Abstract:Focusing on the characteristics of diversity, complexity, and linkage in the formation process of urban flooding disasters, the composition and formation mechanism of urban flooding disasters was analyzed, the uncertainty, instability, and non-uniformity characteristics of the urban flooding disaster risk were summarized, and the exposure, vulnerability, and fragility of the disaster-bearing bodies in the disaster-causing urban flooding were investigated. The applicability of H-V, H-E-V, and H-E-V-R frameworks in urban flooding disaster risk assessment was compared, the process of urban flooding disaster risk assessment was proposed, and the applicable conditions, advantages and disadvantages of historical disaster assessment method, index system assessment method, GIS and RS coupling method, scenario simulation assessment method, and multi-agent model evaluation method were investigated. It is pointed out that future risk assessment methods for urban flood disasters will evolve from qualitative analysis to quantitative evaluation, and the focus of assessment will shift from the flood disasters themselves to the disaster-bearing bodies.

Abstract:This paper reviews the research progress on the unique hydrodynamic and mixing characteristics in open channel confluence areas, focusing on the complex flow structures influenced by factors such as convergence ratio, intersection angle, bed elevation difference, and other parameters. Key features such as separation zones, shear layers, and secondary circulations are discussed. The paper integrates findings from physical model experiments, numerical simulations, and field observations, summarizing the current state of research on hydrodynamics and mixing characteristics. Based on existing challenges, future research should focus on the application of artificial intelligence algorithms, the effects of vegetation, density difference, and the hyporheic zone on mixing characteristics, and the impact of scouring and sedimentation in sediment-laden flow confluence issues.

Abstract:In view of the significance of cavitation water jet technology, this paper analyzes the generation and action mechanisms of cavitation water jets, and provides a review of the experimental and numerical research methods used in recent years, focusing on three aspects: flow field observation and analysis, erosion measurement, and numerical simulation. The research hotspots are summarized as nozzle structure design, development of observation and measurement methods, and optimization of numerical simulation techniques. Additionally, the paper proposes future directions, including improving the observation and measurement capabilities of cavitation water jets and using artificial intelligence technology to optimize numerical calculation methods, providing references for the research and application of cavitation water jet technology.

Abstract:In order to analyze the impact of the underlying surface changes caused by human activities on urban flood risk in plain areas, a hydrological-hydrodynamic model was constructed using MIKE 11 to analyze the changes of the underlying surface of the urban flood control encirclement of Jiaxing City from 1990 to 2020, and the corresponding urban flood process and its change characteristics were simulated using different underlying surface conditions as input conditions. The results show that the urbanization process was rapid from 1990 to 2020, with approximately 46% of the arable land converted to construction land, and the expansion of construction land has increasingly amplified the flood risk as the rainfall return period increases. Under a 50-year return period rainfall event, the highest flood level was 0.206 m higher than a 5-year return period event. Under the underlying surface conditions in 2020, 12.3% of the river channels were unable to meet the 30-year return period drainage standard. It is expected that flood threats will further intensify with continued urban development, and corresponding measures must be taken to enhance urban drainage capacity.

Abstract:To investigate the outflow characteristics of the trapezoidal sluice gate, a novel type of flat gate, model experiments and dimensional analysis were used to conduct experimental studies and theoretical analyses on the flow characteristics of submerged flow through the trapezoidal sluice gate. The experimental results indicate that when the submerged outflow occurs downstream of the trapezoidal sluice gate, the greater the degree of submergence is, the closer the contracted section is to the gate, the smaller the transverse water surface difference at the contracted section is, and the shorter the distance required for the transition from rapidly varied flow to gradually varied flow downstream of the gate is. Based on flow pattern analysis, combined with dimensional analysis and numerical fitting, the flow pattern discrimination criteria for the trapezoidal sluice gate were obtained, and an equation for calculating the submerged discharge was derived. The evaluation and verification of this equation show that the average relative error is within 5%, indicating a high level of calculation accuracy.

Abstract:Based on OpenFOAM, the dynamic behavior of the cavitation bubble near the defective wall surface was investigated using a compressible cavitation bubble dynamics model for two-phase flow. The results demonstrate that the depth and shape of defects significantly affect the dynamics of the cavitation bubble. Compared with rectangular defects, wedge-shaped defects are more likely to concentrate energy when the cavitation bubble collapses, which results in more intense collapse and higher peak wall pressure. With the increase in defect depth, the peak wall pressure caused by the first collapse of the cavitation bubble initially decreases and then remains almost unchanged, while the pressure peak caused by the second collapse of the cavitation bubble continues to decrease.

Abstract:A wave-flow coupled numerical model under the influence of salt marsh vegetation was established using Delft3D software to quantitatively analyze the water and sediment dynamics and sediment deposition processes in the Liaohe Estuary tidal flat wetland. The research results show that the simulated wave, tidal current, and suspended sediment results are consistent with the measured data. The suspended sediment concentration at each measurement point gradually increases from the surface layer to the bottom layer. Different salt marsh vegetation types, such as Phragmites australis and Suaeda salsa , have significant differences in their effects on the tidal flat flow velocity. During the spring tide period, Phragmites australis can more effectively attenuate flow velocity. Compared to Suaeda salsa , Phragmites australis has a more significant effect on the interception of suspended sediment and sediment deposition.

Abstract:In order to effectively protect long-distance, multi-undulation, and high-fall gravity-flow water pipelines, a hydraulic transition process calculation model was established for an actual project based on the wave characteristic method. The value closure laws without protection measures were analyzed, the protection effects of traditional common air valve and three-action air valve were compared, and the impact of the combination of the three-action air valve and two-stage valve closure on water hammer was investigated. The results show that without protective measures, the minimum pressure along the entire pipeline seriously exceeds the standard. After adopting the combination of the three-action air valve and two-stage valve closure, the minimum pressure head of the water pipeline can be maintained above -2 m. For long-distance, multi-undulation, and high-fall gravity-flow water pipelines, priority should be given to reducing the negative pressure in the pipeline. The use of the combination of the three-action air valve and two-stage valve closure can have a good control effect on the negative pressure in the water pipeline and in front of the valve.

Abstract:Based on the entropy generation theory, the hydraulic loss of each component of the pump-turbine is analyzed, and a local coordinate system analysis method is proposed to quantitatively analyze the spatial local loss of the runner under multidimensional conditions. The research results show that, under the operating conditions in the hump region, the hydraulic loss contributed by indirect entropy generation is the highest, accounting for 71%, the hydraulic loss contributed by direct entropy generation is the lowest, accounting for only 1%, and the hydraulic loss contributed by wall surface entropy generation accounts for 27%. The flow separation phenomenon at the runner inlet blade develops into separation vortices, leading to backflow near the shroud region, and a backflow phenomenon occurs in part of the vaneless area, resulting in a significant increase in indirect entropy generation. The decrease in head in the hump region is closely related to the significant increase in hydraulic loss, which is greatly influenced by the backflow effect near the runner inlet and in the vaneless area.

Abstract:In order to efficiently and accurately analyze and predict the flood discharge of the dam breach of a barrier lake, the basic principles of the DL Breach model were reviewed, and the flood discharge process of the dam breach of Tangjiashan Barrier Lake was inversely analyzed and compared with the measured discharge process. The results show that the DL Breach model is reliable and stable. The discharge process of the dam breach of Tangjiashan Barrier Lake calculated by this model is close to the measured value. The calculated peak discharge is 7 323 m³/s, which is approximately 11.2% higher than the measured value of 6 500 m³/s. The calculated peak discharge occurrence time is nearly 1.h earlier than the measured time, mainly due to the fact that the small stone beam at the breach of Tangjiashan Barrier Lake enhances the anti-scouring ability of the barrier body. In addition, an increase in material particle size will reduce the erosion of the breach and decrease the peak discharge, while an increase in material cohesion, upstream slope ratio and initial breach depth will reduce the bottom elevation of the breach, but has little effect on the peak discharge.

Abstract:Based on analysis of the monthly water consumption data from the national water resource management information system, the ARIMA model, the BP neural network model and the BP neural network model optimized by the genetic algorithm (the GA-BP neural network model) were used for monthly water consumption simulation. In the process of constructing the BP neural network model, the combined method of mean impact value algorithm (MIV) and Pearson correlation coefficients was used to screen the key influencing factors of monthly water consumption through the integration and analysis of multi-source socio-economic data. The research results show that all three models exhibit relatively high accuracy in the monthly water consumption prediction in Shaanxi Province, among which the GA-BP neural network model has the highest prediction accuracy. To further verify the impact of influencing factors on the simulation results, different methods were used to screen the influencing factors as the input of the GA-BP neural network model. The simulation results indicate that the combined method of MIV and Pearson correlation coefficients improves the selection accuracy of influencing factors and can effectively enhance the simulation performance of the GA-BP model.

Abstract:In order to optimize the water resources allocation in Taiyuan City, water supply and demand scenarios considering water-saving awareness and unconventional water resources were created, the NSGA-Ⅱ+ARSBX algorithm was used to solve the optimal allocation model of water resources, and an evaluation model of multi-system coupling coordination degree was constructed to evaluate the solving ability of this algorithm. Based on the results of water supply and demand prediction, appropriate water-saving awareness scenarios were selected according to the available water supply under different guarantee rates. In the allocation results, the average proportion of water supplied by unconventional water accounts for 26.08%, which is only lower than the proportion of water supplied by external transferred water (35.77%). The coordination degree of the NSGA-Ⅱ+ARSBX algorithm in different level years under different guarantee rates are more than 0.8, which is better than that of the NSGA-Ⅱ algorithm. Studies show that medium or even high water-saving awareness is needed to improve water resources shortage under the guarantee rate of 75% and 95%. Furthermore, unconventional water resources account for more than a quarter of the total water supply, and incorporating unconventional water resources into the water supply system can play a significant role in alleviating water resources scarcity. Compared with the NSGA-Ⅱ algorithm, the NSGA-Ⅱ+ARSBX algorithm has better feasibility in optimal allocation of water resources and can provide a new approach for solving the optimal allocation model of water resources.

Abstract:Aiming at the issue of slow water flow in the inland rivers of Ningbo City, which requires the improvement of hydrodynamic performance through the reclaimed water replenishment and pump gate operation scheduling, a two-dimensional hydrodynamic model of an inland river network in a certain area of Ningbo City was constructed based on measured topographic data. The model was used to simulate and analyze different engineering measures and combined operation conditions of various pump stations. The results show that excessive culverts and sluice gates, as well as insufficient water sources, limit the water exchange and overall flow in the river channels. Increasing the replenishment amount of reclaimed water cannot effectively improve the water mobility. Adding Pump Station No.1 and physically modifying key river sections can significantly increase the water flow velocity in originally stagnant river sections and improve the mobility of the entire water system, but attention should be paid to potential environmental and water quality impacts on river sections with different water qualities. Increasing the drainage capacity of pump stations significantly increases the river flow velocity and water level, but shortens the duration of high flow velocities. Simultaneously operating multiple pump stations and increasing water supplementation can significantly increase the water velocity of the entire river network. Especially under high water level conditions, although the flow velocities are relatively low, increasing the amount of supplemental water can still effectively improve the water mobility.

Abstract:In order to reveal the impact of the coupling effect of dry-wet cycles and erosion on the properties of solidified silt, dredged silt was solidified with soda residue, slag and carbide slag as solidifying agents. The appearance, unconfined compressive strength and damage of solidified silt were studied under the coupling effect of capillary infiltration wetting-drying cycles and erosion environments such as distilled water, seawater and magnesium sulfate, and the coupling action laws, mechanisms and optimal solidifying agent dosages were explored. The results show that the coupling effect of magnesium sulfate erosion and wetting-drying cycles results in the most serious appearance damage and the most significant reduction in strength of the specimens. Increasing the slag content can improve the durability of the solidified silt. When the slag contents are 20% and 15%, respectively, the soda residue content should not exceed 25% and 35%. The coupling effect of seawater and magnesium sulfate erosion with multiple wetting-drying cycles causes the specimens to quickly reach the damage and failure state with the increase of strain. The coupling effect of seawater erosion and wetting-drying cycles leads to the formation of more ettringite and NaCl crystals in the specimens. With the increase in the number of cycles, the NaCl crystals increase, the inhomogeneity of the specimens is enhanced, and the numbers of mesopores and macropores increase. The coupling effect of magnesium sulfate erosion and wetting-drying cycles results in the reduction of hydration products such as calcium silicate hydrate. Expansive CaSO₄·2H₂O precipitates when the soda residue content is too high, leading to a decline in the durability of solidified silt. The coupling effect of capillary infiltration wetting-drying cycles and erosion causes serious macroscopic and microscopic damages to solidified silt.

Abstract:Electrochemical dechlorination experiments based on the principle of galvanic cell were carried out on reinforced concrete with different water-cement ratios. The evolution of electrochemical parameters of reinforced concrete with different water-cement ratios over time was studied. The results show that the higher the water-cement ratio, the more negative the anodic operating potential at the initial stage of dechlorination, the larger the loop current, and the higher the dechlorination efficiency. The higher the water-cement ratio, the more obvious the positive shift of corrosion potential of the rebar after dechlorination, the greater the increase of polarization resistance, and the smaller the increase of OH^- concentration. After dechlorination, the contents of C-S-H gel and Friedel’s salt in concrete slightly decrease, while the content of Ca(OH)2 slightly increases, and a small amount of AFt and C-S-H gel decomposes.