At present, the issue on the influence of mixed arrangement of variable and constant speed units on the load rejection transition process under the complex water delivery system with multi-units sharing multi-tunnels is scarce. Based on the transient flow theory of one-dimensional pipeline, this paper established the mathematic model of hydraulic transition process of variable-constant speed pumped storage units that four units share two tunnels in the diversion system and one tunnel in the tailrace system by using the characteristic method, and discussed the influence of the mixed arrangement of variable and constant speed units on regulation guarantee parameters under the load rejection condition by combining with practical engineering examples. The results show that regulation guarantee parameters during the load rejection transition process under the layout of two variable speed units sharing one diversion hole are safer than those under the layout of variable speed units sharing different diversion holes in the region with higher power generation efficiency.

From the objectives, variables and relations of the time-varying linear confluence model, it can be seen that the model has some constraints such as static parameters and the inability to consider the influence of interval runoff, and there are significant defects in the application of flood prediction. Therefore, the time-varying linear confluence model is improved by combining the chaotic mapping with the rich model to solve the diversity and adding the influence operator to replace the interval runoff. Using the measured runoff data of Maoergai Hydropower Station in the Heishui River basin for many years, and taking the forecast process, flood volume, flood peak and peak time as the evaluation index, the application analysis of the improved time-varying linear confluence model is carried out. The results show that the overall prediction qualification rate of the improved model is increased by 9.13%, and the certainty coefficient is increased by 0.25, which expands the reliability and practicability of the application of the time-varying linear confluence model.

The phased trend recognition of deformation monitoring sequences for dams can deepen the understanding of the evolution laws of deformation monitoring sequences at different time scales, which is of great significance for the safe operation and management of dams. The heuristic segmentation algorithm (BG algorithm) is adopted to identify the mutation points of deformation monitoring sequences for dams, which can effectively avoid the interference of mutation points in trend recognition. On this basis, the segmented sub-sequences are trend identified using an improved ITA method, which can retain the internal correlation of the sequences and has good applicability. The engineering case analysis shows that the proposed method can effectively identify the mutation points in the deformation monitoring sequences for dams, divide the monitoring sequences into sub-sequences with stable trends, and identify the changing trends of each sub-sequence.

Aiming at the evolution of water resources in Qiandao Lake Basin under the condition of climate change, a WEP-L distributed hydrological model was established to simulate the water cycle process in the basin during 1960-2020. The Mann-Kendall non-parametric test method and Hurst index method were used to analyze the inter-annual variation and annual distribution characteristics of the total water resources in the basin. The temporal and spatial distribution and evolution trend of water resources in Qiandao Lake Basin were evaluated. The results indicate that The WEP-L model performs well in simulation the Qiandao Lake basin, and the Nash coefficient rate is above 0.83 in the calibration period and above 0.85 in the verification period; The water yield coefficient of the whole basin ranges from 0.436 to 0.630. The annual average total water resource is 122.5×10⁸m³, equivalent to 1 176.4 mm of water depth. The annual distribution process shows a unimodal structure, and the water depth of each sub-basin ranges from 742 mm to 1 266 mm, and the spatial distribution is higher in the west and lower in the east; The annual water resources series in the basin show an insignificant upward trend, and the Hurst index is 0.86, indicating a continuous upward trend. From the perspective of monthly water resources, January and February increased significantly, the other months were not significant changes.

In order to realize the reverse power generation operation of large-scale low-lift vertical axial flow pump, using electronic frequency conversion technology instead of mechanical frequency conversion technology, the high voltage four-quadrant frequency converter was applied to Huaiyin second station reverse frequency conversion power generation, and the grid-connected scheme and variable frequency control strategy were analyzed. At the same time, the on-site transformation was carried out to realize the stepless speed regulation of the pump power generation operation. The pump unit can be automatically tracked according to the operating conditions of optimal generating speed to achieve the maximum generating power and maximize the benefit.

Early freezing of concrete is common in the construction of water conservancy projects in northern China. Early freezing damage induces the deterioration of mechanical properties of concrete structures, which seriously affects the safety, stability and service life of engineering structures. Through laboratory uniaxial compression test and CT scan test, the influence law of freezing time and freezing temperature on the mechanical properties of concrete was analyzed, the three-dimensional pore structure of concrete at different freezing time was reconstructed, the pore distribution and pore structure characteristic parameters of concrete at different freezing time were studied, and the correlation analysis between mechanical properties and pore structure of early frozen concrete was carried out. The results show that with the delay of freezing time, the porosity of concrete test blocks increases first and then decreases, the average pore surface area decreases first and then increases, the average pore diameter increases with the trend of quadratic parabola, and the average pore shape factor increases first and decreases then increases and decreases. The correlation between the average pore surface area and the compressive strength and elastic modulus of early frozen concrete is the best. It is suggested that the average pore surface area should be preferred to construct the mesoscopic damage index of early frozen concrete. Relevant research results provide support for revealing the macro and micro damage mechanism of early frozen concrete.

The friction factor of pipeline is a key parameter in the design calculation, operation scheduling optimization and fault diagnosis of water supply system. In order to determine this parameter accurately, an intelligent back-analysis method of pipe section friction factor based on dynamic search fireworks algorithm (dynFWA) coupled with hydraulic calculation model of pipe network was proposed. The partial derivative relationship between node water pressure and friction factor was taken as the node sensitivity. In the improved genetic algorithm, the maximum sum of node maximum sensitivity was taken as the goal to optimize the layout of monitoring points. Based on the optimized water pressure monitoring value at the monitoring point, the dynFWA algorithm was used to inverse the friction factor of each pipe section with the objective of minimizing the average double error between the water pressure monitoring value and the calculated value. In order to verify the inversion performance of dynFWA algorithm, the inversion of friction factor by dynFWA algorithm and particle swarm optimization (PSO) algorithm were compared. The results show that the maximum relative errors of the inverse value of the friction factor are 17.7% and 0.7% before and after the optimization of the monitoring points, which proves the necessity of the monitoring point selection and the superiority of the improved genetic algorithm for the monitoring point selection. Under the condition that the water pressure at the monitoring node is added to noise, the relative errors of the friction factor inversion results based on the dynFWA algorithm and the PSO algorithm are 9.67% and 14.33% respectively, and the maximum relative errors between the actual water pressure value and the simulated water pressure value at the monitoring point are 0.358% and 0.655%, which proves that the dynFWA algorithm has higher accuracy in the parameter inversion problem compared with the PSO algorithm.

Aiming at the shortcomings of slow convergence and easily falling into the local minimum in the learning process for the traditional BP neural network, particle swarm algorithm with fast convergence speed and strong global optimization ability was introduced so as to establish the PSO-BP model. Taking the seepage monitoring data of an earth and rockfill dam as an example, the seepage was predicted. Compared with the prediction model, the BP model and the traditional statistical regression model, the results show that the PSO-BP model has a higher goodness-of-fit and convergence.

The design of culverts in hydraulic engineering involves many common and repetitive tasks. In order to achieve the parametric application of BIM design in culvert engineering, this study has carried out the research on the parametric modelling method of culvert engineering based on Revit platform, and developed a parametric modelling system for culvert through secondary development of Revit according to the relevant technical specifications. By inputting specified parameters, the system can complete the model building, calculation, and drawing, which greatly improves the efficiency of culvert engineering design. The research results achieve a high standard of engineering parametric design, which can provide technical reference for BIM parametric design of similar projects.

In order to study the mechanical characteristics such as fracture mode, crack propagation characteristics, and strength characteristics of intersecting multi-fractured rock masses in uniaxial compression tests, the particle flow program was used to simulate the mechanical characteristics of intersecting multi-fractured rock masses in uniaxial compression tests. The impact of the angle between intersecting cracks on the strength characteristics, failure mode, microcrack development and evolution law of multi-fractured samples during uniaxial compression was analyzed. The experimental results show that the failure strength of the cross multi-crack specimen exhibits a slow bottom "U" shaped characteristic with the increase of crack angle; The failure mode of intersecting multi-crack specimens is mainly tensile shear failure, with some specimens exhibiting shear failure; The failure process of intersecting multi-crack specimens first involves the generation and intersection of cracks between the tips inside the cracks, followed by the generation of cracks at the outer tips of the cracks and their transmission parallel to the loading direction to both ends of the rock mass, ultimately leading to macroscopic failure of the rock mass. The results of this study contribute to the understanding of the mechanical mechanism of cross fissured rock masses in compression failure, and are a supplement to the research on the mechanical properties of cross fissured rock masses.