Journal of Hydroelectric Engineering

水力发电学报

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2024 Vol. 43, No. 12 Published: 2024-12-25

	1	Model experiment analysis of discharge vibration transmission paths in high arch dam piers ^Hot!
		LIU Qingliang, LIU Guangkun, LI Qingbin, SONG Zhiyu, CAI Xiaoning
		DOI: 10.11660/slfdxb.20241201
		High arch dam piers experience intense vibrations during flood discharge, which could lead to certain fatigue damage to the structure or even a failure. A thorough understanding of their dynamic behaviors and the mechanisms of discharge vibration is essential to ensuring safe dam operation. This paper presents a new method for analyzing the transmission path of discharge vibration in high arch dam piers based on model experiments. We construct a water elastic model for the pier of a high arch dam based on the theory of water elastic model vibration test, and collect vibration acceleration information from different parts of the pier. Then, the transfer entropy method is used to analyze the vibration transmission paths in the pier. We have proved the use of transfer entropy allows accurate capture of the energy flow and transmission direction in complex vibration systems, suitable for analysis of the vibration transmission paths in the pier. The results indicate that in a pier structure, vibration transmission starts from three major positions－the top, bottom, and hinged beams on the inner pier side wall; the middle part of this wall and the tail of the gate in the flow are two major zones for vibration to gather. This study would be useful theoretically and practically for the design and maintenance of high arch dam piers.
		2024 Vol. 43 (12): 1-12 [Abstract] ( 23 ) PDF (2294 KB) ( 51 )

	13	Recognition method for multi-elements in human-machine-environment scenarios of concrete dam construction
		CHEN Yun, TU Yuxuan, CHEN Shu, JIN Lianghai
		DOI: 10.11660/slfdxb.20241202
		For concrete dam construction, traditional computer vision target recognition methods are difficult to meet the requirements for intelligent detection in complex construction sites, as it involves narrow spaces, continuous process transitions, and various other elements such as personnel, machinery, and environment (human-machine-environment or HME). These elements often lead to occlusions, dense overlaps, and variations in size and orientation. This paper describes a new method, YOLOv5-SS, for recognition of the multiple elements in the HME scenarios of such construction. By integrating a CBAM attention module, this method improves the performance of the object detector and enhances its sensitivity to HME elements of different sizes and positions. And, it incorporates the weighted bidirectional feature pyramid network (BiFPN) to enable the object detector to focus on key image information related to real-time HME elements. To validate the recognition capability of this method, a dataset based on image information from a concrete arch dam construction site is used. Comparison of YOLOv5-SS with the YOLOv5 and Faster R-CNN models demonstrates it effectively improves the efficiency and accuracy of target detection in concrete dam construction scenarios.
		2024 Vol. 43 (12): 13-22 [Abstract] ( 21 ) PDF (2360 KB) ( 41 )

	23	Automatic annotation and segmentation of dam concrete cracks in images based on Swin-Unet
		YANG Hanlong, CHEN Jinjian, PAN Yue
		DOI: 10.11660/slfdxb.20241203
		A general segmentation model for dam concrete surface cracks in images often faces a shortage of training data due to the high cost of manual annotation, resulting in insufficient accuracy in its results. This paper presents an automatic annotation and segmentation algorithm that integrates image feature extraction and deep learning techniques. The algorithm first adopts a strategy for combining binarization and edge detection to annotate unlabeled crack defects automatically, and constructs a large-scale dataset of 19,101 crack masks. Then, a hybrid model for combining Swin-Transformer and Unet (Swin-Unet) is designed by introducing the hierarchical attention mechanism of Swin-Transformer into the Unet architecture. Finally, the model is validated through experiments and result analyses on the self-constructed datasets. The results show this Swin-Unet model achieves the highest crack classification accuracy (100%) and a segmentation IoU of 93.1% or 7.5% improvement over the Unet segmentation model (85.6%). This indicates the introduction of the Swin-Transformer architecture enhances the model's capability of associating global and local features, significantly improving the crack defect segmentation accuracy. Besides, an analysis of the minimum enclosing rectangle of cracks reveals significant clustering in both the direction and shape distribution of cracks, deepening our understanding of the mechanisms of crack formation and useful for predicting crack propagation direction.
		2024 Vol. 43 (12): 23-33 [Abstract] ( 30 ) PDF (2797 KB) ( 40 )

	34	Investigation of filling capability of self-compacting mortar in rockfill material
		WANG Hui, LIU Jiaying, HE Shiqin, ZHOU Hu
		DOI: 10.11660/slfdxb.20241204
		To evaluate the filling performance of self-compacting mortar in rock piles, a L-B model is constructed and a filling experiment is conducted, using convex polygonal blocks of varying grain sizes randomly arranged to create a complex and irregular void channel. This L-B experiment is numerically simulated using the volume of fluid method and taking self-compacting mortar as Bingham fluid; the relationship is examined between the rock-fill rate and the filling performance of the mortar. We demonstrate the feasibility of characterizing the rheological properties of self-compacting mortars using the Bingham model, the volume of fluid method’s capability of simulating appropriately the mortar flow process, and its filling results for rock piles with irregular boundaries. The mortar filling performance increases and then decreases as the rock-fill rate increases in the range of 45% ~ 60%, with the optimal rate of 50%. This study offers a convenient simulation method for examining the filling performance of self-compacting concrete in rock piles for practical construction.
		2024 Vol. 43 (12): 34-42 [Abstract] ( 16 ) PDF (1934 KB) ( 32 )

	43	Study on multi-objective optimization of underground powerhouse construction ventilation schemes based on surrogate model
		WU Binping, YU Jiahao, WANG Xiaoling, YU Jia, LIU Changxin, GUO Zhangchao
		DOI: 10.11660/slfdxb.20241205
		Formulating a reasonable construction ventilation scheme is the key to ensuring safety and efficiency in underground powerhouse construction. Most of the previous studies on ventilation scheme optimization started from a single optimization objective such as ventilation smoke dissipation time and average pollutant concentration; traditional numerical simulation methods have the shortcomings of high modeling cost and low computational efficiency. This paper presents a new multi-objective optimization method for the construction ventilation schemes of an underground powerhouse based on an improved Least Squares Support Vector Regression (LSSVR) surrogate model of Improved Dung Beetle Optimizer (IDBO). First, a mathematical model for multi-objective optimization of the schemes is constructed, taking ventilation effect and ventilation cost as optimization objectives, and selecting ventilation parameters as design variables, such as fan airflow and the distance from the duct opening to the palm surface. Then, an IDBO-LSSVR surrogate model is constructed for prediction of the ventilation effect by combining the advantage of LSSVR in predicting small-sample data; the IDBO-improved LSSVR regularization parameter is used to optimize the LSSVR regularization parameter γ and kernel parameter σ, thereby overcoming the difficulty in model hyperparameter specification and achieving a fast prediction of the ventilation effect target. And combined with the NSGA-II algorithm, the surrogate model gives a multi-objective optimization solution. Finally, this method is applied to an underground plant project at the Luoning pumped storage power station, achieving the optimized construction ventilation scheme and a fast and accurate prediction of ventilation effect. The results show that the optimized scheme increases the ventilation and dust removal rate by 20.01%, and reduces the ventilation cost by 9.52%.
		2024 Vol. 43 (12): 43-54 [Abstract] ( 20 ) PDF (5661 KB) ( 45 )

	55	High-quality finite element mesh generation method for earth-rockfill dams with material zoning and phased construction
		MENG Xin, ZHOU Wei, LIU Quan, PANG Xiaorong, CHENTANG Zhuoyi, CHEN Zhiguang
		DOI: 10.11660/slfdxb.20241206
		Few of the previous methods for generating finite element meshes for earth-rockfill dams have taken into account material zoning, construction phasing, and the requirements for horizontal layering during filling, but they are essential for accurate simulations. Manual mesh generation is labor-intensive and time-consuming, resulting in variable quality and poorly formed elements. This paper presents a novel method that considers material zoning and phased filling for mesh generation. It is based on manual processing and initially involves horizontal layering and vertical partitioning of the dam's maximum cross-section to create regular grids with controllable segmentation scales. Then, based on node classification and numbering, it refines regular grids into three-node or four-node planar elements through implementing several new techniques, such as node migration, element identification, merging, collapsing, and splitting. Our FEM code developed using this method is efficient in generating two-dimensional high-quality finite element meshes for the maximum cross-section of the Jiangpinghe dam, and has a potential to extend to three-dimensional mesh generation.
		2024 Vol. 43 (12): 55-63 [Abstract] ( 15 ) PDF (1055 KB) ( 49 )

	64	Study on the impact of emergent drought-relief water replenishment scheduling of Three Gorges Reservoir on downstream water level and its benefit evaluation
		LI Yinghai, JIANG Qingchen, WANG Yongqiang, SONG Zhihong, ZHANG Xiaoqi
		DOI: 10.11660/slfdxb.20241207
		In recent years, the Three Gorges reservoir has implemented drought-relief water replenishing operation several times in emergency response to drought events in the middle and lower Yangtze River. However, it is not yet clear how an increase in the discharge replenishment influences the water levels at the main cross sections downstream of the reservoir, and an index system has not been established yet for evaluating the drought-relief water replenishment benefits of a reservoir. This paper develops a water level simulation model for a river section based on long short-term memory neural networks, and simulates the time variations in water level at the typical sections of the study reaches. And an index system for the reservoir’s benefits evaluation is constructed considering comprehensively water supply, ecology, shipping, and power generation. The results show that under the reservoir’s three replenishing schemes of 500, 1000, and 2000 m3/s in August, 2022, the water level and discharge at the main control stations in the study reaches would be able to rise to a certain extent. The restored irrigation area would be 2.9 thousand ha, and the economic benefit of agricultural irrigation be 13.55 million yuan. The increased power generation benefits would be 14.00, 27.25, and 32.25 million yuan under the three schemes, respectively. The ecological and shipping benefits would not change considerably, because of only a small increase in water level and discharge. This study helps formulate drought-relief water replenishing plans for the Three Gorges reservoir.
		2024 Vol. 43 (12): 64-76 [Abstract] ( 21 ) PDF (1363 KB) ( 44 )

	77	Characteristics of flows and sediment settlement under electrocoagulation and their control factors
		LIU Yifeng, BAI Wenwen, WU Miao, WEI Jiahua
		DOI: 10.11660/slfdxb.20241208
		Sediment flocculation in water significantly impacts river dredging and water environment improvement; accelerating sediment flocculation through artificial interventions is of great importance for water treatment and environmental enhancement. This study focuses on the characteristics of bubble motion during electrocoagulation and its effects on sediment flocculation. We design a laboratory experiment and use the particle image velocimetry (PIV) technology to continuously observe the movement of bubbles under 9 different current densities, collecting 5,500 image frames. Sediment particle size and solution turbidity are observed under various conditions, with 4,860 particle size data and 162 turbidity data collected. Comparative analysis is made on sediment particle size variations and solution turbidity evolution under different conditions. The results indicate bubble-driven convection is a crucial mechanism for flow field evolution and flocculation during electrocoagulation. At low electric current densities (e.g., 10 A/m2), the bubble generation rate is relatively low, resulting in a stable flow field that favors floc stability. However, excessively high current densities (e.g., 50 A/m2) can enhance flow field turbulence, disrupting the flocs formed previously and reducing flocculation efficiency. The number and distribution of vortices significantly influence the formation and growth of flocs. The ratio D/V is demonstrated to be an important indicator of flocculation effectiveness, with both D/V and removal efficiency reaching their peaks at a current density of 40 A/m2. Flotation and flocculation settling are the main factors for turbidity reduction, with a critical particle size of 37.2 μm. This study reveals the impact of flow field disturbances caused by bubble motion on flocculation efficiency, laying a basis for further optimizing electrocoagulation performance.
		2024 Vol. 43 (12): 77-88 [Abstract] ( 14 ) PDF (13315 KB) ( 36 )

	89	Analysis of flow characteristics in hump regions of pump turbine with C-type runner blades
		XIAO Yexiang, XIAO Wei, REN Shaocheng, GUI Zhonghua, LIN Hao
		DOI: 10.11660/slfdxb.20241209
		This study conducts numerical simulations and experimental tests of a model pump turbine to explore the improvement and influence of an optimized runner blade profile on the flows in a reversible pump turbine working in the hump region. A simulation analysis on its performance is made for the optimized C-type profile. Based on the vortex identification method, we discuss the flow and vortex distributions in each section of its flow passage in the hump region before and after runner modification, and reveal the influence of the new profile on the flows in the hump region. We find that after optimization, the hump range and hump margin of the pump turbine are smaller, and the trend of its head variations with flow rate is milder. And, the vortex zones become smaller in its draft tube, guide vane section, and runner section under a large flow rate. Compared with the model before optimization, the backflow is significantly reduced, and only a small amount of backflow comes from the rotating runner at the draft tube outlet under the hump region conditions. The zones of flow separation in the guide vane and runner sections are reduced, and the vortices in the vaneless region are significantly reduced, indicating the runner blade profile optimization helps improve the hump characteristics and internal flow characteristics of the pump.
		2024 Vol. 43 (12): 89-97 [Abstract] ( 28 ) PDF (5386 KB) ( 60 )

	98	Study on hydraulic characteristics of pump-turbine in exhaust process from condenser mode to generating mode
		CAO Zhongcheng, ZHOU Daqing, YU An
		DOI: 10.11660/slfdxb.20241210
		The exhaust air pressurization process of a pump-turbine during the shift from this condition is explored to address the issue of instability that is easy to generate in pumped storage units during phase transition from power generation to power generation. Unsteady multiphase flows in a prototype pump-turbine are simulated using the SST k-w model and VOF model. The simulations demonstrate the transient variation trends in the unit's active power, exhaust rate, vaneless zone pressure, and the relationship of the evolution of internal flows in the pump-turbine versus its external characteristics. They also reveal the dynamic distribution of air and liquid phases in the unit in exhaust pressurization process. The study demonstrates that in this process, the unit's active power absorption from the grid and the exhaust rate decreases gradually after their initial rapid decreases, its pressurization effect is evident, and its pressure pulsation frequencies in the vaneless zone are higher. In the vaneless zone, a high-speed water ring forms gradually driven by the inflow coming from tail water, so that air-liquid movements are chaotic and the air is prone to flowing backward into the draft tube, which has a significant impact on the unit's stability. The findings in this study are useful for improving the stability and safety of pumped storage units.
		2024 Vol. 43 (12): 98-106 [Abstract] ( 16 ) PDF (4533 KB) ( 42 )

	107	Noise reduction method of vibration signals from hydroelectric generators based on HO-VMD
		WU Tingwei, PAN Luoping, AN Xueli
		DOI: 10.11660/slfdxb.20241211
		The Variational Mode Decomposition (VMD) algorithm has been used extensively for denoising swing signals from hydroelectric power generation units; it effectively addresses the issue of modal mixing encountered in the traditional algorithm through modal decompositions. However, its modal decomposition number and penalty factor must be optimized to achieve the best accuracy. This paper presents a fusion HO-VMD algorithm for denoising these unit swing signals to overcome the limitations of slow parameter selection and poor generalization capability found in previous VMD algorithms. This new method adopts the Hippopotamus Optimization (HO) algorithm to optimize both the number of modal decompositions and the penalty factor, and its performance is compared with that of the Improved Sparrow Optimization Algorithm (SSA) and Wavelet Transform VMD Algorithm. The results demonstrate this fusion HO-VMD algorithm is effective and suitable for denoising swing signals from hydroelectric power generation units.
		2024 Vol. 43 (12): 107-115 [Abstract] ( 17 ) PDF (3089 KB) ( 28 )

	116	Investigation on dynamic behaviors of tip clearance vortices in mixed gas-liquid two-phase flow pump
		YAN Sina, LUO Xingqi, FENG Jianjun, XIE Hang, SUN Shuaihui, ZHU Guojun
		DOI: 10.11660/slfdxb.20241212
		Tip leakage vortices (TLVs) in a semi-open gas-liquid mixed transport pump are often accompanied by a large number of bubbles, which induce instability in pump operation. This study numerically simulates the flows in a three-stage semi-open mixed flow pump using an Euler-Euler inhomogeneous two-phase flow model and a MUSIG bubble distribution model to study the dynamic behaviors of the TLVs with bubbles. High-speed camera technology is used to capture their trajectory, structure, and developing process in an impeller blade period. The results indicate that in the vicinity of the blade tip clearance, the largest dissipation of vorticity is caused by the Coriolis force term, followed by the stretch-twist term. Under gas-liquid two-phase conditions, the magnitudes of the expansion-contraction term and the diagonal torque term decrease by an order of magnitude compared to the first two terms, while they increase with the increase in inlet gas volume fraction (IGVF). Bubble accumulation zones in the impeller affect the position of vortex dissipation zones, and the rotation of the impeller is the main cause of inducing vortex dissipation.
		2024 Vol. 43 (12): 116-124 [Abstract] ( 11 ) PDF (4807 KB) ( 26 )