Journal of Hydroelectric Engineering

水力发电学报

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2015 Vol. 34, No. 11 Published: 2015-11-25

	1	Review on vibration problems of power units in commissioned pumped storage projects in China
		YUAN Shouqi, FANG Yujian, YUAN Jianping, ZHANG Jinfeng
		DOI: 10.11660/slfdxb.20151101
		As China’s economy is developing and upgrading rapidly, pumped storage technology becomes increasingly important in China’s power-supply system and to China’s policy of enhancing the exploitation of renewable energy. The construction of pumped storage projects (PSP) in China has experienced a rapid development stage and will gradually enter a faster developing stage. Therefore, various issues of power unit vibrations found in the operation of commissioned projects, have attracted great attention of the research community. Using the statistics of the number of runner blades in combination with the number of wicket gates and an analysis on specific cases, this paper presents a detailed explanation for the major causes of unit vibrations such as rotor-stator interaction and phase resonance, and suggests that the scientific research concentrate on the dynamic design of power units and particularly on two blade-gate number combinations of 7/20 and 9/20 and their mechanism of hydraulic excitation. In sight of the vibration problems found in various PSPs at a head range around 300 m, we recommend to focus on the field measurement of prototype vibrations and hydraulic pulsations, and to actively carry out experimental and theoretical studies on the dynamic mechanism. Such research will not only solve the existing vibration problems in the built projects, promote their safe and reliable operation, and prolong their service lives, but also make positive and important senses of ensuring the safe construction of numerous ongoing and future PSP projects.
		2015 Vol. 34 (11): 1-15 [Abstract] ( 230 ) PDF (3754 KB) ( 395 )

	16	A review of rotating stall of pump turbines
		LIU Tao，ZHANG Yuning，DU Xiaoze
		DOI: 10.11660/slfdxb.20151102
		Rotating stall is an important instability phenomenon of rotating fluid machinery (e.g. pump turbine). This paper presents a review of the rotating stall of pump turbines operating in generating mode, focusing on the primary characteristics of such instability and the corresponding pressure wave transmission. We discuss the basic concept, generation conditions, physical mechanisms, and development/transmission of a rotating stall cell in pump turbines, and summarize the methods for identification of rotating stall, including data analysis based on pressure fluctuation measurements and experiments of bubble injection and tuft visualization. To explore the influence of rotating stall on the operation of pump turbines, two important issues are suggested for the future research on rotating stall in pump turbines.
		2015 Vol. 34 (11): 16-24 [Abstract] ( 297 ) PDF (2563 KB) ( 545 )

	25	Dynamic analysis of high-specific-speed Francis turbine runner in channel vortices condition
		RUAN Hui, LIAO Weili, GONG Haipeng, ZHAO Yaping, LUO Xingqi
		DOI: 10.11660/slfdxb.20151103
		In low-discharge operating conditions, serious vortices often appear in the runner blade channels of high-specific-speed Francis turbine runners. Transient dynamic stress of the runner has been numerically simulated and examined in this study to probe the mechanism of channel vortices acting on the blades and the cause of cracks on the runner. First, we calculated the steady and unsteady turbulent flows in the full passage based on the Navier-Stokes equations and a RNG k-ε turbulence model, and obtained the patterns and distributions of channel vortices that are very similar to experimental observations. Then, a finite element method was applied to modal analysis of the runner, showing the inherent frequencies and modal shapes. Finally, we adopted a fluid-structure coupling method to analyze the transient dynamics of the runner. Results show that the frequency of channel vortices acting on the blades is a multiple of the rotational frequency of runner and the most dangerous are the local channel vortices distributed near the joints of blade tailing edges with the crown. Thus, the maximum dynamic stress in the joints is higher than the allowable stress value of common turbine runners, leading to damage even cracks around that location.
		2015 Vol. 34 (11): 25-31 [Abstract] ( 269 ) PDF (1792 KB) ( 480 )

	32	Study on nonlinear responses of characteristic variables to small initial disturbances in reservoir flood routing
		LIU Zhao, XI Qiuyi, WANG Qing, TAO Wangxiong
		DOI: 10.11660/slfdxb.20151104
		Nonlinear behaviors in flood routing of a reservoir system have been analyzed to study the intrinsic stochasticity of the system, aiming to form a basis of uncertainty and risk analysis for reservoir flood control systems. Applying the system dynamics theory and system simulation method, we examined the nonlinear dynamic characteristics of a deterministic mathematic model for reservoir flood routing of water level and outflow under the conditions of free overflow and regulated outflow. The results show that the state variables were not sensitive to the initial disturbance in the stage of free overflow while quite sensitive in the stage of regulated outflow. In the latter case, water level and outflow were evolving in a way of amplified deviations as a response to the initial disturbance of the routing. This phenomenon indicates that nonlinear behaviors in reservoir flood routing could play an important role in system uncertainty and it is a potential risk factor and an underestimated problem. Thus, it should be further studied owing to its importance associated with the interests and risk in reservoir flood control.
		2015 Vol. 34 (11): 32-39 [Abstract] ( 185 ) PDF (901 KB) ( 315 )

	40	Large system decomposition-coordination model for optimal power-generation scheduling of cascade reservoirs
		WU Hao, JI Changming, JIANG Zhiqiang, ZHANG Yanke
		DOI: 10.11660/slfdxb.20151105
		A new optimization model of double-level hierarchical structure has been developed in this study for power-generation scheduling of cascade reservoirs by the principle of large-scale system decomposition-coordination to solve the problem of curse of dimensionality in the standard dynamic programming algorithm. At the level of its system decomposition, multi-thread technology is applied to parallelization of standard dynamic programming that solves an optimization problem for each subsystem of a single reservoir. At the coordination level, different single-reservoir subsystems are coupled and the corresponding information is exchanged iteratively with the level of decomposition to obtain an optimal solution of the system. This model along with the parallelization algorithm was applied to the optimal scheduling of a three-reservoir cascade system in the Lixian River basin. Results show that the method is effective and can improve the efficiency of large system optimization, and thus it would provide theoretical reference for the optimization of complex engineering systems.
		2015 Vol. 34 (11): 40-50 [Abstract] ( 268 ) PDF (383 KB) ( 584 )

	51	Impact of ecological base flow on power revenues and losses of Laluo hydro-junction
		XU Gang, HUANG Di, ZAN Xiongfeng, LIU Xin
		DOI: 10.11660/slfdxb.20151106
		This paper describes a ratio of power revenue losses to ecological benefits for assessment of the losses in the power generation revenues of a reservoir, considering the constraint of different ecological base flows in its medium and long-term optimal operation. This ratio parameter can be used for examining the impact of ecological base flow on the revenue and exploring the possibility of increasing ecological base flow in practice. In a case study of the Laluo hydro-junction in Tibet, we calculated the ecological base flows of its lower reach using a hydrologic method, and developed new schemes for optimal reservoir scheduling under the constraint of irrigation and ecological water demands. In the new schemes the ecological base flow was increased by various amounts, and the ratios of power revenue loss to ecological benefit calculated. Results show that in the Laluo case, it is feasible to increase the ecological base flow and this measure can minimize the relative losses in generation benefits per unit volume of ecological water.
		2015 Vol. 34 (11): 51-58 [Abstract] ( 192 ) PDF (345 KB) ( 290 )

	59	Hydrodynamic mechanism of engineering deposit erosion in Northern Jiangxi Province
		WANG Xuesong, SHEN Weibo, XIE Yongsheng, CHEN Xi, DING Yadong, MA Hongchao
		DOI: 10.11660/slfdxb.20151107
		Engineering deposits have unique soil constitutions and complex conditions of their surface layers that are quite different from those of a regular soil slope. Hydrodynamic mechanisms established through previous studies of the traditional slopes, are not applicable for such deposits with three-dimensional shapes and it is necessary to study the hydrodynamic process of soil erosion on the engineering deposits. In this study, we have conducted laboratory experiments of rainfall erosion on a special type of engineering deposits? roller compacted by construction machinery on the top platform of the slope, focusing on the hydrodynamic process of erosion in the conditions of four artificial rainfall intensities (1.0, 1.5, 2.0 and 2.5 mm/min) and three gravel contents (10%, 20% and 30%). The results show that the soil detachment rate is a linear function of rainfall intensity and percentage gravel mass content with a squared correlation coefficient of R2=0.919. Thus, the sediment yield can be predicted if these two parameters are known. Hydraulic parameters such as flow shear stress, stream power, unit stream power, and the specific energy of flow cross section, could also be used for calculation of the detachment rate. Among them, the stream power is the most suitable parameter and is highly correlated with the detachment rate (R2 = 0.884). This indicates that the effect of water flow on the deposits tested in this study is better described in terms of its energy than its stress. A comparison reveals that for the deposits tested, both their top platform part and slope part contribute to the total detachment rate. The contribution by the former, which is 5.0×10-6 kg/(m2?s) for the experimental condition, depends primarily on the area of the top platform compacted.
		2015 Vol. 34 (11): 59-68 [Abstract] ( 259 ) PDF (476 KB) ( 226 )

	69	ADV-based measurements of instantaneous suspended sediment concentrations in the Three Gorges Reservoir
		LI Wenjie, HUANG Yafei, YANG Shengfa, ZHANG Peng
		DOI: 10.11660/slfdxb.20151108
		Field ADV measurements of suspended sediment concentrations have been taken in the Zhongxian and Fengjie reaches of the Three Gorges Reservoir, which are suffering from serious sediment deposition. From these field data, we have developed an inversion method for instantaneous sediment concentration. ADV acoustic signals are usually contaminated by spikes and high-frequency noises. To despike the signals, this method adopts wavelet analysis to filter out their high-frequency noises, and then processes them using a phase-space density method. Calibration of sediment concentration versus acoustic intensity in double logarithmic coordinates shows a linear relationship whose slope and intercept are both functions of particle diameter, thus providing an inversion formula for instantaneous sediment concentration. Calculations using this formula reveal that turbulent sediment fluxes are closely related to the Reynolds stresses and the scalar spectrums of sediment concentrations follow the Obukhov-Corrsin law of -5/3 power. The results indicate that our new inversion method for instantaneous sediment concentration is feasible and effective.
		2015 Vol. 34 (11): 69-76 [Abstract] ( 213 ) PDF (1320 KB) ( 405 )

	77	Remote-sensing retrieval method of suspended solid concentration and turbidity in lakes and reservoirs based on discrete particle swarm and partial least squares
		CAO Yin, YE Yuntao, ZHAO Hongli, SHI Yubo, JIANG Yunzhong
		DOI: 10.11660/slfdxb.20151109
		Discrete binary particle swarm optimization (DBPSP) has been used in this study to prioritize the characteristic bands of suspended solid concentration and turbidity. This method can reduce the number of input parameters and uncertainty in partial least squares (PLS) modeling, and improve the prediction accuracy of PLS models. In a case study of water quality of the Nansi Lake, we have developed and verified a PLS model and a NDBPSO-PLS model separately for retrieval calculations of suspended solid concentration and turbidity using the hyper-spectral remote sensing data and synchronous sampling data measured on July 21 to 23, 2014. The results indicate that for the NDBPSO-PLS calculations of suspended solid concentration and turbidity, the number of characteristic bands required by it was only 137 and 134 respectively, a great reduction relative to the number of 370 required by the PLS model. And its input feature variables were reduced to 21 from 60 PLS variables. Its prediction accuracy is better than the PLS model. Thus, NDBPSO-PLS would provide an effective method for improvement of the retrieval calculations of suspended solid concentration and turbidity.
		2015 Vol. 34 (11): 77-87 [Abstract] ( 235 ) PDF (871 KB) ( 259 )

	88	Calculation of frictional and minor head losses for hydraulic jump section in rectangular open channels
		ZHANG Zhichang, ZHAO Ying
		DOI: 10.11660/slfdxb.20151110
		A calculation method of frictional head loss in a hydraulic jump section has been developed using turbulent boundary layer theory based on the previous studies of velocity distribution, wall shear stress, and total head loss. Minor head loss is calculated according to the relationship of total loss versus frictional loss, and local resistance coefficient is estimated using the definition of minor loss. Results show that the frictional loss is a function of the velocity distribution on the initial cross section, the length of hydraulic jump, and the kinematic viscosity of water while the minor loss and resistance coefficient a function of conjugate depth ratio and the Froude number at the initial cross section. The analysis includes relationships of the total head ratio of hydraulic jump section over jump area, relative frictional loss, relative minor loss, and local resistance coefficient versus the Froude number. It shows that among these four parameters, the relative frictional loss decreases with the Froude number while the other three increase with it.
		2015 Vol. 34 (11): 88-94 [Abstract] ( 279 ) PDF (374 KB) ( 470 )

	95	Unimpaired flow calculations in regions with great disturbance in groundwater
		ZHANG Hongbo, CHEN Keyu, YU Qijun, GU Lei
		DOI: 10.11660/slfdxb.20151111
		The impacts of human activities on river runoff are becoming more and more serious in recent years, resulting in a difficulty of using the measured runoff in water resources assessment and hydroelectric project design because of the inconsistency of measured time series. This situation is especially common in regions where the impacts are intensive and extensive and the data for groundwater development is lacking or subject to great uncertainty. These difficulties may further cause a complication and low accuracy in estimation of the unimpaired or natural runoff time series. It is therefore necessary and urgent to find a simple, practical and accurate method of time series restoring for the regions of groundwater strongly disturbed by human activities. In this study, we have developed an improved method of natural runoff calculation that incorporates the idea of base flow separation and item-by-item investigation. Three cases were studied to investigate the feasibility of our method. The study shows that this improved method gave results quite close to those of the conventional restoring methods and it shows better applicability to regions with diverse landscapes and different degrees of groundwater disturbances. Particularly, it can complete natural runoff calculations using smaller amount of data in comparison with the conventional methods. Actually, for a restoring calculation it only needs the measured runoff data and the data of surface water consumption that can be obtained using item-by-item investigation, hence avoiding the restoring distortion caused by inadequate groundwater data. Case studies verified that the improved method is rational, reliable, and applicable to water resources engineering designs. Thus, the method is of great value in natural runoff calculation for the regions where groundwater is significantly disturbed or groundwater data is inadequate.
		2015 Vol. 34 (11): 95-105 [Abstract] ( 194 ) PDF (1185 KB) ( 390 )

	106	Spatial variability of groundwater level in midstream oasis of Heihe River basin
		LI Jiang, HAO Xinmei, FAN Linlin, MAO Xiaomin
		DOI: 10.11660/slfdxb.20151112
		The midstream oasis of the Heihe River basin is located in an arid region of severe water shortage in northwest China, where groundwater is crucial to food security and ecology health. Understanding of the spatio-temporal variations of local groundwater level in this area can provide useful information for the sustainable development and utilization of groundwater. This study has focused on an application of linear regression and geo-statistics methods to analysis of the spatial distribution of groundwater level. We compared three methods for spatial interpolation of groundwater level: the ordinary Kriging method, the Yamamoto correction method of Kriging smoothing effect, and the universal Kriging method. Results show a linear correlation of the groundwater level with space coordinates for the period of 1985-2010 when the vegetation cover was relatively stable. In each month, the groundwater level of this oasis area also followed a significant spatial correlation. The Yamamoto correction method can minimize the smoothing effects in Kriging method, although it has an overall accuracy slightly lower than those of the other two methods.
		2015 Vol. 34 (11): 106-115 [Abstract] ( 204 ) PDF (440 KB) ( 336 )

	116	Detection method of leakage passages in karst disease reservoirs. A case study of Luotan reservoir in Quanzhou county of Guangxi
		HAN Kai, CHEN Yuling, CHEN Yixiang, GAN Fuping, ZHENG Zhijie, ZHANG Wei
		DOI: 10.11660/slfdxb.20151113
		It is difficult to accurately locate karst leakage passages due to the extremely complex hydrogeological conditions in karst regions. Field tests have verified that comprehensive geophysical methods are effective in the surveys of reservoir karst disease and its leakage passages, including the high-power mise-a-la-masse method, general mise-a-la-masse method, and self-potential method for pinpointing such seepage channels on a plane. The high-density resistivity method and cross-borehole seismic sonic perspective method can determine the depth of a karst leakage passage and its developing characteristics, providing key information for analysis of the leakage mechanism in corresponding geological conditions. In a case study of the Luotan reservoir region, our field measurements revealed three possible karst leakage passages developing in this region, via a comprehensive analysis of the survey data collected using the first three methods. And Channel No. II, a speculated karst leakage passage, was detected as the major passage of reservoir leakage. All the results had been confirmed by trace experiments. Using the data of the resistivity and sonic methods, we have detected a thrust fault, namely Fault F1 featured with broken rocks of smaller sizes on the plate of fault at the east side of this reservoir, along with a series of parallel tensional fractures Faults F2~F5. Thus, we come to a conclusion that the leakage of Luotan reservoir had a close relevance to the presence of fracture zones that had caused the development of a speculated karst leakage passage, i.e. Channel No. II, approximately along Fault F5.
		2015 Vol. 34 (11): 116-125 [Abstract] ( 196 ) PDF (792 KB) ( 301 )

	126	Calculation of normal stress in longitudinal girder of radial steel gate using curved beam theory
		GAO Ge, WANG Zhengzhong, SUN Danxia, LI Baohui, LIU Jiliang
		DOI: 10.11660/slfdxb.20151114
		The longitudinal main girder of a radial steel gate is essentially a curved beam, but the straight beam theory is commonly used for calculation of normal stress at its cross section up to the present. This article presents a new calculation method using curved beam theory and corresponding flexural differential equations. By deriving a formula of characteristic coefficient for stress calculation, we have formulated a method for calculating the eccentricity of the girder of a radial steel gate with box section, analyzed the influence of curvature on the distribution of bending normal stress over the curved beam section, and compared the accuracies of the two theories. Application to case studies shows an error of 14.23% in the calculation results by straight beam theory relative to the FEM calculation, which is only 2.23% in the curved beam theory. Thus, the curved beam theory is much superior and its calculation results should be more reliable.
		2015 Vol. 34 (11): 126-133 [Abstract] ( 143 ) PDF (513 KB) ( 356 )

	134	Effect of peak ground displacement on seismic responses of high arch dam
		DU Xiuli, WANG Fuyuan, WANG Jinting, ZHAO Mi, JIN Liu
		DOI: 10.11660/slfdxb.20151115
		Two groups of artificial ground motions that are compatible with the hydraulic standardized response spectrum, were input to a high arch dam to study the influence of peak ground displacement (PGD). The two different groups produced the same peak value in acceleration and velocity but different displacements. To demonstrate different seismic responses, we have adopted a time-domain wave method that couples an explicit finite-element method with viscous-spring artificial boundary conditions, and applied it in a case study of the Xiaowan arch dam, using the two groups of artificial motion histories as the exciting SV waves of incidence and observing the influence of PGD on the arch dam-foundation rock system. The results show that the PGD of this dam has great effect on the principal stress in dam body, the arch stress in arch abutments, and the vertical stress at the bottom of crown cantilever, and that its effect on the stream-wise displacements is also quite significant. Thus, the PGD should be accounted for in seismic safety evaluation and design of high arch dams.
		2015 Vol. 34 (11): 134-142 [Abstract] ( 209 ) PDF (687 KB) ( 403 )

	143	Numerical calculation of water head of dynamic tidal power dams
		XU Xuefeng1, YANG Wankang, Kees Hulsbergen, SONG Zekun, WANG Chuankun, YANG Tianzhu, ZHEN Zhijia
		DOI: 10.11660/slfdxb.20151116
		Dynamic tidal power (DTP) is a new way of tidal energy development, a technique that was first proposed by Dutch coastal engineers. The major structure is a T-shape dam of dozens of kilometers long, with its main axis perpendicular to the shoreline, to produce deformation of tidal waves and a difference in water head on the two sides of dam. The head difference for power generation depends on the size of the dam and is often calculated using a theoretical formula or a numerical model. This paper focuses on predicting the dynamic water head difference across the dam using the Kolkman formula and a 2D tidal flow numerical model. Model results show that the difference between the two predictions are relatively small and the values of Kolkman formula are smaller. This means that the seabed resistance is a minor factor of the DTP for open sea areas and for such areas ignore this term is reasonable. A good theoretical formula can reflect the interacting effect of tides and dam, and the accuracy of water level difference calculation will be improved through mutual verification of the Kolkman formula and numerical method.
		2015 Vol. 34 (11): 143-147 [Abstract] ( 266 ) PDF (1165 KB) ( 540 )

	148	Numerical study of wave energy resources in Zhaitang Island sea area
		LIU Qiulin, ZHANG Yongliang, LIANG Sendong
		DOI: 10.11660/slfdxb.20151117
		Over the past years, wave energy as a new type of renewable energy has attracted more and more attention. Assessment of wave energy resources plays a crucial role in research and development of wave energy devices and selection of wave farm sites. Currently, the assessment is carried out by either field observations or numerical simulations. This study has adopted a third generation wave model to simulate wave field in the Zhaitang Island sea area and conducted a primary assessment of local wave conditions and wave energy resource reserve, then focused on an accurate assessment of the wave energy resources in target locations for sea trials of wave energy devices. Results reveal that the wave resources in this area show significant seasonal variation with a peak wave power of 25 kW/m and they are distributed largely in the direction between south and east.
		2015 Vol. 34 (11): 148-156 [Abstract] ( 239 ) PDF (2745 KB) ( 321 )