Journal of Hydroelectric Engineering

水力发电学报

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2017 Vol. 36, No. 6 Published: 2017-06-25

	1	Rainfall-runoff simulations for Xinglong sponge city pilot area of Jinan
		CHENG Tao, XU Zongxue, SONG Sulin
		DOI: 10.11660/slfdxb.20170601
		Jinan has experienced rapid urbanization in recent decades, and extreme rainfall over this city becomes increasingly more frequent, often resulting in serious urban flooding. In this study, the Infoworks ICM (Integrated Catchment Modeling) was used to construct a storm water network model for the Xinglong sponge city pilot area, and its flood inundation was simulated for scenarios of different rainfalls. Distribution of inundation nodes and overload pipes in extreme rainfall events were detected to analyze the cause of flood inundation. The simulations show a good agreement with the observed data. The results show that rainfall intensity was a significant factor in flood events: to determine whether or not a flood happens and how intense of the flood, and that the existing capability of some drainage networks is insufficient. This study has revealed the flow process of pipe networks in a rainstorm event and its mechanism in generating inundation and assessed the capability of drainage networks, thus providing a useful support to the design and construction of sponge city areas.
		2017 Vol. 36 (6): 1-11 [Abstract] ( 249 ) PDF (5541 KB) ( 465 )

	12	River bend planform evolution in Jingjiang reach of the Yangtze since Three Gorges Reservoir operation
		XUE Xinghua, CHANG Sheng
		DOI: 10.11660/slfdxb.20170602
		Effects of the Three Gorges Reservoir (TGR) on its downstream hydrologic and sediment regimes and riverbed erosion have been much addressed, but planform evolution of river bends was less known. In this work, we studied the planform evolution of river bends in the Jingjiang reach of the middle Yangtze since TGR operation using three multi-temporal remote sensing images acquired in low water period. Results showed that (1) significant changes occurred in central-line length, convex bank length, concave bank length, sinuosity, and central-axis length of the bends, (2) that the changes in the lower Jingjiang were more remarkable, and (3) that the evolution of convex and concave banks as well as the evolution in the upper and lower Jingjiang were non-synchronous. In the upper Jingjiang, changes in concave banks occurred prior to those in convex banks, and erosion on concave banks and their extensions played a leading role in the evolution; while in the lower reach, erosion on convex banks and their shrinking were dominant and prior to the occurrence of concave bank erosion. Most of the river bends, especially those in the lower Jingjiang, showed evident increases in bend area and average width and remarkable decreases in central-line length, sinuosity and central-axis length. All this implies that since TGR operation, river bend curving has been weakening and river channels have been broadening. The relation of planform evolution to changes in concave and convex banks is also discussed in this paper.
		2017 Vol. 36 (6): 12-22 [Abstract] ( 184 ) PDF (626 KB) ( 380 )

	23	Impact pressure of water nappes from double narrow slot buckets
		JIANG Qiaofen, YIN Jinbu, HE Junling, WU Baoqin
		DOI: 10.11660/slfdxb.20170603
		The characteristics of jet nappes from a trajectory bucket and their energy distribution and scour depth all depend on the shape of the energy dissipator. This paper presents numerical simulations of the jet nappe flows from a flip bucket of double narrow slot type installed on one spillway chute to explore the energy distribution and scour mechanism of the jet nappes. The characteristics of impact pressure on the scour pool bottom are analyzed. Results indicate that the impact pressure is similar to that of an ordinary oblique submerged jet, but its impacting energy is more dispersed. In the water cushion zone, the flow is structurally complicated with significant interaction between different steams. In different working conditions, the distribution of mean pressure is quite different. All this is conducive to more dissipation of energy.
		2017 Vol. 36 (6): 23-29 [Abstract] ( 167 ) PDF (1637 KB) ( 348 )

	30	Local head loss of 90° lateral diversion from open channels of different cross-sectional shapes
		LI Tao, ZOU Jian, QU Shaojun, LIU Zhe, REN Zhihui, TIAN Wenjun
		DOI: 10.11660/slfdxb.20170604
		Lateral diversion from an open channel is a common flow regime that usually produces a larger head loss due to the vortices caused by the diversion. However, most previous studies focused on flow diversion from the channels of fixed cross-sectional shapes and small bottom slopes. In this work, channels of different cross-sectional shapes (rectangle, trapezoid and triangle) and their local head losses around the diverting mouth were studied using numerical simulations based on Mike21, a code for plane-2D flows. A relationship of local head loss coefficient versus Froude number was constructed for different cross-sectional shapes of the channel. The results show that with a fixed channel shape, this minor loss grows gradually with the increasing channel flow rate; under a fixed flow rate, it takes the largest, second largest and smallest values in the cases of triangular, trapezoidal and rectangular cross sections. Under subcritical flow conditions, the minor loss coefficient decreases gradually with the Froude number.
		2017 Vol. 36 (6): 30-37 [Abstract] ( 146 ) PDF (804 KB) ( 355 )

	38	Simulation of flows in fishways combined with a vertical slot and orifice plates
		LIU Hu, CHENG Wen, REN Jiehui, WAN Tian, JIAO Meng, WANG Min
		DOI: 10.11660/slfdxb.20170605
		Fishway is an ecological passage that allows fishes to pass over the dam or do migratory swimming, and studies on the coordination of its flow and fish migration characteristics are an issue that attracts great attention recently. In this work, we examined the characteristics of flows in a fishway with a vertical slot and orifice plates and analyzed their effects on fish migration, using the k-ε (RNG) turbulence model and VOF model of the Fluent code through a case study of the Changzhou fishway. The results show that under the design flow condition (Q = 6.64 m3/s) of this project, the fishway flow can develop vertical profiles of velocity and turbulent kinetic energy that have little effect on the migration of Chinese sturgeon, shad, and other major fish species, while it will produce a greater obstacle to the migration of the Four Major Chinese Fish species of relatively low swimming ability. However, the inflow of the fishway is linearly proportional to flow velocities inside its chamber, and its hydraulic characteristics will basically meet the migratory needs of all the aforementioned major species if it is operated under a flow rate in the range of 3.64-4.64 m3/s. Thus, this study would be useful for optimizing fishway design and operation.
		2017 Vol. 36 (6): 38-46 [Abstract] ( 172 ) PDF (1691 KB) ( 383 )

	47	Runoff forecasting model based on wavelet decomposition-robust estimation and its application
		JI Changming, ZHANG Pei, WU Yueqiu, ZHANG Yanke, LI Rongbo
		DOI: 10.11660/slfdxb.20170606
		The multiple-scale time-frequency analysis based on wavelet decomposition is widely applied to modeling and forecasting of complicated time series, but a traditional time series model cannot effectively describe the structure of a series containing outliers. To solve this problem, we adopted robust regression estimation to improve the traditional wavelet model and developed a wavelet analysis-robust estimation hydrological time series model that can effectively eliminate the impacts of outliers in observed data by using a multiple-scale wavelet analysis theory and its efficient processing of non-stationary signals. This model was verified against the monthly runoff forecasts of the Auto-Regressive and Moving Average (ARMA) model and Back Propagation (BP) neural network model through comparative analysis. It shows that the model is not only more accurate but also has better reliability and stability and a wider application potential in hydrological forecasting.
		2017 Vol. 36 (6): 47-56 [Abstract] ( 147 ) PDF (1130 KB) ( 303 )

	57	Optimal operation of cascade reservoirs based on parallel hybrid differential evolution algorithm
		ZOU Qiang, LU Jun, ZHOU Chao, ZHOU Jianzhong
		DOI: 10.11660/slfdxb.20170607
		This paper presents a new parallel hybrid differential evolution (PHDE) algorithm for optimal scheduling of cascade reservoirs by combining a chaos algorithm (CA) and a shuffled leapfrog algorithm (SLFA) for their advantages in local search with parallel computation (PC) technique and using a basic framework of difference evolution (DE). PHDE is an organic fusion of DE, CA, SLFA and PC, i.e. conducting chaotic local search for better individuals and leapfrog local search for worse individuals, and its computation of DE, CA and SLFA is combined with PC so as to reduce running time. Therefore, this algorithm has three advantages: it reserves the simplicity and fast convergence of DE; it inherits the ergodicity from CA and SLFA so as to avoid premature convergence; it has a relative shorter computing time. The testing results of typical functions verified its better feasibility, efficiency and robustness. Case studies showed that it can achieve better optimization performance, thus offering an efficient tool for solving optimal operation model of cascade reservoirs.
		2017 Vol. 36 (6): 57-68 [Abstract] ( 161 ) PDF (2232 KB) ( 438 )

	69	Pressure fluctuations in pump turbines in S zone based on weakly compressible modeling
		WANG Like, LIAO Weili, LU Jinling, ZHAO Yaping, RUAN Hui, WANG Jing
		DOI: 10.11660/slfdxb.20170608
		The S characteristics of a high-head pump turbine working in turbine mode could cause difficulty in power grid connection, and in severe cases it may induce vibrations of the generating unit, producing an adverse effect on safe and stable operation of the power station. To study pressure fluctuations in the pump turbines working in the S zone, we focused on a pump turbine at a pumped-storage power station and numerically simulated its steady and unsteady flows. The characteristics of pressure fluctuations in the vaneless sections and draft tube were analyzed for the cases of stable operation, small torque, small discharge, and reverse pump condition. The results show that the fluctuation in static pressure is significant and its behaviors depend on the compressibility of water. In the vaneless section between guide vane and runner, the dominant frequency is equal to the one generated by blades passing when the compressibility is considered, while it is equal to 2fn in the small torque case when incompressible water is assumed. The fluctuating amplitudes are slightly larger in the compressible case, but in both compressible and incompressible cases the characteristic amplitude is increased and then decreased as the unit discharge is decreasing. And the amplitudes at high-frequencies such as 14fn and 21fn are relatively small. In the draft tube, pressure fluctuations are featured with dominant frequencies equal to fn, 3fn and 4fn, but their amplitudes become the smallest in stable operation. In the elbow and outlet section, the amplitudes in other conditions could be more than ten times larger than those in stable operation, showing the effects of spiral vortex structure.
		2017 Vol. 36 (6): 69-78 [Abstract] ( 159 ) PDF (2547 KB) ( 361 )

	79	Pressure fluctuation generated by the vortex rope and improvement measures inside draft tube of Francis Turbine
		ZHANG Xing, LAI Xide, LIAO Jiao, ZHANG Wenming
		DOI: 10.11660/slfdxb.20170609
		Vortex rope in the draft tube of a Francis turbine is a key factor causing vibrations of the turbine unit. To reduce the vibrations, unsteady 3D flows in a Francis turbine were numerically simulated in this work to investigate amplitude and frequency characteristics of the pressure fluctuations in the draft tube. Three improving measures were examined: extending the runner cone, adding a hydraulic disturbance of 0.03Q to the flow rate, and combining these two modifications. Simulations of all these different cases were analyzed and compared, focusing on their effects on the vortex rope-generated pressure fluctuations. The results show that all the three measures can effectively reduce the fluctuations. A longer runner cone has an obvious effect on pressure fluctuations in the conical tube. Compared to disturbing the flow rate, a longer cone or the combination measure is more effective in frequency modification and amplitude reduction of the draft tube fluctuations, but their influences on turbine efficiency are greater.
		2017 Vol. 36 (6): 79-85 [Abstract] ( 164 ) PDF (1627 KB) ( 396 )

	86	Wear resistance of rock aggregate against micro-cutting and its relation to rock properties
		HE Zhen, CHEN Xiaorun, CAI Xinhua
		DOI: 10.11660/slfdxb.20170610
		Wear resistance of rock aggregate against micro-cutting was tested for five different types of rocks (granite, basalt, marble, limestone and dolomite) and their relations to rock properties were analyzed. Results indicate that granite has the highest resistance that is 13 times that of dolomite, followed by basalt of 5 times, then by marble, limestone and dolomite. The resistance is related to Vickers micro-hardness to a certain extent, but no simple relation between these two parameters has been found in this study. Mineral composition and pore structure of the rocks are major factors of the resistance; size and morphology of the mineral grains also have a certain influence on the resistance.
		2017 Vol. 36 (6): 86-93 [Abstract] ( 138 ) PDF (2238 KB) ( 275 )

	94	Numerical analysis of macro-meso fractures in concrete gravity dams using extended finite element method
		QING Longbang, YU Kelai, XU Dongqiang
		DOI: 10.11660/slfdxb.20170611
		Based on physical model tests of a classical concrete gravity dam, a macro-meso structure finite element model of dam bodies was developed that takes the concrete in the region of crack propagation as inhomogeneous materials at meso level and adopts an extended finite element method to simulate the whole propagation process in the dam. Crack propagation trajectories and curves of external load versus crack mouth opening displacement (P-CMOD) were obtained; the impacts of aggregate distribution and its volume content on the trajectories were studied. The results show that the calculated P-CMOD curves agree well with previous experiments. Aggregate distribution has a significant effect on the descending portion of the curves, while little effect on peak load and the trajectories. Differences in the trajectories are small when aggregate volume content varies from 60% to 80%.
		2017 Vol. 36 (6): 94-102 [Abstract] ( 180 ) PDF (3926 KB) ( 267 )

	103	EMD identification of closely-spaced modes and its application to power plant analysis
		RONG Qinbiao, LIU Fang, SU Ce, KANG Hongzhi
		DOI: 10.11660/slfdxb.20170612
		In view of the shortcoming of traditional empirical mode decomposition (EMD), the method is improved by using signal frequency modulation and optimizing mode selection criterion. The relationship of decomposition ability versus selection criterion, iteration number, and frequency modulation was studied, and a detailed procedure of frequency modulation is given. A closely-spaced mode identification method was developed using window functions, signal frequency modulation, and improved selection criterion, and it was validated via simulations of vibration signals observed in-situ. The results show that the improved method can effectively identify the parameters of closely-spaced modes, thus laying a basis for EMD application to power plant analysis and identification of its vibration parameters.
		2017 Vol. 36 (6): 103-113 [Abstract] ( 129 ) PDF (652 KB) ( 205 )

	114	Experimental study of bottom-hinged flap wave energy converters
		LIU Chengguo, NING Dezhi
		DOI: 10.11660/slfdxb.20170613
		This paper presents an experimental study on hydrodynamic performance of a bottom-hinged flap wave energy converter in different conditions and different swing flap mass distributions. The device is composed of a magnetic power extracting system that is controlled with magnetizing current and a torque sensor. The swing flap is a hollow structure vertically divided into five separate chambers, and its mass distribution can be controlled by filling water into different chambers. The design of experiment was verified by comparing experimental and numerical results; the effects of wave condition and flap mass distribution on the captured power-width ratio of the converter and the dynamic pressure on the swing flap surfaces were analyzed. The results indicate that with the increasing wave amplitude, the captured power-width ratio decreases and the flap dynamic pressure increases. And a larger captured power-width ratio and lower dynamic pressure will occur when either the two bottom flap chambers are filled up with water in the case of short waves or only the bottom one is filled up in the case of long waves.
		2017 Vol. 36 (6): 114-120 [Abstract] ( 129 ) PDF (482 KB) ( 191 )