Journal of Hydroelectric Engineering

水力发电学报

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(vi)Chinese Academic Journals (CD).


2020 Vol. 39, No. 1 Published: 2020-01-25

	1	Study on hydrodynamics and regulatory response characteristics of stilling pool under jets from tail-flaring pier spillway
		LIAN Jijian, BIAN Yudi, LI Huiping, YE Dezhen
		DOI: 10.11660/slfdxb.20200101
		Based on a 1:100-scale model of the Jinghong hydropower station, we study the hydrodynamics and regulatory responses of a stilling pool under the jets from a tail-flaring pier spillway, focusing on the influence of water cushion depth, unit discharge and opening mode on hydrodynamic pressure. We found that time-average pressure is dominated by water cushion depth, independent of the unit discharge and increasing with this depth, while pressure fluctuations depend on these two factors, reduced by a thinner cushion and intensified by a larger unit discharge. And dynamic water pressure is different in different gate operation modes. In the test, as the opening mode of surface outlets shifts from the alternate pattern to sectional pattern, the peak values of fluctuating pressure at their centerlines and at the pier centerlines are weakened.
		2020 Vol. 39 (1): 1-11 [Abstract] ( 156 ) PDF (918 KB) ( 390 )

	12	Study on characteristics of secondary flows in smooth rectangular open channel
		JING Siyu, YANG Wenjun, CHEN Yue
		DOI: 10.11660/slfdxb.20200102
		Occurrence of secondary flows in an open channel greatly affects its distributions of flow velocity and energy, and its aspect ratio has a direct impact on the secondary flows. This study uses a high-resolution particle image velocimetry to investigate the behaviors of secondary flows in a straight channel with different aspect ratios, through measuring flow parameters at the sections of one half of the flume by considering flow symmetry. We focus on the influence of aspect ratio on the structure and strength of secondary flows under supercritical conditions; and conduct experimental tests on a narrow, deep chute, using the channel aspect ratio in the range of 3.75 - 7.5. The results indicate that (1) several secondary cells exist at the cross sections with their total number increasing with aspect ratio, and aspect ratio exerts a great influence on the number and strength of secondary flow. (2) Turbulence intensity and velocity distribution are closely related to secondary flow behaviors. (3) A dip phenomenon occurs in the distribution of streamwise velocity, and the location of velocity peak depends on aspect ratio and the distance to the sidewall. (4) Reynolds stress distribution around the cross section center shows no significant difference when the aspect ratio is changed, but it is affected by the gradient in streamwise velocity.
		2020 Vol. 39 (1): 12-20 [Abstract] ( 168 ) PDF (1562 KB) ( 335 )

	21	Inversion of particle size distributions of suspended loads based on ultrasonic attenuation effect
		LI Yeming, XIE Dailiang, HU Heming, XU Zhipeng, XU Ya, LIU Tiejun, WANG Yuebing
		DOI: 10.11660/slfdxb.20200103
		To achieve accurate and rapid measurement of particle size distribution (PSD), a key parameter of two-phase flows, this paper develops a new measurement method by combining ultrasonic attenuation effect and an artificial bee colony inversion algorithm. We design a suspension parameter measurement system that uses a focused ultrasonic sensor to obtain ultrasonic attenuation signals, and calculate an effective experimental attenuation coefficient. A theoretical attenuation coefficient is obtained according to the theoretical sound attenuation model, and an error function for theoretical and experimental attenuation coefficients is constructed and used as the objective function. Then, we adopt an artificial bee colony algorithm to optimize the objective function, and obtain an optimal PSD through inversion calculation. To verify the method, experimental tests are conducted on suspended load samples of three different PSDs, and the sieving method is used as a control experiment to analyze error factors. The results show our new method is practically applicable and of high accuracy in the tested range, and it provides a new approach to measurement of PSD of suspended load.
		2020 Vol. 39 (1): 21-30 [Abstract] ( 193 ) PDF (813 KB) ( 350 )

	31	Guarantee-rate frequency analysis method for designing the lowest navigable water levels with inconsistent characters
		WANG Lu, XIE Ping, SANG Yanfang, CHEN Jie, ZHAO Jiangyan, YU Tao
		DOI: 10.11660/slfdxb.20200104
		The changing environment has brought about time-varying high-order moments of a series of river stage. Therefore, those design lowest navigable water levels considering only variations in the series mean are inconsistent with reality. To solve this problem, we develop a variance variability-based guarantee-rate frequency analysis method based on the idea of decomposition and integration and a second-order moment variation analysis, and demonstrate its application in a case study for the Gaodao hydrological station. Results show that when variance variation is considered, design lowest navigable water levels at guarantee rates of 95% and 98% under the current condition are 2.15 m and 1.60 m higher than those of traditional designs respectively (at frequency of 80%). And the differences in the design values among three cases ? considering variance variation, considering mean variation only, considering neither of them ? are prominent, confirming the necessity of analyzing both mean variation and variance variation.
		2020 Vol. 39 (1): 31-43 [Abstract] ( 119 ) PDF (854 KB) ( 302 )

	44	Instability mechanism study of unstable regulating zone I of hydropower plant
		YANG Xiuwei, YU Xiaodong, ZHANG Jian
		DOI: 10.11660/slfdxb.20200105
		Based on the small fluctuation stability analysis theory, this paper constructs an analytical model for a hydro-turbine governing system with or without a surge tank by using state space method, examines its instability features in the regulating zone I of governor parameters, and analyzes the influence of phase frequency characteristics on its stability. Results support the conclusion that this instability is essentially originated from the inertia of the water volume in the penstock that results in a phase lag of variation in penstock discharge behind guide vane opening, and consequently it generates a regulation error to the extent of instability. And integral gain can cause a phase lag of variation in guide vane opening behind generator speed. The system’s total phase lag, or the sum of these two, can be altered by proportional gain . At a relative small this total lag decreases with an increase in , while at a large it increases with . Generally, the stability of a closed-loop system requires a total phase lag to be less than 90°.
		2020 Vol. 39 (1): 44-52 [Abstract] ( 127 ) PDF (664 KB) ( 389 )

	53	Flow analysis of pump turbine under power cutoff during its shutdown in pump mode
		YOU Guanghua, ZHU Xingbing, ZHAO Yifeng, TAN Lei
		DOI: 10.11660/slfdxb.20200106
		A pump turbine often experiences vibrations and abnormal noises from its distributor during pump mode shutdown from a guide vane opening less than the maximum opening of 20%. To eliminate this instability, we carry out numerical simulations of the transient flow in guide vane section, investigate variations in flow pattern during shutdown, and verify the necessity of power cutoff in advance. Two-dimensional periodic simulations are adopted to consider periodicity in the flow and guide vane movement during shutdown, and a dynamic meshing technique is used to discretize the guide vane domain with a finite volume method and a RNG k-ε two-equation turbulence model. The boundary conditions of 2D modeling are specified using the results of transient calculation for the hydropower station. The results indicate that during a pump mode shutdown, the scheme of power cutoff in advance at an appropriate opening improves the stability of guide vane flow, thereby lowering the probability of generating vibrations and abnormal noises. Further analysis shows that the flow stability of guide vane channels is positively correlated with the opening threshold for power cutoff. And we suggest an opening threshold in the range of 3-6 degrees for practical operation of hydropower plants.
		2020 Vol. 39 (1): 53-61 [Abstract] ( 128 ) PDF (2255 KB) ( 380 )

	62	Study on active power regulation of hydropower unit monitoring system
		FU Liang, BAO Haiyan, HUANG Bo
		DOI: 10.11660/slfdxb.20200107
		At present, closed-loop regulation using a monitoring system is the main method for regulating the power of hydropower units. To simulate the active power regulation behaviors of such a system, this paper develops a mathematical model including LCU, governor, water conveyance system, and hydro turbine; and verifies its accuracy against measurements in-situ. Based on simulations, we analyze the influence of the monitoring system and governor parameters on the transient process of active power regulation. Results show that the system’s pulse width parameter β mainly affects those adjustment processes that are close to the target value in active power regulation, and that a smaller β leads to larger regulating amplitudes of guide vane opening. A short pulse period T accelerates the regulation. A smaller maximum width Tkmax leads to smaller regulating amplitudes of the opening in each cycle, thus prolonging the total regulation time; while the minimum width Tkmin has no effect on regulation speed but affects regulation accuracy significantly. The speed of guide vane opening regulation is determined by the parameter Tiy. A large Tiy slows down power regulation, while reducing Tiy can increase regulation speed but will also increase the inversely regulated power value. Specifying a too small Tiy may lead to overshoot and even oscillation in active power and guide vane opening.
		2020 Vol. 39 (1): 62-71 [Abstract] ( 157 ) PDF (1455 KB) ( 369 )

	72	Evaluation of abrasion resistance of concrete based on volume loss rate
		HE Zhen, CHEN Xiaorun, ZHAO Rixu, CAI Xinhua
		DOI: 10.11660/slfdxb.20200108
		Using sandblasting test and image analysis technology, this study examines time variations in weight loss rate, volume loss rate, density of abraded materials, and scour hole contour of two different concrete specimens. We obtain a steady state criterion of concrete abrasion erosion by combining the apparent morphology of concrete at feature time points, and optimize the reliable assessment index of concrete abrasion resistance based on abrasion calculations. Results indicate the weight loss rate and volume loss rate tend to be stable at a certain point of time. And afterward, the density of abraded material is consistent with the bulk density of concrete, and the scour hole contour and apparent morphology show a steady and uniform abrasion erosion of concrete, thereby providing a criterion for determining the steady state of abrasion. This study demonstrates the volume loss rate that tends to be stable is a reliable assessment index of concrete abrasion resistance.
		2020 Vol. 39 (1): 72-79 [Abstract] ( 112 ) PDF (1041 KB) ( 257 )

	80	Corrosion characteristics analysis of stainless steel bars based on surface scanning and mechanical properties degradation
		WANG Hailong, SUN Xiaoyan, KONG Hangting, ZHOU Bing
		DOI: 10.11660/slfdxb.20200109
		This study adopts an accelerated corrosion method to achieve corrosion of stainless steel bars embedded in concrete with different target corrosion degrees for an accurate description of steel bar corrosion morphology and a better understanding of corrosion effect. We conduct steel bar tensile tests, use a 3D scanning technology to examine the corrosion factors and deteriorated mechanical properties of the corroded steel bars, and extract accurate corrosion information from the measurements of 3D profiles. Corrosion degree and corrosion non-uniformity are represented using the areas loss of the largest cross section and a uniformity parameter. We find that the corrosion of stainless steel is prone to pit corrosion, its unevenness of corrosion is more prominent in comparison to ordinary carbon steel, and the degree of its corrosion non-uniformity increases linearly with corrosion rate. Fracture surface analysis illustrates the necking and fracturing originate from the location of a critical corrosion pit. Through tensile tests, we can examine the degradation of mechanical properties of corroded steel bars with different corrosion degrees, and then develop a model to describe the degradation of their bearing capacity and elongation rate. Comparison to ordinary carbon steel bars reveals stainless steel is much better in ductility and can maintain a certain elongation ratio even in the case of severe corrosion, manifesting a great advantage in preventing structural brittle failure.
		2020 Vol. 39 (1): 80-88 [Abstract] ( 156 ) PDF (1774 KB) ( 247 )

	89	Study on blasting fragmentation prediction model based on random forest regression method
		WANG Renchao, ZHU Pinguang
		DOI: 10.11660/slfdxb.20200110
		During blasting quarry of dam materials, fragmentation control is a key means to ensure dam construction quality. In previous studies of the prediction of blasting material fragmentation, several problems are left unsolved such as low prediction accuracy and poor generalization ability, and difficulty still remains in accurate control on the fragmentation of rockfill dam materials to meet the requirement of blasting quarry. This study develops a blasting fragmentation prediction model based on a random forest (RF) regression method to overcome the shortcomings of previous blasting prediction models and improve the control on blasting fragmentation. Cross-verification and comparison with other RF prediction models shows this RF model is superior. We verify its calculations and applicability using a blasting fragmentation prediction system of a practical project, and demonstrate its usefulness in management and control of the blasting construction of rockfill dams.
		2020 Vol. 39 (1): 89-101 [Abstract] ( 223 ) PDF (2649 KB) ( 740 )

	102	Effect of water-solid ratio on geopolymer synthesized using sol-gel method
		DUAN Yujie, ZHOU Wei, JI Xiang, CHENG Yonggang, MA Gang
		DOI: 10.11660/slfdxb.20200111
		This study first prepares high purity Al2O3-SiO2 powders or geopolymer precursor using the sol-gel method, and then synthesizes alkali-activated geopolymers using water-solid ratios of 0.50, 0.75, 1.00, 1.25 and 1.50, eliminating the effect of complex composition of the raw mineral materials on product properties in conventional geopolymer research. Compressive strength of the geopolymer samples activated by NaOH is experimentally measured, with microstructure observed using X-ray diffraction (XRD) and scanning electron microscopy (SEM), and chemical bond characterization tested via Fourier transform infrared (FTIR). The results show the geopolymer synthesized with a water-solid ratio of 1.00 performs best in compressive strength after 3 day curing. A too low ratio may lead to incomplete geopolymerization reaction, uneven mixing, insufficiently dense microstructure, excessive porosity of the samples, and poor mechanical properties; while under a too high ratio, moisture would hinder the alkali activator’s reaction with Al2O3-SiO2 powders, thereby causing serious bleeding of the samples and affecting the progress of geopolymerization. When NaOH is used to activate the geopolymer precursor synthesized using the sol-gel method, water-solid ratio has significant effects on its mechanical properties and microstructure. Determining an appropriate water solid ratio helps improve the performance of special geopolymers.
		2020 Vol. 39 (1): 102-109 [Abstract] ( 232 ) PDF (3705 KB) ( 451 )

	110	Experimental study on hydro-elastic model of flood discharge and vibration reduction of Wudongde hydropower station
		MA Bin, SHE Xin, GUO Yiliang
		DOI: 10.11660/slfdxb.20200112
		Using experimental tests on the Wudongde hydro-elastic model, this paper studies the effects of different operation modes and gate openings of its flood outlets on the vibrations of the downstream slope and bedrock, and develops two numerical models for vibration prediction using the BP neural network. Flood flows are divided into three levels of discharge, and optimized schemes for flood control and vibration reduction at each level are obtained. The results show that (1) in the mode of only one surface outlet opened, bedrock vibration is intensified substantially with the increasing gate opening; while in the mode of all surface outlets fully opened, bedrock vibration is reduced and slope vibration is always positively correlated with gate opening. In the joint operation of the surface outlets and deep outlets, bedrock vibration is the weakest at a surface outlet opening of 4 m, but slope vibration is more complicated. (2) The two numerical models are good in prediction accuracy, and constructing a specific prediction model for the joint mode can improve accuracy. (3) To release flood at very small flow rates, multiple surface outlets can be used with a small gate opening; at normal flow rates, the middle outlets should be put into full use, combining, if necessary, with a few surface outlets opened at 4 m opening; at large flow rates, the middle outlets must be fully opened and multiple surface outlets working at small openings.
		2020 Vol. 39 (1): 110-120 [Abstract] ( 157 ) PDF (1157 KB) ( 345 )