Journal of Hydroelectric Engineering

水力发电学报

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2017 Vol. 36, No. 4 Published: 2017-04-25

	1	Multi-attribute decision making for construction schemes of concrete gravity dams based on dynamic VIKOR extension method
		ZHONG Denghua, ZHAO Jianghao, REN Bingyu, GUAN Tao, WANG Fei
		DOI: 10.11660/slfdxb.20170401
		Concrete gravity dam projects are often featured with a huge scale, long construction period and technical complexity. The existing methods of multi-attribute decision making mostly focus on the whole construction process of such projects, but ignore variations in the indexes of the process and their weights in selection or analysis of these crucial parameters. The dynamic VIKOR extension method can well describe the construction process and obtain a comprehensive evaluation of construction schemes through quantifying and sorting the performance of each scheme at different stages of the construction under the constraints of acceptable advantages and stable decision-making plans. In this work, this method was applied to multi-attribute decision-making of concrete gravity dam construction schemes. Construction schemes were divided into different stages based on the results of their simulations and construction planning, and the values of their indexes were calculated separately for these stages. A comprehensive evaluation was made by integrating the calculations of different stages, so that an optimal scheme or compromise scheme can be obtained for concrete gravity dam construction, providing more reliable information for multi-attribute decision-making.
		2017 Vol. 36 (4): 1-10 [Abstract] ( 229 ) PDF (768 KB) ( 514 )

	11	Key construction technologies of low heat Portland cement dam concrete
		FAN Qixiang, LI Wenwei, LI Xinyu
		DOI: 10.11660/slfdxb.20170402
		The growth of low heat Portland cement dam concrete strength at early stage is slower than moderate heat Portland cement concrete. It causes certain great differences between these two kinds of concrete in construction technology, construction schedule, temperature measure, their effect, etc. Studies on key construction technologies of this low heat concrete were carried out for dam blocks 30 and 31 of Xiluodu arch dam in June 2013 to analyze the feasibility of its application to ultra high arch dams. Compared with moderate heat cement concrete, the green cutting schedule of low heat cement concrete had delayed 16-20 h and its formwork removal schedule had delayed about 24h, but this did not influence the dam construction schedule since the concreting intermission time of dam concrete is usually around 7 - 10 d. And its highest temperature in the dam blocks was 4.6 ℃ lower and its temperature rise after joint grouting was 1.2 ℃ lower in basically the same conditions of placement temperature, spacing between cooling pipes, and temperature and flow rate of cooling water. When other conditions were the same, low heat cement concrete had a peak stream-wise stress of 19% - 65% lower and its safety factors of crack resistance were generally improved, all reaching a level above 2.0. The transverse joints of a low heat cement concrete dam block can be opened and the required amount of joint grouting is close to that of a moderate heat cement concrete dam block. Up to now, no crack has been found yet in the observed two dam blocks of low heat cement concrete.
		2017 Vol. 36 (4): 11-17 [Abstract] ( 274 ) PDF (376 KB) ( 444 )

	18	Probabilistic flood forecasting considering heterogeneity of error distributions
		LIANG Zhongmin, JIANG Xiaolei, QIAN Mingkai, WANG Kai, YAO Yi
		DOI: 10.11660/slfdxb.20170403
		Guide::null
		A probabilistic flood forecasting method considering the heterogeneity in error distributions of deterministic predictions is presented. In this method, error distributions of different flood magnitudes are constructed using their observed values and model forecasting values (MFVs) and their probabilistic distribution functions (PDFs) conditional on the MFVs are derived; then, by using these PDFs a probabilistic flood forecasting is achieved. In its application to the Wangjiaba station in the Huai River basin, an empirical model was adopted in deterministic flood predictions of the ten flood events occurring in the period of 1996-2007, and variations in the relative errors of the deterministic predictions were examined. This analysis revealed that the means of PDFs of these relative errors differ significantly between different flood magnitudes. To consider such heterogeneity of error distributions, we can construct a functional relationship of the mean value of the relative errors versus their corresponding MFVs, and derive error distributions conditional on the MFVs. This new method was verified by using the data of two floods occurring in 2008. Results show that the probabilistic method is simple and practical and it can give more accurate forecasts than the empirical model when the means of PDFs of discharges are used as deterministic predictions.
		2017 Vol. 36 (4): 18-25 [Abstract] ( 151 ) PDF (700 KB) ( 385 )

	26	Experimental study on anti-scour devices of slotted bridge piers with a semicircular fin
		MOU Xianyou, QIAO Chunlin, JI Honglan, LI Chunjiang, WANG Dan
		DOI: 10.11660/slfdxb.20170404
		A new anti-scour device of slotted piers with a semicircular fin is presented in this paper to overcome the limitations of traditional technologies for better protection of bridge piers from local scour. This device protects riverbed by reducing the flow around the piers and its scour power. To examine the scour reduction, we have conducted laboratory tests on a scale model of a cylindrical bridge pier, using different shapes and sizes of the semicircular fin and its different installation heights combined with different locations of the pier slot. And the scour reducing effects were eveluated and analyzed by measuring the 3D geometrical characteristics of the scour pits around the piers, along with the average velocity, turbulence intensity, and turbulent kinetic energy of the flow around the piers. The results showed that scour depth was significantly reduced by the new device and its reduction in scour depth was 1.8 times greater than that by opening a slot on the pier only. And in front of the piers, the mean values of vertical average velocity, vertical turbulence intensity, and turbulent kinetic energy were all decreased obviously, with the values above the fin plate far larger than those under it. At both sides of the piers, mean longitudinal velocity and longitudinal turbulence intensity were also reduced remarkably. Thus, the device of a slotted cylindrical pier with a semicircular fin has prominent anti-scour effect and provides a basis for further studies and engineering application.
		2017 Vol. 36 (4): 26-37 [Abstract] ( 148 ) PDF (1172 KB) ( 400 )

	38	Calculation methods for 3D concentration distribution and pollutant mixing zones using non-uniform diffusion coefficients
		WU Zhouhu, WU Wen, HUANG Zhenli
		DOI: 10.11660/slfdxb.20170405
		Diffusion coefficients are usually taken as constants in solving the advection-diffusion equations and water quality models of environmental hydraulics. However, sometimes this is a poor simplification, such as in the case of pollutant mixing zones around the municipal sewer outfall in the city of Huangshaxi before the construction of the Three Gorges reservoir. We observed that the shapes of these mixing zones were much different from those that were predicted, under the assumption of constant diffusion coefficients, by using the standard curve equation (for the curved surface) of their outer boundaries or the relationship of their geometric characteristic parameters. In this study, focusing on the cases of point sources of equal intensity located at the sloped banks of rivers or reservoirs, we have solved a simplified three-dimensional advection-diffusion equation of pollutant concentration using non-uniform diffusion coefficients and analyzed the characteristics of concentration distribution. We also derived theoretical formulae of maximum length, maximum width, and maximum depth and their corresponding locations in the mixing zone as well as its surface area and underwater volume. In addition, this paper gives a standard curve equation for the outer boundaries of mixing zones and an analysis of the effects of spatial variation in diffusion coefficients on the shape of mixing zones, including the limitation of constant diffusion coefficient models, and develops a double cross-section method and isocratic line method to determine non-uniform diffusion coefficients and a calculation method for the maximum allowable pollutant load. Applications show that the non-uniform diffusion coefficient model and its calculations can better characterize the pollutant mixing zones around the sewer outfalls in Huangshaxi and the Fuling phosphate fertilizer plant.
		2017 Vol. 36 (4): 38-47 [Abstract] ( 146 ) PDF (1639 KB) ( 209 )

	48	Spatio-temporal distribution of nitrogen concentration in Songhua River basin based on LDA models
		ZHANG Guike, TANG Lihua, LIU Zhiwu
		DOI: 10.11660/slfdxb.20170406
		Nitrogen concentration is an important indicator for evaluating water quality of rivers and lakes. Its spatio-temporal distribution often varies significantly across different river reaches owing to differences in pollutant source, river flow, self-purification capability, and some other factors. To obtain a comprehensive and in-depth understanding of the water quality in the Songhua River basin, we have developed a latent Dirichlet allocation (LDA) model for analysis on spatio-temporal distribution of nitrogen over this basin based on its observation data of 2006 to 2010. Results showed typical distribution patterns of ammonia nitrogen (NH3-N) and total nitrogen (TN) in the river channels, and their meanings were interpreted and analyzed. Annually, nitrogen concentration took three distribution patterns as typical behaviors at high, medium and low concentration levels respectively. In the whole basin, probabilities of NH3-N distribution in these patterns are 1:3:3 respectively while probabilities of TN distribution are 1:1:1. The distribution of peak nitrogen concentration were also conceptualized into three patterns that frequently occur in dry, normal and wet seasons respectively. On average over the basin, their corresponding probabilities are 6:2:1 for NH3-N and 2:1:1 for TN. In addition, this study revealed that differences in pollution loads of the point source and non-point source are possibly the main cause of the difference in spatio-temporal distributions of nitrogen over different river cross sections.
		2017 Vol. 36 (4): 48-57 [Abstract] ( 126 ) PDF (2225 KB) ( 211 )

	58	Sorting of non-uniform bedload in clear water scouring
		JI Kefan, XU Haijue, BAI Yuchuan
		DOI: 10.11660/slfdxb.20170407
		Generally, rolling is the primary form of bedload movement on pebble riverbeds under certain flow conditions. Due to different moving distances of the particles with different sizes on a bed surface, sorted sediment transport will occur, forming a stable structure with coarse particles as the main body of the bed. This work focused on a study of the coarsening process of non-uniform pebble beds during clear water scouring and the sorting modes that were stably formed after scouring. Based on a rolling mechanics model, tracking of the rolling particle movement under different conditions was numerically calculated; a gradation calculation model of stable non-uniform pebble beds washed by clear water was developed. This model was used in a practical example to calculate variations in bedload gradation and gradation curves at different time for different river sections. The theoretical results presented in this paper are applicable to rolling movement of pebbles and provide a theoretical method for further studies of pebble bed sorting.
		2017 Vol. 36 (4): 58-70 [Abstract] ( 128 ) PDF (541 KB) ( 328 )

	71	Analysis on successive load rejection by two pump-turbines sharing one main diversion tunnel
		LIU Rong, YANG Jiandong
		DOI: 10.11660/slfdxb.20170408
		To save engineering cost, two pump-turbines could share the same main diversion tunnel at a pumped-storage station. In this case, load rejection by one turbine produces hydraulic disturbance to the other and consequently induces a load rejection of the latter, thereby resulting in a phenomenon of successive load rejection. Normally, the lowest pressure at the draft tube inlet of the second turbine will be dropping rapidly, but sometimes extreme low pressures may also occur in the first one. In this work, we studied the mechanism of rapid pressure dropping in the first turbine unit during successive load rejection based on numerical simulations. Results indicate that when the first turbine is operated at a point on the slope inflection segment of the S-shaped characteristic curve and the flow in the second turbine is increasing, this flow increase will induce a large head on the first turbine that causes a rapid pressure drop at its draft tube inlet, a situation unfavorable to this unit.
		2017 Vol. 36 (4): 71-77 [Abstract] ( 227 ) PDF (786 KB) ( 377 )

	78	Complementary operation of water, wind and solar power for typical power stations on upper Jinsha River
		ZHU Yanmei, ZOU Zujian, HUANG Weibin, WANG Li, MA Guangwen
		DOI: 10.11660/slfdxb.20170409
		To reduce the effect of instability in outputs of wind farm and solar power, complementary operation modes of them together with hydropower are presented in this paper. We chose three typical power stations on the upper Jinsha, namely the Dechang wind farm, Wanjiashan solar power station, and Gangtuo hydropower station, and analyzed their power output features and complementarity at time scales of a day, a month and a year. A real time model of complementary operation was developed and coded in visual basic and then applied to calculation of reservoir operation modes under the condition that the total power grid load, wind power output and photovoltaic output were all known. The results show that a complementary operation mode of merging three types of outputs before connected to the power grid can lower the negative impact of instable wind and solar power and improve power transmission efficiency, thus showing a great significance in improving the environments and energy structure.
		2017 Vol. 36 (4): 78-85 [Abstract] ( 218 ) PDF (507 KB) ( 444 )

	86	Engineering characteristics of dispersive clay modified with fly ash
		YAN Yingjia, FAN Henghui, YANG Xiujuan
		DOI: 10.11660/slfdxb.20170410
		Dispersive clay is a problematic soil that has too low erosion resistance. To improve its behaviors, we have conducted pinhole tests and crumb tests as well as compression and seepage deformation tests on the dispersive clay modified with different fly ash content. And SEM tests were used to analyze the microstructure and mechanism. The results showed that adding fly ash produced a significant improvement on dispersity, compressibility and permeability of this modified dispersive clay that depended on fly ash content, curing period, and compaction degree. Its dispersity and compressibility were both decreased with an increase in fly ash content or compaction degree; its compressibility was also decreased with an increase in curing period. The mechanism of all the improvement was a series of physical and chemical reactions between fly ash particles and soil particles. Adding fly ash was able to promote the formation of granular structure and reduce soil dispersity through hydration and hydrolysis reaction, ion exchange reaction, and hard condensation reaction. Thus, by mixing fly ash into dispersive clay, it is possible to transform it into non-dispersive clay. For engineering application, this study suggests a fly ash content of 4% - 10%, a curing period of longer than 7 days, and a compaction degree of 96%.
		2017 Vol. 36 (4): 86-94 [Abstract] ( 134 ) PDF (978 KB) ( 283 )

	95	Mechanism of structural tensile damage to concrete face slabs of high CFRDs in narrow valley regions and improvements
		YANG Chao, DANG Faning, XUE Haibin, GAO Jun
		DOI: 10.11660/slfdxb.20170411
		A key issue in construction of high CFRDs in deep narrow valleys is the cracking of their concrete face slabs owing to local tensile stress. This paper presents an analysis on the mechanism of structural tensile damage that already occurred to the concrete face slabs of several existing high CFRDs and demonstrates the major cause of such damage at locations near river bank ? sliding deformation of the rock-fills from river bank to river channel. A 3-D FEM analysis was used to compare the deformation in arch-shaped face slabs with that in widely used planar face slabs. The results show that the arched concrete face slabs can completely avoid this type of structural tensile damage without need to change the main stress or displacement properties of the dam. The arched shape of CFRDs is more favorable to the safety of dams that are built in deep narrow valley regions.
		2017 Vol. 36 (4): 95-103 [Abstract] ( 164 ) PDF (2246 KB) ( 247 )

	104	Calculation methods of bearing capacity for composite square columns under axial compression
		GAO Danying, WANG Dai
		DOI: 10.11660/slfdxb.20170412
		This paper presents an analysis of bearing capacity of FRP-concrete-steel tube composite square columns based on axial compression tests, focusing on the influences of hollow ratio, diameter-to-thickness ratio of inner steel tube, the number of FRP layers wrapped on the columns, etc. to promote their application in hydraulic structures. Based on our test data and previously reported data, we have derived calculation formulas and a corresponding model for simplified calculation of the bearing capacity varying with these three major factors. The results show that the bearing capacity of this composite structure is significantly improved due to its sandwich concrete that is highly confined by its inner steel tube and outer FRP tube. Under axial compression, the most significant factors are the confining degree of the FRP tube and the diameter-to-thickness ratio, and the bearing capacity increases with hollow ratio when the diameter-to-thickness ratio is kept nearly constant. The calculations of the formulas agree well with the results of axial compression tests.
		2017 Vol. 36 (4): 104-111 [Abstract] ( 144 ) PDF (486 KB) ( 213 )

	112	Modified Mesri creep model of soft clays and its engineering application
		WANG Yuanzhan, ZHAI Ying, DONG Yanhe
		DOI: 10.11660/slfdxb.20170413
		Guide::null
		Consolidated undrained triaxial creep tests with a stepwise loading method were carried out on soft clays collected from the coastal area of Tianjin, and by analysing the test data a modified Mesri model was developed. This model takes the final strain in the first stage of creep deformation as an initial strain and describes the deformation in the second stage using the combination of a stress-strain hyperbolic function and strain-time hyperbolic function. It was imbedded into finite element code ABAQUS as a subroutine for soil creep deformation and its calculations were verified by the test data. For further verification, it was applied to simulations of long-term settlement of a soft clay layer in the coastal area of Tianjin. The results show that this modified Mesri creep model fits the test data better than the Mesri model and its calculations can predict the long-term creep deformation characteristics of soft clay layers for engineering projects with a satisfactory accuracy.
		2017 Vol. 36 (4): 112-120 [Abstract] ( 142 ) PDF (773 KB) ( 462 )