Water level updating model for flow calculation of river networks简

Complex water movement and insufficient observation stations are the unfavorable factors in improving the accuracy of flow calculation of river networks. A water level updating model for river networks was set up based on a three-step method at key nodes, and model correction values were collected from gauge stations. To improve the accuracy of water level and discharge forecasts for the entire network, the discrete coefficients of the Saint-Venant equations for river sections were regarded as the media carrying the correction values from observation locations to other cross-sections of the river network system. To examine the applicability, the updating model was applied to flow calculation of an ideal river network and the Chengtong section of the Yangtze River. Comparison of the forecast results with the observed data demonstrates that this updating model can improve the forecast accuracy in both ideal and real river networks.     

A hybrid DEM/CFD approach for solid-liquid flows简

A hybrid scheme coupling the discrete element method(DEM)with the computational fluid dynamics(CFD)is developed to model solid-liquid flows.Instead of solving the pressure Poisson equation,we use the compressible volume-averaged continuity and momentum equations with an isothermal stiff equation of state for the liquid phase in our CFD scheme.The motion of the solid phase is obtained by using the DEM,in which the particle-particle and particle-wall interactions are modelled by using the theoretical contact mechanics.The two phases are coupled through the Newton’s third law of motion.To verify the proposed method,the sedimentation of a single spherical particle is simulated in water,and the results are compared with experimental results reported in the literature.In addition,the drafting,kissing,and tumbling(DKT)phenomenon between two particles in a liquid is modelled and reasonable results are obtained.Finally,the numerical simulation of the density-driven segregation of a binary particulate suspension involving 10 000 particles in a closed container is conducted to show that the presented method is potentially powerful to simulate real particulate flows with large number of moving particles.     

A time fractional model to represent rainfall process简

This paper deals with a stochastic representation of the rainfall process.The analysis of a rainfall time series shows that cumulative representation of a rainfall time series can be modeled as a non-Gaussian random walk with a log-normal jump distribution and a time-waiting distribution following a tempered α-stable probability law.Based on the random walk model,a fractional Fokker-Planck equation(FFPE) with tempered α-stable waiting times was obtained.Through the comparison of observed data and simulated results from the random walk model and FFPE model with tempered α-stable waiting times,it can be concluded that the behavior of the rainfall process is globally reproduced,and the FFPE model with tempered α-stable waiting times is more efficient in reproducing the observed behavior.     

Numerical simulation of hull/propeller interaction of submarine in submergence and near surface conditions简

Hull/propeller interaction is of great importance for powering performance prediction. The features of hull/propeller interaction of a submarine model with a high-skew five blade propeller in submergence and near surface conditions are numerically simulated. The effect of propeller rotation is simulated by the sliding mesh technique. Free surface is captured by the volume of fluid （VOF） method. Computed results including resistance, thrust, torque and self-propulsion factor are compared with experimental data. It shows fairly good agreement. The resistance and wave pattern of the model at different depths of submergence are computed. And the thrust, torque and self-propulsion factor of the model in submergence and near surface condition are compared to analyze the effect of free surface on self-propulsion performance. The results indicate that free surface has more influence on resistance than that on self-propulsion factors.     

Simulation of buoyancy-induced turbulent flow from a hot horizontal jet简

Experimental visualizations and numerical simulations of a horizontal hot water jet entering cold water into a rectangular storage tank are described. Three different temperature differences and their corresponding Reynolds numbers are considered. Both experimental visualization and numerical computations are carried out for the same flow and thermal conditions. The realizable k-e model is used for modeling the turbulent flow while the buoyancy is modeled using the Boussinesq approximation. Polynomial approximations of the water properties are used to compare with the Boussinesq approximation. Numerical solutions are obtained for unsteady flow while pressure, velocity, temperature and turbulence distributions inside the water tank as well as the Froude number are analyzed. The experimental visualizations are performed at intervals of five seconds for all different cases. The simulated results are compared with the visualized results, and both of them show the stratification phenomena and buoyancy force effects due to temperature difference and density variation. After certain times, depending on the case condition, the flow tends to reach a steady state.     

基于GoogleEarth的分蓄洪区水沙模拟与演示系统研究简

 基于Google Earth软件平台,建立了分蓄洪区平面二维水沙演进模拟系统。系统采用数字高程模型(DEM)地形数据插值技术,能快速、简单地完成模型的数据处理;模型采用非结构网格的有限体积算法,能进行快速计算并保持水量和动量的守恒;后处理基于Google Earth软件平台,能实现计算成果在三维虚拟场景中的动态演示。模型系统在荆江分洪区得到成功运用,能适应紧急情况下的快速计算,可为分蓄洪区防洪决策与抢险提供参考。     

An ocean circulation model based on Eulerian forward-backward difference scheme and three-dimensional,primitive equations and its application in regional simulations简

A two-time-level, three-dimensional numerical ocean circulation model is established with a two-level, single-step Eulerian time-difference scheme. The mathematical model of the large-scale oceanic motions is based on the terrain-following coo-rdinated, Boussinesq, Reynolds-averaged primitive equations of ocean dynamics. A simple but very practical Eulerian forward-back-ward method is adopted to replace the most preferred leapfrog scheme as the time-difference method for both barotropic and barocli-nic modes. The forward-backward method is of the second order of accuracy, requires only once of the function evaluation per time step, and is free of the computational mode inherent in the three-level schemes. It is superior in many respects to the original leapfrog and Asselin-filtered leapfrog schemes in the practical use. The performance of the newly-built circulation model is tested by simula-ting a barotropic （tides in marginal seas of China） and a baroclinic phenomenon （seasonal evolution of the Yellow Sea Cold Water Mass）, respectively. The three-year time histories of four prognostic variables obtained by the POM model and the two-time-level model are compared in a regional simulation experiment for the northwest Pacific to further show the reliability of the two-level scheme circulation model.     

Numerical prediction of hydrodynamic forces on a ship passing through a lock with different configurations简

A CFD method is used to numerically predict the hydrodynamic forces and moments acting on a ship passing through a lock with a constant speed. By solving the RANS equations in combination with the RNG k-e turbulence model, the unsteady viscous flow around the ship is simulated and the hydrodynamic forces and moments acting on the ship are calculated. UDF is com-piled to define the ship motion. Meanwhile, grid regeneration is dealt with by using the dynamic mesh method and sliding interface technique. Under the assumption of low ship speed, the effects of free surface elevation are neglected in the numerical simulation. A bulk carrier ship model is taken as an example for the numerical study. The numerical results are presented and compared with the available experimental results. By analyzing the numerical results obtained for locks with different configurations, the influences of approach wall configuration, lock configuration symmetry and lock chamber breadth on the hydrodynamic forces and moments are demonstrated. The numerical method applied in this paper can qualitatively predict the ship-lock hydrodynamic interaction and pro-vide certain guidance on lock design.     

Water flooding optimization with adjoint model under control constraints简

The oil recovery enhancement is a major technical issue in the development of oil and gas fields. The smart oil field is an effective way to deal with the issue. It can achieve the maximum profits in the oil production at a minimum cost, and represents the future direction of oil fields. This paper discusses the core of the smart field theory, mainly the real-time optimization method of the injection-production rate of water-oil wells in a complex oil-gas filtration system. Computing speed is considered as the primary prerequisite because this research depends very much on reservoir numerical simulations and each simulation may take several hours or even days. An adjoint gradient method of the maximum theory is chosen for the solution of the optimal control variables. Conven-tional solving method of the maximum principle requires two solutions of time series： the forward reservoir simulation and the backward adjoint gradient calculation. In this paper, the two processes are combined together and a fully implicit reservoir simulator is developed. The matrixes of the adjoint equation are directly obtained from the fully implicit reservoir simulation, which accelera-tes the optimization solution and enhances the efficiency of the solving model. Meanwhile, a gradient projection algorithm combined with the maximum theory is used to constrain the parameters in the oil field development, which make it possible for the method to be applied to the water flooding optimization in a real oil field. The above theory is tested in several reservoir cases and it is shown that a better development effect of the oil field can be achieved.     

壅水条件下推移质泥沙输沙率变化规律初步研究简

 壅水条件下水流结构特征及推移质泥沙输移规律问题目前尚未得到很好的解决,如天然壅水河段、水库库区壅水等条件下的泥沙输移、河床冲淤等问题,亟需这方面的理论支撑。利用理论分析、实测资料、水槽试验等方法进行对比分析首先分析不同条件下推移质输沙率变化的差异性;然后利用水槽试验观测壅水条件下非均匀流水流结构特征;最后结合天然实测资料和水槽试验资料,回归分析得出了适合在水库库区壅水河道的推移质输沙率计算公式。研究结果为当壅水程度指标β达到1.3以上时,现有各家公式已基本不能用来计算壅水条件下的推移质输沙率;利用水槽试验资料得到了相对床面切应力与壅水程度指标β的定量关系;回归分析得出壅水河道推移质输沙率计算公式可以在三峡库区河段适用。     

THE MACCORMACK SCHEME AND THE BOUNDARY-FITTED COORDINATE SYSTEM FOR NUMERICAL SIMULATION OF SUPER CRITICAL FREE SURFACE FLOWS

1. INTRODUCTIONOpen channels carrying supercritical flows are commonly used in hydraulic engineering. Man-made structures such as spillway chutes, conveyance channels, sewer systems, and outlet works are some typical examples. Similarly, supercritical flo…     

NUMERICAL SIMULATION OF 2-D TIDAL FLOW AND WATER QUALITY UNDER THE CURVILINEAR COORDINATES

This paper presents a numerical method to simulate the 2-D tidal flow and water quality under the curvilinear coordinates. In order to overcome the computational difficulties in natural rivers, such as the complicated boundary figures, the great disparity between length and width of computational domain, etc. , boundary-fitted grid is used, the irregular domain in physical plane is transformed into a rectangular domain in transformed plane, and the depth-averaged momentum equations and mass equation are rewritten and discretized based on the finite volume techniques in curvilinear coordinates. Practical application of the method is illustrated by an example for the Dachangzhen Section of the Yangtze River. A fair agreement between the values measured and computed demonstrates the validity of the method developed.     

NUMERICAL SIMULATION FOR EARLY DEVELOPMENT OF WAKE VORTICES BEHIND A SEMICIRCULAR-SECTION CYLINDER

o.INThoDUCTIONThenumericlmodellingoffluidflowproblemswithwakesisveryimportantinhydrthdynamicsandaeredynamics.Thefiniteelementmethod,withtheflexibilityofavariablemesh,issuperiortothefinitedifferencemethodinsolvingtheseproblems.However,thefi-nitedifferencemethedismuchlesscomplicatedthanthefiniteelementmethodatleastinre-spectofcomputerprogramming.Theboundary-fittedcoordinatesystem,whichhasboththeadvantagesofthegeometricflexibilityofthefiniteelementmethedandthesimplicityofthefinitedifferenceme…     

闸下有压渗流的边界拟合坐标变换数值解

建立了曲线拟合坐标系下闸下渗流的数学模型 ,给出了边界条件和求解方程。计算实例表明 ,该数学模型对水利工程中的复杂边界渗流的数值求解很有效 ,可应用于工程实际     

田市抽水站进水前池水力特性数值模拟

借鉴有关弯道水流流速分布的研究成果,计入弯道环流引起的横向动量交换,对曲线坐标系平面二维浅水方程做了修正;采用边界处正交的曲线网格生成技术,处理复杂的计算区域边界。采用修正后的模型对田市抽水站进水前池改造前后的水流流态作模拟分析,来验证改造设计方案的合理性。     

NUMERICAL SOLUTION OF 2D FLOW USING A LOCAL COORDINATE SYSTEM

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天然分汊河流的平面二维数值模拟

利用边界拟合坐标变换系统下的计算区域分解－组合处理技术、支流耦合迭代计算方法、支流迭合对接型坐标变换网格与非对接型流网正交坐标系统等新思想建立了适应很复杂河道情况与水力条件的平面二维天然分汉河流的流场与浓度场的数学模型．并通过计算实例验证了模型在工程中应用的可靠性与有效性．     

基于MacCormack格式的变网格瞬变流模拟

输水工程中的水锤现象是设计和运行部门极为关注的问题,数值模拟是管路系统中水锤压力预测和控制的重要环节。为了对变特性管路系统的水锤进行数值模拟,建立了基于MacCormack格式的变空间步长的水锤计算模型(V-MCS)。通过与经典的Method of Characteristics(MOC)方法及固定步长的MacCormack(MTMS)方法模拟结果的对比,对V-MCS方法进行了验证。采用V-MCS方法模拟了变特性管路系统中的水锤过程,获得了管道压力与流量波动过程以及全线极值压力分布情况。结果表明,在变特性管路系统中,V-MCS方法可以有效地对复杂管路水锤现象进行模拟。该方法在空间网格划分上更为灵活,可根据计算需求对管道各个区域选取不等的空间步长,能在一定程度上减少计算断面数量,在不改变管路固有波速的情况下可实现对复杂管路系统的同步水锤模拟。     

NUMERICAL MODELLING OF NATURAL RIVER NETWORK

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