Journal of Hydroelectric Engineering

水力发电学报

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2022 Vol. 41, No. 4 Published: 2022-04-25

	1	Numerical simulations on hydraulic characteristics of fully aerated water flows in open channel
		LIAN Jijian, REN Panhong, LIU Dongming, HE Junling
		DOI: 10.11660/slfdxb.20220401
		Self-aeration of open channel flows is common in hydraulic engineering. When flow velocity is high, air bubbles are transported up to the channel bottom under violent turbulences, forming fully aerated water flow. At present, most of the previous studies on water flow aeration are based on the physical model tests, which have a significant scale effect. This paper describes a set of numerical models we have developed recently, including a mixing model, a turbulence model, and a concentration model. These numerical models are discretized and solved using a finite difference method. Then, they are verified through comparing the calculations of air concentration and water velocity in open channel flows with previous self-aeration experiments, achieving a good agreement and showing their applicability to the study of hydraulic characteristics of the fully aerated flows. Further examination of the calculation results reveals that in the fully aerated water flow, entrained air can reach the channel bottom due to violent turbulences, and reduce the wall resistance to the flow, thus resulting in a channel flow velocity higher than that of the corresponding non-aerated flow.
		2022 Vol. 41 (4): 1-8 [Abstract] ( 166 ) PDF (1172 KB) ( 572 )

	9	Recent advances in studying river bedload transport under unsteady flows
		WANG Le, ZHONG Deyu, MENG Changqing, JIA Baozhen
		DOI: 10.11660/slfdxb.20220402
		Bedload sediment transport in unsteady flows is a fundamental research topic in river dynamics. Over the last few decades, a number of researchers at home and abroad have conducted a series of exploratory studies, achieved insightful understanding, and made great contributions to this subject. This paper reviews the recent advances in the knowledge of bedload sediment transport under unsteady flows, in terms of (i) hysteresis, (ii) hysteretic loops of hydraulic and sediment parameters, (iii) bedload sediment transport rate, and (iv) total bedload yield. Based on an analysis of previous works and findings, we highlight related issues with relevant studies, and make suggestions for addressing these issues.
		2022 Vol. 41 (4): 9-17 [Abstract] ( 137 ) PDF (1885 KB) ( 451 )

	18	Risk factor zoning of waterlogging in coastal cities caused by compound of rainstorms and high tides
		XU Kui, LU Zhiwei, BIN Lingling, LIAN Jijian
		DOI: 10.11660/slfdxb.20220403
		Coastal cities are more susceptible to waterlogging disasters in recent years, due to the combined effect of heavy rainstorms and high tides. The division of hazard factors in the areas under such effect is a key factor for deploying disaster mitigation measures. This paper describes a regionalization method of hazard factors and evaluates its application through a case study of the central urban area of Haikou City. We construct a 1D-2D coupled urban waterlogging model based on PCSWMM to calculate the water depth and area of this city’s submerged regions under different combination conditions. The regions are grouped into three types: rainfall-affected, tidal-affected, and joint-influenced; for each type, an optimization analysis of disaster mitigation measures is made. The results show the tidal-, joint- and rainfall-affected regions, in order, gradually become farther away from the coastline. And the reservoirs if arranged in the rainfall-affected region will produce a benefit significantly greater than in the tidal-affected, while the check valves if installed in the tidal-affected region will be more beneficial than in the rainfall-affected. Thus, waterlogging prevention measures are more effective and more efficient through grouping different waterlogging areas.
		2022 Vol. 41 (4): 18-27 [Abstract] ( 122 ) PDF (5138 KB) ( 503 )

	28	Hydraulic characteristics of bifurcated pipes
		REN Weichen, DAI Xiwu, BAO Shihu, ZHANG Hongwei, DING Sheng,
		DOI: 10.11660/slfdxb.20220404
		Stress concentration phenomenon can be addressed by setting a linear-chamfer angle at the bifurcation, given the certain bifurcation angle. In the present work, the hydraulic characteristics of round-chamfered and linear-chamfered bifurcated pipes are numerically investigated, including the flow behaviors, discharge capacity, and characteristics of pressure distribution, with different geometric conditions considered. The results show that in a linear-chamfered pipe, the flow is smooth and its mainstream is in a direction largely along the branch pipe axis, while a round-chamfered pipe shows rather intricate flow patterns. Compared to that without a chamfered angle, the maximum relative declines in discharge capacity are 0.5% and 6.8% for linear- and round-chamfered pipes, respectively; the discharge capacity of a linear-chamfered pipe is greater. The pressure distribution behavior changes little when the pipe is linear-chamfered, but it become significantly different when round-chamfered.
		2022 Vol. 41 (4): 28-36 [Abstract] ( 116 ) PDF (2790 KB) ( 361 )

	37	Medium-term peak-shaving scheduling method of cascade reservoirs coupled with flow time delay
		LIU Huan, LIAO Shengli, LIU Zhanwei, ZHANG Zheng, WU Huijun
		DOI: 10.11660/slfdxb.20220405
		Aimed at addressing the daytime frequent fluctuation of power grid load and the complicated hydraulic connection existing in cascade hydropower stations, a medium-term peak shaving scheduling model for cascade reservoirs considering a piecewise flow delay strategy is developed. First, a peak-shaving multi-objective model for medium-term power grid dispatch is constructed to optimize peak shaving and maximize cascade power generation. Then, based on the principle of water balance, a medium-term piecewise time delay method is formulated to effectively describe the flow delay in calculations of the medium-term dispatching of cascade hydropower stations with a time step of one day. Finally, a comprehensive benefit calculation method to alleviate the generation deviation affected by the lag times for the scheduling period and the time lag period is presented. The method has been applied to a case study of 11 cascade hydropower stations under operation on the Lancang River mainstream. The results show it achieves a better agreement with the real operation through introducing flow delay factors, reducing the delay effects of scheduling deviation effectively. And it improves hydropower utilization benefits and has a good medium-term peak-shaving effect.
		2022 Vol. 41 (4): 37-46 [Abstract] ( 127 ) PDF (536 KB) ( 298 )

	47	Correction to predicted inflow of Three Gorges Reservoir based on division of different scenarios
		JIANG Zhiqiang, WANG Suiling, TANG Zhengyang, ZHANG Hairong
		DOI: 10.11660/slfdxb.20220406
		In this work, we consider the difference in external environments on which the forecasts are based and the difference in forecast errors under different scenarios, and work out a method for division of the prediction scenarios by the key influencing factors, such as rainfall and forecast period. Then, the data of historical forecast errors can be used to obtain their distribution trends and thus determine the confidence interval at the 90% level for different scenarios. Considering prediction scenarios, prediction errors, and their trends, we construct a new multidimensional and multi-attribute method for correcting inflow prediction, using the variable mode decomposition and a long-short term memory neural network model. Through a case study of the Three Gorges reservoir, we find the average relative error of inflow predictions is reduced from 8.32% to 6.36%, with a reduction rate of 23.6%. And other indicators are improved to varying degrees, such as average absolute error, root mean square error, and coefficient of determination. This shows our method has achieved a significant improvement on the accuracy of inflow prediction models through increasing the effective information input to the correction model.
		2022 Vol. 41 (4): 47-61 [Abstract] ( 170 ) PDF (2784 KB) ( 291 )

	62	Multi-dimensional stochastic simulation model of forecast errors of reservoir inflow process
		ZHANG Yanke, TAI Yuhang, WANG Yuankun, MA Qiumei
		DOI: 10.11660/slfdxb.20220407
		Stochastic simulations of the errors in reservoir inflow process forecasts with multiple forecast periods become more difficult as the number of dimensions increases. To examine the variation trends of the errors accurately and quickly, we first generate the characteristics of complex high-dimensional data through numerical simulations using the neural network coupled with low-dimensional hidden variables and the Variational AutoEncoders (VAE) method. Then, we develop a stochastic simulation model of the forecast errors of reservoir inflow process based on VAE. This model is compared with the improved Gibbs method in a case study of the Jinping Ⅰ hydropower station. The results show that it gives better agreement of the mean, standard deviation, and variation coefficient with the real error sequence, and its computational time reduces by 69% to 94% compared with the improved Gibbs method. These results provide more information for hydropower station regulation considering uncertainty in reservoir inflow forecast.
		2022 Vol. 41 (4): 62-70 [Abstract] ( 112 ) PDF (711 KB) ( 306 )

	71	Analysis on flood warning rainfall for railroad bridges and culverts in Gaotai overflow area
		QIN Jun, LI Sheng, HUA Yongli, SHENG Shiyong, CAI Lei, YU Yunyan
		DOI: 10.11660/slfdxb.20220408
		This article presents a flood simulation analysis using Storm Water Management Model (SWMM) to reduce water damage to the bridges and culverts of Lanzhou-Xinjiang Railway in the Gaotai overflow area and to determine the warning rainfall for some of these culverts. First, we construct two types of SWMMs, namely lumped and semi-distributed types, using the software ArcGis, and compare their pros and cons through calibration and accuracy evaluation for the simulations of six rainfall events. Then, the applicability of SWMM to the overflow area is discussed; finally, flood warning rainfalls are determined using a water level inversion method. The results show SWMM is applicable to the rainfall-runoff in this overflow area, with relative flood level errors less than 10% and a determination coefficient greater than 0.7. Of the six rainfall events, four are simulated with an accuracy reaching the level of Class A standard, and two reaching Class B, resulting in a qualification rate of 100%. Lumped hydrological models are better for application to the overflow area than the semi-distributed type. For a given disaster water level, a longer warning time means a greater warning rainfall.
		2022 Vol. 41 (4): 71-82 [Abstract] ( 154 ) PDF (3657 KB) ( 388 )

	83	Analysis of pressure pulsation in high rotating speed pump as turbine in seawater desalination
		ZHAO Yong, WANG Xin, WANG Shenghui, WANG Chengpeng, LIU Jiajie, XIAO Yexiang
		DOI: 10.11660/slfdxb.20220409
		A centrifugal pump used as a turbine is a core power component of the seawater desalination energy recovery machine; its pressure pulsation during operation is a major factor causing vibration and noise. This paper presents full-passage numerical simulations of the three-dimensional unsteady flows in a high rotating speed centrifugal pump as a turbine using a SAS-SST-CC turbulence model. We discuss the unsteady flow characteristics through flow field analysis and pressure fluctuation spectrum analysis. The results show the dominant frequencies of pressure pulsation at multiple measuring points in the volute are the same as the blade passing frequency, indicating the pulsation comes largely from the dynamic and static interference between the runner and volute tongue. Among the six measuring points located in each of the 8 blade channels of the runner, the maximum difference in the peak-to-peak amplitudes at the corresponding positions is 10.3%, revealing a significant uneven feature of flow distribution in the runner. The pulsation frequencies at these rotating measuring points are largely the dominant frequency or secondary dominant frequency near the frequency of 8 times the blade frequency, indicating the dynamic and static interference between the runner and volute is significant. Vortices in the blade channels are the main factor causing pressure pulsation in the runner, and these local vortices cause pressure pulsation stronger than those from the dynamic and static interference of the runner. The results show that pressure pulsation in the runner is more severe than that in the volute, and the former is the main hydraulic cause of unit vibration.
		2022 Vol. 41 (4): 83-92 [Abstract] ( 117 ) PDF (2804 KB) ( 749 )

	93	Analysis on influence of swinging modes of swing hydrofoil on water propulsion
		HUA Ertian, TANG Shouwei, CHEN Wanqian, XIE Rongsheng, GUO Xiaomei
		DOI: 10.11660/slfdxb.20220410
		Small river channels have poor water circulation and low self-purification capacity, while the traditional pumping station suffers from the problem of vibration, cavitation and low efficiency at ultra-low lift operating conditions. To enhance the hydrodynamic force of such rivers, we developed a swing hydrofoil and its calculation model, and studied its water propulsion performance of three swing modes. Numerical calculations were made by using the combination of the realizable k-ε turbulence model and the dynamic grid technology, and the swing mode with better water propulsion effect was tested experimentally. For this hydrofoil, results showed that Mode 3 produced only thrust, while Mode 1 and Mode 2 produced both thrust and resistance. The formation and evolution of vortices are the key factors affecting the performance in water body propulsion. Both propulsion efficiency and pump efficiency are significantly higher in Mode 3 than in those of the other two modes. At a specific frequency with a flow rate of 490 L?s-1 and a lift head of 0.0281 m, Mode 3 has its maximum efficiency of 34.1%, significantly higher than 8.6% of Mode 1 or 9.4% of Mode 2. Swing hydrofoils for water propulsion have the advantages of low lift and large flow, manifesting unique advantages in application to small river basins.
		2022 Vol. 41 (4): 93-103 [Abstract] ( 126 ) PDF (1619 KB) ( 458 )

	104	Study on efficient optimization of spillway construction for barrier lakes
		WANG Lin, WU Yumiao, DUAN Qingwei, CAI Simin, LIU Lipeng, SUN Ping
		DOI: 10.11660/slfdxb.20220411
		Once a barrier lake is breached, it will pose severe threats to the people and infrastructure downstream. Constructing a spillway is the most common measure for risk mitigation, but an urgent, significant issue is how to design its cross section and reduce the excavation volume while ensuring an effective reduction of the breaching flood risk. Based on the soil-water coupling mechanism, this paper develops a new DB-IWHR 2.0 model for automatic spillway optimization design that integrates a hyperbolic erosion model and relevant hydraulic parameters to simulate the vertical and horizontal rapid enlargement of the breach and realize a rapid analysis (in 1 hour) of the whole breaching process. Then, an optimal spillway design is obtained according to the analysis of breaching features. Application to a case study of the "11?03" Baige barrier lake reveals that when the spillway is constructed by the optimal design, the peak flow through the breach is 31041.18 m3/s, nearly the same as its site observed value of 31000 m3/s, while the excavation could be reduced from 135000 m3 to 71029.16 m3, and its deepest section reduced from 15 m to 4.04 m, or a 53% and 27% reduction of the emergency rescue response, respectively. Thus, the stability loss of the barrier dam can be avoided, while the construction time and emergency rescue response time be reduced, implying the emergency rescue work can be faster, more detailed and more effective.
		2022 Vol. 41 (4): 104-112 [Abstract] ( 76 ) PDF (1809 KB) ( 334 )

	113	Effect of coarse aggregate content on fracture behavior of epoxy-repaired concrete
		LV Yanan, QING Longbang, CAO Guorui
		DOI: 10.11660/slfdxb.20220412
		Through three-point bending fracture tests of the concrete beams repaired with epoxy resin, fracture properties of the unrepaired and repaired concrete are compared, and the influence of coarse aggregate content on double-K fracture toughness and fracture energy is analyzed. The results show that the maximum bearing capacity of concrete can be greatly improved after being repaired with epoxy resin, while the critical crack opening displacement is almost unaffected. And the fracture behavior of repaired concrete can be restored and improved effectively. When the coarse aggregate content is 0 (mortar), 18%, 36% and 54%, initial toughness increases by 56.5%, 28.2%, 21.5% and 21.1% respectively; unstable fracture toughness increases by 13.1%, 6.0%, 5.5% and 8.2%, and fracture energy increases by 41.3%, 39.1%, 38.1% and 23.2% respectively. Meanwhile, the fracture parameters of unrepaired and repaired concrete show an ascending tendency with the coarse aggregate content, and their increasing rates gradually slow down.
		2022 Vol. 41 (4): 113-120 [Abstract] ( 121 ) PDF (821 KB) ( 305 )