Journal of Hydroelectric Engineering

水力发电学报

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2016 Vol. 35, No. 5 Published: 2016-05-25

	1	Advances in calculation models and monitoring methods for long-term deformation behavior of concrete dams
		GU Chongshi, SU Huaizhi, WANG Shaowei
		DOI: 10.11660/slfdxb.20160501
		The total number, maximum height and engineering scale of concrete dams in China rank the first in the world, and their long-term safety is a focus of public attention. Deformation is a comprehensive performance of concrete dam structures, especially the long-term deformation, a key index for evaluation of the structure behaviors, health status, and their evolution of a dam in long-term service. This paper summarizes the state of arts in creep calculation models for dam concrete and foundation rock and in the methods and models for safety monitoring and early warning of high concrete dam long-term deformation, based on analysis of the latest construction of concrete dams in China and concrete dam failures caused by long-term dam deformation. To ensure the safety of concrete dams in long-term service, future studies should focus on three issues: evolution of structure performances under the coupling effect of multi-factors, long-term structure deformation behaviors under the coupling effect of multi-fields, and evaluation of performance improvement under reinforcement measures.
		2016 Vol. 35 (5): 1-14 [Abstract] ( 479 ) PDF (523 KB) ( 1509 )

	15	Meso-scale analysis of influence factors on compressive strength of rock-filled concrete using particle-based discrete element method
		ZHONG Wen, PAN Jianwen
		DOI: 10.11660/slfdxb.20160502
		Rock-filled concrete (RFC) is an emerging casting technology for large-scale concrete construction and it has been used in many projects in hydraulic engineering. In this work, we have developed a two-dimensional particle-based discrete element model of RFC and investigated three influence factors on RFC strength, i.e. arrangement pattern of rock aggregates, strength of self-compacting concrete (SCC), and strength of interface between SCC and rocks. The numerical results show that the packing pattern of rock aggregates significantly affects RFC strength. Higher compressive strength is shown in cases where the applied load is carried by rock aggregates than those cases where the load is supported by both constituents. RFC strength becomes higher with increasing strength of interfaces or SCC. However, the compressive strength of RFC may approach its maximum value when the strength of SCC increases up to a certain value, and it is subsequently determined by the arrangement pattern of rock aggregates and the strength of interfaces.
		2016 Vol. 35 (5): 15-22 [Abstract] ( 331 ) PDF (3438 KB) ( 741 )

	23	Construction scheme optimization for high arch dams based on stochastic dominance degrees
		GUAN Tao, ZHONG Denghua, REN Bingyu
		DOI: 10.11660/slfdxb.20160503
		In construction scheme optimization, it is essential to comprehensively consider several random evaluation indexes, and this constitutes a problem of stochastic multiple attribute decision making. Previous studies on construction scheme optimization for high arch dams have not fully considered the random characteristics of these indexes, and therefore resulted in low accuracy in optimization. The existing methods that involve stochastic multiple attribute decision making, normally use artificial specification of the index weights and hence are not able to describe objectively the relative importance of different indexes. This paper presents a new method of construction scheme optimization for high arch dams based on stochastic dominance degrees. Through numerical simulations, we have obtained the probability distribution of construction progress indexes for all the construction schemes and calculated their stochastic dominance degrees using the stochastic dominance theory. Then, a priority order of these schemes can be achieved by calculating the weights of these indexes with CRITIC and fusing the indexes with a modified PROMETHEE II method. A case study shows that this method is effective in optimization of construction schemes for high arch dams featured with randomness in construction progress indexes.
		2016 Vol. 35 (5): 23-30 [Abstract] ( 467 ) PDF (890 KB) ( 696 )

	31	Performance tests on anti-fouling and anti-corrosion of coating materials
		YAO Guoyou, XU Mengzhen, AN Xuehui, ZHOU Jianwei, HUA Pilong
		DOI: 10.11660/slfdxb.20160504
		Golden mussel is corrosive to concrete and anti-fouling coating is a relatively feasible and efficient method for control of its corrosion. Quantifying the corrosion and finding optimal anti-fouling coating materials are of great significance to the control of bio-fouling on hydraulic structures such as Guangdong pumped-storage plants. In this study, we have conducted a natural attachment experiment of nine months long to study the influence of golden mussel corrosion and the performances of commercially available coatings of 15 types: polyurea, silane, epoxy resin, etc. The capabilities of anti-fouling and anti-corrosion were evaluated using measurements of attachment density and physical-mechanical properties. The results show that after nine months of golden mussel attachment, the compressive strength of concrete was reduced by 21%, the porosity and average pore diameter of concrete increased by 29.3% and 31.5% respectively, and carbonation depth of concrete increased by 29.7%. Polyurea 2, epoxy resin 2, and silane impregnation showed the best in anti-fouling; Polyurea 2, epoxy resin 2, and modified elastic epoxy resin showed the best in anti-corrosion. Thus, polyurea 2 and epoxy resin 2 are recommended as the optimal anti-fouling coating materials.
		2016 Vol. 35 (5): 31-39 [Abstract] ( 400 ) PDF (1181 KB) ( 616 )

	40	Return periods of non-stationary hydrological series with trend alteration
		SHI Lixiang, SONG Songbai
		DOI: 10.11660/slfdxb.20160505
		Climate change and human activities often result in non-stationarity in hydrological series, but no general consensus on the methods for calculation of the return period of non-stationary series has been reached yet. In this study, we compared several methods, including traditional method, time point method, expected waiting time (EWT), and component analysis, and took a case study of the annual runoff series for the Linjiacun station on the Wei River. A time-varying parameter model was used to fit the probability distribution of non-stationary series and calculate the design values of runoff at different return periods. The results indicate that the traditional method fails to correctly describe the probability distribution of hydrological series featured with trend alteration. In the condition of a decreasing annual runoff in the study area, the probability of small runoffs is increasing year by year, while the runoffs corresponding to long return periods does not show a decreasing trend. In comparison of EWT and time point method, the former can take the influence of trend alteration into account, while the latter has the advantage of easier calculation. The analysis and comparison of the methods presented in the paper would lay a basis for analysis of non-stationary hydrological series.
		2016 Vol. 35 (5): 40-46 [Abstract] ( 382 ) PDF (658 KB) ( 735 )

	47	Monthly runoff prediction using wavelet transform and generalized regression neural network model
		HAO Lina, SU Xiaoling, HUANG Qiaoling
		DOI: 10.11660/slfdxb.20160506
		In this study, discrete wavelet transform (DWT) and a generalized regression neural network (GRNN) were integrated to forecast monthly runoff and improve the accuracy of medium- and long-term hydrologic forecasting models. First, DTW was used to decompose the runoff series into deterministic and stochastic components, then these two components were inputted into two different GRNN models respectively, and finally the prediction results of the two models were summed up as the final forecasts of monthly runoff. To estimate the forecasting accuracy of this superposition model, we compared it with the best model taking only the deterministic component as GRNN input and the traditional GRNN model without DWT, in terms of three indexes: mean absolute error (MAE), determination coefficient (DC), and correlation coefficient (R). Its application to the monthly runoff of the Yingluoxia station at the Heihe River shows that it has an accuracy slightly higher than that of the best single component model, but these two models are more accurate than the traditional GRNN. Thus, GRNN coupled with DWT improves the accuracy of monthly runoff forecasting and is useful for runoff prediction in practice.
		2016 Vol. 35 (5): 47-54 [Abstract] ( 218 ) PDF (853 KB) ( 610 )

	55	Impact of rapid urbanization on rainfall-runoff processes in urban catchment: Case study for Liangshui River basin
		ZHAO Gang, SHI Rong, PANG Bo, XU Zongxue, DU Longgang, CHANG Xiaodong
		DOI: 10.11660/slfdxb.20160507
		Rapid urbanization has an adverse impact on urban rainfall-runoff processes and may increase the flood risk of urban regions. This study considered intensive human activities, such as increases in impervious area, changes in river network morphology, drainage system laying, and water transfer. We have developed two storm water management models (SWMM) based on remote sensing image and field survey, considering different urbanized scenarios and human disturbances and using measured streamflow data for model calibration and validation. Precipitation with different return periods was taken as model input to analyze the changes in flood characteristics caused by urbanization. The results indicate that these two models can produce good estimation of storms under the scenarios examined. The surface runoff after urbanization was 3.5 times larger than that before urbanization; the coefficient of runoff jumped from 0.12 to 0.41 and the amount of infiltration decreased from 88% to 59%. After urbanization, the time for overland flow concentration was shortened while the time for river concentration became longer; the flood peak time did not indicate much difference in this study. The peak flow of 20-year return period after urbanization is larger than that of 100-year return-period before urbanization. The results in this study would provide technical support to planning and management of urban storm water and evaluation on the low impact development technology.
		2016 Vol. 35 (5): 55-64 [Abstract] ( 490 ) PDF (1215 KB) ( 1084 )

	65	Runoff change in upper reach of Yellow River under future climate change based on VIC model
		WEI Jie, CHANG Jianxia, CHEN Lei
		DOI: 10.11660/slfdxb.20160508
		This study investigated the variations in precipitation, temperature and runoff in the upper Yellow river under the changing environment. A Delta method was used to downscale the BCC-CSM1.1 model data of Global Climate Models (GCMs) to establish future climate scenarios, and a VIC distributed hydrological model to simulate the future runoff process. The results show that the long-term mean annual precipitation will increase by 4.31% to 5.74% under different climate scenarios in the next 40 years (2011-2050) compared with the baseline period (1971-2010). And the long-term mean maximum and minimum temperature will increase by 1.04 ℃ to 1.61 ℃ and the increases in winter will be more distinct than in the other seasons. Under three different scenarios, the increase in annual runoff will be 2.65%, 2.66% and 8.07% respectively, but the increasing rate shows a decreasing trend. Seasonally, winter runoff will increase while summer runoff decrease.
		2016 Vol. 35 (5): 65-74 [Abstract] ( 389 ) PDF (1403 KB) ( 740 )

	75	Application of Bayesian model averaging method to prediction of high-frequency components in runoff series
		WANG Bin, ZHANG Hongbo, XIN Chen, LAN Tian
		DOI: 10.11660/slfdxb.20160509
		River streamflow has gradually developed into a non-stationary and non-linear complex process under the influences of climate change and human interferences. A major technical issue associated with this environmental changing is how to predict accurately the future change in river runoff. At present, a new prediction system, namely decomposition-prediction-reconstruction, has been widely used in the mid- and long-term prediction of runoff series. Its prediction efficiency, however, is unsatisfactory due to large errors in its prediction of high-frequency components that are decomposed using the empirical mode decomposition (EMD). To forecast the high-frequency components in the runoff at the Dingjiagou gauge station on the Wuding River, this study has adopted three approaches: the radial basis function (RBF) neural network, autoregressive (AR) model, and mean generating function (MGF) model. Based on these models, a comprehensive prediction was also made using the Bayesian model averaging (BMA) method. In this paper, we confirm the accuracy of BMA and demonstrate its effective control on the prediction error of high-frequency components through a comparison of its errors with those of the three single models. Thus, this study comes to a conclusion that the BMA method is an effective approach to improve the prediction accuracy of runoff series and would provide valuable references for similar issues in forecasting non-stationary time series.
		2016 Vol. 35 (5): 75-83 [Abstract] ( 396 ) PDF (1844 KB) ( 824 )

	84	Impact of transition ladder with different number of steps on dam surface pressure and energy dissipation of stepped spillway
		WANG Qiang, YANG Jurui, WU Zhenzhong, ZHANG Liang, JIANG Shijun, LI Tantan
		DOI: 10.11660/slfdxb.20160510
		The energy dissipator of flaring gate pier, stepped spillway and stilling basin has effectively solved the problems of high-velocity flows that have occurred under large discharge per unit width and high working head of the dams in China. It often adopts a transition ladder connecting the flaring gate pier to stepped spillway section. This paper presents a numerical simulation study on the transition ladder design for the spillway of Ahai hydropower station, using a 3-D flow model equipped with a RNG turbulence model, water-gas two-phase VOF method, PISO algorithm for velocity-pressure coupling, and a geometry reconstruction scheme for unsteady flow iteration solution to generate free surfaces. The 3-D flow simulations were conducted for four design schemes of this integrated energy dissipator: three schemes with transition ladders of one step, two steps and three steps respectively and the same step sizes of 2 m high and 1.5 m wide, and one scheme for the primary design with no transition ladder. Simulations show that in all the ladder schemes, negative pressure occurs in the head ladder and pressure on the solid surface of the head ladder is distributed in the same pattern. And in all the three cases, the lowest pressure on vertical step faces is negative and occurs at Section 22.56 m, with its value (-0.90 kPa) significantly higher than that of the primary design case (-4.47 kPa). On the horizontal step faces of the transition ladder cases, the lowest pressure (-0.60 kPa) is also higher than the corresponding value (-3.90 kPa) of the primary design. This indicates that the number of ladder steps has no considerable effects on the negative pressure or its distribution. Its effect on energy dissipation, however, is significant. Our results reveal that of the three ladder schemes, the two-step transition ladder can achieve the highest energy dissipation ratio (34.2%) and its head step has a much greater dissipation effect than the other one.
		2016 Vol. 35 (5): 84-93 [Abstract] ( 376 ) PDF (1101 KB) ( 583 )

	94	Behaviors of dam-break flows in contracted channel section based on COBRAS model
		RONG Guiwen, YUAN Yue, DAI Huichao, MAO Jingqiao, SHEN Qiting
		DOI: 10.11660/slfdxb.20160511
		A three-dimensional numerical model that solves the Reynolds-averaged Navier–Stokes equations with the k-ε turbulence closure models based on COBRAS using a finite-volume method, has been adopted to investigate the effects of dam-break flow propagating through a laterally narrowed section. This model uses a pressure-implicit operators-splitting algorithm for pressure-velocity coupling and a volume-of-fluid method for free surface tracking. It was validated by previous laboratory experiments and numerical simulations were made for the dam-break flows in a flume with a narrowed section. The results show that high-intensity flow turbulences, negative waves and hydraulic jumps occurred upstream of the narrowed section. When a dam-break wave front reached the narrowed section, the free surface near its entrance suddenly rose and then waves were spreading gradually upstream and downstream. At the entrance of abrupt contraction, the dynamic pressure reached the maximum during flood peak formation and after that it was decreasing gradually, while the total pressure was able to maintain its relatively stable maximum in a certain time period around flood peak formation.
		2016 Vol. 35 (5): 94-101 [Abstract] ( 341 ) PDF (920 KB) ( 548 )

	102	Cavitation inception in centrifugal pumps based on empirical mode decomposition
		QING Biao, REN Jianjun, SONG Xiaofei
		DOI: 10.11660/slfdxb.20160512
		Cavitation has an important influence on the performance of centrifugal pumps, but in practice it cannot be detected by monitoring the operation state of a centrifugal pump until it has developed into a very serious case. To develop a practical technique for detecting such cavitation in advance, we should examine the behavior of cavitation inception in centrifugal pumps. This study first used a numerical simulation method to predict the cavitation inception point for a centrifugal pump, and then conducted experimental tests on cavitation noises at this inception point and collected the cavitation noise signals. Finally, empirical mode decomposition algorithm (EMD) was used to decompose the signals and find out their characteristics that describe the cavitation inception points. Results show that EMD is an effective algorithm for detection of the changes in cavitation morphology of a centrifugal pump and the cavitation inception points predicted by our numerical simulations agree well with those measured in the experiment.
		2016 Vol. 35 (5): 102-109 [Abstract] ( 291 ) PDF (1351 KB) ( 567 )

	110	Practical method of in-plant economical operation of Xi-Luo-Du hydropower plant with large number of generator sets
		LI Linfeng, TANG Haihua
		DOI: 10.11660/slfdxb.20160513
		In-plant economical operation is an important measure to improve the benefit of a hydropower plant. In cases where a large number of generator sets of various types are in operation, traditional methods or intelligent algorithms come up against problems, such as too much time-consuming and uncertainty in solutions. Through a case study of the large number of complex generator sets at the Xi-Luo-du hydropower plant, a practical method has been developed to achieve in-plant economical operation of generator sets, including operation schemes of how to add new generator sets and shut down some of the existing sets. Results show that our method can give solutions very close to the optimal at less computational cost. The method is fast enough to meet on-line operation needs and it would be useful to the design and operation of similar hydropower plants.
		2016 Vol. 35 (5): 110-116 [Abstract] ( 299 ) PDF (375 KB) ( 711 )

	117	Operation stability analysis of pump-turbine in different working conditions
		TANG Renbo, YANG Jiandong
		DOI: 10.11660/slfdxb.20160514
		In this article, a control model composed of a turbine governor, penstock, pump-turbine, and generator, is developed to study the influence of pump-turbine characteristics on system stability. Classical control theory was applied to derive expressions for the synthetic coefficients. Based on the real pump-turbine characteristics of 19 sets collected from model tests, polynomial surfaces were fitted for the relationships of unit flow and unit torque versus unit speed and guide-vane opening. Combining these relationships with the expressions of synthetic coefficients, we can reveal the trends of variations in the six transfer coefficients and the synthetic coefficient and thus obtain the influence of pump-turbine characteristics on system stability at different water heads. Finally, numerical simulations of several working conditions were conducted, which validates our conclusions.
		2016 Vol. 35 (5): 117-122 [Abstract] ( 418 ) PDF (460 KB) ( 819 )

	123	Physical characteristics of sandstone under freeze-thaw cycles
		LIU Jie, XU Chunlin, WANG Ruihong
		DOI: 10.11660/slfdxb.20160515
		Rock mass failure is a result of internal damage accumulation and development, and it is exacerbated in the condition of seasonal temperature change because the enhanced strength degradation of rock mass in cold regions causes a great increase in the probability of rock mass instability. Hence, it is necessary to study the cyclic freeze-thaw deterioration of damaged rock. This paper describes an experiment of sandstone samples in the conditions of preload damage as well as no load damage in the freeze-thaw process. For the specimens that had experienced freezing, thawing, and drying at low temperature, we measured their longitudinal wave celerity and rock resistivity and analyzed the degradation degree of these two parameters. Results show a quadratic relationship of the celerity versus the number of freeze-thaw cycles and a logarithmic relationship of the resistivity versus the cycle number. And in the same testing conditions, the changes in the resistivity are greater than those in the celerity. This means that resistivity is an evaluation index more sensitive to rock physical properties and it is a useful index for evaluation of the stability of rock structures in cold regions.
		2016 Vol. 35 (5): 123-130 [Abstract] ( 306 ) PDF (665 KB) ( 659 )