Journal of Hydroelectric Engineering

水力发电学报

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2022 Vol. 41, No. 7 Published: 2022-07-25

	1	Text intelligent analysis for hydraulic construction accidents based on BERT-BiLSTM hybrid model
		LIU Ting, ZHANG Sherong, WANG Chao, LI Zhihong, GUAN Wei, WANG Xiaohua
		DOI: 10.11660/slfdxb.20220701
		Construction of a hydraulic project often features a complex environment, difficult operation, and frequent occurrence of accidents. The accident report, as a document for accident analysis, usually includes a summary of the accident and its cause analysis and is used as a basis for accident prevention. However, most of the current analyses on hydraulic construction accidents rely on manual analysis by on-site managers, which is not only of more mistakes but time-consuming and labor-intensive; previous numerical models cannot directly analyze or predict the accident texts with high accuracy. This paper develops a hybrid deep learning model combining the bidirectional encoding representation of transformers (BERT) and the bidirectional long short-term memory model (BiLSTM) for in-depth analysis of the causes of hydraulic construction accidents. This hybrid model uses the BERT model in its upstream to generate a character-level dynamic feature vector of the accident text, and mines the semantic features of the accident report text in its downstream using an improved BiLSTM model, so as to realize an intelligent analysis of accident report texts. Its efficacy is compared with those of seven state-of-the-art deep learning models, and the results show it is superior and useful for analysis and decision-making of hydraulic construction accidents.
		2022 Vol. 41 (7): 1-12 [Abstract] ( 198 ) PDF (535 KB) ( 533 )

	13	Study on key competences identification models for construction project managers
		ZHENG Junping, QIANG Maoshan
		DOI: 10.11660/slfdxb.20220702
		Project managers play a fundamental role in project success and organizational strategy implementation. With the increasing scale and complexity of construction projects, the demand for qualified project managers is also growing. This paper develops a model for identifying the managers’ key competences that need further improvement, so as to support personal development and organizational human resource management practices. Based on the previous competence indicator system in the literature, a questionnaire survey was conducted to obtain the importance and performance of each competence. Importance-performance analysis (IPA) is adopted to identify competences in need of improvement; a priority order of them is then determined through calculation of the priority index of each competence. Case analysis shows our model is effective and easy to use in identifying and ranking the construction project managers’ competences. It helps identify the key competences for improvement and establish corresponding competence building strategies, and our modified IPA method is also a useful tool that can be applied to other similar studies.
		2022 Vol. 41 (7): 13-19 [Abstract] ( 103 ) PDF (624 KB) ( 208 )

	20	Optimization of top-level governance structure of major water conservancy projects using PPP model
		WANG Zhuofu, MEI Yulei, DING Jiyong, QIAO Ran
		DOI: 10.11660/slfdxb.20220703
		Stepping into the new century, China has a number of major water conservancy projects built or under construction. Most of them feature with public welfare or quasi-operation, and adopt the PPP financing pattern and a governance framework of "government leading + market mechanism". This paper chooses three representative major water conservancy projects using the PPP pattern already built or under construction, and examines their top-level governance structure. We find that the pattern can be aimed at a single construction of the project, not necessarily at the whole project. And the responsibility for project implementation can be taken by the project entity established by the government, not necessarily by the financing enterprises. Case analysis indicates that various ways can be found to apply the PPP model or establish the project entity, but both applications are not independent from each other. Hence, it is necessary to combine both and then select a satisfactory project top-level governance structure. In this work, a method for designing feasible schemes is developed and optimal schemes determined using an entropy weight-VIKOR method, on the basis of analysis of the top-level structure as demonstrated above.
		2022 Vol. 41 (7): 20-29 [Abstract] ( 206 ) PDF (506 KB) ( 370 )

	30	Study on coupling effect of confined compression and creep deformation of Lianghekou rockfill material
		HUANG Wenchao, ZHANG Guike, DENG Gang, ZHANG Yanyi, ZHANG Yinqi, CHEN Hui
		DOI: 10.11660/slfdxb.20220704
		In this work, large-scale confined compression and creep tests are conducted using the dry rockfill of slate, which is designed for the shell material of the Lianghekou high gravelly-soil-core rockfill dam. We adopt two types of tests, i.e. single stage loading and multi-stage loading, and examine the confined creep under the loading at a constant stress rate and the confined creep under the loading-unloading-reloading at a constant stress rate, focusing on the influence of historical loading conditions on volumetric creep deformation and the influence of creep deformation on subsequent compression deformation. We find that except for two special creep processes, i.e. after loading-unloading-reloading and after low constant stress rate loading, all the time variations in volumetric creep deformation under different stresses follow a similar normalized trend－creep deformation is positively correlated with stress. The creep rate generally decreases with time, and follows a good double logarithmic linear relationship. The initial creep rate is positively correlated with stress, but its time decay rate seems to be irrelevant to stress, previous loading, or creep history. For the two special creep processes, we find that creep rate increases with time gradually or keeps unchanged in a short initial period, and creep deformation is smaller than in other cases. And the creep deformation in the early stage leads to an increase in the degree of over-consolidation, which generates an obvious hardening effect on the subsequent reloading process. Thus, the confined compression modulus under the initial reloading is significantly higher than that of normal loading. But with more reloading applied, it gradually approaches to the latter, which is less affected by the number and time of previous creeping and shows a similar evolving process.
		2022 Vol. 41 (7): 30-37 [Abstract] ( 80 ) PDF (547 KB) ( 275 )

	38	Investigation on anti-freezing performance of core wall phase change material-incorporated clay with an upper loose-covering layer
		LIU Donghai, ZHENG Han, YANG Jiaqi
		DOI: 10.11660/slfdxb.20220705
		For construction of a high core-wall clay earth-rock dam at negative air temperature, it is common to see compactability degeneration and structural defects (e.g. frost heave, thawing settlement and structure crack) after short-term frozen or freeze-thaw cycles, leading to working performance deterioration in strength and impermeability. Conventional measures, e.g. covering thermal insulations, interfere severely with core-wall clay paving and filling, and suffer difficulty in maintaining continuous construction. In this work, a phase change material-incorporated clay (PCM-clay) is used as core wall material; anti-freezing performances of the lower PCM-clay are investigated considering the effect of an upper loose-covering layer. We analyze the impact of PCM content on thermal characteristics, and verify the effectiveness of a homogenization model for thermal conductivity through thermal tests. Then, heat transfer and thermal performance of the upper layer is examined by conducting thermal cycling tests. Under 48-hour typical temperature, construction time extension for the core wall clay with 4% and 8% PCM contents are 22.6 and 24.9 hours, respectively. For 4% PCM-clay, the total continuous construction time in 2 days is 45.8 hours; 8% PCM-clay even keeps above positive temperature for 48 hours. The results indicate that the anti-freezing measures of PCM-clay and upper loose covering provide a theoretical basis and potential way to extend winter construction time, thus helping accelerate the construction progress of core walls in cold regions.
		2022 Vol. 41 (7): 38-46 [Abstract] ( 108 ) PDF (934 KB) ( 238 )

	47	Nonlinear chaotic Harris hawks optimization model for large-scene video monitoring network coverage of high core rockfill dams
		KANG Dong, ZHANG Jun, WANG Jiajun, WANG Xiaoling, ZHAO Hao, ZENG Tuocheng, QU Xiaofeng
		DOI: 10.11660/slfdxb.20220706
		Coverage rate and cost are two important measures of a video surveillance network for high core rockfill dams, but previous studies in the literature lack a comprehensive consideration of deployment cost, and the commonly-used optimization methods have shortcomings such as slow convergence and easy falling into local optimization. To solve these problems, this paper develops a nonlinear chaotic Harris hawks optimization model for large-scene video monitoring network coverage of a high core rockfill dam. First, a resampling rate per camera is employed to represent deployment cost, and an optimization model is constructed to maximize the coverage rate and resampling rate per camera based on the set covering theory. Then, a chaotic sequence and the nonlinear energy update strategy are adopted to optimize the population initialization and search process of the Harris hawks algorithm, which improves the convergence and avoids falling into prematurity. Finally, an improved algorithm is used to solve this new model. Application to a dam construction project has verified our improved Harris hawks algorithm is effective and superior in the deployment optimization of the surveillance network, achieving a coverage rate and resampling points proportion of up to 99.98% and 60.3% respectively, or 13.8% and 23.2% higher than the empirical scheme, with the video surveillance effect improved significantly.
		2022 Vol. 41 (7): 47-60 [Abstract] ( 209 ) PDF (5859 KB) ( 320 )

	61	Experimental study on water vibration characteristics of underwater shaking table
		ZHENG Renfeng, NIU Zhiwei, HAN Wei, LI Haoran
		DOI: 10.11660/slfdxb.20220707
		The underwater shaking table enriches and broadens the application of shaking tables in the seismic research of engineering structures, but its vibrating water behaviors are often distorted due to its local vibration and the interference of its tarpaulin. In this work, a total of 252 working conditions were tested experimentally to study the characteristics of vibrating water in the zone from the center of the table to the water pool boundary, in the conditions of different excitation amplitude, direction, frequency, and water depths. The results show most of the influence and disturbance of the waterproof device is in the horizontal direction. For the case of vertical sinusoidal excitation, water vibration is in the shape of an inverted iron pot in low frequencies (≤ 1 Hz), while it features multiple wave peaks in medium or high frequencies (≥ 3 Hz) with more wave peaks in high frequencies. An increase in the excitation amplitude causes more wave peaks to be gradually superimposed together and amplified, and a collapsing phenomenon will occur when a certain amplitude threshold is exceeded. The amplitude of water vibration peaks shows a downward trend with an increasing water depth. This study demonstrates how to evaluate and improve the model tests on an underwater shaking table.
		2022 Vol. 41 (7): 61-71 [Abstract] ( 100 ) PDF (4493 KB) ( 336 )

	72	Prediction model of dam structure dynamic deformation based on time attention mechanism
		SU Yan, FU Jiayuan, LIN Chuan, CHEN Zeqin, WENG Kailiang, ZHANG Ting
		DOI: 10.11660/slfdxb.20220708
		Constructing a high-accuracy deformation prediction model of dam structure is of great significance for dam risk assessment and formulation of preventive measures. Previous dam deformation prediction models lack an effective explanation of the time-lag characteristics, and ignore an influence analysis and evaluation of the deformation characteristic factors in model construction, thereby lowering prediction accuracy. This paper presents a Gated Recurrent Unit (GRU) architecture combined with a temporal attention mechanism to overcome these problems. First, a Kalman filter is used to denoise the original dam deformation data series and remove its outliers; then, Random Forest (RF) is used to analyze and evaluate the importance of different deformation characteristic factors, and pick out key model input factors. Finally, to consider the dam deformation lag, a time attention mechanism is used to further improve the attention of the GRU model to the time-dimension dynamic features and to enhance its adaptive learning capability to time-dimension information. This, through visualizing time attention, can further improve the interpretability of a prediction model for the dam deformation in the hidden state stage. The results of engineering case studies show our model, of higher prediction accuracy and strong explanatory power for hidden state levels, can reveal the long-term effects of temperature and water level factors on dam deformation. Thus, it is a new effective method for dam safety monitoring.
		2022 Vol. 41 (7): 72-84 [Abstract] ( 378 ) PDF (4033 KB) ( 969 )

	85	Study on unit commitment algorithm of Three Gorges hydropower plant based on group theory
		XU Gang, RUAN Quansheng, TANG Zhengyang, REN Yufeng, XU Yang, JIANG Ping’an
		DOI: 10.11660/slfdxb.20220709
		Economical operation of a hydropower station is an energy-saving measure to improve water energy utilization efficiency. The load distribution of units in the plant is based on the minimum water consumption, and generally solved using dynamic programming. The Three Gorges hydropower plant features a large number of units and bears a large load; the problem of dimension disaster would easily occur if dynamic programming is adopted. This paper develops a dimensionality reduction method for unit commitment problem based on the group theory. We group the plant’s units by operation characteristics, and calculate the number of essentially different startup and shutdown state combinations and the corresponding combinations based on the Burnside lemma. Then, we use dynamic programming to solve the time-space optimization after dimensionality reduction. Application of this new method to the economical operation of the plant shows it reduces computational cost significantly and responds quickly to the change in the operating conditions of the hydropower system.
		2022 Vol. 41 (7): 85-94 [Abstract] ( 124 ) PDF (663 KB) ( 375 )

	95	Vine Copula-based analysis on uncertainty of short-term streamflow forecasting
		LIU Yuan, JI Changming, ZHANG Yanke WANG Yi, JIANG Zhiqiang
		DOI: 10.11660/slfdxb.20220710
		It is important to evaluate the effect of forecast uncertainty on the decision of reservoir operation. Previous studies usually use the traditional Copula to describe uncertainty information in the short-term forecasting of streamflow sequences, but such methods are ineffective and unsatisfactory. We adopt Vine Copula to characterize the uncertainty of streamflow forecasting, and realize a quantitative evaluation of the uncertainty in the conditions of different streamflow levels and different lead times. And the effect of prior information on the subsequent forecasting uncertainty can also be analyzed. Application of this new method to the Jinxi Reservoir shows that Vine Copula can pass the hypothesis test and achieve the best fitting effect compared to the traditional Copula model, and statistically its simulation error is the lowest against the measured data. When the prior information in the same planning period is used, the expectation of its relative forecasting errors and its 90% confidence level interquartile range can be significantly reduced, thus lowering forecasting uncertainty.
		2022 Vol. 41 (7): 95-105 [Abstract] ( 120 ) PDF (712 KB) ( 432 )

	106	Study on hydropower development strategy for new power systems
		ZHOU Jianping, DU Xiaohu, ZHOU Xingbo
		DOI: 10.11660/slfdxb.20220711
		To implement the dual-carbon strategy, energy is the main battlefield and electricity the main force; developing a new power system with new energy resources as the main body is the only feasible path to achieving carbon neutrality. This paper examines the emission reduction targets, electricity composition, and structure of the power industry under the dual-carbon strategy, and demonstrates that accelerating the construction of conventional hydropower stations and pumped storage power stations is an important basis for solving problems and challenges such as the reliability and long-term regulation capabilities of the new system. Based on the hydropower resources endowment and the development status, we present a strategic idea of strengthening the coordinated development of hydroelectric power and new energy, and redefine the development path of building clean energy bases and energy storage plants and accelerating the construction of pumped-storage power stations and cascaded conventional hydropower reservoirs. This new positioning of hydroelectric power in the new system not only provides basic electricity but plays its capacity function. Thus, we suggest certain policy should be formulated to speed up the construction of clean energy bases and energy storage plants. Our findings could help the revision and compilation of the planning schemes and regulations.
		2022 Vol. 41 (7): 106-115 [Abstract] ( 332 ) PDF (565 KB) ( 1223 )

	116	Channel evolution of river system in Dongting Lake after Three Gorges dam based on flow-sediment model
		WEI Qiangqiang, CONG Zhentao, ZHU Dejun, LIU Xiaoqun
		DOI: 10.11660/slfdxb.20220712
		The river system in Dongting Lake, originating from the Yangtze, has a flow-sediment regime that depends much on the Three Gorges Reservoir. A study on the scour and sedimentation in this system and its time changes can help understand the river’s flood control and the river-lake relationship. In this study, we develop a numerical flow-sediment transport model and simulate the scour and sedimentation and its changes in the river system in the period starting from the reservoir operation. The dominant factors are examined on the basis of the simulations and field observation data. The results show that in this period, a general scour has occurred over the system－a trend that will not change in the near future－but its intensity has been decreasing gradually. And no obvious change has been observed in the trends of the diverted flows, flow diversion ratios, or sand diversion ratios at the estuaries of the river system. In the period, the amount of diverted sediment has been reduced tremendously, as the flow from the reservoir is laden with much less sediment and thus has altered the scour and sedimentation conditions of the river system. In addition, sand mining has also imposed a significant impact on the river system.
		2022 Vol. 41 (7): 116-128 [Abstract] ( 145 ) PDF (3229 KB) ( 369 )

	129	Experimental study of velocity fluctuations in inlet/outlet under outflow diffusion
		ZHU Hongtao, GAO Xueping, LIU Yinzhu
		DOI: 10.11660/slfdxb.20220713
		Under outflow conditions, flows in a side inlet/outlet are in the diffusion mode and produce large velocity fluctuations in the trash rack section. In this work, a test facility for typical inlet/outlet flows is used for an experimental study with flow velocity measured using a laser doppler velocimetry and an acoustic doppler velocimetry. The results show large velocity fluctuations occur at the cross section of the trash rack installed near the exit of the diffuser, with the fluctuating components reaching up to 1.8 times of the mean velocity and an average turbulence intensity of 0.724. The probability density of the fluctuations basically follows a normal distribution. Turbulent intensity shows a streamwise trend of first increasing and then decreasing along the flow starting from the diffuser inlet, through the diffusion section, adjustment section, and anti-vortex section, and to the reservoir. Velocity fluctuations are small in the upstream tunnel section and become relatively large in the diffusion and adjustment sections. Large velocity fluctuations at the trash rack cross section are explained. The results provide a theoretical basis for optimization of the inlet/outlet parameters and analysis of the vibration damage to trash racks.
		2022 Vol. 41 (7): 129-139 [Abstract] ( 121 ) PDF (5356 KB) ( 692 )

	140	Analysis of flow-induced vibrations of pump-turbines during load rejection by CFD-FEM simulations
		TANG Maojia, TAI Rong, CHENG Yongguang, LIU Ke
		DOI: 10.11660/slfdxb.20220714
		Vibrations of pump-turbine units are often severe during load rejection, and the resulted intensive alternating stress may lead to a fatigue failure of the runner. To investigate the flow-induced vibrations of a pump-turbine runner, flow patterns, dynamic stress, and vibration modes are analyzed for typical working conditions based on CFD-FEM simulations. The results show the rotational speed is the key factor that has the greatest influence on the pressure pulsation and dynamic stress of the runner. Working at the highest speed is the most adverse condition, resulting in the worst pressure pulsation, along with a dynamic stress and its fluctuating amplitude that both are larger than those in other working conditions. The fluctuation of runner stress is induced by pressure pulsation, both featured with similar frequency spectra. The peak dynamic stress of the runner is located at its T-shaped joint between the blade leading edge and the hub. In our calculations, the frequencies of hydraulic excitation forces are far away from the natural frequency of the runner, and therefore the runner will not resonate in this case.
		2022 Vol. 41 (7): 140-148 [Abstract] ( 176 ) PDF (1715 KB) ( 487 )