Journal of Hydroelectric Engineering

水力发电学报

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2017 Vol. 36, No. 7 Published: 2017-07-25

	1	Hydro-photovoltaic complementary technology research and application
		PANG Xiulan, ZHANG Wei
		DOI: 10.11660/slfdxb.20170701
		Qinghai Province has excellent solar resources and vast resources of decertified land, providing an ideal condition for large-scale development of solar photovoltaic power. This paper describes a new concept, virtual hydropower, that was aimed at large-scale development of photovoltaic power in Qinghai and ecological protection of the plateau regions in China. In this concept, a photovoltaic power plant is used as an additional unit of a hydropower station that rapidly adjusts its generating units and compensates for fluctuations in the photovoltaic power output so as to achieve an optimized total power output. Besides, studies were carried out on the impact of photovoltaic power plants on the regional ecological systems and on the cultivation of economic crops. Thus, progress has been made in using photovoltaic power plants to improve the ecological environment in the plateau regions.
		2017 Vol. 36 (7): 1-13 [Abstract] ( 301 ) PDF (3536 KB) ( 535 )

	14	TFPW-BS-Pettitt method for detection of multiple change-points in the mean of hydrological series
		ZHANG Hongbo, YU Yinghao, NAN Zhengnian, LI Zhehao
		DOI: 10.11660/slfdxb.20170702
		Hydrological variation is occurring in many areas, which often causes the ‘pollution’ of hydrological data and even makes the traditional hydrological frequency calculation in a difficult position. Although a few approaches to this issue have been proposed, some problems, such as different solutions obtained by different methods, masking effect, impact of autocorrelation, and overlapped variation information, are still barriers to developing hydrological design theories in the changing environment. In this paper, a TFPW-BS-Pettitt method is presented for the issue, which combines trend-free pre-whiting (TFPW), binary segmentation (BS) and Pettitt test to deal with the autocorrelation and masking effects occurring in change-point detection of streamflow data series. And hydrological frequency analysis is used to verify its accuracy in detection of change-point locations by comparing the data distributions before and after the change-points. Results indicate that this method can alleviate the autocorrelation effect on change-point detection through TFPW processing and eliminate the masking problem by BS algorithm, which makes multiple change-points detected effectively. Disadvantage in this new model is that the influence of data length on Pettitt test still remains. Especially when the length of a data sequence beyond the marginalized change-point is less than 5, this point is easily missed and thus a treatment of the edge effect should be done before detection. In addition, it is also found that when only change-points in mean exist in the sequence, an equal near-natural streamflow series can be obtained through calculation according with the data series containing the changes. And it may be used in the design to alleviate the impact of data lack in practical frequency analysis. When change-points in mean and variance both exist, such a series can be obtained only for the piece of data before the first change-point in the variance.
		2017 Vol. 36 (7): 14-22 [Abstract] ( 267 ) PDF (533 KB) ( 452 )

	23	Transformation of multi-objectives in water and sediment joint regulation of cascade reservoirs
		HA Yanping, BAI Tao, HUANG Qiang, JIN Wenting
		DOI: 10.11660/slfdxb.20170703
		To reduce sedimentation in the Ningxia-Inner Mongolia reaches of the upper Yellow, joint operation schemes of the Longyangxia and Liujiaxia cascade reservoirs were studied in this work to scour the river channel using artificial controlled floods. First, we analyzed the best time for regulating water and sediment and established a system of indexes to character the regulation. Then, a multi-objective operation model was developed and solved using a non-dominated sorting genetic algorithm (NSGA-II) to quantify the regulation effect in wet years or partial wet years. Third, four-dimensional vector coordinate systems were adopted to describe the objectives of the regulation schemes, and their sensitivity in different years was analyzed to clarify the impact of variables, such as controlled flow and water supply, on each objective. Lastly, transformation relationships among the objectives were revealed. The results are of great significance for implementing water and sediment regulation in the upper Yellow.
		2017 Vol. 36 (7): 23-33 [Abstract] ( 162 ) PDF (821 KB) ( 383 )

	34	Attribution of discharge changes over Wuding River watershed using a distributed eco-hydrological model
		JIAO Yang, LEI Huimin, YANG Dawen, YANG Hanbo
		DOI: 10.11660/slfdxb.20170704
		During the past five decades, a significant decrease occurred in the river discharge of the middle Yellow River main stream mainly because of climate changes and human activities in the Loess Plateau. Previous studies on the attribution of river discharge changes usually focused on the lumped effects of climate changes and vegetation growth on hydrological processes, neglecting the contribution by the vegetation growth caused by climate changes. This paper analyzed the variation trends of several eco-hydrological variables through a case study of the Wuding River watershed. Two types of simulations, assuming static and dynamic modes of vegetation changes separately, were carried out during the period 1961-2012 using a newly developed physically-based eco-hydrological model, CLM-GBHM. Results show that relative to the 1961-1971 discharge, 79.8% of the decrease in the 1972-2000 discharge was contributed by climate change itself while 74.6% by climate change and vegetation growth. And relative to 1972-2000, vegetation growth over 2001-2012 reduced the increasing trend in river discharge that would be produced directly by climate change, thereby leaving human activities as the major factor in the discharge reduction. All this shows a buffer effect of vegetation growth in the Wuding River watershed.
		2017 Vol. 36 (7): 34-44 [Abstract] ( 172 ) PDF (894 KB) ( 385 )

	45	Optimal operation of water-supply reservoirs in consideration of sensitiveness on operation periods
		PENG Anbang, WANG Xiaojun, LIU Jiufu, SUN Xinguo, HUANG Dui
		DOI: 10.11660/slfdxb.20170705
		This study developed a novel dimension-reduction method based on sensitivity analysis of reservoir operation periods to solve the problems of dimension disaster and local optimum trapping in calculation of complicated multi-objective reservoir optimal operation. In this method, different types of water-supply rule curves in the operation periods (as a time dimension) of one year are disturbed uniformly so as to obtain the sensitive degree to objective functions for each of the periods. Then, the positions (water level or water storage) of these rule curves in the sensitive operation periods are taken as variables to be optimized by iterative searching. After certain steps, the iteration is switched to a finer global searching. The results show that the method has advantages in search efficiency and high-quality solution and improves applicability of water-supply rule curves.
		2017 Vol. 36 (7): 45-54 [Abstract] ( 98 ) PDF (680 KB) ( 256 )

	55	Distribution of staged extreme rainfalls in flood season based on fuzzy set analysis
		SHU Zhangkang, LIU Ji, DONG Xiaohua, YU Dan
		DOI: 10.11660/slfdxb.20170706
		Use of seasonal design flood can improve the utilization of flood resources while satisfying the reservoir safety requirement. Rainfall is the dominant factor in flood formation and hence its multi-stage calculation is a prerequisite and basis for calculating seasonal design flood. This paper presents a study on the distribution of staged extreme rainfalls in flood season based on fuzzy set analysis for the catchment of Dahuofang reservoir. We analyzed the flood season staged characteristics of the reservoir using a fuzzy set method, and constructed membership functions for pre-flood season, main flood season, and later flood season, by the theorem of the unity of opposites of variable fuzzy sets. Then, a staged extreme rainfall fitting model was developed, based on fuzzy set analysis, and the distribution patterns of extreme rainfalls in each stage of the reservoir is discussed. The results show that Gumbel, P-III, Weibull and GEV all are applicable to the distribution of extreme rainfalls over the study area, but the GEV function is optimal. The design rainfalls calculated by this fuzzy staging method is higher for main flood season than those by the actual staging but lower for later flood season, giving estimates favorable to the flood control and beneficial use of reservoirs.
		2017 Vol. 36 (7): 55-64 [Abstract] ( 164 ) PDF (879 KB) ( 344 )

	65	Hydraulic characteristics of sudden lateral enlargement and bottom drop aerators in spillway tunnels with mild slope
		WANG Fangfang, WU Shiqiang, WANG Wei
		DOI: 10.11660/slfdxb.201170707
		When an aerator, with a sudden lateral enlargement and a bottom drop, is operated behind a high-head radial gate in a spillway tunnel with mild bottom slope, its air cavity behind the bottom drop is often partially filled with a certain volume of backwater and water wings protruding above the water surface are generated under sidewall deflection. Based on theoretical analysis and physical model tests, this study demonstrated the main reasons for the air cavity backwater and water wings as two backflow sources and one water withdrawal mechanism, and emphasized the importance of a measure to minimize the angle of water nappe impinging on bottom slab at the reattachment of lower nappe surface. By optimization of aerators and comparative analysis, a new shape of the bottom slab with varying local slope is recommended to reduce the backwater and suppress the water wings. The optimized aerator design suggested by this study, its air concentration along the tunnel, and its effective operation under the range of operating water head were verified in-situ in an engineering project. In addition, relationship between the bottom and side cavities and their influence are also discussed in this paper.
		2017 Vol. 36 (7): 65-73 [Abstract] ( 119 ) PDF (1448 KB) ( 322 )

	74	Effects of changes in water levels on power output and stability of tubular turbine sets
		LI Zhenggui, REN mingyue, YANG Fengyu
		DOI: 10.11660/slfdxb.20170708
		As the convertible energy of a hydroelectric generating set depends largely on the potential energy of its head water relative to tail water, reservoir stage and tail water level are major factors influencing its output capacity and running stability, especially for a tubular turbine that, working in the condition of relatively small potential energy differences, is more sensitive to variation in power output and stability of the water levels. In this work, we simulated and analysed the flows in a tubular turbine working by the design operation curve. Results show that the reservoir stage and tail water level are major factors that affect its power output at fixed working conditions, and that by adjusting them the output can be improved considerably. In addition, by adjusting both the flow structures inside the turbine and these water levels, the stability of the turbine set can be enhanced. The conclusion has been verified using in-situ measurements.
		2017 Vol. 36 (7): 74-82 [Abstract] ( 139 ) PDF (2728 KB) ( 392 )

	83	Fault diagnosis of hydroelectric sets based on EEMD and SOM neural networks
		LI Hui, JIAO Mao, YANG Xiaoping, BAI Liang, LUO Xingqi
		DOI: 10.11660/slfdxb.20170709
		Aimed at the non-stationarity and particularity of the vibration signals of hydroelectric sets, a new fault diagnosis method combining singular spectrum entropy based on ensemble empirical mode decomposition (EEMD) with a self-organizing feature map network (SOM) is presented. First, EEMD was used to decompose the vibration signals of a hydroelectric unit to obtain their intrinsic mode function (IMF), and then singular spectrum decomposition was performed to obtain their singular spectrum entropy: a dynamic eigenvector that characters the signals. Finally, this feature vector was input into a trained SOM neural network for automatic recognition of the fault. The results show that this method can extract the fault characteristics of the unit accurately and it has a higher recognition accuracy and faster calculation speed.
		2017 Vol. 36 (7): 83-91 [Abstract] ( 156 ) PDF (1122 KB) ( 353 )

	92	Water content variations in the process of concrete setting
		XU Wenbin, LI Qingbin, HU Yu
		DOI: 10.11660/slfdxb.20170710
		Interlayer performance of layers-poured mass concrete is closely related to the water state of lower fresh concrete layer. This study focuses on variations in water content of such concrete and the mechanism of water migration and offers a guide for pouring construction in layers. We used the low field nuclear magnetic resonance technology and further developed it to measure the water content and its distribution in fresh concrete with different compositions and different water-cement ratios under various pouring environments. The results indicate that the major factors in water migration during concrete setting are hydration, evaporation and migration and that the trends of variations in water content and its spatial distribution are controlled by changes in the pouring environment, especially those changes in the surface layer. A further examination on the patterns and mechanism of water migrating inside the concrete reveals that the migration is dominated by quasi-laminar flows driven by density differences at early setting stage while by diffusion under humidity gradient at late setting stage.
		2017 Vol. 36 (7): 92-103 [Abstract] ( 161 ) PDF (658 KB) ( 280 )

	104	Optimization of RCC dam construction schemes using an entropy-D model
		WANG Qianwei, ZHONG Denghua, YAN Yuling, SHI Mengnan, REN Bingyu
		DOI: 10.11660/slfdxb.20170711
		Optimization of RCC dam construction schemes is a typical multi-attribute decision-making process that requires a comprehensive consideration of several factors such as construction period, utilization rate of machines, and investment scale. Most previous studies neglected the influence of differences in the experts’ knowledge and the fuzziness in the experts’ judgment on construction scheme decision and assumed the index weights subjectively in optimization of the schemes without a clear mathematical basis. This paper describes an optimization method of RCC dam construction schemes using an entropy-D model that, based on the D-number theory, does not need the completeness of decision-making information. First, the Pearson correlation test method is used to analyze the correlation between evaluation indexes obtained from simulations of four schemes. Then, index weights are determined using an entropy-weighted method and the D-number theory is applied to calculate the D-numbers of each scheme in different identification frames. Finally, combination rules of the D-numbers are determined and recursive combination is carried out according to the trust degrees of different experts and the weights of different indexes. And integration of these fusion results gives a comprehensive evaluation index of the schemes and hence an optimal scheme can be selected. Engineering applications show that this method can achieve an effective scheme optimization for RCC dam construction with incomplete decision information.
		2017 Vol. 36 (7): 104-112 [Abstract] ( 107 ) PDF (712 KB) ( 309 )

	113	Blade design of tidal current turbines using blade element theory
		LI Dongkuo, ZHENG Yuan, ZHANG Yuquan
		DOI: 10.11660/slfdxb.20170712
		The blade element theory was used to design tidal current turbines in this study to improve their hydraulic performance and meet the growing need of tidal current energy utilization. We adopted a correction factor to optimize the chord length and setting angle of the blades and obtained a new horizontal axis tidal current turbine of better hydraulic performance. This new turbine was simulated using a CFD code. Results show that it has a high power factor in the rated condition. Analysis of the flows in the internal and external channels of the turbine reveals that the flows have excellent three-dimensional characteristics, free of local separation or reverse flow.
		2017 Vol. 36 (7): 113-120 [Abstract] ( 131 ) PDF (1306 KB) ( 474 )