Journal of Hydroelectric Engineering

水力发电学报

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2022 Vol. 41, No. 9 Published: 2022-09-25

	1	Grayscale histogram and texture features of wake vortex image behind circular cylinder
		LU Lingjiang, LIU Zhaowei, YANG Tong, CHEN Yongcan
		DOI: 10.11660/slfdxb.20220901
		Image technology is an important approach to fluid mechanics research widely used in flow visualization and flow measurement, and its application in such research is continuously deepening with the development of information technology. By taking the flow past a circular cylinder as an example, this paper analyzes the image characteristics of wake vortices in the Reynolds number (Re) range of 50 to 1725. We examine variations in the image feature parameters of grayscale histogram and texture with Re, and give an interpretation related to flow characteristics. The results show three factors, the turbulent diffusion rate of the wake flow, separation point locations, and the spatial distribution of wake vortices, are responsible for different characteristics of the grayscale histogram and texture. At Re < 600, the mean value of gray level decreases linearly with Re; at Re = 148 ~ 642, the vortex shedding period based on texture analysis agrees well with its empirical calculation; at Re > 170, the skewness of grayscale histogram increases with Re and follows a linear correlation.
		2022 Vol. 41 (9): 1-11 [Abstract] ( 126 ) PDF (1137 KB) ( 295 )

	12	Effect of sediment gradation on cavitation erosion in high velocity flows
		DONG Zhiyong, LI Yuhang, XU Xuyi
		DOI: 10.11660/slfdxb.20220902
		Effects of non-cohesive sediment grain gradation on cavitation erosion in high velocity flows is studied experimentally in a small looped water tunnel. First, eight non-cohesive sediment samples of different gradations are prepared in the inner tank of the tunnel－weight percentages smaller than a certain grain size of P < 2%, 12%, 33%, 47%, 56%, 70%, 86%, 100%; Sediment concentration is measured using an infrared suspended solid analyzer. A dynamic pressure data acquisition system is adopted to measure real-time the pressure in the tunnel working section, including the cavitation zone and cavitation erosion zone in the condition of eight sediment gradations. Second, concrete specimens with different strengths are used for the tests of erosion of 4 hours long under the condition of the same concentration S and different sediment gradations. The results show that at S = 12 kg/m3 and throat flow velocity V = 38.6 m/s, an increase in weight percentage P lowers the pressure in the cavitation zone, promoting the occurrence of cavitation; but it raises the pressures in the erosion zone, enhancing cavitation erosion. At a fixed strength of concrete specimens, their cavitation erosion intensifies with an increase in P; at fixed values of S and P, a specimen with a higher strength (fcu = 17.8 MPa) presents a greater cavitation erosion resistance than that with a lower strength (fcu = 13.7 MPa).
		2022 Vol. 41 (9): 12-20 [Abstract] ( 145 ) PDF (1165 KB) ( 196 )

	21	Full narrow-slot numerical model of open-pressurized transient flows in water distribution system
		MO Tiexiang, LI Guodong
		DOI: 10.11660/slfdxb.20220903
		The alternating process of open-channel and pressurized flows in a water distribution system is a major cause of system damage. Accurate simulation of the transient process of mixed open-pressurized flow in water distribution systems is a technical problem that urgently needs to be solved. However, the commonly used Preissmann narrow slot method cannot simulate the transient process with negative pressure flow, greatly limiting its applicability to these systems. This paper develops a numerical model for unsteady open-channel flow, pressurized transient flow with negative pressure, and open-pressurized mixed flow with negative pressure, through coupling the dichotomy pressure method and the Preissmann negative slot idea. We develop a method for distinguishing negative pressure flows from open-channel flows based on the CFL constraints, and apply the model to complicated flow cases－open-pressurized flow alternation and simultaneous action of water hammer during open channel filling, water hammer in the pressurized pipeline, and valve closing during the filling. The applications show that our new model breaks through the limitation of the Preissmann method and the difficulty in distinguishing open-channel flows and negative pressure flows by the differential pressure method, and achieves accurate simulations of open-pressurized alternation transients without gas-liquid two-phase interaction.
		2022 Vol. 41 (9): 21-30 [Abstract] ( 108 ) PDF (2740 KB) ( 330 )

	31	Water resources allocation model of urban agglomeration in Guangdong-Hong Kong-Macao Greater Bay Area
		ZHANG Zhaoyi, HE Yanhu, TAN Qian, CHEN Xiaohong
		DOI: 10.11660/slfdxb.20220904
		The existing water evaluation and planning system (WEAP) models lack consideration of regional water allocation priorities. In this paper, an improved WEAP model is developed by integrating these priorities determined by water safety degree, and is applied to water resources allocation for Guangdong-Hong Kong-Macao Greater Bay Area. The effects of allocation schemes with different regional and industrial priorities are compared. The results show the water safety of each city in this area varies across regions and industries. Guangzhou, Shenzhen and Dongguan have lower degrees of domestic and industrial water safety. Under the premise of ecological basic flows guaranteed, an allocation scheme that considers regional and industrial priorities improves the satisfaction of domestic and industrial water uses in the key areas, resulting in more reasonable allocation. In the dry period, the water demands by Shenzhen and Dongguan cannot be satisfied, and the river and reservoir connections are essential to the Greater Bay Area. This study demonstrates both regional and industrial allocation priorities are key factors to consider in improvement of the WEAP model.
		2022 Vol. 41 (9): 31-43 [Abstract] ( 123 ) PDF (7128 KB) ( 95 )

	44	Operation modes of cascade hydropower stations considering large-scale integration of wind and photovoltaic power
		TAN Qiaofeng, NIE Zhuang, WEN Xin, DING Ziyu, ZHANG Ziyi
		DOI: 10.11660/slfdxb.20220905
		Combining and bundling the wind and photovoltaic (PV) power with a hydropower system is an effective way to promote the consumption of new energy, but it creates a great challenge to the traditional operation modes of pure hydropower system. This paper presents a systematic study on the operation modes of cascade hydropower stations in long-term, one-day ahead and real-time scales, considering the large-scale access of wind and PV power; and evaluates the benefits and risks of complementary operation via examining a case of the hydro-wind-PV power system in the Yalong River basin of China. The results show that in the complementary mode, the water level at large hydropower stations should be lowered more and in advance to increase power generation in dry season and reduce abandoned water volume in flood season. In this mode, the peak regulation ability of the system can be improved, and the daily output process of hydropower should be adjusted to alleviate the competition of export channels. Cascade hydropower can compensate and adjust the unstable wind and PV power at one day ahead and in real-time scales, significantly improving power transmission quality and power supply reliability.
		2022 Vol. 41 (9): 44-55 [Abstract] ( 232 ) PDF (759 KB) ( 769 )

	56	Analysis of precipitation, drought and flood variability in Chengbi River basin
		SUN Guikai, WANG Xicai, MA Long, HUANG Rui, WANG Lei, MO Chongxun
		DOI: 10.11660/slfdxb.20220906
		To understand the characteristics of variations in precipitation, drought and flood over a karst basin in Southwest China are examined on the basis of the 1979-2019 data series of monthly precipitation at 12 ground stations in the Chengbi River basin, using methods of the Sen’s slope estimation, wavelet cycle analysis, empirical orthogonal function (EOF) analysis, and standardized precipitation index (SPI). The results show that in this basin, its annual precipitation presented a nonsignificant increasing trend over 41 years with the main period of 30 a; its precipitation was concentrated in summer showing nonsignificant changes; and an overall pattern of increase from southeast to northwest. EOF analysis reveals three precipitation patterns in the basin: consistent variation across the basin that is dominant, and the other two showing opposite trends. In the basin, a change from drought events to flood events occurred in 1994, resulting in its frequency of floods higher than its frequency of droughts; the spatial distribution characteristics of its drought and flood events changes are somewhat variable. The results are useful to the basin's precaution and preparation against drought and flood events.
		2022 Vol. 41 (9): 56-66 [Abstract] ( 115 ) PDF (3843 KB) ( 287 )

	67	Flash flood grading and warning based on dynamic rainfall thresholds
		HAN Juntai, WANG Zhengrong, YANG Yuting
		DOI: 10.11660/slfdxb.20220907
		The rainfall threshold method is widely used in flash flood warning and forecasting, but its traditional applications usually rely on static indexes and fail to identify disaster risk levels. In this study, a grading warning method is developed based on dynamic rainfall thresholds and applied to a small watershed in the downstream of the Minjiang River in Fujian Province. It uses an artificial neural network to construct a statistical relationship between runoff thresholds and risk factors to obtain the spatial distribution of runoff thresholds in the ungauged areas. By defining four risk levels of flash floods, it determines the corresponding runoff thresholds and rainfall thresholds through a frequency analysis based on long-term hydrological simulations. Results show that by considering the effect of antecedent soil moisture on flash floods, this method can prolong the forecast period and improve the monitoring capability significantly. Compared with traditional methods, its adoption of flash flood risk levels enhances its applicability to real flash flood warning.
		2022 Vol. 41 (9): 67-76 [Abstract] ( 199 ) PDF (4207 KB) ( 382 )

	77	Estimating probable maximum precipitation based on multi-source data of precipitation in the Lancang-Mekong River basin
		XIONG Jinghua, GUO Jing, GUO Shenglian, LI Na, WANG Jun, YIN Jiabo, TANG Junlong
		DOI: 10.11660/slfdxb.20220908
		Multi-source precipitation products play important roles in estimation of possible maximum precipitation (PMP), especially for data-sparse regions. This study evaluates the accuracy of three global precipitation products－i.e. Climate Hazards Group Infrared Precipitation with Station (CHIRPS), Multi-Source Weighted-Ensemble Precipitation (MSWEP), and Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN)－based on the Asian Precipitation-Highly-Resolved Observational Data Integration Towards Evaluation (APHRODITE) dataset and in-situ measurements in the Lancang-Mekong River basin. An improved statistical method is used to estimate the 1d and 3d PMPs. Results show that (1) the MSWEP dataset presents the satisfactory accuracy and precipitation detection ability; (2) the MSWEP-based PMP is significantly correlated with the APHRODITE results at the grid-cell scale; (3) the MSWEP-based 1 d and 3 d PMP estimates are 122 and 192 mm, respectively, comparable to the previous estimation results. This study indicates that the global precipitation products are useful to PMP estimation for data-sparse regions.
		2022 Vol. 41 (9): 77-86 [Abstract] ( 152 ) PDF (4441 KB) ( 313 )

	87	Simulation study of variable speed hydraulic turbine operation in load adjusting conditions
		KOU Pangao, ZHU Guangming
		DOI: 10.11660/slfdxb.20220909
		Aimed at the research demand for variable speed hydropower unit control, this paper develops a numerical simulation model based on MATLAB/Simulink, focusing on the dynamic modeling and control strategy of the governor system of variable speed hydraulic turbines. We simulate the sudden loading and large load rejecting processes, considering the speed limitation and lag time of servomotor motion in the simulation of load rejecting, and examine their effects on the dynamic response of variable speed hydraulic turbines. Results show that (1) our newly-developed double PID control strategy, through considering speed errors and guide vane errors, can control isochronously the turbine speed and guide vane opening in steady state. (2) The load rejecting in operation of a variable hydraulic unit is similar to the case of a conventional fixed speed unit, resulting in excessive rise or fall of turbine speed and pressure. (3) During load adjusting, the speed limitation and lag time of servomotor motion have significant effects on the dynamic response of system variables, such as turbine speed, servomotor motion, pressure, and other unit parameters, thus limiting the amplitudes of primary frequency regulation and load regulation.
		2022 Vol. 41 (9): 87-97 [Abstract] ( 122 ) PDF (612 KB) ( 327 )

	98	Study on failure criterion of cemented sand-gravel dam model test based on catastrophe theory
		DING Zelin, XUE Jianghan, WANG Jing, BAO Chuang
		DOI: 10.11660/slfdxb.20220910
		Geomechanical model testing is a key approach to studying the safety and stability of a cemented sand-gravel (CSG) dam. However, displacements of a tested model dam are relatively small and the overturning trend of the dam is usually difficult to capture, so its compression failure interval and overload safety factor (or ultimate safety factor in failure stage) cannot be determined with enough accuracy. To overcome this problem, we conduct geomechanical tests on a model CSG dam, and measure strains in the dam foundation and at the dam surfaces and surface displacements at the downstream dam face. The overload safety factor Kp of the model dam are estimated in the range of 4.6 ~ 6.2. To determine this factor accurately, first we use the catastrophe theory to fit a quadratic polynomial to the model test data, and then the fitted values and instability discriminant are used to finalize its values－an accurate Kp range of 6.0 ~ 6.2. This method solves the accuracy problem in calculation of the overload safety factor of a geomechanical model CSG dam, and helps promote its development and application.
		2022 Vol. 41 (9): 98-107 [Abstract] ( 80 ) PDF (1208 KB) ( 402 )

	108	Resistance reduction measures for thick-walled bucket foundation in silty clay
		LIAN Jijian, ZHAO Hao, LIU Run, ZHENG Hongjie, YANG Xu
		DOI: 10.11660/slfdxb.20220911
		Bucket foundation is an innovative type for supporting offshore wind turbines (OWT), and more than 60 foundations of this type have been installed in the wind farms in China due to its low cost and efficient installation. With the developing trend of large scale and deep water, the size of foundation grows, resulting in a high buckling failure probability of its steel bucket skirts during prefabrication, transportation and sinking. This paper develops a thick-walled bucket foundation that adopts a concrete skirt and steel bulkheads to further reduce its cost and skirt buckling possibility. However, as the penetration resistance of this foundation increases, how to reduce it becomes the key to successful installation. In this work, we conduct a laboratory test of the foundation in silty clay, and examine the resistance reduction effect of two measures: ring stiffeners and thick-skirt water flushing. And a calculation method of penetration resistance is developed to take the reduction effect into account. Results show that the ring stiffeners with the same size as the steel bulkheads can reduce the friction drag by 50%, and the flushing measure can reduce the end resistance by 88%. To avoid the influence on the suction operation caused by synchronous water flushing, an alternate operation of the two processes is suggested.
		2022 Vol. 41 (9): 108-117 [Abstract] ( 143 ) PDF (4610 KB) ( 197 )

	118	Knowledge graph intelligent establishment for concrete dam construction management
		SHEN Yang, TIAN Dan, LIU Hao, REN Qiubing, ZHANG Dongliang, LI Mingchao
		DOI: 10.11660/slfdxb.20220912
		Most of the concrete dam construction management (CDCM) knowledge is recorded and stored in text form, which features a huge amount of data, severe fragmentation, and poor hierarchy. An important issue for the management is to mine construction knowledge from unstructured text data, clarify the logical relationship of knowledge, and improve the efficiency of knowledge application. This paper presents an intelligent method for generating CDCM knowledge graphs, or converting massive text data into directly usable knowledge. We combine word vectors, char vectors, a Bi-directional Long Short-Term Memory-Conditional Random Field (BiLSTM-CRF) network, and the attention mechanism; and build an intelligent model for CDCM entity recognition. It strengthens construction entity characteristics and extracts entity words from the management texts. Relationship types between entities are defined by the construction entities identified; mutual information is used to extract entity relationships and obtain construction knowledge chains; a CDCM knowledge graph is established by combining these chains. Application to a real management case shows this model gives an F1 value of 92.48%, outperforming other entity recognition models. Thus, this study demonstrates that the knowledge graphs can be established using the relationships between the construction entities recognized and that based on the graphs, a retrieval mechanism of the construction knowledge can be worked out for its rapid extraction and high application efficiency.
		2022 Vol. 41 (9): 118-128 [Abstract] ( 215 ) PDF (1183 KB) ( 513 )

	129	Corrosion rates of carbon steel and stainless steel reinforcements in cracked concrete
		WANG Hailong, YU Ning, WU Yuanjian, XU Hongquan, SUN Xiaoyan
		DOI: 10.11660/slfdxb.20220913
		Based on the electrochemical theory, numerical models are developed to reveal the effect of crack width on the corrosion rate of carbon steel and stainless steel reinforcements in concrete, considering the effect of cracks on chloride ion and oxygen transportation in concrete and the effect of oxygen on steel corrosion process. Experimental tests are conducted to verify the accuracy of numerical simulations, and the parameter sensitivity of the simulations is examined. The results show the anodic polarization process and oxygen supply are two dominating factors of the steel corrosion rate. The occurrence of cracks moves up the critical time for steel bars to transform from passive to corrosive, and also affects the corrosion rate of carbon steel in the stable corrosion stage. Reducing the crack width and chloride diffusion coefficient can significantly limit the steel corrosion rate. Compared with carbon steel, stainless steel shows higher corrosion resistance in harsh erosive environments.
		2022 Vol. 41 (9): 129-138 [Abstract] ( 240 ) PDF (4902 KB) ( 256 )

	139	Dynamic characteristics and energy consumption laws of concrete impact failure
		LI Yutao, DANG Faning, REN Jie, ZHOU Mei
		DOI: 10.11660/slfdxb.20220914
		Impact compression tests on concrete specimens are conducted using a split Hopkinson pressure bar (SHPB) device, with impact velocities of 5, 6 and 7 m/s and concrete aggregate volume ratios of 0, 32%, 37% and 42%, to explore comprehensively the influence of these two factors on the dynamic characteristics and energy transfer laws of concrete. We study the variations in dynamic deformation, dynamic strength growth, and energy transformation of concrete with the two factors, and examine their influence on the dynamic strength using two-factor variance analysis. The results indicate that under impact compression, concrete specimens are subjected to failure dominated by the tensile splitting mode. Aggregate content imposes a great influence on dynamic elastic modulus, while impact velocity affects little. Concrete dynamic strength increases as aggregate content or impact velocity increases, and impact velocity has a greater effect on dynamic strength than aggregate content. With an increasing aggregate content, the dynamic increasing factor (DIF) increases in the impact velocity range of 5 to 5.8 m/s, while it decreases in the range of 5.8 to 7 m/s. The transmitted energy increases with impact velocity or aggregate content; the reflected energy, absorbed energy, and the ratio of absorbed energy to incident energy all increase with impact velocity but decrease with aggregate content.
		2022 Vol. 41 (9): 139-149 [Abstract] ( 140 ) PDF (2159 KB) ( 383 )

	150	Multi-factor probability prediction method of arch dam construction simulation parameters
		SONG Wenshuai, GUAN Tao, REN Bingyu, WANG Jiajun
		DOI: 10.11660/slfdxb.20220915
		Construction simulation parameters are essential to the accuracy of actual arch dam construction schedule implementation. Of the previous studies on analysis of these parameters, most adopted a univariate model and some resorted to the multivariate analysis method to build a point prediction model, both facing a difficulty in evaluation of their uncertainty under the influence of various factors. To analyze the probability distribution of the parameters effectively, a probability prediction method based on a broad learning system along with the elastic network quantile regression (BLS-ENQR) is presented. BLS is a neural network that, without demanding a deep network structure, has an efficient nonlinear learning capability, so that it can overcome the deficiency of the traditional quantile regression model limited to linear relationship analysis. The method uses the elastic network regularization penalty to reduce the regression coefficient and improve its sparsity so as to avoid model overfitting. Engineering application shows that this new method can effectively analyze the probability distribution of construction simulation parameters, and it has prediction performance better than the support vector machine-ENQR (SVM-ENQR), extreme learning machine-ENQR (ELM-ENQR), or broad learning system-QR (BLS-QR).
		2022 Vol. 41 (9): 150-160 [Abstract] ( 82 ) PDF (609 KB) ( 384 )