always been difficulty in characterizing the foundation material. This paper discusses an approach to this problem as well as how the safety of the dam was subsequently confirmed, following a comprehensive program of research, investigations, and analysis from 1991 to 1997.     

高炉煤气重力除尘器内部流场及除尘效率的数值模拟

为了提高高炉煤气重力除尘器的除尘效率,在高炉煤气重力除尘器内进行了安装漏斗型挡板和将进气管由中心管改为锥顶进气两项技术。采用FLUENT软件对除尘器内的气相流场和颗粒的运动轨迹进行数值模拟。模拟结果表明：改变进气方式以后,与旋风除尘器相似在重力除尘器内部产生了旋流;加入挡板后,在挡板下部形成一个气流死区,避免了二次扬尘的出现,而含尘气体与挡板间的碰撞是颗粒被分离出来的主要原因。固体颗粒的运动轨迹较为复杂,且带有一定的随机性,计算得出的除尘效率和实际试验数据吻合较好。     

Earth Dam on Liquefiable Foundation and Remediation: Numerical Simulation of Centrifuge Experiments

A series of four dynamic centrifuge model tests was performed to investigate the effect of foundation densification on the seismic performance of a zoned earth dam with a saturated sand foundation. In these experiments, thickness of the densified foundation layer was systematically increased, resulting in a comprehensive set of dam-foundation response data. Herein, Class-A and Class-B numerical simulations of these experiments are conducted using a two-phase (solid and fluid) fully coupled finite element code. This code incorporates a plasticity-based soil stress–strain model with the modeling parameters partially calibrated based on earlier studies. The physical and numerical models both indicate reduced deformations and increased crest accelerations with the increase in densified layer thickness. Overall, the differences between the computed and recorded dam displacements are under 50%. At most locations, the computed excess pore pressure and acceleration match the recorded counterparts reasonably well. Based on this study, directions for further improvement of the numerical model are suggested.     

Thermal-Structural Modeling and Temperature Control of Roller Compacted Concrete Gravity Dam

A coupled thermal-structural analysis is carried out using both a two- and a three-dimensional finite-element method. The computer program ANSYS is used and simulates the construction process of a roller compacted concrete (RCC) dam. Thermally induced stresses are computed for the 60 m high RCC Tannur Dam in Jordan. The actual temperature distribution in the body of the dam measured by thermocouples is compared with that obtained by ANSYS; generally, a good agreement is obtained. The study demonstrates that detailed thermal stress analysis should be performed for large RCC dams to provide a basis to minimize and control the occurrence of thermal cracking.     

Composite Element Analysis of Gravity Dam on a Complicated Rock Foundation

This paper presents the formulation and application of a composite element method, which is intended for numerical modeling of discontinuous rock masses. This method allows analysis of fractured rock masses using regular meshes that do not need to rigorously respect the orientations and positions of discontinuities. It can be incorporated in conventional finite-element programs. The performance of this method are illustrated through its use for the analysis of the mechanical behavior of the Baozhusi gravity dam which is constructed on a complex rock foundation.     

超重力强化分离铜渣中铜的数值模拟及辅助工业设计

由于当前铜冶炼工艺产生的铜渣铜含量比较高,采用传统的电炉贫化技术分离铜液滴时间长、回收率低,因此引入超重力技术对贫化过程进行改善。采用数值模拟的方法,以卧式离心机为模型基础,选用转炉铜渣作为试验对象进行研究,借助COMSOL Multiphysics软件构建模型,模拟铜渣中铜液滴的沉降过程。根据计算结果分析重力系数（G）、温度（T）对不同粒径铜液滴沉降行为的影响。结果表明,在T=1 300 ℃、G=1的条件下,粒径低于80 μm的铜液滴无法自由沉降;在恒定温度下,重力系数以及铜液滴粒径的增加均有利于铜液滴在铜渣中的沉降;温度升高会降低铜渣和铜的黏度,促进二者分离。最后,根据铜液滴的沉降数据,对离心机半径、给料速度等工业参数提出优化建议,以提升铜的回收率,降低企业生产成本。     

Numerical Simulation of Swirling Flow in Complex Hydroturbine Draft Tube Using Unsteady Statistical Turbulence Models

A numerical method is developed for carrying out unsteady Reynolds-averaged Navier-Stokes (URANS) simulations and detached-eddy simulations (DESs) in complex 3D geometries. The method is applied to simulate incompressible swirling flow in a typical hydroturbine draft tube, which consists of a strongly curved 90° elbow and two piers. The governing equations are solved with a second-order-accurate, finite-volume, dual-time-stepping artificial compressibility approach for a Reynolds number of 1.1 million on a mesh with 1.8 million nodes. The geometrical complexities of the draft tube are handled using domain decomposition with overset (chimera) grids. Numerical simulations show that unsteady statistical turbulence models can capture very complex 3D flow phenomena dominated by geometry-induced, large-scale instabilities and unsteady coherent structures such as the onset of vortex breakdown and the formation of the unsteady rope vortex downstream of the turbine runner. Both URANS and DES appear to yield the general shape and magnitude of mean velocity profiles in reasonable agreement with measurements. Significant discrepancies among the DES and URANS predictions of the turbulence statistics are also observed in the straight downstream diffuser.     

3D Numerical Simulation for Water Flows and Sediment Deposition in Dam Areas of the Three Gorges Project

This paper presents a three-dimensional (3D) mathematical model for suspended load transport in turbulent flows. Based on the stochastic theory of turbulent flow proposed by Dou, numerical schemes of Reynolds stresses for anisotropic turbulent flows are obtained. Instead of a logarithmic law, a specific wall function is used to describe the velocity profile close to wall boundaries. The equations for two-dimensional suspended load motion and sorting of bed material have been improved for a 3D case. Numerical results are in good agreement with the measured data of the Gezhouba Project. The present method has been employed to simulate sediment erosion and deposition in the vicinity of the Three Gorges Dam. The size distribution of the deposits and bed material, and flow and sediment concentration at different times and elevations, are predicted. The results agree well with the observations in physical experiments. Thus, a new method is established for 3D simulation of sediment motion in the vicinity of dams.     

Rapid Graphical Detection of Weakness Problems in Numerical Simulation Infiltration Models Using a Linearized Form Equation

Recently, Valiantzas proposed a new two-parameter vertical infiltration equation that can be transformed to a linearized-form equation that essentially states that the shape of the cumulative infiltration data, when presented in the form of (i2/t) versus i, is linear. In this paper, the presentation of the numerical data to the Valiantzas linearized-form equation is proposed as an additional criterion to detect easily and rapidly possible errors of the numerical solutions and eventually to choose the best spatial discretization for a simulated infiltration event that is used as setup parameter to the numerical infiltration models. Numerical data and analytical solutions were used to validate the proposed method.     

Analysis of Gravity Dam on a Complicated Rock Foundation Using an Adaptive Block Element Method

In this Technical Note, the adaptive block element method of rock masses is formulated, in which the elastoplastic characteristics of both rock blocks and discontinuities are taken into account. The concept of an overlay element is illustrated first; then the displacement fields of rock blocks are expressed as functions of so-called general degree of freedoms using the shape functions of the hierarchical finite element method; the governing equations of the rock block system are deduced on the basis of the virtual work principle; and the p-version adaptive algorithm based on the energy norm error estimation of each block element is proposed. The method is applied to the deformation and stability study of a gravity dam, and the parallel laboratory physical test is used to check the validity and ability of the method.     

基于FLUENT某尾矿库溃坝数值分析

为提出有效避险方案,减少溃坝造成的社会经济损失、人员伤亡和生态环境风险,需正确评估溃决尾砂的流滑运移特征及对下游建构筑物的影响范围,即引入CFD软件(FLUENT)对某尾矿库溃决尾砂的流滑过程进行数值分析。结果表明,FLUENT能较好地模拟溃决尾砂的流动过程,解决了尾砂流滑大变形现场试验的高成本难题。当未采取任何防护措施时,该尾矿库溃坝水砂流会漫到居民区,对下游左侧民宅存在一定影响;溃决尾砂将冲击下游公路,存在中断交通的风险;携带大量尾矿废水的尾砂,对下游流域带来较大生态环境风险。研究成果可为进一步研究尾矿库溃坝防护措施提供参考。     

石灰窑喷射器的数值模拟

利用计算流体力学软件Fluent,根据不可压缩流体流动基本原理和流热固耦合有限体积方法,对石灰窑燃烧系统喷射器的工作特性进行了研究,得到了在不同结构和边界条件下喷射器的流场特性及工作特性,为优化设计喷射器结构及操作工况提供了理论参考。     

Unsaturated-Flow Simulation with Green Element Models

Flows in variably saturated media are of profound interest to numerical analysts, engineers, and scientists because of not only the challenge they pose as a result of their highly nonlinear constitutive relations but also their importance in many fields of engineering such as drainage, irrigation, hydrology, environmental, soil, and petroleum engineering. In this paper, the Picard and Newton-Raphson (N-R) algorithms are incorporated into the Green element method (GEM) to simulate these flows. The GEM offers a viable means of implementing the singular boundary integral theory so that the theory is more generally applicable and computationally efficient. Here GEM discretizes the integro-differential equation in space with suitable polygonal elements and in time with a difference scheme, and the system of nonlinear discretized element equations are linearized by the Picard and N-R algorithms. Calculations carried on three numerical examples of infiltration into unsaturated soils in two spatial dimensions indicate better convergence of the N-R algorithm than the Picard algorithm at comparable computational cost.     

中间包自由表面的数值模拟与物理模拟

应用计算机数值模拟研究了坝高、堰深、坝堰间距以及液面高度对中间包自由表面的影响,并通过水力学模拟验证数值计算结果的正确性。实验证明,计算机模拟的结果与水模实验结果基本相符,说明计算机模拟结果可以满足工程的需要。为优化设计中间包、减少卷渣的发生提供了有利的依据。     

1923 Gleno Dam Break: Case Study and Numerical Modeling

On the morning of December 1, 1923, the Gleno Dam (located in the Central Italian Alps) suddenly collapsed a few days after the first complete reservoir filling. Nearly 4.5×106??m3 of water was released. The consequent inundation caused significant destruction along the downstream valley and a death toll of at least 356 lives. This failure is the only historical case of dam break caused by structural deficiencies that has occurred in Italy. As a result, it has deeply influenced the evolution of Italian regulations regarding dam design and hydraulic risk evaluation. However, in spite of its relevance, this event has never been characterized from a hydraulic standpoint. This paper reports the main information obtained from the analysis of a vast amount of historical documents regarding the Gleno Dam break to set up a case study useful for validating dam-break models in mountain settings. Moreover, it presents the main results of one-dimensional (1D) modeling of the dam break wave propagation accomplished with a first-order finite volume numerical scheme recently proposed in the literature for field applications. The overall effectiveness and reliability of the model are evaluated for this case characterized by very irregular topography. Finally, the practical relevance of several choices that the numerical reconstruction of this kind of event demands is tested.     

Simulation of Temperature and Stress Fields during RCC Dam Construction

The worldwide experience in the construction of roller-compacted concrete (RCC) dams together with the use of numerical solutions, allows the simulation of different scenarios in a computer. It is well documented that thermal control is one of the most important problems for RCC dam construction. The dam temperature changes due to the heat produced by the internal hydration of concrete and the environmental boundary conditions influencing the elastic modulus and creep properties of concrete. The construction process was simulated to study how the temperature and stress change during dam construction. The numerical methodology considers the effect of temperature on the elastic modulus and the creep behavior of concrete. A 3D finite-element program was developed to simulate the construction process. An engineering application of this methodology is presented by simulating the construction of an RCC gravity dam in southern China. The results show how the temperature and stress change with the construction process. The results also show that it is feasible to build RCC dams in low temperature seasons without additional temperature control measures.