Journal of Hydroelectric Engineering

水力发电学报

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2021 Vol. 40, No. 4 Published: 2021-04-25

	1	Channel degradation and river stage variations in reaches downstream of Three Gorges Reservoir ^Hot!
		LI Yitian, XUE Juli, SUN Zhaohua, ZHOU Weixing
		DOI: 10.11660/slfdxb.20210401
		Field observation data for the middle and lower Yangtze before and after the operation of Three Gorges reservoir (TGR) have been collected and analyzed in this study to examine the relationship between channel erosion and sediment transport in the reaches downstream of TGR and to evaluate the impact of channel degradation on the river stage in flood season and low flow season. Our detailed analysis includes variations in flow and sediment regimes at the hydrological stations, spatial distributions and time variations in erosion volume in the river channel, and river stage variations with different discharges. The results show that the concentrated scour in low-flow channels is related not just to the decrease in flood frequency and longer duration of medium flows, but to the characteristics of channel scour at a high rate under medium flows and a low rate under flood flows. The main erosion zone has been moving downstream over time, and up to the present it has been staying in the Jingjiang reach. At the Jianli station, the annual mean transport of coarse sediment (d > 0.125 mm) has recovered to the same multi-year mean level as before TGR impoundment, while most of the erosion in the long reach immediately downstream of Chenglingji was related to fine grain sediment. Channel erosion caused a significant drop in the medium and low river stages, and such a tendency showed a growing rate in the sandy reaches upstream from Chenglingji. However, the river stage did not drop considerably when the channel flow was above a certain threshold around the bankfull discharge. We estimate the main characteristics of river stage changes discussed above will be maintained in quite a long period in future.
		2021 Vol. 40 (4): 1-13 [Abstract] ( 388 ) PDF (1048 KB) ( 569 )

	14	Characteristics of non-uniform sediment transport in braided reach of the Lower Yellow River
		GE Xiangyang, XIA Junqiang, ZHOU Meirong, DENG Shanshan, CHENG Yifei
		DOI: 10.11660/slfdxb.20210402
		The Lower Yellow River (LYR) is featured with complicated processes and trends of sediment transport due to its high sediment concentration and rapid channel adjustment. Its sediment transport characteristics are an essential factor for flow-sediment control and river planning. This study examines non-uniform sediment transport in the Huayuankou-Jiahetan reach (HJR) and Jiahetan-Gaocun reach (JGR) based on the 1986-2015 survey data of flow, sediment, and cross-sectional profiles, achieving the following results. (i) For fine sediment, an empirical formula of its transport rate manifests an excellent correlation coefficient of 0.99. (ii) The sediment discharge ratio (SDR) is negatively correlated with both the sediment coefficient of incoming flow and hydraulic geometry, but its variation becomes very mild when the latter factor is increased up to a rather large value (30 m-1/2). In JGR, the SDR of medium-grained sediment is more correlated to these two factors than fine or course sediment, while in HJR, the SDR of its fine sediment and coarse sediment more correlated. (iii) When the influences of both the flow and sediment conditions and the channel geometry are considered, all the empirical formulae are improved greatly, offering much better prediction accuracy and higher correlation coefficients in the range of 0.48 - 0.65.
		2021 Vol. 40 (4): 14-24 [Abstract] ( 199 ) PDF (1347 KB) ( 507 )

	25	Power generation benefit distribution mechanism of cascade hydropower stations grouped by aggregation and dimensionality reduction
		HE Yong, ZHANG Lechen, LI Wenbin, ZHANG Taiheng, SHI Chaobo
		DOI: 10.11660/slfdxb.20210403
		Aimed at a large number of cascade hydropower stations, this article aggregates all the stations into a small number of groups according to their operating management relationship, upstream/ downstream relationship, regulation performance, and joint dispatch relationship. For these cascade groups (hydropower stations), we consider the types of their cooperation under joint dispatching for the goal of maximizing their multi-year average power generation. We model their generation benefit and allocate the compensation benefits to groups and the hydropower stations within each group based on the cooperative game theory and a method of comprehensive weights assignment, achieving a corresponding benefit distribution mechanism. Application to the cascade stations shows our method effectively reduces the number of models and improves calculation efficiency through the aggregation and dimensionality reduction of the stations. More important, it can reasonably quantify and distribute the compensation benefits among the groups and among all the hydropower stations, which is of great significance for coordinating different groups and different hydropower stations and promoting their participation in cascade joint dispatching.
		2021 Vol. 40 (4): 25-34 [Abstract] ( 222 ) PDF (463 KB) ( 537 )

	35	Analysis on influence of eccentric pins on opening of cylindrical water distributor of hydro turbines
		DU Zhipeng, WU Jianjie, LIU Xuedong, XU Haibo
		DOI: 10.11660/slfdxb.20210404
		In the cylindrical water distributor of a hydro turbine, eccentric pins are usually used to compensate manufacture deviations and worn surfaces, but their influence on the opening of wicket gates is often ignored. First, this paper develops an ideal model for the gate opening and derives a motion relationship among the assembled parts to realize the gate opening mechanism for the case without eccentric pins. Then, using this model, we examine two types of eccentric pins and use Matlab to calculate and depict curves representing the influence of the pins on the angle of the fully opened gates. The analysis shows that two dominant factors are the eccentricity of the pins and those parts that are locked to the pins, and the latter factor is more significant and should be emphasized. In design and installation, a reasonable eccentricity and appropriate locked parts should be considered and selected, and the same eccentric direction should be guaranteed for the eccentric pins locked to the regulating ring.
		2021 Vol. 40 (4): 35-42 [Abstract] ( 181 ) PDF (1890 KB) ( 436 )

	43	Study on body shapes of bifurcated pipe guide plate for pumped-storage power stations
		DAI Yuan, FANG Jianyin, WU Yang, WU Wenping
		DOI: 10.11660/slfdxb.20210405
		The shape of the bifurcated pipe has a great impact on the head loss of a pumped-storage power station, and affects its operating benefits indirectly; optimizing the shape is a research hotspot. To reduce head loss, this paper develops a new design method of the guide plate to improve the traditional bifurcated pipe and verifies its accuracy of numerical simulations of the flows in an abrupt contraction pipe. We also compare its velocity distributions with those in the flow without this plate through numerical simulations and optimize its shape. The result shows the guide plate reduces the head loss in the bifurcated pipe section and helps stabilize flow patterns. The reduction is 43.4% and 12.6% in pumping mode and power generation mode respectively, showing a significant improvement on the power plant benefit by the optimized guide plate.
		2021 Vol. 40 (4): 43-49 [Abstract] ( 126 ) PDF (1513 KB) ( 523 )

	50	Cavitating flow characteristic analysis of flow and pressure regulating valve with piston
		TANG Zerun, ZHANG Baiyun, JIANG Jin, LIAO Zhifang, LI Yanhui
		DOI: 10.11660/slfdxb.20210406
		This paper presents a study of a flow and pressure regulating valve of DN200 type, using numerical modeling that combines a realizable k-ε turbulence model with a Zwart-Gerber-Belamri cavitation model. We focus on the cavitating characteristics of flows in the valve with small, medium and large openings, and the effects of valve opening and inlet-outlet pressure difference on these characteristics. The results show that high pressure and large velocity gradients occur in the orifice, flow separation appears near its inlet edge, and wall attaching shear vortices form at the wall. Flow separation and generation of these vortices are the mechanism of flow cavitating in the orifice. Under fixed inlet and outlet pressures, the total volume of cavitation bubbles increases linearly with valve opening, while cavitation strength varies insignificantly. As the cavitation coefficient is decreasing, the flow coefficient keeps stable first, then increases slightly, but decreases sharply after that. The results are useful for the structural optimization and operation maintenance of DN200 valves.
		2021 Vol. 40 (4): 50-58 [Abstract] ( 145 ) PDF (1889 KB) ( 639 )

	59	Analysis on flow structures and pressure pulsation in vaneless space of reversible pump turbine
		WANG Xiaolong, LIU Demin, LIU Xiaobing, TANG Wen, XU Lianchen
		DOI: 10.11660/slfdxb.20210407
		For a high-head Francis pump turbine, the instability during operation is mainly caused by hydraulic vibrations inside the machine. As a major cause of vibrations, the pressure pulsation in the vaneless space can possibly lead to fatigue failure under certain circumstances. This paper studies the flow field and pressure pulsation in the vaneless space between the guide vanes and runner of a model pump turbine under the generation conditions, by combining numerical simulations and physical model tests. We focus on the amplitude-frequency characteristics of flow instability and pressure pulsation, and analyze their variations under different loads. We also examine the flow field in detail on a physical model using particle image velocimetry (PIV). The mechanism and development of vortices and its influence on pressure pulsation in the vaneless space are emphasized.
		2021 Vol. 40 (4): 59-72 [Abstract] ( 280 ) PDF (12445 KB) ( 179 )

	73	Improved design method of gradation band curves for granular filters
		ZHANG Gang, WANG Hongyu, Israr Jahanzaib
		DOI: 10.11660/slfdxb.20210408
		Filter structures are extensively employed in various hydraulic and geotechnical structures as a key seepage control measure to prevent leakage and erosion. Based on different filter design criteria, several gradation band curve design methods are introduced, thereby offering apparent evidence for filter design. This paper reviews these design methods specified in Chinese and foreign granular filter design standards, their applications, and previous filtration tests; reveals the problems in the previous methods of gradation band curve type; suggests an improved method. This new method uses a new self-healing index to control the upper half of gradation curves, so that it can efficiently choose appropriate filters to avoid potential internal erosion, and make gradation curves more comprehensive and more straightforward. It is verified against previous filtration tests and engineering examples, and the results show that it efficiently discriminates between valid and invalid filters from the optional grading curves. Thus, our method provides new ideas and would be helpful in revising the relevant existing standards.
		2021 Vol. 40 (4): 73-83 [Abstract] ( 169 ) PDF (843 KB) ( 571 )

	84	Experimental study on 1-D consolidation permeability of saturated clay considering stress history
		ZHANG Le, DANG Faning, GAO Jun, DING Jiulong
		DOI: 10.11660/slfdxb.20210409
		A series of one-dimensional consolidation permeability tests were carried out using the GDS triaxial apparatus to study the influence of consolidation stress ratio and stress history on the characteristics of saturated clay. The results indicate that the permeability coefficient and void ratio of normal- and over-consolidated saturated clay decrease with the increase in consolidation stress ratio under different consolidation stress conditions with the same stress history. And the final compression of the specimens increases with consolidation stress ratio. Under the same consolidation stress ratio but different stress history conditions, the final compression of over-consolidated saturated clay is smaller than that of normal consolidated saturated clay. In addition, the difference σdv between consolidation stress σ and gravity stress σcz is fitted to the final compression sf of the specimen, and a good linear relationship between these two parameters is obtained for each consolidation stress. This study finds that for saturated clay, it is necessary to consider simultaneously the influence of both consolidation stress ratio and stress history on its 1-D consolidation and permeability, and the final compression can be accurately predicted if knowing its gravity stress.
		2021 Vol. 40 (4): 84-96 [Abstract] ( 98 ) PDF (873 KB) ( 429 )

	97	Influence of water content in fine-grained filling on continuous compaction indexes for dam construction
		GUO Huajie, JIAN Huihuan, GAO Mingxian, WU Longlian
		DOI: 10.11660/slfdxb.20210410
		To study the influence of water content in fine-grained filling material on continuous compaction control technology for earth-rock dam construction, laboratory model tests were conducted according to the similarity theory, and variations in vibration measurements are studied under different water contents in the filling. Influences of water content variations on the correlation calibration and applicability of the continuous compaction control indexes of different types are examined through linear regression analysis. Results show that: (1) the vibration compaction value (VCV) index is less affected by the water content under the same vibration compaction conditions, but the index Ks is just the opposite; (2) Water content no higher than its optimal value should be ensured when using a compaction meter value (CMV) or compaction control value (CCV) indicator for on-site rolling; (3) When water content falls in the range of 2% around its optimal value, CCV and vibratory control value (VCV) are highly correlated with compaction degree K; (4) Attention should be paid to the influence of water content on the continuous compaction indexes when determining the index of fine-grained filling in rolling compaction of earth-rock dams.
		2021 Vol. 40 (4): 97-105 [Abstract] ( 150 ) PDF (2404 KB) ( 527 )

	106	On seismic input method for layered foundation simulations
		BI Zhonghui, ZHANG Liaojun, ZHAI Yafei, CUI Binghui, ZHANG Hanyun
		DOI: 10.11660/slfdxb.20210411
		At present, most of the ground motion inputs for layered foundation simulations consider only the influence of different materials on wave speed, ignoring the refraction and reflection of waves at the interfaces of different media. To improve the simulations of elastic wave propagation in layered foundation, this study derives an equivalent load calculation formula considering the media interface refraction and reflection based on the wave theory, and constructs an artificial viscous-spring boundary model of layered foundation. We verify the model through example analyses. The results show this seismic input method can better meet the accuracy requirements of anti-seismic engineering, and is effective and practical for layered foundation design.
		2021 Vol. 40 (4): 106-113 [Abstract] ( 144 ) PDF (1116 KB) ( 368 )

	114	Intelligent fusion model and analysis method for rock parameter inversion of water diversion tunnel
		HE Yinpeng, SUN Xinjian, ZHANG Ye, GUO Huashi, LI Qiaoying
		DOI: 10.11660/slfdxb.20210412
		Back analysis of the mechanical parameters of surrounding rocks using a method without sufficient geotechnical tests, has been at the forefront in geotechnical engineering research. To obtain more reasonable and accurate surrounding rock parameters for a water diversion tunnel, an intelligent inversion model integrating multiple machine learning algorithms is developed, and the influence of the parameters on tunnel displacement is examined via sensitivity analysis. Parameters of 25 groups are designed using orthogonal experiment, and the displacements at the monitoring points are calculated through FLAC3D simulations. Then, based on these data, different algorithms are selected to construct an intelligent fusion model for calculations of elastic modulus, Poisson's ratio, cohesion, and internal friction angle. Finally, through a case study of the Yindajihuang water diversion tunnel in Qinghai, the influence of mechanical parameters of surrounding rocks on its displacements is analyzed. By back analysis using this model and FLAC3D forward calculations of the parameters, the settlements at the different positions are obtained with the errors of 5.01%, 3.21%, 3.87% and 4.17% in calculations of the crown settlement, bottom heave, and left and right spandrel displacements respectively relative to on-site measurements. These relative errors, smaller than those of the single models, indicate our intelligent inversion fusion model and analysis method are a significant improvement on surrounding rock parameter calculations.
		2021 Vol. 40 (4): 114-126 [Abstract] ( 186 ) PDF (2465 KB) ( 806 )