Journal of Hydroelectric Engineering

水力发电学报

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2020 Vol. 39, No. 4 Published: 2020-04-25

	1	Experimental study on Backward Bent Duct Buoy wave energy converter with a plate
		CHEN Wenchuang, ZHANG Yongliang, YU Huifeng, SHENG Wanan
		DOI: 10.11660/slfdxb.20200401
		This study develops a novel Backward Bent Duct Buoy (BBDB) Oscillating Water Column (OWC) wave energy conversion device with a plate to improve Capture Width Ratio (CWR) and widen response frequency band width. To examine its performance and the effect of the plate, this study tests its physical model in a wave tank and calculate its pneumatic energy conversion through air pressure measurement and using a formula of the flow rate-air pressure relationship. Its behaviors are examined for the conditions of various orifice area ratios, mooring locations, and drafts; and compared with those of a conventional BBDB-OWC converter under a set of wave conditions. The results reveal that this device has the maximum CWR 13.8% larger and its wave frequency range of CWR > 70.0% is widened by 21.9%. Thus, the plate helps improve CWR and response frequency band width.
		2020 Vol. 39 (4): 1-9 [Abstract] ( 262 ) PDF (1453 KB) ( 486 )

	10	Experimental study on effect of fluid shear on juveniles of four major Chinese carp species
		WANG Yu, ZHAI Zhennan, LI Jinfeng
		DOI: 10.11660/slfdxb.20200402
		Severe fluid shear is believed to be a source of injury and mortality to fishes that pass through hydroelectric turbines. Developing fish-friendly hydroelectric turbines requires an understanding of the effect of water shear stress occurring in turbine passage on fishes. This study conducts experimental tests of this effect for the juveniles of four major Chinese carp species, using a test facility that was designed specifically for testing the response and injury degree of these fishes. The results indicate that all the four types of juveniles will suffer injuries when impacted by a water jet with flow strain no less than 2179 m?s-1m-1, and the injury degree is increased with the increasing strain. And the injury degree depends not only on the species, but on the orientation of the water jet relative to the fish body. The results can be used to estimate the possibility of the Chinese carp juveniles passing the turbine to be injured by water shear, thus helping design fish-friendly turbine systems.
		2020 Vol. 39 (4): 10-20 [Abstract] ( 174 ) PDF (1206 KB) ( 409 )

	21	Experimental study on flow structures in sine-generated meandering channel
		CAO Yufen, GAO Shuxian, BAI Yuchuan
		DOI: 10.11660/slfdxb.20200403
		To study the three-dimensional structure of the flows in a narrow, deep curved main channel in a river reach, we conduct acoustic Doppler velocimetry (ADV) measurements of the 3D flows in a sine-generated meandering laboratory channel, using 12160 gauge points located at 40 cross sections. The results show that in the channel, the curved bank boundaries cause changes in flow structure, and near the cross sections of zero curvature occurs a transition zone where the dynamic axis of flow swings between two banks. In near-bank regions, streamwise velocity takes fluctuating variations along the banks, with low velocity zones occurring near the concave bank; fluctuations along the left and right sides feature the same wave length but a phase difference of 180o. At all the cross sections, a main circulation near the bottom of the channel center and small reverse circulations near the water surface of the near-bank regions can be observed; the main circulation takes the lowest intensity around each bend vertex. At certain cross sections, small circulations rotating in the same direction as the main one also occur near the water surface of the near-bank regions. The experimental data can provide validation for numerical simulation with continuous multiple curves.
		2020 Vol. 39 (4): 21-32 [Abstract] ( 142 ) PDF (1630 KB) ( 442 )

	33	Riverbed adjustment characteristics in braided reaches of lower Yellow River under small and medium discharges
		JING Huan, ZHONG Deyu, ZHANG Hongwu, WANG Yanjun, HUANG Hai
		DOI: 10.11660/slfdxb.20200404
		The regimes of flow and sediment entering the Lower Yellow River (LYR) have changed significantly since the Xiaolangdi Reservoir started to operate, causing a great reduction in high flood frequency and enhancing the role of small and medium discharges. To reveal the bed evolution of the LYR braided reaches under small and medium discharges, this study conducts physical model tests on the Heigangkou-Jiahetan Reach using constant discharges of 500, 1000, 1500, and 2000 m3/s. The results reveal three key conclusions. (i) Vertically, riverbed erosion and deposition are distributed alternately along the channel, manifesting a typical evolution of braided reaches. (ii) Laterally, considerable lateral migration of the main channel can also occur in the LYR braided reaches under small and medium discharges. With the discharge increasing, the bending coefficient decreases from 1.18 to 1.13 and the main channel develops from winding to straight. (iii) Longitudinally, the adjustment trends in thalweg profile under all the test discharges are basically consistent with the variations in the amounts of sediment erosion and silting along channel. This paper examines the spatiotemporal adjustments in the riverbed near training works and a bridge downstream, and presents the results of numerical simulations using a stochastic model. It reveals that temporally, vertical adjustment is relatively fast in early stage and then slows down rapidly; spatially, the accumulated riverbed degradation downstream of the bridge decreases nonlinearly along the channel until it diminishes, exhibiting significant spatial decay characteristics. Applications show that our stochastic model has good adaptability to spatiotemporal adjustments of typical short reaches, and that the correlation R2 between measured and calculated results can be up to 0.74. The results of this study would help the future channel regulation and protection of the LYR braided reaches under small and medium discharges.
		2020 Vol. 39 (4): 33-45 [Abstract] ( 128 ) PDF (1136 KB) ( 323 )

	46	Denoising vibration signals from hydroelectric generating units using EMD-based consecutive geometric distribution similarity measure algorithm
		DANG Jian, LI Ji, JIA Rong, FAN Pengfei
		DOI: 10.11660/slfdxb.20200405
		Given the fact that hydroelectric generating units are often used for peak and frequency modulation and spinning reserve, noise reduction of their vibration signals is dramatically significant to promoting the incipient fault identification and safe operation of power systems. This paper develops a novel EMD-based denoising algorithm using the similarity measure between consecutive geometric distributions. The signals was reconstructed by using different intrinsic mode functions generated from EMD sifting, and fitted the probability density functions of these reconstructed signals by the nonparametric kernel density estimation theory. Then, a Hausdorff distance was adopted to calculate the indexes for evaluating the similarity measure between the consecutive geometric distributions of probability density functions, and an optimal separation between characteristic IMF components and noisy IMF components is carried out through variation trend analysis of the similarity measure indexes. This method is validated using model simulations and engineering application, and the results demonstrate it achieves a remarkable effect on noise reduction of hydroelectric generating unit signals.
		2020 Vol. 39 (4): 46-54 [Abstract] ( 142 ) PDF (937 KB) ( 323 )

	55	Second-order approximate solution of weight-function unsteady friction model of transient flows
		LIU Jing, ZHOU Ling, CAO Bo, LIU Deyou
		DOI: 10.11660/slfdxb.20200406
		For one-dimensional water hammer simulations, the weight-function unsteady friction model is considered to be the most accurate model compared with steady-state friction models, as it describes pressure attenuation accurately through fully considering the influence of the past velocity and acceleration on shear stress in hydraulic transients. Due to the complexity of convolution integral terms and the consideration that a first-order accurate solution is satisfactory for most of the problems, its previous solutions are based on the first-order methods of characteristics (MOC). To improve accuracy, this paper derives a second-order approximate solution of the MOC convolution integral, and verifies its accuracy against experimental data. Results show that the new scheme is second-order accurate and the first-order scheme leads to computational errors that increase with the increase in grid size, flow velocity and viscosity.
		2020 Vol. 39 (4): 55-61 [Abstract] ( 144 ) PDF (1487 KB) ( 256 )

	62	CFD simulations of pump-trip runaway process pressure pulsation of a model pump-turbine
		ZHANG Chenghua, YOU Jianfeng, TAI Rong, WANG Xi, LIU Ying, CHENG Yongguang
		DOI: 10.11660/slfdxb.20200407
		The runaway transient process after pump-trip accompanied by invalid wicket gates is an event very dangerous to pumped-storage power stations. Violent fluctuations in water hammer, flow patterns, pressure pulsations, and runner forces are the issues that lack understanding and need further studies. In this work, A CFD method coupling the one-dimensional waterway flow and three-dimensional flow was adopted in a model pump-turbine to simulate this fast-evolving process. Analyzing the histories of discharge, rotational speed, and runner forces, it find that the fluctuations of these parameters are obvious in the hump and S regions of the characteristic curves. Examining pressure pulsations at different monitoring points, it find that the pulsating characteristics all over the four-quadrant characteristic plane are complicated and can be classified to four types: high frequency-low amplitude, high frequency-high amplitude, middle frequency-middle amplitude, and low frequency-high amplitude. In the hump and S regions, both high- and low-frequency components become stronger, while in the normal operation regions all the components calm down. The flow patterns shows that high-frequency components come from rotor-stator interaction, and middle- and low-frequency components are from the vortices in the sections of guide vanes, runner blades and draft tube.
		2020 Vol. 39 (4): 62-72 [Abstract] ( 232 ) PDF (2102 KB) ( 350 )

	73	Numerical simulation of triaxial tests on gravelly soil based on DEM of irregular-shaped particles
		CUI Bo, DENG Boqi, LIU Minghui, YU Jia, WANG Xiaoling
		DOI: 10.11660/slfdxb.20200408
		Mechanical properties of the gravelly soil of an earth-rock dam core wall directly affect its settlement deformation and structure safety. Most previous studies focus on the proportion and spatial distribution of its gravel blending, and lack consideration of the influence of different gravel shapes on the soil mechanical properties. This paper presents a numerical discrete element method (DEM) for simulating the gravelly soil of irregular-shaped particles to explore this shape influence. First, we construct a model library of three-dimensional irregular gravels based on the test data collected using 3D laser scanning technology, and suggest a three-variable shape evaluation standard to classify the particle shape characteristics. Then, we formulate a particle in-situ replacement method and use it to construct a particle flow model for gravelly soil. Finally, numerical tests of triaxial compression on different gravel shapes are carried out to investigate the mechanical properties of gravel soil. Results show that this standard is simple and effective and can identify accurately the multiple shape characteristics of irregular gravel. Gravel shape has a significant influence on the macroscopic mechanical properties of gravel soil; uniformity in blending various gravel shapes helps increase the strength of soil samples, thus suggesting a new direction for improving the gravel soil of earth-rock dam core walls.
		2020 Vol. 39 (4): 73-87 [Abstract] ( 165 ) PDF (5889 KB) ( 594 )

	88	Comparative study on comprehensive methods for dispersive soil discrimination
		ZHANG Lu, YANG Xiujuan, FAN Henghui, QIU Weizhao, TAO Ran, ZHAO Wenhe
		DOI: 10.11660/slfdxb.20200409
		The dispersivity results of certain soil samples are often inconsistent when tested using the five common methods of pinhole, double hydrometer, crumb, pore water soluble cation, and exchangeable sodium ion; a variety of other comprehensive methods for discriminating soil dispersivity have been developed in previous studies. This paper presents an analysis of the advantages and disadvantages of these five methods based on 45 sets of soil samples collected from 8 water conservancy projects, focusing on comparison of the qualitative discrimination results of the original authors with our comprehensive quantitative results obtained using weight analysis and a rating system. The results show that the weight analysis and the rating system are reliable and the rating system leads to comparatively low safety. We also verify the accuracy of an empirical formula. This formula features simple parameters and clear physical meanings and its results have a tendency toward higher reliability and security. Therefore, we suggest that it could be adopted for preliminary discrimination and then more accurate dispersive soil characteristics are examined through weight analysis or a rating system.
		2020 Vol. 39 (4): 88-100 [Abstract] ( 114 ) PDF (597 KB) ( 334 )

	101	Experimental study on creeping of artificial ruin soils
		WANG Kai, HU Zaiqiang, SHE Haicheng, LIANG Zhichao, FENG Zhe, JIAO Hanwei
		DOI: 10.11660/slfdxb.20200410
		Glutinous rice pulp has a great influence on the strength of ancient ruin soil. To study its effect on soil creeping properties, we prepare artificial ruins adding different water contents and different amounts of glutinous rice paste, conduct uniaxial creep tests, and examine the creeping properties of these artificially prepared ruins under different pressure conditions. The test results show that larger water content results in more obvious soil creeping. As the amount of added glutinous rice pulp is increased, the creep shows a trend of decreasing first and then increasing, and it reaches its minimum value when the mass ratio of soil to glutinous rice is 90:10. To simulate the creeping properties of the artificial ruin soils, we develop an empirical creep model and a fractional calculus-based nonlinear viscoelastic model. Comparison indicates that this nonlinear model can make up for the defect of traditional empirical models that fail to describe instantaneous strain, thus better reflect the creeping characteristics of artificial ruin soils.
		2020 Vol. 39 (4): 101-109 [Abstract] ( 110 ) PDF (686 KB) ( 235 )

	110	Neural network model for evaluating compaction quality of rockfill materials by compaction meter value
		AN Zaizhan, LIU Tianyun, HUANGFU Zehua, ZHANG Qinglong, LI Congshi, LI Qingbin
		DOI: 10.11660/slfdxb.20200411
		Compaction quality of earth-rock dams is crucial to dam safety, and for rockfill material it can be monitored in real time via a compaction quality assessment model. Rolling parameters are kept constant during traditional compacting construction using a fixed scheme, while in intelligent compaction they are adjusted and optimized based on the compaction state in-situ. Thus a good model for compaction quality assessment should take rolling parameters into account. This paper presents an analysis of the correlation of compaction meter value (CMV) with the relative density of rockfill materials and rolling parameters based on field compaction tests. Results show that CMV is strongly correlated with the relative density and it can be used as a good index for compaction quality assessment of rockfill materials. And it is significantly influenced by roller vibrating frequency and roller speed, while driving direction is an insignificant factor. Using the field test data and a radial basis function (RBF) neural network, we develop a compaction quality assessment model involving rolling parameters which achieves a high accuracy verified by the field test results.
		2020 Vol. 39 (4): 110-120 [Abstract] ( 331 ) PDF (1903 KB) ( 475 )