Journal of Hydroelectric Engineering

水力发电学报

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2016 Vol. 35, No. 12 Published: 2016-12-25

	1	New seepage-proof and reinforcing technologies for dikes and dams and their applications
		WANG Fuming, LI Jia, SHI Mingsheng, GUO Chengchao
		DOI: 10.11660/slfdxb.20161201
		Anti-seepage and reinforcement for dikes and dams have been a huge and heavy task in China. The current technologies of dikes and dams using vertical impermeable and reinforced structures have disadvantages and limitation and become a bottleneck in design of practical seepage-proof and reinforcing works. In contrast, non-water reacted two-component polyurethane has a good overall performance and environmentally friendly properties; it is suitable for seepage-proof and reinforcing material of dikes and dams. This paper describes a new method for constructing polymer flexible anti-seepage walls that is based on the material properties and the mechanism of diffusion in soils. Compared with the conventional anti-seepage walls of cement concrete, this method has advantages of little disturbance, good anti-seismic, anti-cracking property, and convenience in construction. We also present three corresponding technologies of polymer grouting ? underwater grouting, membrane bag grouting, and compound grouting ? which are based on the characteristics of polymer reaction and expansion in water and the mechanism of polymer diffusion in coarse-grained soils. All these grouting technologies are particularly suitable for treating localized leakage and piping in water conservancy projects. Polymer grouting technologies for earth dikes and dams have been applied in a variety of major projects and their seepage-proof and reinforcing effects are excellent.
		2016 Vol. 35 (12): 1-11 [Abstract] ( 271 ) PDF (2167 KB) ( 1016 )

	12	Scale effects of rockfill materials considering size effect of particle strength
		LI Xiang, MA Gang, ZHOU Wei, YANG Lifu, LIU Jiaying
		DOI: 10.11660/slfdxb.20161202
		By statistical analysis of previous studies and laboratory tests on scale effects of rockfill materials, it could be argued thatthe size effect of particle strength should be the major cause for the scale effect obtained in the condition of the same particle source and the same sample preparation method. Then, in this study an expressionfor describing the strength of particles with different sizes was integrated into a survival probability model based on the Weibull distributions, and the size effect of particle strength was calculated using a combined finite-discrete element method (FDEM). The mechanism of scale effect was also examined at meso-scopic level. The simulation results show that the scale effect was dominated by anisotropy in normal contact force. With the same size effect parameter of particle strength, peak internal friction angle was decreased with the increasein the maximum particle size, while volume strain at damage point took a reverse trend. For the tests of same particle size, a decrease in the size effect parameter led to a decrease in peak internal friction angle but an increase in volume strain. When the size effect of particle strength was considered, increasing the maximum particle size caused the particle strength to decrease and the average particle normal and tangential contact forcesto increase. This explains why particles with different sizes show an obvious scale effect in laboratory tests.
		2016 Vol. 35 (12): 12-22 [Abstract] ( 371 ) PDF (3104 KB) ( 626 )

	23	Development history and frontiers of river environmental flow research
		LIU Yueyi, ZHU Jinfeng, ZHAO Jianshi
		DOI: 10.11660/slfdxb.20161203
		Construction and operation of reservoirs, dams, channels and other hydraulic projects altered the flow regime of rivers and their morphology evolution, and caused other problems including degradation in the ecological functions and reduction in the species diversity of rivers. This paper reviews the research on river environmental flow and its development in recent three decades, points out its three developing stages, and examines the characteristic of each stage. Facing with changing environments, further studies of river environmental flow should pay more attention to the integrity of ecosystem, modeling its mechanism, and the applicability in practice of ecological operation. In such studies, climate change, spatial heterogeneity, and correlation between ecological and social systems would become the frontiers and major focuses.
		2016 Vol. 35 (12): 23-34 [Abstract] ( 345 ) PDF (373 KB) ( 922 )

	35	Optimal operation model of cascade reservoirs based on grey discrete differential dynamic programming
		SHI Yajun, PENG Yong, XU Wei
		DOI: 10.11660/slfdxb.20161204
		In this paper, a grey discrete differential dynamic programming (GDDDP) algorithm based on the grey system prediction is presented for solving the problems of poor global convergence and low calculation efficiency in application of the discrete differential dynamic programming (DDDP) to optimal operation of cascade reservoirs. As an improved DDDP method for better accuracy and efficiency, this new algorithm adopts the grey system prediction and makes forecasting before each iteration, and then starts the iteration using the forecasted trajectories of all the reservoirs and taking the data sequences of optimal trajectories and forecasted trajectories obtained in previous iterations as an input of the ongoing iteration. It also adopts a recursive arithmetic progression formula to eliminate the low accuracy defect of the grey system prediction method in its forecasts of oscillatory sequences. A case study of the operation of Baishan-Fengman cascade reservoirs is given to verify the effectiveness of GDDDP.
		2016 Vol. 35 (12): 35-44 [Abstract] ( 345 ) PDF (1529 KB) ( 499 )

	45	Analysis on operation of pumped storage power plants for reducing surplus water
		LIU Minghao, WANG Liping, LI Chuangang, WANG Boquan
		DOI: 10.11660/slfdxb.20161205
		This paper presents a new operation scheme of pumped storage power plants for improving their capability of peak load regulation with no increase in power system load. First, according to the working principle and working characteristics of pumped storage plants in a power system, we analyzed their peak load regulating role in power balance of the system and the losses in the power outputs due to abandoning surplus water by hydropower plants in flood season. Then, a scheme was formulated for better use of the surplus water through adjustment of the operation of the plants. In this scheme, a higher priority is given to the power generating efficiency of the plants and their storage capacity is preferably used to improve the efficiency. If the system peak load is shifted by daily regulation of the plants in this case, the peak-valley load difference and peaking capacity demand of the power system can be reduced. Calculation results show that this method produces a significant improvement on the system capability of reducing surplus water consumption, relative to the case that all the power plants share the reserve and adopt the traditional operation mode of peak load shifting. Thus, this new scheme is effective and feasible and it brings about significant benefit of power generation.
		2016 Vol. 35 (12): 45-55 [Abstract] ( 289 ) PDF (597 KB) ( 503 )

	56	Effects of trend-free pre-whitening methods on trend detection in Mann-Kendall test of runoff series
		ZHANG Hongbo, WANG Bin, XIN Chen, LAN Tian
		DOI: 10.11660/slfdxb.20161206
		Trend-free pre-whitening (TFPW) is a key method for removing the effect of autocorrelation when a non-parametric Mann-Kendall (MK) trend test is used in analysis of river runoff series. However, its rationality and applicability are questioned in the cases that some hydrological changes occur in a changing environment, thus catching researchers’ increasingly attention. In this study, we adopted a hybrid TFPW for data-preprocessing prior to applying the MK trend test to evaluate its performance in analysis of the runoff series featured with hydrological changes, focusing on six detrending measures, i.e. the slope method (SM), EMD method, first order differential method (FD), log-linear detrending method (LLD), 5-point linear moving average method (LMA), and linear regression moving average method (LRMA). This approach is coupled with two pre-whitening methods, one for removing autocorrelation AR(1) only, and the other for removing all the AR(n)s where n stands for all the lag orders of significance. A case study was taken testing the runoff series gauged at the three gauge stations of Dingjiagou, Shenmu and Suide in northern Shaanxi that represent three types of trend changes in the series respectively. These calculations, as results of different hybrid TFPW-MK testing, were compared with those by conventional and modified MK methods. The comparison shows that different hybrid TFPWs give different MK test results of the runoff series. All the detrending methods are good and similar when only AR(1) is removed, while when all the AR(n)s are removed, only LMA and LRMA work satisfactorily and even the SM, if coupled with the conventional TFPW, works poorly deviating far away from the real case. This indicates that among all the TFPW methods, LRMA with AR(n) being retained is the best owing to less autocorrelation information lost in its detrending process and more autocorrelation removed in its pre-whitening. In addition, the conventional TFPW-MK, or SM coupled with the AR(1) removal, can still achieve acceptable results, and the original TFPW procedure is effective only when AR(1) is removed.
		2016 Vol. 35 (12): 56-69 [Abstract] ( 588 ) PDF (613 KB) ( 759 )

	70	Regulation model of ecological water demands by sluice-controlled rivers based on hydrological regime analysis
		ZUO Qiting1, LIANG Shikui
		DOI: 10.11660/slfdxb.20161207
		Construction and operation of hydraulic projects have changed the hydrological regime of natural rivers and produced negative influences on river ecosystems. To improve and recover the deteriorated river environment, it is of great significance to analyze and make effective regulation of the ecological water demands by rivers. This paper describes a calculation model of these demands that was constructed through analysis of river hydrological regime and its influence on river ecosystem. This model takes river ecological restoration as its optimization goal and considers the demands and the economic and social water use. It adopts a multi-scheme simulation technique to simulate the demands under different regulation modes of dam and gate control on sluice-controlled rivers. Results show that the sluice regulation by the natural flow target highest aimed at ecological water demands can achieve better improvement on highly-affected hydrological indicators than that by the water allocation goal highest aimed at higher priority on social and economic water use, and thus it would offer a better support to healthy development of river ecosystems.
		2016 Vol. 35 (12): 70-76 [Abstract] ( 262 ) PDF (370 KB) ( 456 )

	77	Development of turbulent boundary layer in submerged hydraulic jump regions of rectangular flat bottom channels
		ZHANG Zhichang, WANG Xuebing, FU Minghuan
		DOI: 10.11660/slfdxb.20161208
		Methods for determining the development of a turbulent boundary layer and its wall distances of half maximum velocity and zero-velocity line in submerged hydraulic jump regions are presented in this paper. To derive these methods, we have applied Verhoff’s formula of local velocity distribution in wall jet regions and the momentum integral equation of turbulent boundary layers to a detailed analysis of Rajaratnam’s experimental data: local velocity distribution, local maximum velocity, bed shear stress and the wall distance of half maximum velocity collected from the submerged hydraulic jump regions in a rectangular flat-bottom channel. The analysis gives an approximate formula of maximum velocity distribution and theoretical formulae for calculating the thickness of a turbulent boundary layer and its wall distances of half maximum velocity and zero-velocity line. Using the measured data, we verified the new formulae and improved the coefficient in Rajaratnam’s empirical equation for calculation of the wall distance of half maximum velocity. The results show that the development of a turbulent boundary layer in submerged hydraulic jump regions is rather similar to that in the smooth plate case: its thickness is proportional to the 1.14 powers of wall distance x and inversely proportional to the one fifth power of . And the wall distances of half maximum velocity and zero-velocity line are proportional to x and inversely proportional to the Reynolds number at the initial section of the jump.
		2016 Vol. 35 (12): 77-85 [Abstract] ( 236 ) PDF (447 KB) ( 514 )

	86	Effect of disturbance in overlying water on nitrogen and phosphorus release from aquaculture pond sediments
		CHENG Xiangju, ZHU Dantong, LIN Jun, YU Deguang
		DOI: 10.11660/slfdxb.20161209
		To better understand the effect of disturbance in overlying water on nitrogen and phosphorus release from aquaculture pond sediments, we collected sediment samples from aquaculture ponds, designed laboratory experiments of nitrogen and phosphorus release in the condition of overlying water stirred mechanically for seven consecutive days at different stirring speeds, and measured concentrations of ammonia nitrogen, nitrate nitrogen and SRP in the overlying water and sediment pore water. The results showed that faster mechanical stirring increased the concentration of ammonia nitrogen at the early stage but in hydrodynamic conditions it was a short-term effect and a dynamic equilibrium between release and adsorption was gradually reached. A higher stirring speed promoted the release rate of nitrate nitrogen with a higher peak concentration, indicating the release rate of nitrate nitrogen from the pore water in dynamic ponds to be significantly different from that in the static pond case. The release rate of SRP was also increased to a certain degree by increasing the stirring speed. Fitting of pseudo-first-order kinetic equations to the process of SRP release reveals multiple correlation coefficients R2 greater than 0.92 and an extremely significant level (P < 0.01) of the equations fitted, showing a satisfactory representation of the process.
		2016 Vol. 35 (12): 86-96 [Abstract] ( 733 ) PDF (582 KB) ( 539 )

	97	Response of water temperature in intake channel of Dongfang Power Plant to meteorological conditions
		ZHANG Wenjun, DUAN Yafei, ZHAO Yijun, JI Ping
		DOI: 10.11660/slfdxb.20161210
		Drawing water through open channels is a common way for once-through or recirculating cooling water systems of thermal power plants. Water temperature in open channels is usually rather sensitive to local meteorological conditions due to its large water surface open to the air. In design, attention should be paid to the variation range and trend in the meteorological impact on the water temperature. In this study, thermal dynamics of the water in different climate conditions have been examined by combining numerical simulations and prototype observations on the intake channel of the Dongfang power plant. Results show that in normal meteorological conditions, a weak temperature rising (less than 0.1 ?C) along the channel in the daytime and an even weaker decreasing trend in the nighttime were observed. In the wide seawater intake section of the channel, both the stream-wise rise and the temperature difference between its surface and bottom water layers were larger than that in the inland section. And adverse weather conditions in summer result in a higher stream-wise rise, and cloudless weather produces a stream-wise rise in the daytime significantly larger than that in the nighttime.
		2016 Vol. 35 (12): 97-104 [Abstract] ( 250 ) PDF (793 KB) ( 369 )

	105	Fault diagnosis of vibration for hydropower units based on empirical mode decomposition and support vector machine
		LI Hui, LI Xintong, JIA Rong, BAI Liang, LUO Xingqi
		DOI: 10.11660/slfdxb.20161211
		Vibration signals of hydropower units are typically non-linear and non-stationary. To diagnose and analyze such signals, this paper presents an original signal processing method of applying empirical mode decomposition (EMD) and demonstrates the then calculation procedure of intrinsic mode functions and their complexity features. Fault diagnosis of the signals was carried out using the least squares support vector machine (LS-SVM), and by taking the radial basis function as the kernel function, its relevant parameters were determined through grid search and cross validation. The results show that coupling EMD decomposition with SVM in analysis of complexity features provides a rather accurate device for fault diagnosis and determination of fault type, thus laying a basis for operation and maintenance of hydropower units.
		2016 Vol. 35 (12): 105-111 [Abstract] ( 259 ) PDF (438 KB) ( 510 )

	112	Influence of Francis runner crown profile on hydraulic performance of water turbines
		ZHAO Daoli, WANG Huayou, WU Zijuan, LIANG Wuke, LUO Xingqi, GUO Pengcheng
		DOI: 10.11660/slfdxb.20161212
		Modifying runner crown profile is a common method of turbine retrofit design, and for optimization and technical reform of a water turbine, exploring the influence of its crown profile on hydraulic performance is very significant. For this purpose, a Francis model runner was selected in this work, and four schemes were examined to modify its crown profile. Then, a CFD method was used to simulate and compare different crown profile schemes in terms of internal flow behaviors, energy characteristics, cavitation performance, and discharge capacity of this runner in three working conditions: small flow, optimal operation, and large flow. The results show that an appropriate elevation of the crown increases the discharge capacity through raising the lowest pressure on the runner blades, and that in large flow cases, it also improves energy characteristics and cavitation performance. However, an excessive crown height, in small flow cases, would produce negative impacts on the location and intensity of those vortices in the blade channels. Compared with the original runner design, scheme 4 can increase efficiency by 0.33% and 0.67% in large and small flow cases respectively. In small flows, a higher crown moves the blade channel vortices toward the blade inlet edge and intensifies their strength, thus resulting in a greater hydraulic loss and lower efficiency of the runner. In large flows, elevating crown profile may lead to a backflow zone near the crown and at the runner blade inlet, and consequently to an uneven distribution of pressure on the blades. Our study also reveals that runner efficiency and its internal flow at optimal operation generally vary little under different elevation of the crown, while the internal flow is very sensitive to even a subtle change in the flow parameters of a practical water turbine remodeling project. Thus, in estimating the change in energy characteristics of a new runner, we cannot rely on any intuitive judgment but rather, we must be very careful and perform multiple checking in making choice based on CFD analysis. This is the way to ensure the hydraulic performance of the new runner, the only way to reduce to the lowest the risk in technical improvement of a Francis turbine. The conclusions above would be helpful for runner remodeling design and performance prediction of Francis turbines for hydropower stations.
		2016 Vol. 35 (12): 112-119 [Abstract] ( 230 ) PDF (2458 KB) ( 469 )