Journal of Hydroelectric Engineering

水力发电学报

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2021 Vol. 40, No. 7 Published: 2021-07-25

	1	Study on Liuxihe model for inflow flood forecast of Shangyoujiang Reservoir
		LI Chu’an, CHEN Yangbo, YE Sheng, WANG Chenyu, CHEN Weidong
		DOI: 10.11660/slfdxb.20210701
		This paper uses digital elevation model (DEM) data with a spatial resolution of 90 m to construct a Liuxihe River model, and discusses its applicability to the Shangyoujiang Reservoir basin with different river channel grades and rainfall station densities. Its optimal parameters are determined using the particle swarm optimization (PSO) algorithm, and then it is used to simulate 18 flood events measured in 2009-2020. The results show that for this model, its simulation index is slightly better when the river channels are divided into three grades for model construction than the case of four grades, and the flood forecasts with the former are more accurate. Comparison of the model schemes based on 9 and 15 rainfall stations and their simulations of 31 flood events of 2000-2020 shows that the scheme of 15 stations is better, and high density of gauge stations is conducive to improving the Liuxihe model and its forecasting accuracy. Therefore, the Liuxihe model can be used in the flood forecasts of the Shangyoujiang Reservoir.
		2021 Vol. 40 (7): 1-12 [Abstract] ( 170 ) PDF (1703 KB) ( 461 )

	13	Runoff forecasts using combined model of extreme-point symmetric mode decomposition and Elman neural network
		LI Jiqing, WANG Shuang, WU Yueqiu, TIAN Yu
		DOI: 10.11660/slfdxb.20210702
		Aiming at the nonlinear and non-stationary characteristics of runoff sequences, we develop a combined model of extreme-point symmetric mode decomposition (ESMD) and Elman neural network, and apply it to annual and monthly runoff forecasts at eight stations in the upper reaches of the Yangtze River. First, ESMD is used to decompose a runoff sequence into modal components and trend remainders; then, the Elman neural network model is used to predict each of the stationary sequences; lastly, final prediction results are obtained by adding and reconstruction. The results show this combined model has forecast accuracy higher than that of a single model. Compared with the ESMD-BP neural network combination model, for annual runoff forecasts, it has an average reduction of 3.6% in mean absolute percentage error (MAPE) and 7.8% in root mean square error (RMSE), and an average increase of 5.0% in determination coefficient for the eight stations; while for monthly runoff forecasts, the MAPE is decreased by an average of 3.0% and the RMSE decreased by an average of 2.8%. Our combined model, characterized by decomposition-prediction-reconstruction, improves prediction accuracy.
		2021 Vol. 40 (7): 13-22 [Abstract] ( 151 ) PDF (2922 KB) ( 374 )

	23	Optimal allocation model of unconventional water resources based on reinforcement learning
		WU Xin, CHEN Zhixin, WEN Qingbo, WANG Zhongjing, HU Liming
		DOI: 10.11660/slfdxb.20210703
		Development and utilization degree of unconventional water resources in China are relatively low at present, and water resources allocation is complicated with a variety of uncertainties. Aimed at this problem, this paper applies the method of reinforcement learning to water resources allocation, and develops an optimal allocation model of Python coding with the objective function of maximizing the economic benefit. This model is applied in a case study of Beijing, taking the unconventional water resources into account, and focusing on comparison of different allocation schemes and their interval scales of economic profits. Results show it predicts the overall profits under different water inflow conditions satisfactorily, giving larger values than those predicted using the two-stage stochastic programming method. And utilizing the unconventional water resources would play a significant role in alleviating the city’s water shortage.
		2021 Vol. 40 (7): 23-31 [Abstract] ( 273 ) PDF (969 KB) ( 609 )

	32	Optimization of overall layout of sponge city facilities for flooding alleviation effect
		CHENG Tao, HUANG Bensheng, QIU Jing, ZHAO Bikui, XU Zongxue
		DOI: 10.11660/slfdxb.20210704
		To address urban flooding and other water issues, a sponge city program (SCP) and its implementation have been promoted across China since 2015. Various SCP measures come into play in different mechanisms, and their overall spatial arrangement influences flooding alleviation effect significantly. This study uses a hydrological-hydrodynamic multi-process coupled model to examine the responses of urban flooding to different SCP measure combinations and different rainfall scenarios in the SCP pilot area of Jinan. We analyze the effect of different overall SCP measure layouts and work out urban flood control schemes from the perspective of watershed hydrological cycling. Results show that implementing low impact development (LID) measures in the upstream area results in a significant decrease in the risk area, while the runoff and inundation are effectively controlled when the measures are implemented downstream. And a comprehensive effect of risk area reduction and inundation control is achieved when a scheme of implementing LID measures in the upstream and upgrading the drainage pipeline network in the downstream is applied. Cities with features similar to Jinan could adopt such schemes or take site-specific schemes through analysis of their runoff generation and concentration processes from a perspective of watershed hydrological cycling. Areas with distinct characteristics should follow the cycling pattern and implement corresponding measures.
		2021 Vol. 40 (7): 32-46 [Abstract] ( 231 ) PDF (5485 KB) ( 659 )

	47	A SEM-ANN model of vegetation water use efficiency in Hotan, Xinjiang
		LU Na, NIU Jun
		DOI: 10.11660/slfdxb.20210705
		Water use efficiency (WUE) of vegetation reflects the amount of its dry matter through consuming per unit amount of water, a comprehensive indicator for assessing its growth conditions. However, contributions of multiple forcing factors to WUE are unclear due to the complicated influencing mechanism. Combining a structural equation model (SEM) with the artificial neural network (ANN), this paper develops a hybrid SEM-ANN model for analysis of the direct and indirect influences of WUE multiple factors to achieve an improvement on the simulations. It determines the structural relationship among the factors and their degrees of influence by using SEM, and then constructs the topology of ANN. The results show that in the Hotan region, various vegetation types have different WUE factors at different levels. We divide them into direct factors and intermediate variables that impact WUE indirectly－with the former including temperature (T), precipitation (P), vapor pressure deficit (VPD), and wind speed (WS); the latter including an enhanced vegetation index (EVI) for grassland and cropland and a standardized precipitation evapotranspiration index (SPEI) for shrub land and evergreen needle leaved forest. The SEM-optimized structure of ANN fits better, and the SEM-ANN model has high explanatory capacity and higher accuracy in the ecosystem’s environmental control and simulations of WUE, thus providing a theoretical basis and simulation method that can improve efficient water use and predict future WUE responses to climate changes in Xinjiang.
		2021 Vol. 40 (7): 47-60 [Abstract] ( 196 ) PDF (1264 KB) ( 702 )

	61	Influence of regulating small and medium floods on algal blooms in tributaries of Three Gorges Reservoir in flood season
		WANG Hongyang, YANG Xia, MA Jun, YANG Zhengjian, LIU Defu
		DOI: 10.11660/slfdxb.20210706
		To study the influence of regulating small and medium floods into the Three Gorges reservoir in flood season on the algal blooms in its typical tributaries, we focus on a case study of Xiangxi Bay and examine the environmental factor parameters and their variations during its regulation from 2010 to 2019. The results show that in flood season, an outbreak of algal blooms will occur in the bay because it is featured with favorable conditions－suitable water temperature, sufficient light, and adequate nutrient content; and to suppress and prevent the blooms, flood regulation is still the most direct, effective method at present. In 2010-2019, flood regulation by this reservoir modified the hydrodynamic and water environmental conditions in this bay. The depth ratio of its mixing layer over photic zone was correlated positively with its river stage fluctuation (P = 0.32) and negatively with Chlorophyll a concentration (P = -0.239). Flood regulation was a frequent practice in the reservoir operation, often with a long regulation duration and a relatively large overall flow. During flood regulation, the depth of density currents in the bay was increased, and its form was switched to plunging in middle and bottom layers. Reservoir dispatching promoted disturbance to the tributary water bodies, weakening their stratification and suppressing algal blooms. This study offers new insights for effective use of flood regulation to improve water environment in the tributaries of the Three Gorges reservoir and is useful for further studies on the methods of flood regulation and its optimization.
		2021 Vol. 40 (7): 61-72 [Abstract] ( 122 ) PDF (1912 KB) ( 319 )

	73	Three-dimensional simulations of structure of temperature and dissolved oxygen and its variations in Guanting Reservoir under ecological regulation
		SUN Xianren, TONG Sichen, HUANG Guoxian, YU Jingshan, LI Xinghua, TANG Xiaoya, LEI Kun
		DOI: 10.11660/slfdxb.20210707
		Water temperature (WT) and dissolved oxygen (DO) are important parameters to characterize the healthy status of an aquatic ecosystem. This study develops a three-dimensional model of water temperature and dissolved oxygen in the Guanting Reservoir (GTR) to quantify the impact of its ecological regulation. This model is calibrated and verified against on-site measured data, demonstrating its capability of predicting the reservoir’s temperature and oxygen conditions. Combined with real reservoir operation, different scenarios are designed to analyze structural changes in WT and DO in the reservoir area. (1) The simulations show obvious WT and DO stratification in GTR. Water transfer operation causes a delay in stratification start time and a decrease in stratification duration and surface-bottom temperature difference, while ecological discharge brings about a further decrease in the thickness and intensity of thermocline up to the variation ranges of 0.5-1.7 m and 1.25-3.58oC/m respectively. Simultaneous operation of the transfer and discharge strengthens water body mixing in the reservoir, resulting in an increase in the thermocline depth up to an average range of 6.2-8.6 m, an increase in thermocline intensity, and a slight change in thermocline thickness. (2) Either water transfer or ecological discharge will damage the oxycline of water body and has a significant effect of increasing oxygen content in the bottom layer, but its effect on the surface DO that varies in a range of -4.7% to 7.3% is insignificant. (3) DO concentration in the bottom water is increased by 1.85-8.52 mg/L under the operation of ecological discharge only, while increased by 2.71-12.83 mg/L under both the transfer and discharge, producing more prominent oxygen enriching effect. This will eliminate the anaerobic environment in the reservoir bottom layer, reduce the low oxygen area, and prolong the oxygen rich period, revealing significant measures for improving anoxic environment in lakes and reservoirs.
		2021 Vol. 40 (7): 73-86 [Abstract] ( 150 ) PDF (1140 KB) ( 500 )

	87	Study on hydrodynamic performance of shaftless rim-driven ducted turbines
		SONG Ke, YANG Bangcheng
		DOI: 10.11660/slfdxb.20210708
		As a new concept of tidal current power generation device, the shaftless rim-driven ducted (SRD) turbine has many advantages and a wide application prospect. We apply a computational fluid dynamics (CFD) method to simulations and a comparative study of this type of turbine and the conventional shaft ducted turbine, focusing on the differences in hydrodynamics between these two ducted turbines and the influence of shaft diameter ratios on the SRD turbine. The results show that in a certain range of shaft diameter ratios, the SRD turbine has a higher output power and lower axial thrust than those of the shaft ducted turbine. However, the fluctuation amplitudes of its instantaneous power output and axial thrust are slightly larger, and they further increase with a decreasing shaft diameter ratio. We find that for the SRD turbine with a swept gap of a certain size, pressure will force water to "leak" through the gap forming an axial jet. This will result in a significantly higher wake recovery rate that is further accelerated with a decreasing shaft diameter ratio.
		2021 Vol. 40 (7): 87-94 [Abstract] ( 177 ) PDF (1206 KB) ( 408 )

	95	Numerical simulations of fish movement in axial pump using immersed boundary method
		YANG Dandan, ZHAO Mingxiang, YE Weixiang, SHEN Lian, LUO Xianwu
		DOI: 10.11660/slfdxb.20210709
		This research adopts a method of combining immersed boundary (IB) with fluid-structure interaction (FSI) method and the large eddy simulation (LES), to simulate the internal flow of an axial pump and the fish movement in the pump passage for a refined analysis on the characteristics of fish motions in hydraulic machinery. The results show that the calculated head coefficient has a deviation of only 2.7% against the experimental data under the design condition at the same Reynolds number, verifying the feasibility of this new method for the pump flow simulations. Compared with the traditional methods where fishes are simplified into flow tracers, the method adopted in this study is capable in capturing the complexity of fish trajectories, sudden changes in fish orientation after hitting the blade, and the vortex formation, shedding and structure in the fish wake, thereby helping to obtain accurate assessment of fish injury and design optimization of fish friendly hydraulic machinery.
		2021 Vol. 40 (7): 95-104 [Abstract] ( 199 ) PDF (3699 KB) ( 520 )

	105	Investigation on thermal properties of core-wall clay incorporated with phase change material for winter construction in cold regions
		WANG Youle, LIU Donghai, LIANG Jianyu
		DOI: 10.11660/slfdxb.20210710
		During the core-wall clay construction of an earth-rock dam in cold regions, the freeze-thaw impact on core-wall clay is a major challenge. Conventional anti-freezing measures slow down normal construction process because of their serious interference with core-wall clay compaction. The core-wall clay incorporated with phase change material (PCM-clay) is able to ensure its surface temperature above the freezing point, consequently extending the winter construction time of earth-rock dams in cold regions and avoiding construction interference. This paper investigates the thermal properties of PCM-clay, based on the feasibility of using it as core-wall clay (i.e., permeability and mechanical strength). We analyze the impact mechanism of PCM content on these thermal parameters, and develop homogenized models to estimate the thermal parameters of PCM-clay (i.e., latent heat, thermal conductivity and specific heat). Numerical analysis based on these models is used to verify the effectiveness of PCM-clay in temperature control for winter construction of earth-rock dams in cold regions. Results indicate that the latent heat of phase change clay is dominated by the PCM content and its crystallinity, and the thermal conductivity and specific heat are both negatively correlated with the PCM content. Numerical models based on the phase change heat transfer theory can provide reliable simulation of temperature history, which is useful in further research of temperature control with PCM-clay.
		2021 Vol. 40 (7): 105-117 [Abstract] ( 124 ) PDF (2337 KB) ( 292 )

	118	Mixed mode I-II fracture and acoustic emission characteristics of rock-concrete interfaces
		LUO Danni, XIE Yuqing, SU Guoshao, CHENG Shoushan, XUE Zixi
		DOI: 10.11660/slfdxb.20210711
		Mechanical behaviors and acoustic emission (AE) characteristics of mixed mode I-II fractures at rock-concrete interfaces are studied through three-point bending tests and four-point shear fracture tests on composite rock-concrete specimens. The results show the failure modes can be divided into three categories. A higher modal ratio or a rougher interface results in higher possibility of the occurrence of non-interfacial complex failure modes. Incipient cracking and unstable failure can be identified by abrupt changes in AE parameters; microcracks be classified into tensile and shear cracks byaverage frequency (AF) and the ratio of rising time to amplitude (RA value). Fracture damage evolution can be revealed by predicting the propagation direction of interface cracks using the space distribution of AE events. When the final overall destruction of the specimens is imminent, the dominant frequencies of AE signals change significantly, manifesting a sharp increase in both the number and amplitude of low-amplitude, low-frequency AE signals and sudden emergence of a few low-amplitude, high-frequency AE signals. Meanwhile, the dominant frequencies are shifting from discrete to continuous and their distributions span a relatively large range under the condition of high modal ratios.
		2021 Vol. 40 (7): 118-130 [Abstract] ( 165 ) PDF (2074 KB) ( 365 )

	131	Pattern recognition combination model for locating damage in concrete faced rockfill dams using acoustic emission and its experimental verification
		YAO Kefu, SU Huaizhi, YANG Lifu, ZHAO Haichao
		DOI: 10.11660/slfdxb.20210712
		A combined pattern recognition model that comprises a localization method for the domains and space coordinates of acoustic emission sources is presented. First, to reduce the irrelevant domain searching, we decompose the monitoring data of the whole structure health into an array of multiple sub-monitoring acoustic emission sensors, and formulate a control equation for the rapid identification of the array and subdivision of the acoustic emission source area. Then, a strategy for nonlinear variations and the Lévy random flight step is adopted in the calculation of the control parameters to improve global searching ability and avoid falling into local optimizations in application of the Gray Wolf Optimizer (GWO) algorithm. Wave speed is regarded as a variable and the improved GWO is used to localize those acoustic emission sources with unknown wave speeds in the source sub-domains aforementioned. The results of pencil lead broken test on a concrete slab show that this method has a positioning accuracy higher than that of the Least Square, LS-Geiger, or GWO localization algorithm, and it is effective in detecting damage in hydraulic concrete slab structures.
		2021 Vol. 40 (7): 131-140 [Abstract] ( 151 ) PDF (2174 KB) ( 362 )

	141	Time-dependent characteristics of concrete fracture process under long-term constant loads
		LU Yingpeng, GAO Hongbo, XU Shilang, HAN Xiaoyan
		DOI: 10.11660/slfdxb.20210713
		Time-dependent fracture behaviors in mass concrete closely relate to the safety of concrete structures in service. To investigate these behaviors of concrete under sustained loads, this study conducts wedge-splitting tests under a long-term constant load at 85% of the maximum load, using compact tension specimens in three different sizes. The test results indicate three development stages occur in time-dependent crack mouth and crack tip opening displacements and time variations in crack mouth opening rate: deceleration, stable development, and accelerated failure. Compared with the static fracture test on the same specimen size, a larger critical crack mouth opening displacement occurs in the present long-term constant load test. And a highly linear correlation can be observed between the displacements at the crack mouth and the tip. In addition, the geometry relation between the opening displacement and propagation length of cracks fits in well with the hinge model.
		2021 Vol. 40 (7): 141-151 [Abstract] ( 143 ) PDF (1039 KB) ( 452 )

	152	Numerical simulations of coastal overwash based on coupled wave-current and sediment transport model
		LI Songzhe, JI Chao, ZHANG Qinghe
		DOI: 10.11660/slfdxb.20210714
		Coastal overwash is a natural process, usually occurring during severe storms and hurricanes, and may cause rapid profile changes in the nearshore. Up to present, only a limited number of three-dimensional numerical models have been developed previously for the effects of overwash, especially runup overwash. This study develops an overwash algorithm and applies it in a three-dimensional coupled wave-current-sediment transport model that integrates the FVCOM model and SWAN wave model, so that we can achieve a morphological model for prediction of the overwash profile evolution. This model is validated using two sets of laboratory data. The results show it is capable of simulating beach profile changes caused by the overwash under different hydrodynamic and morphological conditions. In addition, sensitivity analysis of the empirical coefficients in the overwash algorithm is carried out, and the influences of the coefficients on the model results are discussed.
		2021 Vol. 40 (7): 152-162 [Abstract] ( 170 ) PDF (546 KB) ( 610 )