Journal of Hydroelectric Engineering

水力发电学报

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2018 Vol. 37, No. 11 Published: 2018-11-25

	1	Advances and prospect of flash flood forecasting
		LIAN Jijian, YANG Weichao, XU Kui, HUA Zhengcao
		DOI: 10.11660/slfdxb.20181101
		Flash flood forecasting is a worldwide hot issue of flood control and disaster mitigation. Based on an analysis of previous research, this paper reviews its technical connotation and key aspects, including data acquisition, model calculation, index determination, and uncertainty analysis for the early warning of flash flood. In the previous studies of flash flood forecasting, we can find several shortcomings: the comprehensive analysis of multi-source warning data needs to be strengthened; the research on the rainfall-runoff relationship under complicated underlying surfaces is not deep enough; the accuracy of flash flood forecasts is still poor; how to improve the predictability of such forecasting needs further research. We suggest three directions for future studies: tackling the mechanism of flash flood formation, constructing a stereoscopic perception forecasting system of flash floods, and determining an index threshold of early flood warning.
		2018 Vol. 37 (11): 1-14 [Abstract] ( 407 ) PDF (415 KB) ( 736 )

	15	Efficiency of Bayesian probabilistic hydrological forecast system based on Box-Cox transformation
		XU Wei, JIANG Hongguang, YANG Xun, YU Pei, YIN Yuzhen
		DOI: 10.11660/slfdxb.20181102
		Aimed at the normal transformation of input data in the Bayesian processor of forecasts (BPF), the impacts of the meta-Gaussian model (MG) and Box-Cox transformation (BC) on the performance of a BPF model are compared and discussed. We make the normal transformation of the BPF model’s input data using MG and BC separately, construct a BPF-MG model and a BPF-BC model for probability forecasting, and analyze the forecasting capabilities of these two models in the conditions of different forecast periods and different data sizes. Results indicate that when the number of data samples is small, BPF-MG can achieve a higher stability through its complicated MG procedure, but it involves more complicated transformation than the BPF-BC model that has a very sensitive transform coefficient. With an increasing data size, the BPF-BC model is improved in forecasting capability and its BC coefficient becomes more stable.
		2018 Vol. 37 (11): 15-23 [Abstract] ( 92 ) PDF (671 KB) ( 327 )

	24	Hybrid quantum-behaved particle swarm optimization for operation of cascade hydropower plants
		XIA Yan, FENG Zhongkai, NIU Wenjing, QIN Hui, JIANG Zhiqiang, ZHOU Jianzhong
		DOI: 10.11660/slfdxb.20181103
		In solving the joint scheduling problem of cascade hydropower stations, the standard quantum-behaved particle swarm optimization (QPSO) algorithm suffers from premature convergence and local trapping, among other shortcomings. This paper presents a hybrid QPSO (HQPSO) that combines the advantages of the two-fold improvement strategy. This new method first does mutation search for individual extremes at a given probability to increase the diversity of individuals and enhance the global exploiting capability of the population. Then, it establishes an external archive set to conserve certain particles found in the evolutionary process. Finally, it uses the Nelder-Mead operator for dynamic probability identification to help particles searching in the neighborhood, improving its searching capability and avoiding falling into a local optimum. Application to the Wu River shows that the HQPSO is faster in convergence and global searching and practically applicable, avoiding the shortcomings of QPSO.
		2018 Vol. 37 (11): 24-35 [Abstract] ( 217 ) PDF (461 KB) ( 431 )

	36	Performance tests of ADV using towing-tank velocity calibration facility
		ZHU Yunlong, HU Heming, WANG Zhigang, XIE Dailiang
		DOI: 10.11660/slfdxb.20181104
		To examine the velocity measuring capability of Acoustic Doppler Velocimeter (ADV), especially for the low-velocity flows, the SonTek 16M MicroADV was taken as an example and the independently developed towing tank with high-precision velocity calibration facility was employed. During the tests, the indication errors for the velocities were measured. Besides, the influences of the signal intensity, the sampling frequency were analyzed on the velocity measuring capacity. The results verify that MicroADV can well indicate velocities with the relative errors smaller than 1% and absolute velocity errors not larger than 2.5 mm/s when the signal-noise ratios are above 15 dB in high-frequency sampling cases. As the sampling frequency increases, the measuring capacity for the time-averaged velocities will be influenced. Once the sampling frequency increases above 10 Hz, the probability that the measuring errors of the time-averaged velocities exceed 1% will become larger.
		2018 Vol. 37 (11): 36-42 [Abstract] ( 193 ) PDF (597 KB) ( 283 )

	43	Experimental study on open-channel flow confluence based on PIV technology
		CHEN Kailin, FENG Minquan, ZHANG Tao
		DOI: 10.11660/slfdxb.20181105
		The confluence of water flow that occurs in many hydraulic systems is usually very complicated in flow structure, and an in-depth examination of its behaviors is practically significant to the study of the confluences of a river main channel and the tributaries. This study adopts the PIV technology to overcome the shortcomings of single-point velocity measurements, observes the asymmetrical 3D flow structures of an open-channel confluence at different discharge ratios, and analyzes their variations with the discharge ratio. Results show that with an increasing discharge ratio, water surface slope decreases upstream of the confluence, while it increases over the junction area and in its downstream. And for the depth average velocity under an increasing discharge ratio, it is increased upstream of the confluence responding to the increasing backwater effect and over the junction area, but decreased in the flow separation zone. The PIV technology can better reveal the flow structure of a flow confluence and is applicable to the experimental study of the flows in open-channel confluences.
		2018 Vol. 37 (11): 43-55 [Abstract] ( 122 ) PDF (1996 KB) ( 403 )

	56	Experimental study on discharge capacity and hydraulic characteristics of oblique practical weirs
		HU Lin, ZHANG Yaozhe, WANG Wen’e
		DOI: 10.11660/slfdxb.20181106
		Oblique practical weirs are often the designers’ choice for mid- and small-scale water conservancy projects that are limited by natural riverbed boundary conditions, but their discharge capacity is still a technical issue. This paper examines the characteristics of flows around oblique practical weirs, analyses discharge coefficient and its influencing factors, and develops a discharge calculation method, based on 20 sets of experimental tests covering four oblique angles (0°, 30°, 45°, and 60°) and five discharges. Results show that in comparison to the normal weir in a channel with the same width, these weirs have larger approaching velocities and generally create no circulation zone, but in front of them the mainstreams are deflected. An oblique weir is more applicable when the water head is low, while under high water heads its discharge capacity still exceeds the normal weir. We work out a formula for calculating the discharge of oblique practical weirs and show its error in the range of 4.63% relative to the measurements, meeting the need of most engineering designs.
		2018 Vol. 37 (11): 56-64 [Abstract] ( 79 ) PDF (550 KB) ( 311 )

	65	Experimental tests and 3-D numerical simulations of water-filling process in free-flow branch tunnel
		WANG Kezhong, DENG Haohao, RU Rong
		DOI: 10.11660/slfdxb.20181107
		In water filling process, a free-flow branch tunnel shows transient flow characteristics and complicated flow conditions. In this work, we model the flow process using experimental tests on a normal scale model of a branch tunnel and 3D numerical simulations based on the standard turbulence modeling, focusing on velocity distribution, pressure distribution and flow pattern under different gate openings. By comparing test data and numerical simulations, we obtain water surface profiles at different time instants during the filling process, an optimized combination of the openings of two gates that meets the design discharge ratio, and a better tunnel shape.
		2018 Vol. 37 (11): 65-74 [Abstract] ( 116 ) PDF (2126 KB) ( 291 )

	75	Calculation and optimization analysis of multistage energy dissipation
		HUANG Chaoxuan
		DOI: 10.11660/slfdxb.20181108
		This paper analyzes multistage energy dissipation using the theory of hydraulics, mathematical derivation, and numerical analysis with Matlab to simplify repeated calculations in the design of multistage dissipators of water drops or practical weirs and lay a basis for optimal design of such dissipators. First, we derive analytical formulae for calculating contracted flow depth, depth after the hydraulic jump, and jump length, among other hydraulic parameters, by applying the Cartesian solution theory of cubic equations. And for the given flow coefficient φ = 0.80, 0.85, 0.90, 0.95 and 1.0, we work out high-accuracy lookup tables and curves for calculating relative flow depth hc'/T0 and relative hydraulic jump length Lj/T0 in engineering application. Then, an analytical formula for the depth of the last stage pool is obtained using the extreme value theory of stilling pool depth. Finally, two examples are used for comparative calculation and analysis, demonstrating the accuracy and convenience of applying our formulae. This study indicates that the design scheme of a multistage dissipator adopting equal head drops may not be optimal if considering the topography, geological conditions and excavation costs of the project. Thus, a variety of head drop alternatives should be compared and optimized to save project cost.
		2018 Vol. 37 (11): 75-84 [Abstract] ( 100 ) PDF (520 KB) ( 247 )

	85	Modeling cantilever bank collapse of peat-type meandering channel in Yellow River source region
		YANG Hanyuan, LI Zhiwei
		DOI: 10.11660/slfdxb.20181109
		Cantilever bank collapse is the dominant pattern in the peat-type meandering river of the Zoige basin in the Yellow River source region, but few previous studies were aimed at revealing this type of bank failure and its threshold conditions that determine the lateral migration rate of a meandering river. In this work, we apply a combination method of field measurement, theoretical model and numerical simulation to study the bank collapse process and its threshold conditions of a Ω-shaped bend in the upper Maiqu, a tributary of the Black River in the Zoige basin, focusing on the five cross sections of the bend where we take field measurements. A theoretical model of cantilever riverbank stability, namely BSTEM, is developed for this peat-type meandering river with composite bank layers of different soils, and static equilibrium equations are derived to describe cantilever tension failure and shear failure of the upper and lower layers. BSTEM is used to simulate the bank failure process of the silt layer at the five sections, and verified using the field-measured data of bank profile, bank soil composition, and hydrological parameters. We calculate the bank stability coefficient at a threshold collapse condition of the bank in flood period, and predict time changes in bank profiles at the five sections caused by three straight occurrences of bank failure, achieving a good agreement with measurements.
		2018 Vol. 37 (11): 85-96 [Abstract] ( 95 ) PDF (1787 KB) ( 303 )

	97	Impacts of drainage pipe network complexity on urban stormwater modeling
		LYU Heng, NI Guangheng, TIAN Fuqiang
		DOI: 10.11660/slfdxb.20181110
		Drainage pipe network is a key element in urban storm water routing, but it is often simplified in modeling because of data availability and modeling capability. To identify the function of such networks and understand the influence of its complexity on hydrological responses, we develop a routing-enhanced detailed urban stormwater model (REDUS) and apply it to simulations of the Tsinghua campus drainage, focusing on comparative analysis of typical storm water processes in two systems: a single drainage system and a dual drainage system. Results show that in either system, the network contributes to a rapid and directional discharge of flood water, and that a lower complexity in modeling dramatically underestimates the flood peak and volume when smaller pipelines are excluded from the system. Compared to the cases with no simplification, a drainage system only including the truck pipelines underestimates the flood peak and volume both by 27% for the single system, and it underestimates by 37% - 56% and 18% - 32% respectively for the dual system. Although the dual system ensures more accurate and reliable results, it relies on more detailed data of the pipe network. This study provides a useful tool and helpful suggestions on how to model drainage pipe networks for sponge city construction.
		2018 Vol. 37 (11): 97-106 [Abstract] ( 354 ) PDF (1830 KB) ( 522 )

	107	Experiment and analysis of river evolution under different planting densities of riparian vegetation
		BAI Yuchuan, YANG Shuqing, XU Haijue
		DOI: 10.11660/slfdxb.20181111
		To study the effects of different riparian vegetation densities on river evolution is practically significant for predicting the river evolution process in flood period and the ecological river engineering of artificial planting vegetation. In this work, a natural model experiment method is used to study the influence of different riparian boundary conditions of a river channel on its stability characteristics, bank erosion, and sediment transport intensity, by varying planting density and comparing single-bank planting and double-bank planting. The results show that (1) The riverbank is eroded differently with or without vegetation coverage. (2) With single-bank planting, the river bend has a poor stability, while with double-bank planting of larger coverage rate, it is easier for a river to form composite cross sections with a stable narrow, deep channel. (3) The variation in near-bank bed elevation is increased with an increasing coverage rate. Riparian vegetation plays a positive role in river bend stability and bank erosion resistibility, but it intensifies near-bank bed cutting.
		2018 Vol. 37 (11): 107-120 [Abstract] ( 151 ) PDF (1310 KB) ( 345 )