Abstract:To investigate the effects of restrictive ventilation conditions in a covered vertical shaft on air-pocket motion and geyser characteristics, a combined approach of physical model tests and numerical simulations was employed to systematically examine the influences of shaft diameter, ventilation ratio, external head, and initial air-pocket volume on air-pocket motion and geyser occurrence. The results show that the water-level rise in the shaft during air-pocket release can be divided into an air-pocket-driven stage and a pressure-difference-driven stage, resulting in four typical flow regimes: no geyser, an air-pocket-driven geyser only, a pressure-difference-driven geyser only, and both an air-pocket-driven geyser and a pressure-difference-driven geyser. The air-pocket morphology is jointly influenced by the shaft-to-pipe diameter ratio, ventilation ratio, and air-pocket length. In small-diameter shafts, the air pocket tends to be symmetric and intrudes into the upstream pipe, whereas in larger-diameter shafts, the air pocket exhibits significant asymmetry and remains trapped in the downstream pipe. For small-diameter shafts, the air-pocket head morphology varies non-monotonically with the ventilation ratio: it is approximately symmetric at a ventilation ratio of 0, becomes irregular at ventilation ratios of 0.01 and 0.02, returns to a nearly symmetric shape at ventilation ratios of 0.05 and 0.1, and develops into a sharply asymmetric shape inclined toward the downstream direction at a ventilation ratio of 1 (fully ventilated condition). A larger air-pocket length results in stronger disturbances to the free surface and a higher release position. The rising velocities of both the air-pocket head and the free surface increase significantly with increasing ventilation ratio, external head, and air-pocket length, and decrease with increasing shaft diameter.

Abstract:To investigate the geyser phenomenon characterized by sudden water-air eruptions and localized pressure surges during the filling process of water conveyance systems, an experimental system for transient water-air two-phase flow was designed and constructed. By utilizing the water level difference between upstream and downstream water tanks to indirectly control the base flow, the water-air two-phase transient process during the filling of a water conveyance system equipped with a ventilation shaft was investigated, aiming to explore the triggering mechanisms and dynamic characteristics of geyser phenomena. The experimental results indicate that the geyser transient process considering base flow can be divided into the air pocket impact stage and the eruption stage. During the air pocket impact stage, the air pocket undergoes repeated compression and expansion, accompanied by periodic pressure fluctuations. During the eruption stage, violent water-air interactions occur, a higher base flow rate results in less gas entrainment into the riser, and geyser phenomena are more likely to occur if the entrained gas arrives at the top orifice of the riser later than the free water surface. The geyser phenomena can be classified into four types: multiple-eruption type, no-eruption type, single-eruption type, and damped-eruption type. Additionally, the propagation and superposition of pressure waves induced by air pocket rupture and coalescence during geyser events are identified as significant contributing factors to the unstable pressure fluctuations.

Abstract:The take-off angle of the jet from aeration facilities is a critical hydraulic parameter for accurately calculating the aerated cavity length. The turbulent characteristics of the jet indirectly influence the take-off angle through modifying the diffusion angle, and the underlying physical mechanism is considerably complex. To rigorously account for the effect of flow turbulence on the diffusion angle, the turbulent diffusion angle at the lower jet nappe was quantified based on the theory of two-dimensional free turbulent jets, leading to the derivation of a modified formula for the take-off angle of jet from aeration facilities. A total of 193 test conditions were examined through laboratory experiments conducted in a precision tilting flume, together with engineering applications. The prototype cavity lengths predicted by six alternative take-off angle estimation methods were compared with measured prototype data. Both the model experiments and engineering validations confirm that the proposed correction method for the take-off angle of jet from aeration facilities is reasonable and reliable.

Abstract:To address the deterioration of concrete exposed to high-sulfate environments, sulfate wet-dry cycling tests were conducted to systematically investigate the effects of different combined incorporation methods of polyester fiber, basalt fiber, and U-type expansive agent on the sulfate erosion resistance of concrete. By analyzing the deterioration patterns of specimen appearance damage, mass loss, and pore structure evolution, the sulfate erosion resistance of concrete was evaluated, and the synergistic mechanism by which fibers and expansive agent inhibit concrete deterioration was revealed.The results show that the concrete incorporating 0.15% basalt fiber by volume and 4% U-type expansive agent by mass of cementitious materials exhibited the best sulfate erosion resistance. After 50 cycles, the specimens remained intact in appearance, with no paste spalling observed. The mass loss rate was 6.12%, compared with 9.52% for the control group. The proportion of harmless pores decreased by 5.55 percentage points relative to that before the test, while that of the control group decreased by 10.00 percentage points. The synergistic effect of the expansive agent and fibers optimized the pore structure of concrete, thereby improving its impermeability and resistance to sulfate erosion.

Abstract:To address the problems of sand boiling and structural deformation failure induced by internal erosion in gap-graded soils under seepage action, erosion tests under different hydraulic gradients were conducted on gap-graded soil specimens with fine particle contents of 20%, 30%, and 40% using an internal seepage erosion apparatus. Based on the discrete element method, the evolution processes of particle loss, contact force chains, and porosity were analyzed, and the mesoscopic erosion characteristics of gap-graded soils were explored. The results show that specimens with higher fine particle contents exhibit higher erosion rates and more intense erosion processes. Under low hydraulic gradients, seepage-induced compaction occurs, resulting in a decrease in porosity, and the variation of porosity exhibits spatial heterogeneity. The fine particle content affects the contact modes among particles within the soil and serves as a triggering factor for particle loss. The combined effects of contact force chain transformation and particle loss lead to erosion-induced failure of the soil.

Abstract:To investigate the effects of porosity and pore water saturation on the elastic modulus of concrete at different scales, a multi-scale prediction model for the elastic modulus of wet concrete considering porosity and pore water saturation was established based on the micromechanical inclusion theory. The influence of porosity and pore water saturation on the elastic modulus at multiple scales was analyzed. The results show that the predicted results from the proposed model are in good agreement with multiple sets of experimental results, and the model can accurately predict the elastic modulus of concrete across various scales. The elastic modulus of concrete at the cement paste, mortar, and concrete scales decreases with increasing porosity, and the influence of porosity on the elastic modulus of materials is more pronounced in the dry state than in the saturated state. The elastic modulus of concrete at the cement paste, mortar, and concrete scales increases with increasing pore water saturation, and the higher the porosity, the more significant the increase in elastic modulus with increasing saturation.

Abstract:To investigate the microscopic mechanism of erosion damage in hydraulic machinery, a qualitative study on the movement characteristics of cavitation bubbles near a single spherical particle was conducted using high-speed photography experiments, based on Weiss’s theorem and Kelvin impulse theory. The Kelvin impulse of cavitation bubbles was quantitatively analyzed with respect to important parameters such as the particle radius and cavitation bubble radius. The results indicate that the theoretical model of Kelvin impulse of cavitation bubbles can effectively predict the movement characteristics of cavitation bubbles under the influence of a single particle. The absolute value of the Kelvin impulse decreases with increasing dimensionless distance between the particle and the cavitation bubble. Compared with linear sinks, virtual point sources contribute more significantly to the Kelvin impulse of cavitation bubbles.

Abstract:Based on Landsat remote sensing imagery and in-situ measurements, machine learning methods were used to construct inversion models for total nitrogen (TN) and total phosphorus (TP) mass concentrations across the entire Poyang Lake. Combined with water quality data from the five rivers (the Ganjiang, Fuhe, Xinjiang, Raohe and Xiushui rivers) flowing into the lake, the spatiotemporal distribution characteristics of TN and TP mass concentrations in Poyang Lake from August 2021 to January 2023 were systematically analyzed. The results show that the TN mass concentration inversion model constructed using a back propagation (BP) neural network achieves a good fit ( R 2=0.91), and the TP mass concentration inversion model based on the GA-optimized BP neural network (GA-BP) performs well ( R 2=0.82). The TN and TP mass concentrations in Poyang Lake exhibit strong seasonal variation, and the water quality in the wet season is generally better than that in the dry season. The spatial distribution of TN and TP mass concentrations in the lake area during the wet season shows strong heterogeneity. Areas with high TN and TP mass concentrations in Poyang Lake are mainly concentrated in the central and northeastern parts of the lake area and the entrances of the five rivers flowing into the lake. The extreme drought exacerbated water quality deterioration in Poyang Lake, leading to an increase in the TN and TP mass concentrations across the entire lake.

Abstract:In order to investigate the effects of different groundwater depths on the yield and water use efficiency of summer maize under rainfed conditions, four treatments with groundwater depths of 0.7, 1.3, 1.8 m and the normal field depth (recorded as D0.7, D1.3, D1.8, and D2.4, respectively) were set up using the groundwater automatic control system. The soil moisture content, rainfall utilization rate, phreatic evaporation, plant height, leaf area index, yield and water consumption during the growth period of summer maize under rainfed conditions were analyzed. The results show that the groundwater depth has significant effects on the average soil water content, rainfall utilization rate, and water use efficiency under rainfed conditions. Compared with D2.4, the average soil moisture content during the whole growth period of summer maize under D0.7, D1.3, and D1.8 treatments increased significantly by 6.9%~28.6%, the rainfall utilization rate decreased by 23.2%, 11.4%, and 2.8%, respectively, and the plant height, leaf area index, and dry matter accumulation decreased by 1.7%~5.2%, 5.8%~13.7%, and 9.4%~19.5%, respectively. Compared with other groundwater depths, the D1.8 treatment can ensure the highest yield and water use efficiency of summer maize in this area.

Abstract:To quantitatively evaluate water resources security in mining areas, this study takes the X mining area in northern Shaanxi as the research object and constructs an evaluation index system comprising four dimensions (water quality status, water resources quantity, water use efficiency, and ecological sustainability) with a total of 16 secondary indicators, and classifies the risk levels of the indicators. The game theory combination weighting approach is employed to optimize the integration of indicator weights derived from the analytic hierarchy process and the entropy weight method. The combined weights are then incorporated into the TOPSIS method to analyze the multi-year water resources security of the mining area based on the closeness of each indicator to the ideal solution. The results indicate that the comprehensive water resources security level of the mining area from 2017 to 2023 is relatively safe, which is consistent with the actual conditions of the mining area. The primary factors affecting water resources security in the mining area are the surface water quality compliance rate, the wastewater discharge compliance rate of the mining area, and the groundwater pollution index.

Abstract:To accurately evaluate the compaction quality of embankment soil materials, a comprehensive assessment method based on multi-source information fusion of roller acceleration data in both the time and frequency domains is proposed. Quantitative relationship models between compaction degree and different indicators, including compaction energy per unit volume, frequency-domain indicator CV, and time-frequency-domain indicator CWT-THD, were established. Utilizing the Dempster-Shafer (D-S) evidence theory as the information fusion framework, the basic probability assignment values of the three indicators and conflicting evidence were optimized through integration with construction practice and Murphy’s rule. The case validation results demonstrate that the proposed method can improve the accuracy of compaction quality evaluation, avoid the limitations of single-indicator assessments, and enable the analysis of spatial uniformity of compaction quality, thereby achieving rapid and accurate evaluation of soil compaction quality.

Abstract:To investigate the causes of plane gate jamming in the closing process, a combined approach of physical model experiments and CFD numerical simulations was employed to examine the hydrodynamic characteristics of plane gates during dynamic closure under free-flow conditions. The results show that under the upstream pressure head, plane gates equipped with upstream seals experience significant hydrodynamic thrust forces with minimal contribution from water-induced gravitational forces, rendering gate closure primarily dependent on self-weight. After a period of gate operation, excessive friction coefficient is identified as a significant cause of closing jamming. Under free-flow conditions, the permissible friction coefficient of the plane gate is mainly governed by the gate self-weight, the upstream-downstream head difference, and the effective area subjected to water thrust. Five countermeasures were proposed to facilitate the successful closure of the plane gate: reducing the friction coefficient of supporting materials, increasing counterweights, decreasing the upstream-downstream head difference, reducing the water thrust action area, and appropriately closing the radial gate.

Abstract:To reveal the causes of efficiency degradation in a large Francis turbine under high-load conditions, a numerical simulation investigation was conducted on the mechanism of vortex-induced energy losses. The mean kinetic energy theory was employed to quantify hydraulic losses in each flow passage component, while the rigid vorticity theory was adopted to identify complex vortex structures in the runner and draft tube. The results show that once the discharge exceeds the rated value, the runner and draft tube become the dominant sources of hydraulic loss, accounting for up to 30% and 75% of the total hydraulic loss, respectively. The flow separation-induced vortex at the leading edge of the runner blade merges with the horseshoe vortex at the blade root, producing intense shear flow and significantly increasing energy loss near the leading edge. The velocity gradient between the low-velocity flow near the vortex core of the cylindrical vortex rope in the draft tube and the high-velocity main flow in the outer region significantly enhances turbulent kinetic energy dissipation. The separation vortex in the runner and the cylindrical vortex rope in the draft tube are the primary loss sources under high-load conditions. Their intensities increase with discharge, leading to a substantial reduction in turbine efficiency.

Abstract:To address the limitations of traditional outlier detection methods for seepage monitoring data in processing nonlinear and nonstationary water level monitoring data, a hybrid model based on variational mode decomposition (VMD), long short-term memory network (LSTM), and variational autoencoder (VAE) is proposed. In the proposed model, VMD is used to perform multiscale decomposition of the water level time series and obtain intrinsic mode functions with different frequency characteristics. A two-layer LSTM is then employed to capture the temporal dependencies of each modal component. VAE is used for feature compression and reconstruction, and outlier detection is achieved based on the reconstruction error. Case validation results show that the hybrid model can effectively identify isolated outliers and continuous outlier sequences. In scenarios where outliers were randomly added to the test set at proportions of 1%, 2%, and 3%, the model exhibited good detection performance, verifying its effectiveness in outlier detection for seepage monitoring data.

Abstract:Aiming at the problem that hydraulic structures are prone to deterioration such as water stains and calcium precipitation under complex natural environments and operating conditions, thereby complicating surface crack detection, this paper proposes a crack detection model YOLO-SEH integrating a deformable convolutional network (DCNv2) and scaling efficient decoupled head (SEH). An efficient channel attention mechanism is introduced into the model neck to suppress noise interference from complex backgrounds. In the backbone, DCNv2 is adopted to replace the C3 module of YOLOv5, improving the model’s adaptability to irregular crack shapes. SEH is incorporated into the detection head to strengthen the model’s sensitivity and discriminability to crack features. The proposed model was applied to crack detection on sluice and dam images captured by unmanned aerial vehicles (UAVs), achieving mAP@0.5 values of 86.2% and 84.9%, respectively. Ablation experiments show that compared with the YOLOv5 model, the mAP@0.5 of the YOLO-SEH model increased by 3.1 and 4.1 percentage points, the precision increased by 4.8 and 6.6 percentage points, and the recall increased by 3.4 and 4.7 percentage points for the two datasets, respectively. Furthermore, comparative experiments with the Faster R-CNN, SSD300, YOLOv5, YOLOv7, and YOLOv8 models demonstrate that the YOLO-SEH model achieves superior detection performance for crack detection of hydraulic structures.