In view of the uncertain factors of natural inflow and electricity price during participating in bilateral transactions at different time scales for cascade hydropower plants, there are problems of market share determination, water resources utilization and profit risk since electricity allocated irrationally. Therefore, this paper presented a risk-based optimal combination model of medium- and long-term contract electricity for cascade hydropower stations. To realize the goal of the minimum profit risk under a given confidence, the monthly inflow process was randomly generated by annual inflow data. Three electricity price functions were fitted by different proportions of hydropower stations in the market. The combination of power output and contract electricity of cascade hydropower plants were solved by the loop-Iteration method of hybrid progressive optimization with successive approximation method. The model was demonstrated using the hydropower plants in the southwest region. The results show that proposed model can determine the declaration strategy between monthly and annual bilateral contract electricity, and reduce the profit risk. It can provide reliable basis for bilateral transactions at different time scales of cascade hydropower plants.

To determine the key water quality indicators for influencing the Weihe River tributaries of Chanhe, Bahe, Fenghe and Zaohe Rivers and the minimum water quality index (W_WQImin) is of great significance for simplifying water quality evaluation. The research set up a total of 30 sampling points in the 4 rivers and collected water quality samples in April, August, and December 2019, respectively. Fifteen water quality indicators were analyzed by laboratory experiment and mathematical statistics. It was found that the content of DO in Fenghe River was obviously highest, and the contents of EC and nitrite in Zaohe River and the Bahe River reach after the convergence of Chanhe River were higher than other rivers. In addition, based on 15 water quality indicators, the water quality index (W_WQI) was calculated to evaluate the temporal and spatial changes of water quality of the 4 rivers. This study shows that the water quality indices were generally above the medium level (W_WQI≥51) in all four rivers, and the water quality of the Fenghe River was better among the four rivers. On time scale, the water quality in the spring of 2019 was better than the other two periods. Besides, stepwise multiple linear regression analysis and empirical method were used to determine the appropriate minimum water quality index (W_WQImin), which contains DO, ammonia nitrogen, COD_Mn, turbidity, nitrate nitrogen, $\mathrm{SO}_{4}^{2-}$, and EC. Compared with the W_WQI based on 15 water quality indicators, the relative error (P_PE) is only 4.78%, the linear correlation coefficient R² reaches 0.95, and the root mean square error (R_RMSE) is only 3.99. Finally, the spatial and temporal distribution of W_WQI and the appropriate W_WQImin in the 4 rivers are consistent. Therefore, it can be considered that the selected appropriate W_WQImin can be replaced of WQI, which is more efficient for time-saving, low-cost and high-efficiency water quality evaluation in the basin near the Chanhe, Bahe, Fenghe and Zaohe Rivers.

In order to analyze the flow characteristics of the plane S-type axial extension tubular pump unit, the software CFX was used to conduct three-dimensional full channel numerical simulation, and the energy gradient theory was used to analyze the flow characteristics of pump unit under different working conditions. The results show that under different flow conditions, the water flow in the inlet passage of the plane S-type axial extension tubular pump is very smooth, and the overall difference is small. The flow pattern in the outlet channel is quite different, and the smaller the flow rate is, the worse the flow pattern in the outlet channel is. The pressure pulsation at the same position in the plane S-type axial extension tubular pump unit is the largest under low flow conditions. The difference of energy gradient in the outlet channel is the largest under the condition of small flow, which indicates that a large energy loss will occur in the outlet channel under this condition. When designing the outlet passage of the plane S-type axial extension tubular pump unit, the length of the smooth section of the outlet passage should be increased as much as possible to ensure the uniform distribution of energy gradient. The research results can provide theoretical guidance for better understanding of the plane S-type axial extension pump device and optimization design.

In order to improve the prediction accuracy of ultra short-term wind power, a combined wind power prediction model based on IEWT-FE-BO-LSTM was proposed. Firstly, an improved empirical wavelet decomposition (IEWT) was used to decompose the historical wind power data. The Fuzzy Entropy (FE) algorithm was introduced to calculate the complexity of each decomposed submodel and reconstruct the submodel. For each recostructed component, a prediction model based on long short term neural network (LSTM) was established. Bayesian optimization algorithm (BO) was used for hyper parameters to solve the problem of poor training results caused by manual parameter adjustment. The example analysis based on historical wind farm data shows that the IEWT-FE-BO-LSTM model has high prediction accuracy and efficiency for ultra short-term wind power.

Coral sand is an important material for island and reef engineering construction. Its physical and mechanical properties in different marine environments directly affect the design, construction and long-term operation of island and reef structures. In order to study the shear mechanical properties of coral sand under the influence of temperature and salinity, the triaxial drainage shear tests of coral sand in the South China Sea were carried out at different temperatures and salinity by using the self-developed temperature controlled pile-soil interface triaxial tester. The results show that similar to ISO standard sand, the shear stress-strain curves of coral sand have peaks, presenting its characteristics of strain softening; The shear strength of coral sand is not significantly affected by temperature, but it is sensitive to salinity. Compared with fresh water environment, the peak shear strength of coral sand in salt water environment decreases by 2.5%-8.5%, and the lower of confining pressure, the greater of decrease range; Salinity has a deterioration effect on the cohesion of coral sand, and its reduction range is about 30%, but the effect on the internal friction angle of coral sand is not obvious.

The internal defects of rock mass have a significant effect on its mechanical properties and damage and fracture. The influence of fissure angles and bridge lengths on rock mechanical properties and failure was analyzed by uniaxial compression test and DIC technique. The research findings are as follows: The peak stress and elastic modulus of the samples have an obvious change trend with the change of the fissure angle. Compared with the length of the rock bridge, the fissure angle has a more significant effect on the mechanical properties of the rock. With the increase of fissure angle, the number of surface cracks, main failure cracks and surface spalling decreases, while the area of falling blocks increases obviously. However, with the increase of bridge length, the characteristics of crack propagation and spalling are basically the same. In the process of crack propagation, the connection of rock bridge is related to the fissure angle and the length of rock bridge. In the low fissure angle, the failure mode of rock samples is dominated by tensile failure cracks; With the increase of the fissure angle, the performance is as follows: the tension damage crack to shear damage crack transformation to form a mixed tensile shear damage mode; At the same time, with the increase of bridge length, the more difficult the rock bridge is to penetrate, and the local crack expansion failure changes from tensile-shear crack to tensile crack.

In order to optimize the dispatching mode of Luntan hydropower plant, the process of socio-economic and ecological water demand in the downstream were analyzed. Considering the downstream water demand, the monthly generation dispatching function were extracted from the results of optimal generation dispatching by use of stepwise regression method. The results show that the dispatching of Luntan reservoir plays a great role in the downstream water demand process. The main period of water replenishment is from July to the following February, which directly changes the process of power generation diversion flow of Luntan hydropower plant. The NSE coefficients of the generation dispatching function of Luntan hydropower plant based on multiple linear regression model and BP neural network are greater than 0.90 in most months. Considering the advantages of simple structure and convenient implementation, the generation dispatching function based on multiple linear regression model is selected for Luntan hydropower plant. Compared with the results of actual dispatching and dispatching diagram of Luntan hydropower plant, the generation capacity of the dispatching function is increased by 338.4×10⁴ kW·h/month and 183.8×10⁴ kW·h/month from March 2017 to February 2019, respectively. As a result, the water level of Luntan Reservoir can be significantly increased by use of the dispatching function. The research can provide a support for the generation optimal dispatching process of Luntan hydropower plant, and provide a useful reference for many other hydropower plants to improve the practical way of the generation dispatching.

To study the evolution law of member properties of hydraulic concrete materials under the coupling effect of freeze thaw cycles and salt erosion, early frozen specimens with different air-entraining agent admixtures (0, 0.005%, 0.01%) were selected and placed in a composite solution with a mass fraction of 3.5% sodium chloride +5% sodium sulfate for freeze-thaw cycle tests. Based on nuclear magnetic resonance (NMR)-fractal theory, the coupling relationship between the fractal dimension of the concrete pore volume and the damage degree of the specimens was constructed. The results show that the addition of air-entraining agents in concrete materials in appropriate amounts can effectively improve the mechanical properties such as elastic modulus and compressive strength of the members under the effect of salt freezing, and can improve the pore structure and frost resistance. The fractal dimension of concrete pore volume tested by nuclear magnetic resonance gradually decreases with the increase of freeze-thaw cycles, which indicates that the addition of air-entraining agent can change the internal pore structure of concrete in the initial state, and the effect is more obvious with the increase of air-entraining agent mixture. The correlation model between fractal dimension of pore volume and compressive strength was established by combining fractal theory, and the best functional relationship between fractal dimension D_MAX and compressive strength was found to be approximately exponential function. The regression coefficients R² is greater than 0.85, and the fitting effect is ideal, which provides a reference for durability assessment of concrete structures.

The safe and economic support of pressure tunnel under the condition of high head and low crustal stress has always been a difficult design problem in water conservancy and hydropower projects. Based on the diversion and power generation pressure tunnel of Coca Codo Sinclair hydropower station in Ecuador, the combined support type of steel lining and reinforced concrete permeable lining was adopted within the framework of the Norwegian guidelines. The coupling theoretical model of steel lining and reinforced concrete permeable lining considering the influence of crustal stress was constructed to determine the starting point of steel lining. Based on the three-dimensional seepage field analysis, the optimal grouting depth and pressure of reinforced concrete permeable lining of high-pressure tunnel were determined. The analysis of monitoring data during operation shows that the selection of various indexes of the combined support of the pressure tunnel is appropriate. This study effectively solves the problem of safe and economic support of high head and low crustal stress tunnel, and ensures the safety and stability of pressure tunnel structure.

Taking 16 cities and prefectures in Hubei Province as the research object, from the perspective of unexpected output, DEA-SBM model was used to calculate the water environment governance efficiency from 2014 to 2018. Combined with GIS spatial analysis method, the temporal and spatial variation characteristics of urban water environment governance efficiency were explored, and the influencing factors of urban water environment governance efficiency were analyzed by multiple linear regression model. The results show that the efficiency of urban water environmental governance in Hubei Province has rising trend, but there is a difference in time-order changes in water environmental governance between different cities; The efficiency of urban water environment treatment in Hubei Province shows a spatial distribution trend of low in the central region and high in the eastern and western regions; The level of infrastructure and environmental regulation have a significant positive impact on urban water environmental governance, and urbanization level has a significant negative impact on water environmental governance efficiency.