DEVELOPMENT OF COUPLED 1D-2D MATHEMATICAL MODELS FOR TIDAL RIVERS

Some coupled 1D-2D hydrodynamic and water quality models depicting tidal water bodies with complex topography were presented. For the coupled models, finite element method was used to solve the governing equations so as to study tidal rivers with complex topography. Since the 1D and 2D models were coupled, the principle of model coupling was proposed to account appropriately for the factors of water level, flow and pollutant flux and the related dynamical behavior was simulated. Specifically the models were used to probe quantitative pollution contribution of receiving water from neighboring Jiangsu and Zhejiang Provinces to the pollution in the Huangpu River passing through Shanghai City. Numerical examples indicated that the developed coupled 1D-2D models are applicable in tidal river network region of Shanghai.     

LARGE EDDY SIMULATION （LES） OF TURBULENT FLOW BY FINITE DIFFERENCE METHOD

A Large Eddy Simulation (LES) technique was applied to solve the turbulent channel flow for Rer = 150.Three types of turbulence models are employed, such as the Smagorinsky model, the Dynamic Sub-Grid Scale(SGS) model and the Generalized Normal Stress (GNS) model. The simulated data in time series for the LES were averaged in both time and space to carry out the statistical analysis. Results of LES were compared with that of a DNS. As an application, a LES technique was used for 2D body in order to check the validation by investigating the turbulent vortical motion around the afterbody with a slant angle.     

Quantitative comparison of semi- and fully-distributed hydrologic models in simulating flood hydrographs on a mountain watershed in southwest China

To investigate the performance of fully- and semi-distributed hydrologic models in simulating the process of transformation from rainfall to runoff in mountain areas, the fully-distributed models Basin Pollution Calculation Center （BPCC） and HEC- HMS are calibrated for the Zhenjiangguan watershed located in the upper stream of Minjiang River Southwest China using streamflow observations at the basin outlet. Semi-automatical optimization method is implemented to both models to improve simulated resuits by removing artificial errors. Based on the consistency of the simulated hydrographs with the observed ones, the statistical coefficients such as the relative error, the probability distribution and the correlation coefficient, are further introduced to evaluate quantitatively the performance of the two models. Analyses indicate that the hydrographs simulated by the BPCC are relatively closer to the observed ones than those simulated by the HEC-HMS in view of the spatial heterogeneity in terrain, soil texture, land cover and meteorological conditions in mountain areas.     

LARGE-EDDY AND DETACHED-EDDY SIMULATIONS OF THE SEPARATED FLOW AROUND A CIRCULAR CYLINDER

The separated turbulent flow around a circular cylinder is investigated using Large-Eddy Simulation (LES), Detached-Eddy Simulation (DES, or hybrid RANS/LES methods), and Unsteady Reynolds-Averaged Navier-Stokes (URANS). The purpose of this study is to examine some typical simulation approaches for the prediction of complex separated turbulent flow and to clarify the capability of applying these approaches to a typical case of the separated turbulent flow around a circular cylinder. Several turbulence models, i.e. dynamic Sub-grid Scale (SGS) model in LES, the DES-based Spalart-Allmaras (S-A) and k ? ω Shear-Stress-Transport (SST) models in DES, and the S-A and SST models in URANS, are used in the calculations. Some typical results, e.g., the mean pressure and drag coefficients, velocity profiles, Strouhal number, and Reynolds stresses, are obtained and compared with previous computational and experimental data. Based on our extensive calculations, we assess the capability and performance of these simulation approaches coupled with the relevant turbulence models to predict the separated turbulent flow.     

Revisit of advection-dispersion equation model with velocity-dependent dispersion in capturing tracer dynamics in single empty fractures

An accurate quantification of the contaminant transport through fractured media is critical for dealing with water-quality related scientific and engineering issues, where the dispersion coefficient is an important and elusive parameter for the solute transport modeling. Many previous studies show that the dispersion coefficient(D) in the standard advection-dispersion equation(ADE) model can be approximated by D=av~λ(where a is the dispersivity), a formula to be revisited systematically in this study by laboratory experiments and model analysis. First, a series of tracer transport experiments in single empty fractures are conducted in cases of different hydraulic gradients. Second, the tracer breakthrough curves are determined by simulations based on the ADE model, to obtain the dispersion coefficients corresponding to various fracture roughnesses and flow velocities. A varying trend of λ is analyzed under different flow conditions. Results show that although the standard ADE model cannot be used to characterize the late-time tailing of the tracer BTCs, likely due to the solute retention, this simple model can simulate most of the solute mass dynamics moving through fractures and may therefore provide information for estimating the dispersion in parsimonious models appropriate for the non-Fickian transport. The following three conclusions are drawn:(1) the peak of the breakthrough curves comes earlier with increasing the roughness, according to the ADE simulation,(2) the value of λ generally decreases as the relative roughness of the fracture increases,(3) the value of λ is approximately equal to 2.0 when the dispersion is dominated by the molecular diffusion in the smooth fracture.     

Entropy generation in bypass transitional boundary layer flows

The primary objective of this study is to evaluate the accuracy of using computational fluid dynamics(CFD) turbulence models to predict entropy generation rates in bypass transitional boundary layers flows under zero and adverse pressure gradients. Entropy generation rates in such flows are evaluated employing the commercial CFD software, ANSYS FLUENT. Various turbulence and transitional models are assessed by comparing their results with the direct numerical simulation(DNS) data and two recent CFD studies. A solution verification study is conducted on three systematically refined meshes. The factor of safety method is used to estimate the numerical error and grid uncertainties. Monotonic convergence is achieved for all simulations. The Reynolds number based on momentum thickness, Re_θ, skin-friction coefficient, fC, approximate entropy generation rates, S'', dissipation coefficient, dC, and the intermittency, γ, are calculated for bypass transition simulations. All Reynolds averaged Navier-Stokes(RANS) turbulence and transitional models show improvement over previous CFD results in predicting onset of transition. The transition SST k-ω 4 equation model shows closest agreement with DNS data for all flow conditions in this study due to a much finer grid and more accurate inlet boundary conditions. The other RANS models predict an early onset of transition and higher boundary layer entropy generation rates than the DNS shows.     

FVS SCHEME FOR SEVERE TRANSIENT FLOW IN PIPE NETWORKS

1.INTRODUCTIONWater hammer problems are i mportant aspectin the designs and operations of piping systeminpower plant.In pipe networks,the influences ofaccidental events such as power outage and controladjust ment generate sudden transient conditionsthat could make great damages.Hence it is neces-sary to develop the numerical models to si mulatewater hammer problems andsuddentransient flowsin complex pipe networks in order to get the diag-noses gist.Computerized water hammer models[1-5]are…     

NUMERICAL MODELLING OF BORES DUE TO DAM-BREAK

In this paper TVD explicit schemes developed recently in CFD are used to simulate five models of bores due todam-break. Numerical experiments are presented to demonstrate that they achieve high resolution and generate nospurious oscillations and to show the versatility of the schemes.     

NUMERICAL SIMULATION OF 2D HORIZONTAL COOLING WATER DISCHARGE IN GENERALIZED CURVILINEAR COORDINATE

1. INTRODUCTIONResearch on the movement characteristics ofcooling water is a hot spot presently , which hasgreat significance to maintain the balance of eco-logical system. Mathematical models and physicalmodels are major means for this study .In recentyears , Chen[1 ,2]has presentsed a 2D horizontalmathematical model based on the hybrid methodand finite element mesh, Zhang[3]has provided afinite layer model for 2D thermal density flowinopen channel . Wu[4]has developped an unsteady2D h…     

Application of TOPMODEL in Buliu River Basin and comparison with Xin'anjiang model

Along with the rapid development of computer and GIS technology, hydrological models have progressed from lumped to distributed models. TOPMODEL, a bridge between lumped and distributed models, is a semi-distributed model in which the predominant factors determining the formation of runoff are derived from the topography of the basin. A test application of TOPMODEL in the Buliu River Basin is presented. For the sake of comprehensively evaluating the TOPMODEL, the Xin’anjiang model, a classic lumped hydrological model, was also applied in the basin. The structural differences and the simulation results of the two models are compared and analyzed.     

一维河网非恒定流及悬沙数学模型的节点控制方法

本文的一维河网非恒定流及悬沙数学模型，是根据以一维圣维南方程组，悬沙非平衡输运方程及水位、含沙量节点控制法而建立。首先，利用单一河流有限差分方程组转换形式和节点处质量、能量守恒性，写出所有节点的水位控制方程组。求解此不规则稀疏矩阵方程组得到得有节点的水位，再由单一河流非恒定流的求解方法可获得所有单一河流的断面水位和流量。基于水注的节点水位控制法，本文提出了节点悬沙控制法。假设节点处冲刷或淤积较小，所有节点的含沙量控制方程组可通过输沙量守恒方程用矩阵形式写出。求解此不规则稀疏矩阵方程组，得到所有节点处的含沙量。所有单一河流断面处的含沙量通过单一河流悬沙输运的求解方法获得。本文介绍的模型适用于各种河网类型。作为检验，该模型成功地应用于珠江三角洲流域河网水流及悬沙的数值计算。     

Experimental study on the bed topography evolution in alluvial meandering rivers with various sinuousnesses

The bed morphology in alluvial meandering rivers is composed of both alternatively distributed free bars and curvature related point bars. To study the influence of channel sinuousness on the flow and sediment transport, and consequently the bed morphology in meandering rivers, experiments were carried out in a series of curved channels with erodible bed fixed side walls. Measurements on the surface flow field, bed topography evolution and sediment transport rate were performed. Experimental results show a high velocity area near convex bank at a streamwise position a little bit upstream of the apex and the increasing in sinuousness of channel tends to increase the cross-sectional variation of flow velocity at the apex of bends. Point bars and pools appear in the channel bends in all experimental runs the bedform has an obvious tendency of downstream migration as a whole. The quasi-equilibrium bedform in the channel bends are dominated by two independent factors: the influence of curvature and the influence of flow-bed instability inside the channel. The increasing of flow rate leads to a faster development of bars and pools, as well as faster downstream migration of the entire bedform. The increase of sinuousness in channel bends leads to the increase of both the spatial and the temporal fluctuation of bedforms. Bedload is dominant in the sediment transport and the sediment transport rate tends to increase with the increasing of the inlet flow rate but decrease with the increasing of the channel sinuousness. Computational results on the bed topography in river bends was also presented based on empirical models, showing that the highly sinuous channels have more uncertainty in bed morphology and more difficult to be predicted with mathematical models when compared with slightly sinuous channel bends. The coupled interaction of point bars, mid-channel bars, alternative bars and even sand ripples are thought to complicate the mechanism and make the bed morphology difficult to predict. The experiment results can be useful for further theoretical study on the dynamics of river meanders with water depth-width ratio as small as 1/10 to 1/20 and bedload dominated sediment transport.     

明渠水流泥沙运动水深平均及力矩方程的理论和验证

首次提出了水流泥沙运动水深平均及其力矩方程的概念 ,并从理论上推导出这套方程组。提出水流泥沙运动力矩方程的目的有两个 ,一是在不增加空间维数的情况下可以有效地恢复水流泥沙因子沿水深分布信息 ,克服目前普遍使用的水深平均方程过多地忽略沿水深分布信息的缺点 ;二是增强模型的模拟能力。针对这两个目的是否能真正得到体现 ,分别从理论和实验室资料两个方面对新推导的力矩方程进行了全面的检验。理论验证结果表明 ,一维的力矩方程除了能模拟水深平均的流速和含沙量 ,还能够较好地模拟水流泥沙因子沿水深分布信息 ,这充分说明了一维力矩方程的二维特性。为了检验力矩方程的模拟能力 ,特别选取了一些极端的水流泥沙运动实验 ,如清水冲刷、点源加沙和深槽回淤等。模拟结果表明 ,力矩方程对于这些极端的水沙运动具有较好的模拟能力     

有浮泥水域的平面二维泥沙数学模型研究

近底泥沙存在底沙和悬沙的频繁交换,数学模型难以精确模拟,浮泥的发育更使近底泥沙边界条件趋于复杂,一个有效的平面二维泥沙数学模型需要正确处理挟沙力、起动流速、泥沙沉速等泥沙参数,本文应用罗肇森对浮泥研究得到的理论和经验公式,成功模拟了椒江口和灵江河段的潮流运动及水体含沙量分布特征,合理预测了水下地形的冲淤变化特点,对有浮泥发育的河口及近海水沙模拟研究作了有益的探索。     

Simulation of Runoff and Suspended Sediment Transport Rate in a Basin with Multiple Watersheds

Accurate runoff and suspended sediment transport rate models are critical for watershed management. In this study, a physiographic soil erosion–deposition (PSED) model is used in conjunction with GIS, to simulate the runoff and sediment transport process during storm events in a multi-watershed basin. This PSED model is verified using three typhoon events and 33 storm events in Cho-Shui River Basin, located in central Taiwan. Cho-Shui River Basin has 11 sub-watersheds displaying a variety of hydrologic and physiographic conditions as well as high concentrations of suspended sediment in river flow and a steep average channel bed slope of 2%. The results show the capability, applicability, and accuracy of the PSED model for multi-watershed basins.     

长江口全沙数学模型研究

在正交坐标系下，建立了能较好拟合长江口边界的平面二维潮流和全沙数学模型。应用１９９６年洪、枯两季大、中、小潮水文泥沙资料和１９９５年、１９９６年地形及８３１０和８６１５台风暴潮引起的南北槽淤积资料，对长江口的潮位、流速、流向、含沙量特别是南北槽的地形变化和航道回淤进行了验证，结果表明该全沙数学模型较好地复演了长江口流场、含沙量场和地形变化。     

长江河口南槽近期滩槽水沙输移特性分析

为了深刻认识近期长江河口演变趋势,依据2005,2006年和2010年长江口南槽滩槽洪枯季实测水文泥沙数据,分析了主槽与浅滩的水动力条件及悬沙浓度的时空分布特征。利用机制分解法,研究了河口滩槽间泥沙输移及交换机制。研究结果表明,长江口南槽主要以往复流为主,落潮流速大于涨潮流速。随着水深变浅,水流流速过程线存在差异,使不同区域的水流挟沙能力和输沙过程不同。输沙以平流项输沙通量为主,但潮泵作用在南槽地区泥沙输移中也占有重要地位,形成"主槽出沙、浅水进沙"的输沙模式,促使南汇边滩前缘缓慢淤涨。     

A VERTICAL 2-D NUMERICAL SIMULATION OF SUSPENDED SEDIMENT TRANSPORT

Numerical simulation of sediment transport and bed evolution has become an important technique in the sediment research. In this article,a numerical model of suspended sediment transport was proposed,which was established in the vertical σ coordinate for fitting the free surface and bottom. In the research of the sediment transport,the predominant factors were found to be the eddy diffusion,the settling velocity,the bed condition and so on. By the aid of the model in the article,the contribution of the Rouse parameter to the vertical profile of sediment concentration was clarified,which was identical to the theoretical results. In the comparison of the numerical results with laboratory data,the agreement between experimental data and numerical results was reached except for some data. And the possible reasons for the disagreement were discussed.     

Investigating a Suitable Empirical Model and Performing Regional Analysis for the Suspended Sediment Load Prediction in Major Rivers of the Aegean Region,Turkey

This study investigates the appropriateness of four major empirical methods [Lane and Kalinske, Einstein, Brooks, Chang—Simons—Richardson] for predicting suspended sediment loads (SSLs) in three major rivers in the Aegean Region, Turkey. The measured data from 1975 to 2005 were used to test performance of the models. It was found that Brooks method was more appropriate, among the others, for predicting suspended sediment loads from each river. The prediction results of Brooks method were further improved by the use of genetic algorithm (GA_Brooks) optimizing a fitting parameter and showing a comparable performance to those of artificial neural networks (ANNs) and neuro-fuzzy (ANFIS) models for the same rivers. GA_Brooks, ANNs, and ANFIS models can be used for predicting loads at a regional scale. The sensitivity analysis results revealed that suspended and bed material particle diameters affect suspended sediment loads significantly.     

黄河下游河槽泥沙扬动与输移特性

本文利用大量水文资料,在前人研究的基础上,分析研究了黄河下游河槽泥沙扬动与输移特性。首先根据水文测验尤其是泥沙级配实测资料,间接分析各家公式的合理性,从而选择出物理概念清晰、符合黄河下游实际的扬动流速计算公式。对于粒径较小的泥沙,沙玉清、窦国仁等现有扬动流速计算公式都适用于黄河;随着泥沙粒径增加,几家公式差异变大,张罗号和罗诗琦公式同实测资料更为符合。在此基础上分析了黄河下游河槽不同粒径泥沙的扬动特性,认为“粗颗粒”泥沙在黄河下游河槽中水流量下亦能扬动。然后,选取黄河下游花园口、高村和利津站为下游代表水文站,采用汛期非漫滩情况下的实测数据,分别绘制了三站流量与泥沙以悬移形式运动的百分比关系图。引入扬动临界流量的概念后,各站泥沙输移特性变化规律基本遵循统一表达形式。进一步定量分析了各水文站泥沙输移特性,给出了扬动临界流量、扬动概率系数、输沙指数同泥沙粒径等因子的关系式,从而建立了泥沙以悬移形式运动的百分比与水沙因子的计算公式。结合未来30年内年均沙量减小的预测结果进行计算,表明黄河下游汛期日平均流量只要大于971 m³s,悬移质泥沙组成中的粗颗粒能保持悬移运动状态,同时表明加大流量是直接提升水流输沙能力的有效手段。