Journal of Hydroelectric Engineering

水力发电学报

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2023 Vol. 42, No. 2 Published: 2023-02-25

	1	Relative instability acceleration method for slope stability analysis ^Hot!
		JIE Yuxin
		DOI: 10.11660/slfdxb.20230201
		Slope stability analysis is a classical subject of soil mechanics, through which the safety factor of a slope can be obtained. However, the critical slip surface corresponding to the minimum safety factor is not necessarily the first failure surface to slide, while the one relating to instability acceleration possibly slides first. The theory of instability acceleration is applicable to all structures with free faces such as slopes and tunnels; for the calculations, we can use the conventional assumption of the limit equilibrium method, or a stress analysis via a numerical method such as the finite element method. Besides instability acceleration, traditional safety factors can also be calculated through minimizing the modulus of instability acceleration, a case similar to the special pattern recognition method. This paper sums up the historic evolution and main principles of the instability acceleration method. And we extend the theory to the calculation of relative instability acceleration and relative safety factors, relax its related constraints, and allow it to have a wider application prospect.
		2023 Vol. 42 (2): 1-11 [Abstract] ( 111 ) PDF (2743 KB) ( 267 )

	12	Evaluation of gravel-soil blending uniformity based on improved Harris-Susan algorithm
		CUI Bo, LIU Fukun, GUAN Tao, TAN Tianwen, WANG Jiajun
		DOI: 10.11660/slfdxb.20230202
		The uniformity of gravel-soil blending is very important to the safety of gravel-soil core wall dams. Digital image processing methods are widely used in the field of mixture recognition, but over-segmentation or under-segmentation often occurs in processing images with adhesion characteristics, resulting in a low accuracy of evaluation. Aimed at these problems, this paper develops a new method for evaluating the uniformity of gravel-soil blending using an improved Harris-Susan algorithm. First, this algorithm is used to segment under-segmented regions and repair over-segmented regions so as to improve the accuracy of binary images. Then, the image’s uniformity of single quantile is evaluated using the concept of gravel neighborhood. Finally, particle distribution sampling is used to construct an evaluation index of spatial uniformity of gravel soil. We have applied this method to the construction of a gravel-soil high-core rockfill dam on the Dadu River at Shuangjiangkou, and achieved a relative statistical accuracy of 0.935, proving its significant improvement over the Otsu algorithm (0.353) or watershed algorithm (-3.101). This study shows that its results agree well with those of the screening method; it can effectively save manpower, material resources and time costs and it is applicable to engineering evaluation with high efficiency.
		2023 Vol. 42 (2): 12-23 [Abstract] ( 100 ) PDF (2719 KB) ( 205 )

	24	Optimal factor set based long short-term memory network model for prediction of dam deformation
		LUO Lu, LI Zhi, ZHANG Qiling
		DOI: 10.11660/slfdxb.20230203
		To handle the massive dam safety monitoring data, quick and reasonable determination of the variable factors of a dam deformation prediction model can effectively improve prediction efficiency and accuracy. This paper constructs a dam deformation prediction model by combining the least absolute shrinkage and selection operation (LASSO) variable selection and a long short-term memory (LSTM) network. First, a set of relevant influencing factors of dam deformation is determined through analysis of the dam deformation mechanism; then, the LASSO algorithm is used to remove the insignificant factors and select the optimal influencing factors as the model input variables, and a dam deformation prediction model is constructed using the LSTM network. Finally, this new method is verified and discussed with application to a case study of a roller compacted concrete gravity dam of Zaoshi Water Control. The results show it improves the accuracy significantly with relatively small mean absolute errors (MAE), mean square errors (MSE) and root mean square errors (RMSE). Compared with the conventional model, its variable selection based on the LASSO algorithm makes the model construction simpler and more efficient, and thus it is conducive to processing and analysis of massive dam monitoring data.
		2023 Vol. 42 (2): 24-35 [Abstract] ( 169 ) PDF (4652 KB) ( 243 )

	36	Short-term dispatching method for equivalent power plants of hydropower-photovoltaic complementation
		LI Xiufeng, LI Gang, ZHANG Yangke
		DOI: 10.11660/slfdxb.20230204
		Complementary dispatching of cascade hydropower plants and photovoltaic (PV) power plants is always a hot topic in research. To improve the complementary effect of the hydropower plants of different regulation types on the PV power output, this paper presents a new method of short-term complementary dispatching based on a concept of equivalent power plants. Considering the different characteristics of PV power generation, we use the K-means clustering method to divide multiple PV convergence areas. Each hydropower plant is combined with its corresponding convergence area for complementary operation; through analysis of peak regulating indexes, the optimal combination of hydropower and PV plants is found for every time period to construct an equivalent power plant. Then, these equivalent plants and the other hydropower plants are taken as the object for joint peak regulating and dispatching. This new method is verified through simulating a system of five cascade hydropower plants on the Lancang River and seven photovoltaic power plants in Yunnan. It improves the overall peak regulation significantly in comparison with several other models.
		2023 Vol. 42 (2): 36-44 [Abstract] ( 94 ) PDF (749 KB) ( 273 )

	45	Analysis on water consumption by forest and grass in lower reach of Yarkand River
		FU Xiangyong, YANG Hanbo, XIE Yanling, YU Xin
		DOI: 10.11660/slfdxb.20230205
		The Yarkand River is one of the main tributaries of the Tarim River. Understanding the water balance in its lower reach and the water consumption by riparian forests and grasses is greatly significant to the allocation of water resources in the basin. This paper develops a water balance model to describe water loss and water transformation and their variations based on the relationship between groundwater and vegetation. A phreatic water evaporation model and a groundwater transport model are coupled to construct a water consumption model of riparian forest and grass that is applied in a case study of the lower Yarkand River in 2000-2020. The results show that in this reach, most of the river water loss comes from leakage, which is more than 95% of the total water loss; multiyear average water consumption by forest and grass is 128 mm, with the left bank of 226 mm that is greater than 93 mm on the right bank. This model gives satisfactory calculations of the water balance components and the water consumption by forest and grass for the study river reach, and thus it would be applicable to other northwest inland rivers where riparian froest and grassland depend on river leakage recharge.
		2023 Vol. 42 (2): 45-55 [Abstract] ( 84 ) PDF (2628 KB) ( 296 )

	56	Optimal medium to long-term operation of large hydro-photovoltaic hybrid systems considering operational risk and peak shaving performance
		GUO Xiaoya, LI Gengda, CUI Qingru, JIANG Jianhua, MING Bo, HUANG Qiang
		DOI: 10.11660/slfdxb.20230206
		It is difficult to consider intraday operational risk, energy curtailment, and peak shaving performance of a traditional medium to long-term operation model for hydro-photovoltaic power system, which results in an overestimation of the hybrid power system’s performance. To address this issue, we construct a series of long short-term response functions for describing the relationships of medium to long-term hydropower output versus operational risk, residual load fluctuation, and electricity curtailment rate. Then, these functions are integrated into a medium to long-term optimization model so as to derive optimal operating rule curves considering intraday operational risk, energy curtailment, and peak shaving. We have applied this method to the Zhongyu hydro-photovoltaic hybrid power system. The results show the optimized operating rule curves increase the energy production (+2.61%) and generation guaranteed rate (from 46.7% to 85.7%) and reduce the residual load fluctuation (-10.0%) and operational risk rate (from 9.51% to 5.43%), compared with the standard policy-based operation model. Thus, our model can significantly increase the utilization of photovoltaic.
		2023 Vol. 42 (2): 56-65 [Abstract] ( 108 ) PDF (790 KB) ( 281 )

	66	Effect of rainwater runoff reduction by bioretention system improved with excess sludge
		ZHANG Wei, HAN Chengmei, LI Cheng, LIU Xiaomeng, DAI Mengde, ZHANG Xingchen, YUN Xi, LI Simin
		DOI: 10.11660/slfdxb.20230207
		Excess sludge from sewage treatment plant is utilized in this work to modify the substrate of a bioretention system to cope with the problems of urban non-point source pollution control and disposal of excess sludge. We determine the optimal content range of excess sludge added to the substrate based on its physical and chemical properties, and examine the effect of rainwater runoff reduction by the sludge-improved bioretention system. The results show that adding the sludge up to a content of 44.8% in the upper substrate layer of 15 cm thick could effectively enhance the system’s capability of runoff regulation. A higher content leads to a better effect of this system in controlling the total stormwater runoff, but a slightly upward trend the concentration of pollutants in effluent. Compared with sandy-soil substrate, a bioretention system with 40% sludge substrate increases the total runoff reduction rate by 16.9%. The average effluent concentration of COD, TN, NH4+-N and TP are 29.10, 3.25, 1.66 and 0.093 mg/L respectively, meeting the standards of Class ΙⅤ, Class Ⅴ, Class Ⅴ and Class Ⅱ of the Environmental Quality Standard for Surface Water (GB 3838-2002).
		2023 Vol. 42 (2): 66-73 [Abstract] ( 89 ) PDF (1011 KB) ( 169 )

	74	Experimental study on effect of trash rack structure on hydraulic characteristics of inlet and outlet
		GAO Xueping, YUAN Ye, LIU Yinzhu, ZHU Hongtao, LIU Shuai
		DOI: 10.11660/slfdxb.20230208
		In the study of hydraulic characteristics of the inlet and outlet, especially in physical model tests, the trash rack structure is generally not simulated because of the difficulty in modelling its closely spaced thin fence bars. To investigate the influence of a barrier structure on the hydraulic characteristics of an inlet and outlet under two-way flow conditions, we build a large-scale inlet and outlet test facility, conduct an experiment on a model inlet and outlet that is equipped with a trash rack structure, and compare it with the no trash rack case. The results show adding this structure results in a uniform distribution of time-average flow velocity behind it. In the outlet mode, the coefficient of flow uniformity is reduced by 7.1% from the no rack to the trash rack case; in the inlet mode, it is nearly the same in both cases. The rack disturbs the flow and intensifies velocity pulsation and turbulence intensity. Under its disturbance, the average turbulence intensity is increased by 49.0% and 38.5% in the outlet mode and inlet mode respectively, but flow distribution across different channels has little change in either flow mode. The trash rack structure produces head loss: the loss coefficient in the trash rack case is increased by 6.3% and 7.2% in the outlet mode and inlet mode respectively. The hydraulic indexes of the inlet and outlet in the two cases are not very different except for a large difference in turbulence level. This demonstrates the fact that the results obtained from a model inlet and outlet of no trash rack modeling can basically reflect its hydraulic characteristics.
		2023 Vol. 42 (2): 74-86 [Abstract] ( 86 ) PDF (3153 KB) ( 142 )

	87	Study on urban stormwater process simulations for areas with no sewer network data
		DU Jiakai, XU Menghua, CHEN Yuhong, JIANG Zhihong, XIAO Sufen, WANG Zhaoli
		DOI: 10.11660/slfdxb.20230209
		To solve the problem in urban waterlogging simulations caused by the difficulty in obtaining urban sewer network data, this paper uses different generalization methods to construct numerical models for areas with no sewer network data, based on the SWMM model, a two-dimensional TELEMAC-2D model, and the coupled model TSWM. Using a case study of the Liede River basin in Guangzhou, we compare the results with the scenario of sewer network data available, and discuss the applicability of different generalization methods. The results show that the flows of one-dimensional simulations and the submergence depths of two-dimensional simulations by the models with a sewer network basically agree with the measurements, demonstrating a good reliability of the models for the study area. Our simulations of the scenario with the sewer network for different return periods of rainfall are correlated satisfactorily with the inundation extents simulated by the rainfall discount method, the infiltration increase method, and the pipe network generalizing method. Of the three methods, the infiltration increase method has the largest correlation coefficient and its inundation extent and depth are the closest to the scenario with the sewer network, showing its better applicability to highly urbanized areas with no sewer network data.
		2023 Vol. 42 (2): 87-96 [Abstract] ( 192 ) PDF (5479 KB) ( 230 )

	97	Study on hydraulic performance of pump-turbine in startup process
		HUANG Wenlong, BI Huili, YE Yongjin, ZHANG Shaozheng, YIN Xilong, HUANG Xingxing, WANG Zhengwei, JIN Zhou
		DOI: 10.11660/slfdxb.20230210
		During startup, severe pressure fluctuations usually occur in a pump-turbine; complex flows and pressure pulsations in its runner are two main causes for the strong vibration of its stationary parts. In-depth research is necessary on the physical mechanism of startup. This paper presents numerical simulations of a large pumped-storage power station, coupling a one-dimensional characteristic method hydraulic model of its pipeline system and a three-dimensional calculation model of the whole water passage of its pump-turbine unit. We focus on the analysis of the instantaneous flow characteristics of the unit and the internal correlation between its runner’s radial force and axial hydraulic thrust and its external characteristics during startup. The results show that when the unit is in no-load state, due to its small guide vane opening and a rapid increase in its rotational speed, a high-speed water ring is formed in its vaneless area, resulting in a sudden drop in its flow discharge and runner torque. The corresponding variations in the radial force and axial hydraulic thrust are complex and directly impacted by the variations in the guide vane opening and rotational speed. The trend of radial force roughly follows that of guide vane moving, while the trend of axial hydraulic thrust is nearly the same as that of the unit speed, both gradually increasing on the whole during startup. This study provides an in-depth understanding of the physical mechanism of the startup process and its variations of pumped-storage units and high-head Francis turbines.
		2023 Vol. 42 (2): 97-104 [Abstract] ( 120 ) PDF (2165 KB) ( 383 )

	105	Bearing capacity calculations and experimental study on fluid pivot tilting pad journal bearings of hydraulic turbine
		MAO Ming, CHEN Jianneng, XU Gaohuan, XIE Rongsheng, XIA Xudong, XU Yongli
		DOI: 10.11660/slfdxb.20230211
		The fluid pivot tilting pad journal bearing has been widely used in hydraulic turbine units because of its good vibration damping performance and large bearing capacity. To examine its bearing capacity, this paper first discusses its basic dynamic lubrication mechanism, and constructs a new method of oil film pressure distribution for the bearing, using the Reynolds equation, flow balance equation between the inner and the outer oil film, and the Walther equation. The calculation results show that the hydrodynamic pressure oil film follows a bimodal distribution, while the hydrostatic film is steady in the pressure tap; the bottom pad is in a one-sided floating state under the test conditions. Then, we design and build a bearing test stand of inverted type, test the three-tilting pad bearing with an inner diameter of 125mm, and measure the oil film pressure under different rotational speeds and load conditions. The results show that rotational speed is the first factor of bearing capacity to consider in bearing design. Under higher rotational speeds, the oil film shows higher stiffness and better bearing capacity.Therefore, it can be widely applied to hydraulic turbine units.
		2023 Vol. 42 (2): 105-115 [Abstract] ( 120 ) PDF (2694 KB) ( 359 )

	116	Advances and development trends in technologies of impulse turbines
		LUO Xingqi, GE Zhenguo, ZHU Guojun, FENG Jianjun
		DOI: 10.11660/slfdxb.20230212
		As the core equipment in high-head hydropower harvesting, the impulse turbine has the advantages of higher operating head and wider high-efficiency range compared with reaction turbines. However, features of flow fields within a Pelton turbine are open, unsteady and multi-phase. Complex flow characteristics affected by multiple flow transitions and component-matching of the Pelton turbine may exert influence on its performance and utilizing efficiency of high-head hydropower. Recent advances in impulse turbine technologies have been accelerated by the rapid development of visual test technology, computational fluid dynamics (CFD), finite element method (FEM), and artificial intelligence optimization design algorithm. The technology of impulse turbines developed late but rapid in China, summarizing by three stages from scratch, independent design to optimization, and breakthrough progresses have been accomplished especially in the past 20 years. Based on a comprehensive synthesis of researches from both national and international impulse turbines researching field, this paper focuses on the main progresses of impulse turbine technology in the past 20 years, and reviews the recent advances in the research of internal flow characteristics, sediment abrasion, failure analysis, and optimization design theories. Several issues with performance analysis and optimization design are discussed, and the development trend of impulse turbine technology is summarized and prospected.
		2023 Vol. 42 (2): 116-134 [Abstract] ( 305 ) PDF (3934 KB) ( 484 )