Journal of Hydroelectric Engineering

水力发电学报

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2019 Vol. 38, No. 10 Published: 2019-10-25

	1	TBM construction ventilation simulation for deep buried headrace tunnels considering heat transfer in surrounding rock
		WANG Xiaoling, YU Wang, LIU Changxin, LV Mingming, HU Lianxing
		DOI: 10.11660/slfdxb.20191001
		In TBM construction of a deep buried headrace tunnel, it is very difficult to lower the temperature and control the dust due to thermal storage effect and heat transfer in surrounding rock. Previous studies have not considered the influence of thermal conduction in the rock, and lack an analysis method for calculating its effective thermal conductivity. To address these two issues, first we develop a new analytical method for effective thermal conductivity calculations based on fractal analysis using a polygonal discrete fracture network model. Then, we construct an Euler-Lagrange two-phase flow model for the TBM construction of deep buried headrace tunnels, considering the effects of heat conduction in the surrounding rock and its heat exchange with the wind flow over its surface. Results of a case study show that the effective thermal conductivity of surrounding rock is 0.47 W/m?K, which is far less than that of normal rock. The accuracy and reliability of our model is verified by comparing the simulation results with our field experiment data and other models. This study would lay a theoretical and technical basis for similar TBM construction ventilation of deep buried headrace tunnels.
		2019 Vol. 38 (10): 1-13 [Abstract] ( 163 ) PDF (4313 KB) ( 716 )

	14	Time-dependent chloride diffusivity of fly ash concrete in marine tidal environment
		GAO Yanhong, ZHOU Xiaoyun, LÜ Meng, ZHANG Yurong, ZHANG Junzhi
		DOI: 10.11660/slfdxb.20191002
		Through field exposure tests of concrete in marine tidal environment, the influence of fly ash additive on chloride diffusivity and its time dependency is studied. First, free chloride concentration of the concrete is measured at four exposure times for fly ash contents of 0%, 20%, 30%, 40% and 50%, and porosity of the concrete is tested using a mercury intrusion porosimetry (MIP). Second, apparent diffusion coefficient of the concrete is calculated by Fick’s second law and used to determine instantaneous diffusion coefficients. An equation is formulated to describe the relationship of fly ash content versus diffusion coefficient. Finally, a time-dependent model of instantaneous diffusion coefficients is developed and verified against the measurement of concentrations. Calculation results of this model show that both apparent and instantaneous diffusion coefficients decrease with exposure time and fly ash content. And the time dependency of diffusion coefficients indicates that chloride resistance of fly ash concrete is greater in the early stage than that in the late stage. The age reduction factor of diffusion coefficients keeps increasing with fly ash content. However, at the exposure time of 360 d, this factor of instantaneous diffusion tends to be stable. Thus, our time-varying model of instantaneous chloride diffusion coefficients after 360 d exposure is accurate in prediction of free chloride concentration of concrete.
		2019 Vol. 38 (10): 14-23 [Abstract] ( 187 ) PDF (1429 KB) ( 438 )

	24	Dynamic compressive behavior of hydraulic asphalt concrete under different temperatures
		NING Zhiyuan, LIU Yunhe, XUE Xing
		DOI: 10.11660/slfdxb.20191003
		Dynamic compression tests on hydraulic asphalt concrete are carried out to study the dynamic mechanical properties under different temperatures. The test results show a strong dependence of the concrete failure mode on strain rate. At strain rates of 10-5/s and 10-4/s, the specimen mainly takes the mode of bond failure, while at strain rates of 10-3/s and 10-2/s, it takes bond failure and aggregate cracking. Temperature has a significant effect on the stress-strain characteristics of specimens. When the strain rate is ? 10-4/s, strain softening occurs at -5℃ and 0℃; strain hardening gradually develops from the threshold of 5℃.At a constant temperature of the concrete, its energy absorption capacity, elastic modulus, and compressive strength are all increased with the increase in strain rate. We analyze the dynamic increase factors (DIFs) of elastic modulus and compressive strength, and suggest an empirical formula for calculating the DIFs of elastic modulus for different strain rates at different temperatures. It is found that the S criterion of nonlinear uniaxial dynamic strength is a good parameter of hydraulic asphalt concrete reflecting the characteristics of growth in its dynamic compressive strength at different seismic response rates.
		2019 Vol. 38 (10): 24-34 [Abstract] ( 216 ) PDF (1519 KB) ( 418 )

	35	Impact of urbanization on regional rainfall-runoff processes in Xiaoqing River basin, Jinan
		ZHAO Yanjun, XU Zongxue, ZHAO Gang, CHENG Tao, CHANG Xiaodong, TAN Qiuyang
		DOI: 10.11660/slfdxb.20191004
		Rapid urbanization has resulted in changes in the rainfall-runoff characteristics and increases in the risk of urban area flooding. This study examines the impact of land use changes caused by urbanization on rainfall-runoff processes through a case study of the Xiaoqing River basin in Jinan. We develop a storm water management model (SWMM) for different urbanization scenarios on the basis of land use data of 2000 to 2017 of the study area, and use the design rainfall events of different return periods as model input for analysis of the changes in flood processes. The results indicate that urbanization has produced a significant amplification effect on design rainfalls. During 2000-2017, the surface runoff of this area was increased by 42%, infiltration volume decreased by about 50%, runoff coefficient increased from 0.56 to 0.71, and peak flow increased from 285.7 to 311.7 m3/s. The peak time of floods at relatively high frequencies became earlier, while those at low frequencies changed little.
		2019 Vol. 38 (10): 35-46 [Abstract] ( 194 ) PDF (2337 KB) ( 565 )

	47	Study on multi-objective mutual feedback relationships of reservoirs based on structural equation modeling
		WANG Liping, YAN Xiaoran, MA Haoyu, LI Ningning, YU Hongjie, JI Changming
		DOI: 10.11660/slfdxb.20191005
		The multi-objective optimization problem of cascade reservoirs involves high factor dimensions and complicated inter-objective relationships. Traditional statistical methods are difficult to consider the target information contained in different indicators comprehensively, and can give only qualitative analysis of their mutual feedback relationships. Aiming at the problem, this paper constructs a power generation-water supply-ecology multi-objective optimal scheduling model for cascade reservoirs, solves it using a fast non-dominated sorting genetic algorithm (NSGA-Ⅱ), and formulates a preliminary hypothesis of mutual feedback relationships among the three objectives. And we apply a structural equation modeling (SEM), conduct a high-dimensional confirmatory factor analysis using the index values given by the multi-objective non-inferior solution set of cascade reservoirs, and present visual and quantitative calculation results for the mutual feedback relationships among the objectives. The results of the Xiluodu-Xiangjiaba cascade reservoirs show that under different inflow frequencies, the power generation-water supply conflict is the most severe, followed by power generation-ecology; while compared with these conflicts, the water supply-ecology feedback relationship is insignificant. As the frequency of inflow increases, the conflict between power generation and water supply sharpens rapidly.
		2019 Vol. 38 (10): 47-58 [Abstract] ( 175 ) PDF (1245 KB) ( 548 )

	59	Effect of gravel on runoff and sediment yield from Lou soil engineering accumulation in Guanzhong region
		SU Huan, WANG Wenlong, KANG Hongliang, GUO Mingming, BAI Yun, LI Jianming, NIE Huiying, JI Lijing
		DOI: 10.11660/slfdxb.20191006
		Indoor artificial rainfall simulation tests are used to study the effect of gravel on the runoff and sediment yield from the engineering accumulation slopes in Guanzhong Plain and to analyze the relationship between water and sediment, under the rainfall intensities of 1.0, 1.5, 2.0 and 2.5 mm?min-1 for gravel mass fractions of 10%, 20% and 30% in comparison to a pure Lou soil slope (i.e. no gravel). The results show that 1) the runoff rate and mean flow rate are correlated insignificantly with gravel fraction (P > 0.05), but significantly with rainfall intensity (P < 0.05). 2) At rainfall intensity of 1.0-2.5 mm?min-1, mean sediment yield is decreased with the increasing gravel fraction, following a power function relationship. Relative to the no-gravel case, sediment yield of the slope is decreased by 17.1%-67.5%, 13.8%-81.1% and 25.5%-92.0% at gavel fractions of 10%, 20% and 30% respectively. 3) As the rainfall intensity decreases from 2.5 mm?min-1, the curve of accumulative water and sediment changes from a linear function to a power function (P < 0.01). This study helps predict and reduce soil and water loss of the engineering accumulation in Guanzhong region.
		2019 Vol. 38 (10): 59-74 [Abstract] ( 135 ) PDF (538 KB) ( 393 )

	75	Stochastic model of reservoir runoff forecast errors and its application
		JI Changming, LIANG Xiaoqing, ZHANG Yanke, LIU Yuan
		DOI: 10.11660/slfdxb.20191007
		To effectively improve the accuracy in formulated operation schemes under the condition of quantifying reservoir runoff forecast errors, a Gaussian mixture model (GMM)- Copula stochastic model is developed to describe runoff forecast errors for multiple forecast periods. This model is based on the characteristic of the GMM that accurately describes the distribution of runoff forecast errors for a single forecast period due to good adaptive performance. It incorporates the advantage of the high-dimensional meta-student t Copula function through dynamically coupling multiple types of marginal distributions. In a case study of the Jinping I hydropower station in the Yalong River basin, we conduct stochastic simulations and analysis of the reservoir runoff forecast errors for forecast periods of 6 h, 12 h, 18 h and 24 h. The results show that for different forecast periods, simulation errors and actual errors share the same changing pattern and similar major statistical eigenvalues, meeting the predetermined accuracy requirement. This verifies that our stochastic model is feasible and effective and it helps formulate and implement reservoir operation schemes.
		2019 Vol. 38 (10): 75-85 [Abstract] ( 184 ) PDF (862 KB) ( 687 )

	86	Study on distribution of pollutant concentrations in intersection of open channel
		CHEN Kailin, FENG Minquan, ZHANG Tao, TENG Sufen
		DOI: 10.11660/slfdxb.20191008
		The confluence of water flows occurs in a great number of hydraulic systems, and its flow structure is often complicated but crucial to understanding the systems. To examine the flow behaviors of the confluence of an open channel and a tributary, this study uses the PIV technology to measure pollutant concentration distribution so as to overcome the limit of single point measurement, focusing on pollutant diffusion and concentration field in an asymmetrical intersection with different confluence angles. Results show that near the tributary outlet, surface pollutants are more uniform than those in deeper layers, and along with the further development of mixing between the two streams, pollutants in the deep layers become more uniform than those in the surface layer. At small confluence angles, a long and narrow contaminated zone is formed at the tributary side of the main channel, while large angles will shift this zone laterally further toward the other side. Higher pollutant concentration leads to a longer contaminated zone, and a change in pollutant concentration will greatly impact the location and width of the mixing layer. This study demonstrates that the PIV technology is satisfactory in measuring pollutant diffusion in channel intersection areas and thus is applicable to detailed studies of the pollutant concentration field.
		2019 Vol. 38 (10): 86-100 [Abstract] ( 147 ) PDF (1757 KB) ( 425 )

	101	Experimental study on influence of low atmospheric pressure on dynamic pressure of water jet plunging
		LIAN Jijian, DONG Zhao, LIU Fang, LIU Dan
		DOI: 10.11660/slfdxb.20191009
		As high dams are built on the high-altitude plateau of Western China, the issue of high-speed jet nappes under low atmospheric pressure emerges as a new challenge to dam construction. In this study, an experiment is conducted to examine the influence of ambient air pressure on the trajectory distance of water jets and their dynamic pressure produced at the plunge pool bottom. The study shows that a drop in atmospheric pressure increases the dynamic pressure of the plunging jet. An air pressure drop of 10 kPa causes a dynamic pressure rise of up to 3.9% and a pulsating pressure rise of up to 5.5%. In low-pressure air, the trajectory distance of a jet nappe is affected by the aeration and diffusion of the nappe flow in the air. By the similarity of model and prototype, the influence of air resistance on the trajectory distance of a jet is different between model and prototype. With air pressure dropping, air density and air resistance are decreased and the air volume entrained by a jet nappe in the air will also be reduced. This means that the diffusivity of the nappe will be reduced, and a low-pressure jet nappe will be more concentrated.
		2019 Vol. 38 (10): 101-110 [Abstract] ( 186 ) PDF (867 KB) ( 512 )

	111	Study on sediment diffusion in no-storage-pit dredging operation
		ZHUANG Fulai, ZHANG Jixiang, HAO Yuchi, MAO Xiaodan, ZHANG Yun
		DOI: 10.11660/slfdxb.20191010
		Sand storage pits play a temporary role in dredging and reclamation process for large offshore projects such as port and land reclamation, but their setting is limited by site conditions and construction period. At present, little previous research or practical experience is available on the process and mechanism of sediment loss during no-storage-pit operation, and its estimation method is lacking. This paper reports a study on the loss of sediment storage in dredger fill with no sand storage pit during the construction of the Gulei sand fill project by combining site observations of its construction process with numerical simulation of its typical working conditions. Results show that under the condition of no storage pit, sediment loss mainly occurs in the stage of sand accumulation, and that the loss rates obtained by numerical simulations and field observations are in a range of 14%-16%. This study would lay a basis for further studies on mathematical modeling and field observation of dredger fill with no sand storage pit.
		2019 Vol. 38 (10): 111-120 [Abstract] ( 219 ) PDF (3235 KB) ( 469 )