Journal of Hydroelectric Engineering

水力发电学报

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2021 Vol. 40, No. 9 Published: 2021-09-25

	1	Evolution and probability distribution of precipitation extreme values in typical urbanized basin in southern China
		SONG Mingming, ZHANG Jianyun, LIU Yanli, WANG Guoqing, LI Chang
		DOI: 10.11660/slfdxb.20210901
		This study selects a typical urban basin in the southern China, the Qinhuai River basin, to analyze the spatiotemporal evolution and inconsistency frequency distribution of extreme rainfalls expressed in terms of extreme rainfall indicators. The results show that in the Qinhuai River basin of 1979 to 2015, the annual rainfall was increased slightly manifesting an increasing trend in summer and winter and a decreasing trend in spring and autumn. Intensity and frequency of its extreme rainfalls were increased significantly, and the abrupt change point and high value area were consistent with the time point and region of its urbanization pattern evolution. For this typical basin, the Pearson type III distribution was optimal for its extreme rainfall series after consistency correction, with its maximum 1-day rainfall (R1d) and annual total rainfall from days with daily rainfall > 99th percentile (R99p) featured with large non-stationary. In the case of the uncorrected R1d used in calculation, the design values were low. The maximum 3-day (R3d) and 7-day (R7d) rainfalls and annual total rainfall from days with daily rainfall > 95th percentile (R95p) were relatively stable. The areas of high R3d and R95p design values for different return periods were distributed in the lower part of the basin and the upstream Lishui district; the areas of high R7d design value were distributed in the upstream Jurong city. Thus, the superimposed effects of extreme rainfalls in both the upper and lower reaches could impose a high flood risk on the lower reaches.
		2021 Vol. 40 (9): 1-13 [Abstract] ( 169 ) PDF (6491 KB) ( 586 )

	14	Reservoir inflow forecasting for island areas based on multiple recurrent neural networks
		GUO Yuxue, XU Yueping, CHEN Hao, YU Xinting
		DOI: 10.11660/slfdxb.20210902
		Accuracy of short-term runoff forecasting is often lowered due to low or even zero river flows in island areas. This study adopts three different recurrent neural networks (RNNs) to forecast several runoff series at different lead times and input combinations. Application to a case study of the Zhoushan Island shows that runoff forecasting coupled with future meteorological forecasting information achieves better performance than that based on runoff information only. As forecasting lead time increases, the long short-term memory network and gated recurrent unit are becoming better than the simple RNN model. RNN models perform better on stationary runoff series than non-stationary ones, and their stability and reliability in calculation of non-stationary runoff series can be improved by coupling meteorological information and through parameter optimization.
		2021 Vol. 40 (9): 14-26 [Abstract] ( 165 ) PDF (1587 KB) ( 433 )

	27	Runoff analysis based on local mean decomposition and maximum entropy spectrum estimation
		MEN Baohui, CHANG Rongrong
		DOI: 10.11660/slfdxb.20210903
		Analyzing the variation trends in runoff series is a basis for hydrological forecasting. How to decompose a nonstationary nonlinear runoff series into a stationary series becomes a difficult issue in the current research of hydrology. This paper presents a coupling model of local mean decomposition (LMD) for time-frequency decomposition and maximum entropy spectral estimation (MESE) for the frequencies of each decomposed component. Monthly runoff series of the Xiahui hydrometric station, located upstream of the Miyun Reservoir, is used to verify the decomposition results and extract more effective frequency information from these series. The results show that LMD gives good decomposition results for the series, and MESE reveals one dominant cycle in each of the components: 2 months, 6 months, 18 months, 5 years, 11 years, and 22 years respectively. This demonstrates LMD-MESE coupling is a new useful approach to analysis and prediction of hydrological time series.
		2021 Vol. 40 (9): 27-34 [Abstract] ( 118 ) PDF (1262 KB) ( 406 )

	35	Reasons for China owning largest number of water dams in the world
		HUANG Qiang, LIU Dong, WEI Xiaoting, YANG Yuanyuan
		DOI: 10.11660/slfdxb.20210904
		China is the country that has built the largest number of dams in the world, with more than 23000 large dams of over 15 m that accounts for 40.6% of the global total. Against the backdrop of international disapproval of water dams, clarification of why China needs such a huge number of dams matters most. This study reviews the historical development of dam construction, clarifies the reasons for this huge-scale construction in China through examining its national conditions, and looks into the future of Chinese dams. The results show that China owning the largest number of dams is a natural outcome of its population, natural geography, climate, water situation, and other national conditions, and also for the purpose of meeting the major national needs－flood control, disaster reduction, agricultural irrigation, urban water supply, hydropower generation and so on. Water dams have enormous social, economic, and ecological benefits. To satisfy the future needs of the national strategy, the existing number of dams in China is not excessive, but deficient. China needs to further build and improve its dam system from a national strategic prospective of ecological civilization construction and high-quality development. The results cast light on scientific, reasonable, and fair understanding and evaluation of water dams.
		2021 Vol. 40 (9): 35-45 [Abstract] ( 423 ) PDF (660 KB) ( 1233 )

	46	Multi-objective operation rules for cascade reservoirs. Case study of Xiluodu-Xiangjiaba cascade
		ZHONG Jiaxing, DONG Zengchuan, YAO Hongyi, NI Xiaokuan, CHEN Mufeng, JIA Wenhao, YE Haichao
		DOI: 10.11660/slfdxb.20210905
		To fully utilize the Pareto frontiers’ information of multi-objective optimization of cascade reservoir, we present a new method for extracting operation rules through optimizing their parameters to approximate successively the operation results toward Pareto frontiers. We develop a multi-objective optimal operation model, solve it using the nondominated sorting genetic algorithm II (NSGA-II), and then obtain the sets of Pareto frontiers for three typical years of wet, normal and low flows. These Pareto frontiers are used as the training samples of a surrogate model to realize a function expression of two-dimensional Pareto frontiers. We construct the basic form of the operation rules using multiple linear configurations, and optimize their parameters used for the typical years through successive approximation to Pareto frontiers. This method avoids destroying the integrity of Pareto frontiers in extraction of multi-objective optimization operation rules due to decision-making, and seek the approximated Pareto solution as the optimized results. It is verified in the case study of the Xiluodu-Xiangjiaba cascade reservoirs. We have extracted successfully the typical years' operation rules for the two goals of power generation and ecology in non-flood season, and verified the rules under similar conditions.
		2021 Vol. 40 (9): 46-54 [Abstract] ( 306 ) PDF (1863 KB) ( 695 )

	55	Experimental study on rheological properties of turbid water with high flow velocity
		BAI Yuchuan, WEN Zhichao, XU Haijue, HUANG Zhe, ZHANG Jinliang
		DOI: 10.11660/slfdxb.20210906
		Flood water in the accelerating section of a sediment-laden river is characterized by high sediment concentration, high flow velocity, and coarse particle sizes. Previous studies on the rheological properties of flood water focuses on high sediment concentration, ignoring the factor of high flow velocity, more preciously high shear rate. This study examines systematically the effects of sediment concentration, shear mode, temperature and salinity on the rheological properties of turbid water in the lower Yellow River under high velocity shear conditions. The results show that under high shear rates (≥ 1200 s-1 at the velocity of 3.6 m/s), the rheological properties of turbid water with sediment concentration of 106.6 - 957.8 kg/m3 follow the laws of Newtonian fluid, no yield stress is observed, and its apparent viscosity has an exponential relationship with sediment concentration. A temperature drop does not change its rheological properties but its apparent viscosity is increased, and lower temperature will result in a greater viscosity increase. At the same temperature, the gradient of viscosity increase is about several times to ten times that of clear water. A change in salinity has little effect on the apparent viscosity or rheological properties. The results are useful for further theoretical study of high velocity flow sediment carrying capacity and long-distance sediment transport.
		2021 Vol. 40 (9): 55-66 [Abstract] ( 126 ) PDF (1442 KB) ( 510 )

	67	Influence of shaft location on hydraulic characteristics of bidirectional tubular pump systems
		JIN Kangliang, CHEN Ye, TANG Fangping, SHI Lijian, LIU Haiyu, ZHANG Wenpeng
		DOI: 10.11660/slfdxb.20210907
		Bidirectional shaft tubular pump, a type of low-head pump device for bidirectional pumping, is widely used in plain urban areas, and the location of its shaft has always been a problem to be considered in engineering practice. In this study, a three-dimensional modeling software is used to construct the model of the pump flow system comprising the shaft runner, straight pipe runner, impeller section, and guide vane section, using structured meshing method to generate the grid of all sections. Steady flows in the two-way shaft tubular pump device are simulated by solving the continuity equation, k-ε turbulence model equations and Reynolds average equations; Hydraulic performances of the pump are calculated for the forward and reverse operation modes of its impeller and two schemes of front shaft and rear shaft. The results show that under the design condition, the forward mode efficiency is higher than that of reverse mode regardless of the rear or front position of the pump shaft. In either forward or reverse operating mode, the flows in the shaft runner and straight pipe runner, when both located at the pump inlet side, manifest relatively smooth patterns, the difference between the hydraulic performance of both modes is small; In forward operating mode, when these two components are located at the outlet side, their flow patterns are different due to different shapes, but the overall head loss of the pump is small. In reverse operating mode, the circulation of the outlet runner cannot be fully suppressed by guide vanes, resulting in a head loss greater than that in forward operating mode. Under this condition, the hydraulic performance of the shaft runner as the outlet runner is worse than the straight pipe runner as the outlet runner.
		2021 Vol. 40 (9): 67-77 [Abstract] ( 106 ) PDF (4034 KB) ( 480 )

	78	Influence of added mass on modal characteristics of pump turbine runners
		YANG Xiaolong, WANG Chao, CHEN Zhiming, CHEN Funan, BI Huili, LUO Yongyao, WANG Zhengwei
		DOI: 10.11660/slfdxb.20210908
		Acoustic fluid-structure coupling has obvious influence on pump-turbine runners due to their flat structure, and the natural frequency is greatly lowered in working channel. In addition, the hydraulic excitation in the start-up and shut-down processes of the unit could lead to the resonance of the runner. Therefore, it is necessary to carry out modal analysis of the runner to ensure its safety and stability during operation. This paper adopts an acoustic fluid-structure coupling method to analyze the modes of the runner, taking the added fluid mass outside the runner entity in consideration. We change the diameter and height of the runner, and examine the effect of the ratio of the diameter to height of the runner on its working mode. Results show that the effect of added mass from fluid is in a decreasing order of upper clearance, lower clearance, and inner channel. We also find that, as the ratio of the runner diameter to height decreases, the natural frequencies of the runner increases, but the added mass effect decreases. The results can help evaluate the runners’ vibration and resonance characteristics, and therefore are instructive on predicting the runner safety of large pumped storage units.
		2021 Vol. 40 (9): 78-85 [Abstract] ( 168 ) PDF (984 KB) ( 520 )

	86	Operation reliability evaluation method of pumped storage unit shafting based on improved PCM
		JING Xiuyan, JI Liantao, HAO Feng, WANG Pu, ZHUANG Jun, LI Chaoshun
		DOI: 10.11660/slfdxb.20210909
		Pumped storage units are more prone to failure than conventional hydropower units because of their frequent start-up, shutdown and changing working conditions. This paper presents an improved proportional covariate model (PCM) based on a real-time evaluation method for the operational reliability of pumped storage units. This new method first solves for the initial failure rate using an ideal solution approximation method based on the Marxian distance, not demanding large sample failure data; then, a relationship between the failure rate and response covariate is established through a multiple linear regression model to avoid subjective variability brought in by artificial determination of the basic covariate. Finally, operational reliability is updated repeatedly using a multivariate linear function to dynamically reveal the mapping between the condition monitoring data and the reliability. The method has been applied to reliability assessment to the shaft system of pumped storage units, and it achieves satisfactory results that can reflect the operation status of the shaft system in real time, demonstrating its effectiveness and validity.
		2021 Vol. 40 (9): 86-94 [Abstract] ( 132 ) PDF (660 KB) ( 436 )

	95	Analysis on vortex ropes and pressure pulsations in draft tube of variable-speed Francis turbine
		WANG Tongtong, ZHANG Changbing, XIE Tingting, CAO Wenzhe
		DOI: 10.11660/slfdxb.20210910
		Vortex ropes and pressure pulsations in a hydropower unit－under regulating operation of frequency, peak load, or new energy fluctuation－severely restrict regulation capability of the unit and have attracted much attention. In this work, a RANS-LES method is used to simulate the vortex ropes and pressure pulsations in the draft tube of a Francis turbine under the mode of variable-speed operation. The results show that the strength of vortex ropes is decreased obviously near the vortex elimination speed (VES) but increased when the speed deviates from VES. From VES to the optimal speed, turbine efficiency is increased, though the number of vortex ropes and the amplitude of pressure pulsations are increased. At the optimal speed, the turbine achieves its highest efficiency, 7% higher than that in the conventional fixed-speed operation mode.
		2021 Vol. 40 (9): 95-101 [Abstract] ( 204 ) PDF (1229 KB) ( 566 )

	102	Analysis on coupled bending-torsional vibration behaviors of rotor-runner system of hydropower units
		ZHANG Leike, ZHANG Jinjian, WANG Xueni, MA Zhenyue, WU Qianqian
		DOI: 10.11660/slfdxb.20210911
		Aimed at the nonlinear vibration problem caused by multi-source excitation in hydraulic generating set shaft systems, a coupled bending-torsional vibration model for the shaft system under the combined action of its unbalanced magnetic pull and nonlinear sealing force considering both dynamic and static eccentricity factors is developed, and numerical simulations are used to investigate its dynamic characteristics. This paper analyzes the effects of mass eccentricity and sealing clearance on its vibration behaviors using nonlinear analysis methods such as bifurcation diagram, axis trajectory diagram, and spectrum diagram. Results show that dynamic and static eccentricity of the shaft system poses a significant impact on its dynamic characteristics and amplitudes, and improves its stability to a certain extent, where new dynamic phenomena such as period-three and period-six modes appear. Mass eccentricity will weaken the effect of its unbalanced magnetic pull while aggravating its rotor vibration, resulting in its more regular motions; but excessive mass eccentricity is bound to cause the full annular rubbing of the unit, which is likely to provoke potential system instability. A larger sealing gap can reduce the damping and friction of the shaft system and help stabilize its movement, but an excessively large gap will increase fluid leakage and reduce the operating efficiency of the hydraulic generating set.
		2021 Vol. 40 (9): 102-112 [Abstract] ( 128 ) PDF (3450 KB) ( 497 )

	113	Analysis of seepage mechanism on clayey soil-structure interface under shear
		LIU Qianhui, WANG Xiangnan, ZHAN Zhenggang, YU Yuzhen, LÜ He
		DOI: 10.11660/slfdxb.20210912
		High earth-core rockfill dams are often designed with a contact layer inserted between the earth core and concrete cushion to reduce the otherwise too large deformation gradient at the interface while retaining strong impermeability. Large shear deformation induced by high water pressure puts this contact layer under a complex strain-stress and seepage state, and much attention is drawn to whether it is more susceptible to seepage damage. Previous experimental studies have shown its permeability is lowered under large shear displacement between the earth core and structure, but the mechanism is not clear yet. This study conducts multi-field simulations using a multi-body model to shed light on the mechanism of interface seepage. Based on Biot’s consolidation theory, we develop a mathematical model to simulate the seepage across the interface under large shear deformation, adopting joint elements to describe the contact relations between different layers at the interface. The simulation results reveal the evolution process of stress-strain and void ratio in the soil specimen as well as the seepage mechanism of the interface under shear.
		2021 Vol. 40 (9): 113-121 [Abstract] ( 168 ) PDF (1901 KB) ( 386 )

	122	Long-term deformation prediction model of concrete dams and its application
		ZHOU Renlian, SU Huaizhi, HAN Zhang, XU Lang, LIU Mingkai
		DOI: 10.11660/slfdxb.20210913
		Deformation prediction is of great significance to the safe operation and risk control of concrete dams. In view of the difficulties in long-term accurate prediction and modeling, this study uses a MR model to decompose a deformation sequence into the components of hydrostatic pressure, temperature, aging and remainder, and apply the SARIMA model to mine the information buried in the unstable and irregular sequences of the remainder component. Thus, we have developed a new MR-SARIMA prediction model of long-term deformation of concrete dams. Analysis and application to a dam case show that this new simple model is easy to use, more accurate, more stable, and obviously superior in the prediction of long-term concrete dam deformation featured with periodicity and trends to the previous models reported.
		2021 Vol. 40 (9): 122-131 [Abstract] ( 213 ) PDF (847 KB) ( 543 )

	132	Shear behaviors of sandstone with different water contents in low temperature cycling environment
		SHI Li, HE Jingjing, MA Lingyun, LIU Jing, ZHANG Ying, HUANG Peng
		DOI: 10.11660/slfdxb.20210914
		This experimental study examines the shear behaviors of sandstone and its performance in different water conditions under low temperature cycling environment. The results show that after a sandstone sample experienced low temperature cycles, its internal friction angle and cohesion are reduced to varying degrees and the reduction amplitude increase with the water content. And the roughness coefficient of its shear failure surface increases with saturation coefficient. For water-enriched sandstone, we find that its shear failure mode is significantly affected by low temperature cycling, and the increase in its failure surface roughness coefficient with the cycling number follows the power law. And the damage factor of internal friction angle and cohesion with the increasing roughness coefficient take an exponential form. This study lays a basis for further study of the shear failure model of sandstone in low temperature environment and its shear behaviors through inversion analysis from the original state of damaged sandstone in cold regions.
		2021 Vol. 40 (9): 132-140 [Abstract] ( 156 ) PDF (1415 KB) ( 308 )

	141	Durability and service life of fiber concrete with sulfate admixtures under wet-dry cycling
		QIN Yuan, GUAN Ke, MA Yingbiao, LIU Haimin
		DOI: 10.11660/slfdxb.20210915
		Based on the concrete erosion mechanism in the cold, dry and saline-alkali areas in the western China, we design and prepare fiber concrete specimens with fly ash contents of 0%, 10%, 20% and 30% (with the same fiber content of 0.9%) and conduct two sets of sulfate addition and wet-dry cycling tests: Set I with no fly ash and sodium sulfate solutions of 2%, 5% and 10%; Set II with fly ash contents of 0, 10%, 20% and 30% and sodium sulfate solution of 5%. We examine variations in the mass, compressive strength and splitting tensile strength of the specimens, simulate the trends of the corrosion resistance coefficient of compressive strength using the GM (1, 1) model, and predict the service life of concrete under different conditions. The results show the eroding rate of 10% sodium sulfate solution is faster than that of 2% or 5% solution. Adding 10% fly ash can slow down the decline of compressive strength of fiber reinforced concrete and enhance its durability. The GM (1, 1) predictions show the service life of concrete with 10% fly ash is longer than the other three contents, agreeing well with the test results.
		2021 Vol. 40 (9): 141-150 [Abstract] ( 167 ) PDF (859 KB) ( 665 )