Journal of Hydroelectric Engineering

水力发电学报

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2019 Vol. 38, No. 5 Published: 2019-05-25

	1	Prediction of chloride diffusivity of concrete with polygonal aggregates
		ZHENG Jianjun, ZHANG Jian, LI Qingbin, WANG Zongmin, ZHOU Xinzhu
		DOI: 10.11660/slfdxb.20190501
		A numerical method is presented for calculating the chloride diffusivity of concrete with polygonal aggregates. Through uniform scaling and unidirectional scaling, we generate polygonal aggregates for a given gradation, aspect ratio and content, and reconstruct the mesostructure of concrete by placing the generated particles into a simulation element with periodic boundary conditions. The mesostructure of concrete is then discretized on a regular grid, and a pixel-counting method is used to analyze the convergence of aggregate content and interfacial transition zone content to determine the required number of pixels. By applying Fick’s first law, we derive a solution for the chloride concentration gradient in heterogeneous media in the Fourier space, and based on this solution, develop an iterative algorithm for calculating the chloride diffusivity of concrete. Compared with the finite element method, our numerical method has the advantages of no need for complicated mesh generation, smaller data storage, and easy calculation. Finally, the method is verified through comparison with two sets of experimental data, and the effect of aggregate aspect ratio on the chloride diffusivity of concrete is discussed.
		2019 Vol. 38 (5): 1-8 [Abstract] ( 213 ) PDF (455 KB) ( 438 )

	9	Reliability analysis on anti-sliding stability of gravity dams using cat swarm optimization
		ZHU Xiaobin, WANG Xiaoling, LI Xiao, XIE Huaiyu
		DOI: 10.11660/slfdxb.20190502
		The response surface method is in wide use for calculating the reliability of gravity dams against sliding, but traditionally it is short of parameter screening analysis and its previous studies lack calculations of reliability index using an intelligent algorithm. Aiming at the problems, this paper develops a weighted dynamic response surface reliability analysis method using the cat swarm optimization that can overcome the shortcoming of massive repeated sampling in the Monte Carlo method. First, considering the dam foundation seepage-stress coupling, we choose key rock mass parameters through quantitative global sensitivity analysis. Then, the implicit performance function is approximated by a weighted response surface, and dynamic updating along with reliability index calculations is achieved using the cat swarm optimization. Finally, we analyze the sensitivity of dam foundation parameters and its engineering reliability in a case study. The results show that the shear strength parameters of dam foundation have a significant influence on dam stability and the reliability index is 2.71, which agrees well with the calculation results using the standard method. Our new response surface method is effective and reliable and would help further research.
		2019 Vol. 38 (5): 9-17 [Abstract] ( 232 ) PDF (1748 KB) ( 256 )

	18	Time-domain analysis of tunnel-layered soil system based on doubly asymptotic transmitting boundary
		ZHENG Siyuan, LIU Tingjin, TANG Xinwei
		DOI: 10.11660/slfdxb.20190503
		Developed from the modified scale boundary finite element method and continued fraction solution, the high-order doubly asymptotic transmitting boundary can realize time localization and generate a stiffness matrix that converges rapidly to the exact solution over the whole frequency range, thereby achieving a high accuracy and good efficiency. This paper applies such a transmitting boundary to the propagation of elastic waves across complicated layered soil, and develops a time-domain coupled model by combining with FEM to study the dynamic responses of a tunnel-layered soil system. This coupled model divides the domain into a near field and a far field by a transmitting boundary, and calculates both separately using a FEM model and a high-order doubly asymptotic transmitting boundary method. Results of numerical examples demonstrate that the solutions are stable and agree well with those of the extended mesh method, achieving a good balance between accuracy and efficiency. And it is also applicable to long-time seismic response analysis of tunnel-layered soil interaction. Thus, the coupled model would provide a new approach for seismic analysis of tunnel-layered soil interaction and should be developed further for engineering application.
		2019 Vol. 38 (5): 18-26 [Abstract] ( 168 ) PDF (604 KB) ( 603 )

	27	Influence of adverse structural planes on overall stability and abutment reinforcement
		LIN Peng, SHI Jie, NING Zeyu, PENG Haoyang
		DOI: 10.11660/slfdxb.20190504
		Abutment stability is the most important factor in the overall stability of high arch dams, and reinforcement measures against adverse structural planes are crucial to guarantee the overall stability. Under complicated dam foundation conditions, unfavorable structural planes usually have a potential influence on the overall stability, such as wedge stability at abutment and uncoordinated deformation and force transmission due to faults and weak belts. This paper presents an analysis on the overall stability for typical high arch dam projects under the conditions of natural and reinforced structural planes based on the results of geomechanical model tests and nonlinear FEM calculations, and summarizes four typical types of structural planes at dam abutments and the corresponding reinforcement measures.
		2019 Vol. 38 (5): 27-36 [Abstract] ( 203 ) PDF (3098 KB) ( 707 )

	37	Analysis on meso-scale damage of concrete using CT images and K-Means clustering algorithm
		ZHU Lin, DANG Faning, DING Weihua, ZHANG Le
		DOI: 10.11660/slfdxb.20190505
		No obvious grayscale feature can be detected in the mesoscopic damage area of concrete CT images, and it is difficult to extract mesoscopic damage information with an image segmentation method that is based on thresholding or edge detection. This paper describes a new K-Means clustering algorithm for deeply excavating such information from the CT images of concrete. First, we conduct uniaxial static compression tests on concrete cylinder specimens. Then, we determine the number of optimal clusters according to the outline coefficient, use this algorithm to search for the optimal partition of a CT image in non-supervised state, and obtain a partition map that carries mesoscopic damage information. Finally, the degree of damage is calculated by counting the total number of pixels over the damage area. The results show that at each compression stage, the evolution of mesoscopic damage in concrete can be observed intuitively on the map of failure zones and mesoscopic damage zones. It reveals the trend of mesoscopic damage degree varying with stress ? a relatively stable initial period and a stable growing period before the load peak, and after that an unstable decaying period. Thus, this study demonstrates the significant advantage of the K-Means clustering algorithm in analysis of the damage evolution of concrete.
		2019 Vol. 38 (5): 37-45 [Abstract] ( 271 ) PDF (3612 KB) ( 442 )

	46	Numerical prediction of flood discharge atomization induced by complicated aerial collisions
		LIAN Jijian, LIU Dan, LIU Fang
		DOI: 10.11660/slfdxb.20190506
		To predict the characteristics of atomized jet nappes in high dam flood discharge caused by complicated aerial nappe collisions, this paper presents a numerical method for plane-facade nappe collision modes, considering the features of atomized sources and atomized rainfall fields, together with its engineering application at the Xulong hydropower station. The calculations show that the distributions of atomized sources and atomized rainfalls depend on the shape of flip buckets. For optimized bucket scheme II under the adverse wind condition, the area of atomized heavy rain is larger under the flood of 5000-year period than that of 100-year period. In the former case, the downstream boundary of the protection area is shifted downstream by 50 m up to pile number 0+895 m, and the highest protection elevation is raised by 9 m and 13 m on the left and right banks respectively, exceeding the dam crest by 69 m and 55 m respectively. Under the adverse wind and rain, the design flood protection standard requires a longitudinal range of 0+(-3 m) to 0+862 m with the bank protection elevations of 2382 m on the left and 2391 m on the right, and the check flood protection requires a longitudinal range of 0+(-9 m) to 0+938 m with the bank protection elevations of 2370 m on the left and 2371 m on the right.
		2019 Vol. 38 (5): 46-56 [Abstract] ( 189 ) PDF (1605 KB) ( 359 )

	57	Hydrological responses and stormwater control effects of typical urban LID measures
		ZHANG Man, ZHOU Keke, ZHANG Ting, LI Jianzhu, FENG Ping
		DOI: 10.11660/slfdxb.20190507
		Rapid development of urbanization has aggravated the problem of urban waterlogging and water pollution. In the present study of a residential area in Jizhou District of Tianjin, a SWMM model is developed on the basis of its planning scheme and a physical experiment of permeable pavement, and the stormwater control effects of seven planning schemes for different rainfall events are simulated. We explore the feasibility of adopting a natural drainage system in replacement of a rainwater pipe network in a certain area, and examine the control of different schemes ? separate permeable pavement, depressed green, vegetative swale, bio-retention facility, and combined low impact development (LID) measures. The results indicate that it is feasible for the natural drainage system to complete the flow convergence through permeable pavement, etc. and these measures can achieve a better control effect. Combined LID measures can reduce total runoff, flood peak flow and water accumulation, and delay peak time, thereby producing a more effective stormwater control for the rainfalls with a short return period and short duration. Among all the measures examined, the scheme of combined LID measures is best in stormwater control, the combination of permeable pavement and bio-retention facility is best in reduction of peak flow, and vegetative swale has a poor stormwater control effect.
		2019 Vol. 38 (5): 57-71 [Abstract] ( 386 ) PDF (1720 KB) ( 787 )

	72	PIV experiment and numerical simulations of behaviors of residual air mass in water pipelines
		HUANG Haocheng, CHEN Qi, JIANG Jin, LIAO Zhifang, LIU Laiquan, TAN Kai
		DOI: 10.11660/slfdxb.20190508
		An experimental platform is constructed to test the stagnant air mass in the top bend section (like an inverted siphon bend) of a pressurized pipeline, and water flow velocity in this bend section is measured using a particle image velocimetry (PIV) system, focusing on the influence of flow velocity and the local pipeline slopes on the motion characteristics of residual air mass. To simulate numerically the flow details in the bend section, we construct a local gas-liquid two-phase fluid dynamics model equipped with a RSM turbulence model and a VOF multiphase flow model, and use it to analyze the influence of water velocity, local pipeline slopes, and air mass volume. The results show that with the increasing water flow velocity, the residual air mass presents three flow regimes: no bubble generated, air bubble generated but discharged partially, and air mass discharged at one time. If other conditions are the same, the threshold water flow rate required for the third regime is relative low when the trapped air volume is greater than a certain value; the threshold water flow velocity for the third regime become greater at larger local slopes of the top bend section.
		2019 Vol. 38 (5): 72-80 [Abstract] ( 245 ) PDF (1517 KB) ( 687 )

	81	Water hammer protection of long-distance water supply projects with special terrain conditions
		SHI Lin, ZHANG Jian, NI Weixiang, CHEN Xuyun, LI Min
		DOI: 10.11660/slfdxb.20190509
		In a long-distance water supply project, generally the pipeline is arranged according to topography. In view of certain special topographic conditions, this paper presents a water hammer protection scheme of combining an air vessel with an outlet overflow tank, and develops a mathematical model of the overflow tank. For the air vessel of fixed shapes and sizes, we derive a theoretical formula for calculating the cross-sectional area of the tank, which can effectively reduce the blindness and labor cost in the initial selection of the tank parameters. In a case study of a real long-distance water supply project, we compare the water hammer protection performance of the combination scheme with that of no overflow tank. The results show that the combination scheme is better for long-distance water supply projects pipelines with a steep slope in front and a mild slope behind, and that it achieves a better protective effect against negative pressure if a higher overflow threshold level in the tank is adopted.
		2019 Vol. 38 (5): 81-88 [Abstract] ( 228 ) PDF (843 KB) ( 510 )

	89	Control strategies for rapid power responses of doubly-fed hydro generators
		YU Xiangyang, ZHU Yong, GAO Chunyang
		DOI: 10.11660/slfdxb.20190510
		Doubly-fed hydro turbine units have a higher response speed and a wider working head than those of conventional hydro turbine units. But application of doubly-fed generators and frequency converters requires more complicated control methods. First, this paper develops a new method based on the load optimization theory for finding the minimum unit flows on equal unit power curves to improve the optimization method of optimal speeds. Then, according to the theory of stator flux orientation vector control and through double-channel excitation and multivariable error superposition, we integrate the current hysteresis vector control into a doubly-fed turbine generator excitation control strategy and obtain a method for rapid generation of the trigger signals of voltage source converters. Finally, we construct a simulation model of the single-machine infinite-bus system with doubly-fed turbines and achieve a variable speed and constant frequency (VSCF) function. And the operation cases of changing the given power are examined and compared with the conventional cases. The results show that our new control method significantly shortens the adjusting time of power response of a hydropower station.
		2019 Vol. 38 (5): 89-96 [Abstract] ( 236 ) PDF (762 KB) ( 898 )

	97	Effects of low pressure edges of short blades on cavitation performance of pump-turbine
		NING Nan, LAI Xide, LI Ping
		DOI: 10.11660/slfdxb.20190511
		To investigate the influence of the low pressure edge locations of short blades on the cavitation performance of a high-head pump-turbine with a splitter blade runner, three types of short blades are designed with the different locations according to the structural characteristics of splitter blade runners. The short blades are named as Scheme A, B, and C from the largest to smallest ratio of the diameter of low pressure edges at the upper crown over the runner diameter at the throat. A smaller ratio indicates the low pressure edges located further behind. We use a Rayleigh-Plesset cavitation model to simulate the steady states of the pump-turbine under three turbine conditions and two pump conditions, and compare the forms and energy of cavitation in the pump-turbine. The results show that at low flow rates, the cavitation performance of the runner is improved as the low pressure edges are moved backward, while at high and medium flow rates, Scheme B is better. In pump modes, the cavitation degree of the runner at high working heads is lowered first and then aggravated with the relative edge location moving backward, while the low pressure side in scheme A is most conducive at low heads. Considering both working modes, we conclude that Scheme B with a diameter ratio of 0.9487 is better in cavitation performance and its efficiency and working head are higher.
		2019 Vol. 38 (5): 97-105 [Abstract] ( 198 ) PDF (2289 KB) ( 501 )

	106	Low frequency oscillation mechanism and stability characteristics of hydraulic turbine generator units
		YE Wei, CHEN Diyi, XU Beibei, ZHANG Jingjing, WANG Pengfei
		DOI: 10.11660/slfdxb.20190512
		To intensive study the low frequency oscillation mechanism of hydraulic turbine generator units and reveal the stability behaviors of the system, this study develops a dynamic model of a turbine generator unit coupling a hydraulic turbine model, a governor model, and a third order generator model. First, the dynamic model is verified against the prototype measurements of the turbine generator unit. Then, according to the damping characteristics of the unit, we optimize its PID parameters through numerical experiments and analyze the mechanism of low frequency oscillations and the stability characteristics of the system under different governor parameters. Finally, to evaluate quantitatively the influence of sensitive parameters on system stability, damping sensitivity of the system in the steady oscillation mode is examined, and key parameters significant to system stability are determined.
		2019 Vol. 38 (5): 106-113 [Abstract] ( 292 ) PDF (473 KB) ( 558 )

	114	Coupled fluid-solid analysis of observation galleries in Rumei dam with multi-body contact
		WANG Wei, BAO Qichang, ZHAN Ling, ZHANG Bingyin
		DOI: 10.11660/slfdxb.20190513
		Problems of multi-body contact with seepage are common in hydraulic engineering, but traditional joint element-based methods have a number of shortcomings. In this paper, we develop a new algorithm of multi-body contact with consolidation using a Lagrange multiplier method to handle the pore pressure continuity condition at contact interfaces, based on the computational contact mechanics and fluid-solid coupling. This algorithm is applied to a stress-deformation analysis of the observation galleries in the earth core of the Rumei dam. Numerical calculations show that it is capable of handling non-conforming meshes and effectively solves the enormous difficulties in mesh generation arising from the complicated 3D form of the galleries and the huge dimensional differences between the gallery blocks and dam body. The calculated gallery displacements are reasonable, and the behaviors of discontinuous deformation such as the separation and sliding between the gallery blocks are captured. By refining the local gallery mesh, we can further achieve better results and a higher accuracy in the calculations of stress distribution over the gallery blocks.
		2019 Vol. 38 (5): 114-120 [Abstract] ( 231 ) PDF (1505 KB) ( 358 )