Water Science and Engineering - 开云电竞网

Impact assessment of climate change and human activities on annual highest water level of Taihu Lake

Qing-fang HU, Yin-tang WANG — 2009-03-30

Qing-fang HU, Yin-tang WANG The annual highest water level of Taihu Lake (Z_m) is very significant for flood management in the Taihu Basin. This paper first describes the inter-annual and intra-annual traits of Z_m from 1956 to 2000. Then, using the Mann-Kenall (MK) and Spearman (SP) nonparametric tests, the long-term change trends of area precipitation and pan evaporation in the Taihu Basin are determined. Meanwhile, using the Morlet wavelet transformation, the fluctuation patterns and change points of precipitation and pan evaporation are analyzed. Also, human activities in the Taihu Basin are described, including land use change and hydraulic project construction. Finally, the relationship between Z_m, the water level of Taihu Lake 30 days prior to the day of Z_m (Z₀), and the 30-day total precipitation and pan evaporation prior to the day of Z_m (P and E₀, respectively) is described based on multi-linear regression equations. The relative influence of climate change and human activities on the change of Z_m is quantitatively ascertained. The results demonstrate that: (1) Z_m was distinctly higher during the 1980-2000 period than during the 1956-1979 period, and the 30 days prior to the day of Z_m are the key phase influencing Z_m every year; (2) P increased significantly at a confidence level of 95% during the 1956-2000 period, while the reverse was true for E₀; (3) The relationship between Z_m, P and E₀ distinctly changed after 1980; (4) Climate change and human activities together caused frequent occurrences of high Z_m after 1980; (5) Climate change caused a substantially greater Z_m difference between the 1956-1979 and 1980-2000 periods than human activities. Climate change, as represented by P and E₀, was the dominant factor raising Z_m, with a relative influence ratio of 83.6%, while human activities had a smaller influence ratio of 16.4%. Water Science and Engineering. 2009 2(1): 1-15 .

Eutrophication model for river-type reservoir tributaries and its applications

Ling-ling WANG, Zhen-zhen YU, Hui-chao DAI, Qing-hua CAI — 2009-03-30

Ling-ling WANG, Zhen-zhen YU, Hui-chao DAI, Qing-hua CAI With the impoundment of the Three Gorges Reservoir, algal blooms have been found in some tributaries. In this study, according to the theoretical analysis of the eutrophication mechanism in a river-type reservoir tributary, a one-dimensional eutrophication model was developed for the Xiangxi River tributary of the Three Gorges Reservoir, and the influence of hydrodynamic conditions on the primary growth rate of algae was investigated. Furthermore, numerical predictions of hydraulic variables and eutrophication factors, such as the concentration distribution of TP, TN, and Chl-a in the spatial and temporal domains, were carried out. Comparison of computation results of TP, TN, and Chl-a concentrations along the river in the spring of 2005 with experimental data demonstrates the validity of the model. The agreement between the computation results and the experimental data of TP and TN concentrations is better than the agreement between those of Chl-a concentration. The simulated results also show that the Chl-a concentration downstream is much higher than that in the upstream tributary, which potentially indicates the outbreak of algae in this area. Therefore, this study provides a feasible method of accurately predicting the state of eutrophication in river-type reservoirs and their tributaries Water Science and Engineering. 2009 2(1): 16-24 .

Tide forecasting method based on dynamic weight distribution for operational evaluation

Shao-wei QIU, Zeng-chuan DONG, Fen XU, Li SUN, Sheng CHEN — 2009-03-30

Shao-wei QIU, Zeng-chuan DONG, Fen XU, Li SUN, Sheng CHEN Through analysis of operational evaluation factors for tide forecasting, the relationship between the evaluation factors and the weights of forecasters was examined. A tide forecasting method based on dynamic weight distribution for operational evaluation was developed, and multiple-forecaster synchronous forecasting was realized while avoiding the instability cased by only one forecaster. Weights were distributed to the forecasters according to each one’s forecast precision. An evaluation criterion for the professional level of the forecasters was also built. The eligibility rates of forecast results demonstrate the skill of the forecasters and the stability of their forecasts. With the developed tide forecasting method, the precision and reasonableness of tide forecasting are improved. The application of the present method to tide forecasting at the Huangpu Park tidal station demonstrates the validity of the method. Water Science and Engineering. 2009 2(1): 25-31 .

General displacement arch-cantilever element method for stress analysis of arch dam

Hao REN, Tong-chun LI, Zhi-wei NIU, Lan-hao ZHAO — 2009-03-30

Hao REN, Tong-chun LI, Zhi-wei NIU, Lan-hao ZHAO Based on the general displacement method and the basic hypothesis of the trial load method, a new advanced trial load method, the general displacement arch-cantilever element method, was proposed to derive the transformation relation of displacements and loads between the surface nodes and middle plane nodes. This method considers the nodes on upstream and downstream surfaces of the arch dam to be exit nodes (master nodes), and the middle plane nodes to be slave nodes. According to the derived displacement and load transformation matrices, the equilibrium equation treating the displacement of middle plane nodes as a basic unknown variable is transformed into one that treats the displacement of upstream and downstream nodes as a basic unknown variable. Because the surface nodes have only three degrees of freedom (DOF), this method can be directly coupled with the finite element method (FEM), which is used for foundation simulation to analyze the stress of the arch dam with consideration of dam-foundation interaction. Moreover, using the FEM, the nodal load of the arch dam can be easily obtained. Case studies of a typical cylindrical arch dam and the Wudongde arch dam demonstrate the robustness and feasibility of the proposed method. Water Science and Engineering. 2009 2(1): 32-42 .

Reservoir water effects on earthquake performance evaluation of Torul Concrete-Faced Rockfill Dam

Alemdar BAYRAKTAR, Murat Emre KARTAL, Hasan Basri BASAGA — 2009-03-30

Alemdar BAYRAKTAR, Murat Emre KARTAL, Hasan Basri BASAGA This study presents earthquake performance analysis of the Torul Concrete-Faced Rockfill (CFR) Dam with two-dimensional dam-soil and dam-soil-reservoir finite element models. The Lagrangian approach was used with fluid elements to model impounded water. The interface elements were used to simulate the slippage between the concrete face slab and the rockfill. The horizontal component of the 1992 Erzincan earthquake, with a peak ground acceleration of 0.515g, was considered in time-history analysis. The Drucker-Prager model was preferred in nonlinear analysis of the concrete slab, rockfill and foundation soil. The maximum principal stresses and the maximum displacements in two opposite directions were compared by the height of the concrete slab according to linear time-history analysis to reveal the effect of reservoir water. The changes of critical displacements and principal stresses with time are also shown in this paper. According to linear and nonlinear time-history analysis, the effect of the reservoir water on the earthquake performance of the Torul CFR Dam was investigated and the possible damage situation was examined. The results show that the hydrodynamic pressure of reservoir water leads to an increase in the maximum displacements and principal stresses of the dam and reduces the earthquake performance of the dam. Although the linear time-history analysis demonstrates that the earthquake causes a momentous damage to the concrete slab of the Torul CFR Dam, the nonlinear time-history analysis shows that no evident damage occurs in either reservoir case Water Science and Engineering. 2009 2(1): 43-57 .

Three-dimensional stochastic seepage field for embankment engineering

Ya-jun WANG, Wo-hua ZHANG, Chang-yu WU, Da-chun REN — 2009-03-30

Ya-jun WANG, Wo-hua ZHANG, Chang-yu WU, Da-chun REN Owing to the complexity of geo-engineering seepage problems influenced by different random factors, three-dimensional simulation and analysis of the stochastic seepage field plays an important role in engineering applications. A three-dimensional anisotropic heterogeneous steady random seepage model was developed on the basis of the finite element method. A statistical analysis of the distribution characteristics of soil parameters sampled from the main embankment of the Yangtze River in the Southern Jingzhou zone of China was conducted. The Kolomogorov-Smirnov test verified the statistical hypothesis that the permeability coefficient tensor has a Gaussian distribution. With the help of numerical analysis of the stochastic seepage field using the developed model, various statistical and random characteristics of the stochastic seepage field of the main embankment of the Yangtze River in the Southern Jingzhou zone of China were investigated. The model was also examined with statistical testing. Through the introduction of random variation of the upstream and downstream water levels into the model, the effects of the boundary randomness due to variation of the downstream and upstream water levels on the variation of simulated results presented with a vector series of the random seepage field were analyzed. Furthermore, the combined influence of the variation of the soil permeability coefficient and such seepage resistance measures as the cut-off wall and relief ditch on the hydraulic head distribution was analyzed and compared with the results obtained by determinate analysis. Meanwhile, sensitivities of the hydraulic gradient and downstream exit height to the variation of boundary water level were studied. The validity of the simulated results was verified by stochastic testing and measured data. The developed model provides more detail and a full stochastic algorithm to characterize and analyze three-dimensional stochastic seepage field problems Water Science and Engineering. 2009 2(1): 58-73 .

Numerical simulation of transient flow in horizontal drainage systems

Ze-yu MAO, Han XIAO, Ying LIU, Ying-jun HU — 2009-03-30

Ze-yu MAO, Han XIAO, Ying LIU, Ying-jun HU A numerical simulation model based on the characteristic-based finite-difference method with a time-line interpolation scheme was developed for predicting transient free surface flow in horizontal drainage systems. The fundamental accuracy of the numerical model was first clarified by comparison with the experimental results for a single drainage pipe. Boundary conditions for junctions and bends, which are often encountered in drainage systems, were studied both experimentally and numerically. The numerical model was applied to an actual drainage system. Comparison with a full-scale model experiment indicates that the model can be used to accurately predict flow characteristics in actual drainage networks Water Science and Engineering. 2009 2(1): 74-85 .

Vibration analysis of large bulb tubular pump house under pressure pulsations

Xin WANG, Tong-chun LI, Lan-hao ZHAO — 2009-03-30

Xin WANG, Tong-chun LI, Lan-hao ZHAO A 3D finite element model of the Huaiyin third pumping station of the Eastern Route of the South-to-North Water Transfer is described in this paper. Two methods were used in the calculation and vibration analysis of the pumping station in both the time domain and the frequency domain. The pressure pulsation field of the whole flow passage was structured on the basis of pressure pulsations recorded at some locations of the physical model test. Dynamic time-history analysis of the pump house under pressure pulsations was carried out. At the same time, according to spectrum characteristics of the pressure pulsations at measuring points and results of free vibration characteristics analysis of the pump house, the spectrum analysis method of random vibration was used to calculate dynamic responses of the pump house. Results from both methods are consistent, which indicates that they are both reasonable. The results can be used for reference in anti-vibration safety evaluation of the Huaiyin third pumping station. Water Science and Engineering. 2009 2(1): 86-94 .

Modeling in SolidWorks and analysis of temperature and thermal stress during construction of intake tower

Hong-yang ZHANG, Tong-chun LI, Zong-kun LI — 2009-03-30

Hong-yang ZHANG, Tong-chun LI, Zong-kun LI With a focus on the intake tower of the Yanshan Reservoir, this paper discusses the method of modeling in the 3D CAD software SolidWorks and the interface processing between SolidWorks and the ANSYS code, which decreases the difficulty in modeling complicated models in ANSYS. In view of the function of the birth-death element and secondary development with APDL (ANSYS parametric design language), a simulation analysis of the temperature field and thermal stress during the construction period of the intake tower was conveniently conducted. The results show that the temperature rise is about 29.934 ℃ over 3 or 4 days. The temperature differences between any two points are less than 24 ℃. The thermal stress increases with the temperature difference and reaches its maximum of 1.68 MPa at the interface between two concrete layers. Water Science and Engineering. 2009 2(1): 95-102 .

Effect of electroosmotic flow on brine imbibition in porous media

Rui WANG, Xiang-an YUE, Xu WEI, Wei ZHANG — 2009-03-30

Rui WANG, Xiang-an YUE, Xu WEI, Wei ZHANG Based on Darcy’s Law and the Helmholta-Smoluchowski equation, an imbibition velocity formula for the water phase with an electric field was deduced, showing that the imbibition velocity with an electric field is to various extents not only related to the rock permeability and characteristic length, the fluid viscosity, the oil-water interface tension and the gravity of the imbibing brine, but also to the fluid dielectric permittivity, zeta potential, applied electric field direction, and strength. Imbibition experiments with electric fields that are different in direction and strength were conducted, showing that application of a positive electric field enhances the imbibition velocity and increases the imbibition recovery ratio, while application of a negative electric field reduces the imbibition velocity and decreases the imbibition recovery ratio. The imbibition recovery ratio with a positive electric field increases with the strength of the electric field, and the imbibition recovery ratio with a negative electric field is lower than that without an electric field. Water Science and Engineering. 2009 2(1): 103-111 .

Spatial variation of reference crop evapotranspiration on Tibetan Plateau

Yong-hong YANG, Zhan-yu ZHANG, Xin-yi XIANG — 2009-03-30

Yong-hong YANG, Zhan-yu ZHANG, Xin-yi XIANG This study is based on meteorological observation data collected at 38 weather stations on the Tibetan Plateau over several decades. Daily reference crop evapotranspiration (ET₀) was calculated with the FAO-56 standard Penman-Monteith formula. A test of normality was performed with Statistica 6.0 software, isotropic and anisotropic semi-variogram analysis was conducted with the GS+ (geostatistics for the environmental sciences) system for Windows 7.0, and the characteristics of spatial variation of daily ET₀ were obtained. The following results can be obtained: Daily ET₀ for different periods on the Tibetan Plateau are distributed normally; Except for daily ET₀ in the E-W (east-west) direction in the summer, which showed a slight negative correlation with distance change, the Moran’s indexes of daily ET₀ for different periods in all directions on the Tibetan Plateau within a 100-km distance were positive, demonstrating a positive correlation with distance change; Variograms of daily ET₀ in June, the dry season, the wet season, as well as annual average daily ET₀ fit well with the Gaussian model; A variogram of daily ET₀ in December fit well with the exponential model; Variograms of daily ET₀ for the four seasons fit well with the linear with sill model. Water Science and Engineering. 2009 2(1): 112-120 .