Abstract:Major research results achieved in China during the past recent years were systematically reviewed and summarized from four aspects, including main analysis methods and main evolution laws of river runoff, main attribution methods and main attribution analysis of river runoff, case study analysis, as well as the regional distribution characteristics of the main runoff evolution laws and runoff attribution analysis in China. The results show that the Mann-Kendall non-parametric trend test method is a commonly used method for analyzing runoff evolution law. Hydrological modeling method, statistical analysis method, and the coupled energy-water balance equation based on Budyko hypothesis are commonly applied methods for attribution analysis of runoff changes, among which the coupled energy-water balance equation based on Budyko hypothesis is widely employed. Except for the rivers in the northwest regions and southwestern rivers showing an increasing trend, the runoff of major rivers in other regions of China is decreasing. Human activities are the main cause of runoff variations for major rivers in China.

Abstract:Based on regional water balance theory and SWAT model, the construction idea of distributed water budget balance model and calculation method of water budget balance were proposed. The water budget balance of the Qinhe River Basin was simulated under human activities and future climate change, and the main factors affecting the water budget balance and its evolution patterns were analyzed with the Pearson correlation coefficient and Mann-Kendall test method. The results show that the total water storage in the Qinhe River Basin decreased from 2010 to 2016, and precipitation and outlet runoff are the key factors affecting the water budget balance in the Qinhe River Basin. In the future, the total water storage will increase under multiple climate scenarios, and the overall changes of annual mean precipitation and outlet runoff are positively correlated with the radiative forcing level. Under the typical climate scenario SSP2-4.5, the precipitation and outlet runoff may have abrupt changes from 2037 to 2041 and from 2061 to 2063.

Abstract:In order to study the effect of fluid viscosity on the flux during salt-finger double diffusion convection, an experimental tank with a moving baffle plate in the middle was used. The sugar-salt double-layer system was formed and was initially stationary. The experimental study for double diffusion convection flux was carried out by adjusting the mass fractions of the sugar and salt components to obtain a series of experimental conditions with the same density stability ratio and different fluid viscosities. The experimental results show that the influence of fluid viscosity on the flux of salt-finger double diffusion convection could not be ignored. Under the condition of the same double diffusion convection intensity, the greater the viscosity of the experimental fluids, the smaller the fluxes for the salt-finger double diffusion convection. When the kinematic viscosity coefficients of experimental fluids are less than 1.15 mm²/s, double diffusion convective fluxes of sugar and salt decrease with the increase of the fluid viscosities. When the mass fractions of the two component continue to increase, the viscosity of the salt solution still increases slowly while the viscosity of the sugar solution increases rapidly. The flux of sugar component between the stratified interface still decreases with the increase of the sugar solution viscosity. However, the flux of the salt component does not change. The Stern number is negatively correlated with the viscosity of the fluid.

Abstract:Aiming at the adverse effects of wall concrete spalling, effective cross section reduction and water quality deterioration due to the phenomenon of biological fouling occurring frequently in Chinese water diversion projects, based on water diversion project in the middle route of the South-to-North Water Diversion Project, laboratory model experiments were carried out under different area ratios, and porous media domain was used to simulate the three-dimensional flow field of a pressurized pipeline under biological attachment dominated by limnoperna fortune.The influence of limnoperna fortunei attachment on the flow capacity of the pressurized pipeline was analyzed.The results show that the flow in the pressurized pipe presents the main flow deviation, and the particle momentum exchange near the wall is more intense.Section roughness was positively correlated with the attachment thickness and the area ratio.At low density, the main influencing factor was the attachment number of limnoperna fortunei.At high density, adhesion thickness is the main factor.

Abstract:In order to explore the influence of mineralization on clay permeability, clay was treated by induction of mineralization through Sporosarcina kp-22. The carbonate formation rate of clay after treatment was measured and the clay permeability characteristics were studied. The permeability coefficient variation with the OD₆₀₀ of bacteria, the concentration of cementation solution and cadmium content were investigated. The influence rule and mechanism of each factor on permeability coefficient were discussed. The empirical formulas to calculate permeability coefficient of clay after mineralization considering the OD₆₀₀ and concentration of cementation solution were established. The results show that carbonate crystal was formed in the mineralized soil samples, which can fill some pores in the soil, and the permeability coefficient of clay can be reduced by at most one order of magnitude. With the increase of OD₆₀₀, the carbonate formation rate in mineralized soil first increased and then gradually stabilized, but the permeability coefficient first decreased and then tended to be stable. When the OD₆₀₀ was greater than 0.9, the carbonate formation rate and the permeability coefficient changed little. With the increasing concentration of cementation solution, the formation rate of carbonate first increased and then decreased. On the contrary, the permeability coefficient first decreased and then increased. When the concentration of cementation solution was 0.8 mol/L, the permeability coefficient was the lowest. With the increasing cadmium content in soil, the mineralization reaction was inhibited and the permeability coefficient increased gradually. Permeability coefficient after mineralization is negatively correlated with carbonate formation rate, which satisfies a linear relationship. The calculated coefficients of the empirical formulas established for permeability coefficient of clay after mineralization agree well with the experimental results.

Abstract:Aiming at the problems of diversified maintenance operations, numerous risk factors, and frequent safety accidents in hydropower station units, the safety factors affecting the maintenance operations of hydropower station units are classified through literature mining and expert interviews.Based on the DEMATEL-ISM method, a multi-level hierarchical ISM model of safety accident causes was constructed to determine the level of accident causes. By analyzing the centrality and weight of accident causes, mining the key causal factors and deriving the path weights of the accident causal chain, the key causal chain was determined. The model was used to analyze the key causal chain of a hydropower station as an example. The results show that inadequate safety inspections are the key cause factor, and the key causation chain is inadequate safety inspections→illegal operations→equipment problems→dusts, paints, and other harmful substances.

Abstract:In order to optimize the capacity configuration scheme for a hydro-photovoltaic complementary clean energy base, a comprehensive evaluation index system was constructed by selecting 14 indicators from the 4 aspects of safety, environmental protection, economy, and technology. An improved cloud model method was used to evaluate the capacity configuration scheme. The improved cloud model based on analytic hierarchy process was used to solve the subjective weights, the entropy weight method was used to solve the objective weights, the combined weighting was used to obtain the indicator weights, and then a conditional cloud generator was used to calculate the membership degree of each indicator. Finally, based on the level eigenvalue method, the capacity scheme rating was calculated to determine the optimal scheme. The method was applied to the optimization of the capacity configuration scheme for a hydro-photovoltaic complementary clean energy base in Southwestern China. The optimization results are consistent with the set pair analysis method and the actual selection scheme, proving the effectiveness and applicability of the method.

Abstract:In order to quantify the impact of the Guxian Reservoir’s participation in the joint operation of cascade reservoirs on key and non-key multi-objective benefits, including water supply, power generation, water-sediment regulation and ecology, in the middle-lower Yellow River, two scenarios with and without the Guxian Reservoir in 2030 were set. Based on the theory of multi-objective synergetic optimal operation of cascade reservoirs, the multi-objective synergetic optimal operation model by cascade reservoirs in the middle-lower Yellow River was constructed and solved.The response of multi-objective benefits in the middle-lower Yellow River to the joint operation of the Guxian Reservoir under the background of runoff reduction and comprehensive water demand growth in the future was analyzed. The results show that, compared with the scenario without the Guxian Reservoir, the total synergetic degree of the reservoir system with the Guxian Reservoir operation increased slightly, the order degree of subsystems of water supply and power generation increased,the average annual water shortage in the critical period and non-critical period of agriculture decreased,the average annual power generation of cascade reservoirs increased. In addition to a slight decrease in the frequency of water-sediment regulation, the key and non-key benefits of ecology and water-sediment regulation increased in the scenario with the Guxian Reservoir.

Abstract:To study the influence of nonlinear contact between structure and anchored rock mass on the seismic performance of a lock head under earthquake, taking the first stage lock head of a double-line five-stage ship lock as an example, a three-dimensional finite element model for the dynamic interaction of reservoir water-structure-anchor-bedrock was established in the finite element software ADINA. The various contact problems in the lock head structure were simulated by the nonlinear contact elements based on constraint function. The dynamic responses of the lock head structure, the distribution law of the anchor force, and the contact state of different contact surfaces under the design earthquake were analyzed by time-history analytical method. The results show that the piers on each side of the lock head are deformed to the side of the navigation channel under the design earthquake, and the displacement increases along the height direction. The maximum axial tensile stress of the anchor is less than its tensile strength. The upper parts of the contact surfaces between different contact pairs are repeatedly opening and closing. The maximum opening of the contact surface increases with elevation. At the end of the earthquake, the contact surface is restored to the state before earthquake. Therefore, the structural deformation, structural stress, anchor stress and contact surface contact state of the lock head all meet specification requirements under the design earthquake with good seismic capacity.

Abstract:To investigate the effect of calcium carbonate whiskers on the shrinkage properties of cement paste, dry shrinkage, chemical shrinkage and autogenous shrinkage of specimens with three kinds of water cement ratios were tested at different ages, respectively. The phase composition and pore structure changes of the autogenous shrinkage specimens were characterized using X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP), respectively. The results show that calcium carbonate whiskers have the characteristics of adsorbing and transferring free water in cementitious materials. Under different water cement ratios, calcium carbonate whiskers exhibit different effects on drying shrinkage, and the degree of influence shows a trend of initially increasing and then decreasing with the dosage of calcium carbonate whiskers. The chemical shrinkage shows a tendency of increasing and then decreasing with its dosage. Calcium carbonate whiskers can significantly improve the self-shrinkage, especially the early autogenous shrinkage, and the increase of the water cement ratio makes the improvement of the early autogenous shrinkage by calcium carbonate whiskers more significant. The whiskers refine the pore structure without generating new hydration products.

Abstract:In order to solve the problems of short construction period, large engineering quantity and high construction requirements of the upstream cofferdam for the Julius Nyerere Hydropower Station in Africa after the river closure, a high-efficiency filling technology for composite cofferdam is proposed. Five efficient filling construction processes and key technologies have been focused, including bottom water-rushing concrete pouring, rockfill concrete pouring on the left bank, downstream prefabricated block formwork construction, upstream clay impermeable layer leveling construction, and main cementitious sand and gravel metamorphosis rolling construction. Engineering practice shows that the new high-efficiency filling technology for composite cofferdam can greatly optimize the construction organization and efficiency, and finally completes the safe, efficient and high-quality construction of the cofferdam before the flood season arrives.

Abstract:To scientifically explain the mechanism of piping disaster and reveal its formation, evolution process and burst law on the basis of considering the action of loam transition layer between the strong and weak permeable layers of dike foundation, the whole process of piping of a binary dike foundation structure from single bubble spring to piping group and finally resulting in collapse of dike foundation was completely simulated by indoor model test. The results show that the overlying soil layer uplifts upward under the jacking effect of seepage and produces horizontal channels between layers inside the dike foundation, leading to submerged sand boiling and eventually develops upward to the seepage failure of surface sand boiling. The piping development of binary dike foundation structure can be divided into six stages, including crack development, latent layer failure, overlay damage, upward development of piping channel, damage of dike foundation and dike break.The surface sand boiling is developed from the submerged sand boiling. The submerged sand boiling is caused by the damage of the soil structure induced by the seepage force due to the vertical slope in the soil layer greater than the floating bulk density of the upper soil. The critical vertical slope is between 0.9 and 1. The existence of loam layer accelerates the development of piping group in the free boundary area behind the dike, but it can delay the upstream of piping channel and protect the dike foundation.

Abstract:Aiming at the problem of monitoring and identification of dike piping phenomenon, a method for dike piping identification based on the YOLO model was proposed. A Piping YOLO model based on region of interest (ROI) extraction was proposed to improve the performance of YOLO v3 network by introducing improved residual block and activation function of replacement model. After the ROI was extracted, the two-dimensional principal component analysis method was used to extract the characteristics of piping phenomenon, which was used as the input of multi-weight neural network to realize the classification and recognition of piping state through training. The experimental platform of dike piping was built, and the data set was established to verify the effectiveness of the proposed method. The results show that the proposed method can effectively identify the phenomenon of dike piping, and has a certain application prospect in the field of unmanned inspection of dike piping.