Abstract:To investigate the optimal range of the planar diffusion angle, this study employed a numerical simulation method to analyze the hydraulic characteristics of a lateral inlet/outlet in a pumped storage power station under different planar diffusion angles. The influence of the planar diffusion angle on the velocity distribution at the trash rack section, orifice flow distribution, and head loss of the inlet/outlet was analyzed. The results demonstrated that when the planar diffusion angle increased from 25° to 45°, the non-uniformity coefficient of the velocity at the trash rack section decreased gradually under the outflow condition, while the non-uniformity of the orifice flow distribution and head loss of the inlet/outlet increased gradually. The velocity distribution at the trash rack section, orifice flow distribution, and head loss of the inlet/outlet remained unchanged under the inflow condition. Considering the hydraulic indices of the inlet/outlet comprehensively, it is concluded that the optimal range for the planar diffusion angle is 30° to 40° when the average velocity at the trash rack section meets the design requirement. This range provides higher precision than the current specification and aligns with the diffusion angle range associated with minimal resistance coefficients in rectangular expanding conduits.

Abstract:To investigate the impact of carbonation on the mesostructure and mechanical properties of dam concrete, scanning electron microscope (SEM), X-ray computed tomography (X-CT), and combined uniaxial compression-acoustic emission tests were conducted on concrete specimens from the Meishan Arch Dam. Based on Avizo images and acoustic emission parameters, the mesostructural characteristics (including porosity, pore size distribution, and pore morphology) and material damage evolution characteristics of carbonated dam concrete were analyzed. The results show that carbonation alters the microscopic morphology of concrete, numerous calcium carbonate particles appear on the surface of the C-S-H gel, and the porosity decreases. As carbonation progresses, the proportion of pores with equivalent diameters larger than 160.μm increases, while the proportion of pores with equivalent diameters lower than 160.μm decreases. After 14-day and 28-day accelerated carbonation, pores with a sphericity of 0.9 to 1.0 increase by 8.9% and 6.5%, respectively, compared with that of the non-carbonated concrete, indicating that carbonation fills the irregular edges of pores. After carbonation, the overall activity of acoustic emission signals of dam concrete decreases, and the compressive strength and elastic modulus of concrete decline.

Abstract:In order to reveal the groundwater movement rule of peatland, using a typical peatland watershed in the upper Heihe River in the Zoige Basin as an example, a numerical model of groundwater movement along the headward erosion channel in the watershed was set up based on Visual MODFLOW, and the groundwater dynamics under different channel morphologies were simulated. The results show that groundwater movement in the peatland is influenced by precipitation, gully, and terrain. The increase of precipitation will accelerate the movement of groundwater to the gully, and the movement speed reaches the maximum after the peatland reaches saturation, and the effect of precipitation is weakened. The increase of gully depth will speed up the rate of groundwater discharge and enlarge the area of drainage zone, and the drainage capacity of the gully after cutting through the peat layer is 3.21 times that of the gully without cutting through the peat layer. There is a significant linear relationship between groundwater hydraulic gradient and topographic slope.

Abstract:In order to predict the transport processes and distribution laws of point source pollutants in continuous bend flow when water pollution accidents occurs, a three-dimensional continuous bend flow pollutant transport model was constructed using the WALE-based large eddy simulation method. Numerical simulations were conducted under four different Reynolds number conditions to investigate the hydrodynamic structures and transport characteristics of point-source pollutants. The effects of Reynolds number variation on hydrodynamic structure and turbulence characteristics were analyzed. By comparing the spatial distribution characteristics and mixing rates of point-source pollutants in the lower reaches of curved channel under different Reynolds number conditions, the transport mechanisms of pollutants under the combined action of secondary circulation and turbulent transport were revealed. The results show that with the increase of the Reynolds number, the average circulation intensity on the cross-section is weakened, and the flow structure becomes more uniform. The average lateral and vertical dispersion coefficients of pollutants along the route are exponentially negatively correlated with the Reynolds number. The spatial mixing degree of pollutants is positively correlated with the Reynolds number. The percentage of fully mixed area of pollutants is negatively correlated with the Reynolds number.

Abstract:Most existing water hammer calculations in drainage pipe networks are based on the assumption of constant friction, neglecting the damping effect of dynamic friction on pressure fluctuations. To address this issue, a dynamic friction water hammer model was developed and solved using the method of characteristics. A water hammer test system was designed to verify the model, and the verified model was used to calculate and analyze an actual complex drainage pipe network with a pump group system. The results indicate that, compared with the conventional constant friction water hammer model, the dynamic friction water hammer model not only accurately simulates the first peak pressure but also precisely simulates the fluctuation peaks and periods of water hammer pressure throughout the entire transient process. For continuous and sustained water hammer events, the cumulative calculation error caused by neglecting dynamic friction cannot be ignored. The installation of air valves can reduce the maximum water hammer pressure by 22.7% and increase the maximum negative pressure in the pipeline by 73%.

Abstract:In order to explore the clogging mechanism of filter cakes, a combined approach of prototype experiments and CFD-DEM coupled simulation was used to investigate the variation laws of filter cake thickness and thickness uniformity during the clogging of horizontal screen filters under different conditions. The results show that the cake thickness of the filter is determined by the number of particles in contact with the unit screen area, the flow field force, the inter-particle interaction force and the particle gravity. In the experiments, the filter cake thickness first increases and then decreases with the increase of particle mass concentration, while in the simulations, the filter cake thickness first increases and then stabilizes with the increase of particle mass concentration. Under the same particle mass concentration, the filter cake thickness in both experiments and simulations slowly decreases and then stabilizes with the increase of inlet flow rate. As the particle mass concentration increases, the thickness uniformity of the filter cake first increases and then tends to be stable after reaching the saturation concentration. As the inlet flow rate increases, the thickness uniformity first increases, and then significantly decreases after reaching the critical flow rate. Based on the comprehensive analysis of the thickness and thickness uniformity of the filter cake under various conditions, the operating flow rate of the filter in actual irrigation should not exceed 200 m³/h.

Abstract:Based on the moving particle semi-implicit (MPS) method, an equivalent momentum transfer method was developed to solve the interaction between fluid and rigid structures, and the solitary wave generation was numerically simulated using the water level difference method and box-dropping method. In this method, the structure is discretized to rigid body particle groups, which are replaced by corresponding fluid particle groups. After solving the momentum equation of the single-density fluid in the entire domain, the momentum obtained by these fluid particle groups is transferred to their corresponding rigid particle groups, and the initial geometric configuration of the rigid body is restored, thus completing the dynamic coupling motion process between the fluid and structure. The numerical simulation results show that the flow field change near the structure, wave propagation, and structural motion during the solitary wave generation process simulated by this method are in good agreement with the results of physical modeling experiments. Compared with the box-dropping method, the water level differences method can generate solitary waves with greater height and faster propagation speed, but it needs more time to generate stable solitary waves.

Abstract:In order to effectively cope with the over-standard floods from the Taihu Basin and to coordinate the basin flooding and regional flood control safety, a hydrological and hydrodynamic mathematical model for the refined river network pump gate scheduling in the mainland region of Shanghai was constructed. Through multi-scenario numerical simulations of rainstorm and flood events, an optimal flood scheduling strategy was proposed using the entropy-weighted TOPSIS evaluation method to ensure flood safety in megacities. The results indicate that when over-standard floods in the Taihu Basin coincide with heavy or moderate rainfall events in Shanghai, a conditionally feasible basin diversion strategy can be implemented to achieve the optimal coordinated dispatching goal for both flood control and urban drainage.

Abstract:In order to enhance the predictability of seasonal streamflow, numerical weather prediction was coupled with the Xin’anjiang model, the distributed hydrological soil vegetation model (DHSVM), and the long short-term memory model (LSTM) for ensemble forecasting of monthly streamflow in the Jiaojiang River Basin from 2012 to 2020. Three different methods, namely, equal weighting, unequal weighting, and BP neural network-based weighting, were employed to fuse the outputs from the three models. Comparison was made between the fused forecasts and the optimal forecasts of single models. The results indicate that the BP neural network fusion method significantly enhances the forecasting accuracy, demonstrating superior performance over other methods. Notably, this method substantially extends the effective forecast lead time across all four distinct seasons (spring, summer, autumn, and winter), thereby providing more reliable hydrological predictions for water resources management and utilization in the basin.

Abstract:In order to accurately predict the peak discharge of earth-rock dam failure, a database containing 156 cases of earth-rock dam failure was established. Based on the failure process and correlation analysis, the dam type, failure mode, the height of water above the breach, and the volume of water stored above the breach were selected as control variables. Considering the constraints of limited available data and the difficulty in obtaining dam failure data, a conditional tabular generative adversarial network (CTGAN) was used to augment the earth-rock dam failure data, so as to increase the diversity of samples, enrich the model training information, and improve the generalization ability. Based on the augmented data, a peak discharge prediction model was constructed using the CatBoost algorithm. The results show that the model based on the augmented data achieves higher prediction accuracy, with a coefficient of determination reaching 0.93, demonstrating excellent prediction performance. Combined with the shapley additive explanation (SHAP) analysis, it is found that the volume of water stored above the breach has the most significant impact on the peak discharge, followed by the height of water above the breach.

Abstract:In order to solve the problem that current machine learning-based dam safety monitoring models cannot give the explanation of the model prediction, the Shapley additive explanations (SHAP) value theory was introduced, and combined with the light gradient boosting machine (LightGBM) model, an interpretable safety monitoring model for concrete gravity dam deformation was established. The model can quantify the specific contribution of each impact factor. The verification results of an engineering example show that the model considers the complex nonlinear relationship between deformation and the environmental quantities, which is closer to the real situation, and it not only has good fitting accuracy and prediction accuracy, but also can interpret the model globally and locally.

Abstract:To address the issue that a single geophysical exploration technology cannot accurately locate local seepage in earth-rock dams, through combining the surface wave method and high-density electrical method to transform multi-source original exploration data into resistivity, an integrated geophysical information fusion technology was proposed using principal component analysis. A physical model experiment was conducted on a homogeneous earth-rock dam with three preset seepage hazard channels. By comparing and analyzing the localization areas of seepage channels identified by two single geophysical techniques and the integrated geophysical information fusion technology, the accuracy of seepage hazard localization of the integrated geophysical exploration technology was demonstrated, and the criteria for identifying seepage hazard areas were established. The integrated geophysical information fusion technology was applied to an earth-rock dam project with seepage problems, and the results indicate that this technology has the advantages of non-destructive detection, high efficiency, operational convenience, and clear results, and can achieve precise localization of seepage hazards.

Abstract:Based on measured data of Taihu Lake from 2005 to 2022, the Mann-Kendall test and BP neural network model were used to analyze the interannual variation characteristics of chlorophyll-a mass concentration and its synergistic response to hydrodynamic factors (water level, wind speed, precipitation), nutrient factors (total nitrogen, total phosphorus, CODMn), and thermal factors (air temperature, daylight duration, total radiation). The results show that the chlorophyll-a mass concentration has shown an upward trend since 2005, with the average mass concentration from 2015 to 2022 being about 95% higher than that from 2005 to 2014. However, the peak mass concentration of chlorophyll-a has exhibited a declining trend since 2020. The variation process of chlorophyll-a mass concentration shows the highest sensitivity to the synergistic effects of total radiation, water level, and air temperature. The thermal factors have the most significant impact on the variation process of chlorophyll-a mass concentration.

Abstract:In response to the diversity of planting structures in tropical regions and under the constraints of total water use control and the construction of agricultural “two zones”, a multi-objective optimization model was developed based on the water footprint theory to maximize both economic and ecological benefits. This model focused on the planting structures of four typical crops (rice, corn, fruit, and sugarcane) in three counties (or cities) in Xishuangbanna Prefecture, Jinghong City, Menghai County, and Mengla County, in the tropical region of Yunnan Province. The NSGA-Ⅱ genetic algorithm was used to solve the model, resulting in two sets of optimized schemes: one that maximizes the net economic benefit per unit of water and the other that minimizes the grey water footprint for optimal ecological benefit. Using the coupled entropy weight method and TOPSIS evaluation method, optimal agricultural planting structures were determined for the three counties (or cities). The optimization results show that reducing the corn planting area and increasing the fruit planting area by 18.8% to 57.4% in Xishuangbanna Prefecture can significantly reduce the grey water footprint and improve the net economic benefit per unit of water. In Menghai and Mengla counties, increasing the rice planting area by 13.6% to 67.7% did not reduce the net economic benefit per unit of water. Sugarcane can have its planting area appropriately expanded in Jinghong City and Mengla County, based on improved agricultural production conditions. After optimizing the planting structure, the net economic benefit per unit of water can increase by 13.0% to 62.0%, and the grey water footprint can decrease by 1.9% to 28.0%.

Abstract:Taking the gravity dam of the lower reservoir of a pumped storage power station as an example, according to the basic theory of the mode decomposition response spectrum method, the natural vibration characteristics and seismic response of the dam were calculated using the cantilever beam method. The dynamic responses such as natural vibration frequency, modal shape, acceleration, dynamic stress and anti-sliding stability were obtained, and the results were compared with those calculated using the finite element method. The results show that the relative error between the dam fundamental frequency values calculated by the cantilever beam method and the finite element method is 4.24%. Under the normal water level and design earthquake conditions, the distribution law of the dam acceleration along the river calculated by both methods is basically the same, and the relative error of the acceleration extreme value is 2.13%. The distribution patterns and extreme values of the vertical normal stress of dam after static and dynamic superposition obtained from both methods are similar. The safety factor of anti-sliding stability along the foundation surface calculated by the cantilever beam method is greater than that calculated by the finite element method. The dynamic response calculation of the cantilever beam method is simple, and the results are reasonable and reliable, which is of practical value for the rapid seismic safety analysis of gravity dams.