Aiming at the impact of large-scale ecological water replenishment (four times of ecological water replenishment in Beijing section of Yongding River) on the long-term cut-off river, a MIKE 11 hydrodynamic model was established. The variation characteristics of runoff and infiltration capacity before and after water replenishment were quantitatively evaluated by scenario simulation analysis. The results show that the inflow runoff sequence of Guanting Reservoir can be divided into three stages: natural stage, human weak interference stage and human strong interference stage. During the three ecological replenishment periods from 2019 to 2020, the flow of the main section of the Beijing section of Yongding River is much larger than the ecological flow of human strong interference stage. In the autumn of 2021, the loss of permeability coefficient and leakage of ecological water supplement was the lowest, indicating that the leakage of Yongding River was significantly reduced through three consecutive years of large-scale ecological water supplement. Taking the ecological replenishment in autumn of 2021 as an example, the fitting functions of channel storage and replenishment flow, submerged area and replenishment flow, submerged area and channel storage, permeability coefficient and replenishment flow were established, which can provide some guidance for the development of ecological replenishment in Yongding River. The results of this study can effectively guide the optimization and formulation of ecological water supplement scheme in the Beijing section of the Yongding River, and provide reference for the comprehensive management of the Yongding River Basin and the exploration of ecological restoration of long-term river courses in North China.

The change of channel storage capacity is an important content of river evolution analysis. In the past, the section method was mostly used for simplified calculation. However, in the complex river pattern with multistage branching or tributaries, the section method often needs to be dealt with separately, and the calculation efficiency is low. By introducing the water surface width ratio of the branching channel, optimizing the distribution of the calculated area of the section at the branching point, adding the section, estimating the storage capacity of the channel in the missing section near the tributary estuary, and using the topographic method to restore the section spacing under different water levels, the calculation model of the section method under the complex river pattern is improved. The comparison results show that the calculation accuracy of tank storage capacity is greatly improved by using the above method, which can provide a reference for batch calculation of tank storage capacity under various complex river types.

Flow and sediment are the driving force and material basis for shaping the riverbed. The process of flow and sediment changed by the operation of Three Gorges Reservoir leads to severe riverbed adjustment downstream of the dam. This paper selects the straight-braided channel-Bailuoji as typical which locates in the middle reaches of the Yangtze River, and analyzes the channel development characteristics from perspectives of channel storage capacity, beach-trough scouring and silting and branch channel diversion capacity variation after the impoundment of the Three Gorges Reservoir. Combined with the change in the duration of floods above the channel forming discharge, the impact of the flow process change on the development of the Bailuoji Reach is quantitatively calculated. The results show that in recent years, the channel storage capacity of the Bailuoji reach has increased and scouring mainly locates in the low-flow channel. The right branch is the main branch and the diversion ratio has increased under the low-discharge. The flow and sediment conditions after the impoundment of the Three Gorges Reservoir can maintain the development of the main branch of the Bailuoji reach. Compared with the flow process without reservoir regulation and storage, the duration of high flow above the channel forming discharge is relatively shortened under the current dispatching mode, the total amount of erosion in the Bailuoji reach is relatively small and the diversion ratio of the right branch is slightly reduced. The research results can provide reference for middle-small flood dispatch of Three Gorges Reservoir.

New energy grid connection is easy to cause voltage fluctuation, frequency oscillation and other problems. For this, the paper adopts a frequency division control strategy of hybrid energy storage unit, which based on the storage of photovoltaic grid-connected system as the research subject, thus improving the dynamic stability of DC bus voltage, and proposes an improved virtual synchronous generator. According to the characteristics of flexible adjustment of inertia parameters, the virtual inertia and parameters are adjusted adaptively to suppress the frequency and power oscillation caused by the disturbance. Finally, a simulation model of photovoltaic storage grid-connection is established. It verifies that the proposed strategy can not only stabilize the DC bus voltage and supplement the power deficiency under different operating conditions. At the same time, it can slow down the sudden change of the system frequency and reduce the overshoot, showing good grid-connected performance.

The low voltage winding interturn insulation fault of dry-type transformer is not easy to find directly through the appearance of the phenomenon, and is difficult to real-time monitoring, seriously affecting the safe and stable operation of power systems. In view of the lack of fault detection methods due to insufficient research on the electromagnetic characteristics of single-turn interturn short-circuit faults in low-voltage windings of dry-type transformers, and the difficulty in setting interturn short-circuit faults in practical projects, finite element simulation software was used to establish a field-circuit coupling model which is consistent with the actual dry-type transformer, and the accuracy of the model was verified under rated operating conditions. On this basis, the variation rules of electromagnetic parameters of short-circuit turns at different positions were explored when interturn short-circuit faults occur in low-voltage windings. The distribution of electromagnetic force on short-circuit turns when interturn short-circuit faults occur in windings at different positions was simulated. The results show that when the interturn short circuit occurs at different positions of the winding, the maximum magnetic density appears in the outermost short-circuit turn; the outermost short-circuit turn is subjected to the largest radial force, and the innermost short-circuit turn is subjected to the largest axial force. Therefore, it provides a theoretical basis for on-line monitoring and protection technology of dry-type transformer interturn insulation, which is conducive to the research and implementation of measures to improve short-circuit resistance.

In order to study the response relationship between sediment discharge ratio (SDR) and influencing factors under actual water and sediment conditions, based on the measured water and sediment data of the Three Gorges Reservoir (TGR) from 2003 to 2018, this paper discussed the response relationship between SDR and various influencing factors on the basis of analyzing the characteristics of water and sediment from the reservoir, and established the formula of SDR in the main flood season. The results show that the correlation between SDR and single factor is not obvious, indicating that the SDR is affected by multiple factors. From the perspective of reservoir operation and regulation, the SDR is negatively related to the flood detention time, and the sediment discharge efficiency should be improved by shortening the flood detention time; From the perspective of incoming water and sediment, the greater the amount of sediment entering the reservoir, the greater the sediment discharge ratio of fine sediment is; Coarse sediment, on the contrary, is characterized by more coming and less discharging. In the main flood season, the relationship between the SDR and the proposed expression is good. This study can provide reference for the operation of TGR.

To study the diversion risk of pumped storage power station construction under extreme rainfall, based on the idea of system risk analysis, the Copula-Monte Carlo method for diversion risk prediction was proposed by considering the correlation between upper and lower reservoir inflow. Joint distribution of the upper reservoir extreme rainfall and the lower reservoir flood volume was constructed to simulate the construction flood process caused by extreme rainfall. According to the characteristics of the upper and lower reservoirs diversion engineering, the risk model of the diversion system in the pumped storage power station was established to simulate the risk rate by considering hydrological and hydraulic uncertainty. Finally, a pumped storage power station under construction in southwest China was taken as an example, the results show Gumbel-Copula joint distribution fits the construction flood well in extreme rainfall cases, the diversion system risk rate is higher and more realistic when considering the correlation. It provides a reference for pumped storage power station construction diversion scheme selection and flood standard design under extreme rainfall.

In order to realize the safe monitoring of the operation status of hydroelectric units and solve the problem of automated watch keeping, based on speech recognition technology, the normal status model of measurement points based on the operation monitoring information of generating units was established to implement abnormality detection. Firstly, the experimental data of the bearings of Western Reserve University were used to verify the correctness of the selected modeling method of deep convolutional neural network (CNN) and Gaussian mixture model (GMM). Secondly, a total of forty-two measurement points were arranged for the turbine set, and ten sensitive measurement points were selected for position classification based on the rise rate of RMS before and after overspeed. Then some data were selected as training data to get CNN model and unit sound features. The GMM model was obtained by further training. Finally, the scoring results of the test data were used to determine the machine operation status, i.e., the degree of deviation from the normal status was determined to achieve abnormal status detection. The experimental scheme was confirmed by manual annotation, thus verifying the feasibility of the method, which realizes the design of sound-based abnormality detection algorithm for hydropower units.

The Lhasa River Basin is a typical arid and semi-arid basin in the Qinghai-Tibet Plateau, where the ecosystem is extremely fragile. It is of great significance to study the spatio-temporal variation of vegetation index (NDVI) in response to the changes of meteorological factors, and to explore the adaptability of vegetation on the Qinghai-Tibet Plateau to the meteorological factors under the background of climate change. Based on the monthly NDVI, precipitation (P), and average temperature (T) time series dataset in the Lhasa River Basin from 1982 to 2017, using Pettitt, Mann-Kendall trend test and Pearson correlation analysis, this paper analyzed the spatio-temporal variation characteristics of growing period NDVI (G-NDVI) and meteorological factors, and identified responses patterns of G-NDVI to climate factors. The results show that the G-NDVI changed abruptly in 1997, and there was a trend shift from increasing to decreasing. The climate of the watershed changed from “wetting-colding” before the abrupt point to “drying-warming” after the abrupt point, and its effect on vegetation growth changed from promoting to inhibiting. There are two zones in the watershed where the responses patterns of G-NDVI to meteorological factors changed before and after the abrupt point. In the western permafrost areas, G-NDVI shows significant correlation with P and T in the second phase after 1997, i.e., emerging the “responding” function on meteorological factors variation. In the southern seasonal frozen zone, after the abrupt point, time lags of G-NDVI to P were elongated, and meanwhile the “responding” of G-NDVI to T has been triggered. The latency of NDVI response to P in the western permafrost region is longer than that in the southern seasonal frozen zone. In the second phase after 1997, the response area of NDVI to meteorological factors increased compared with that before the abrupt point, and the effect of meteorological factors on vegetation growth in the Lhasa River basin was enhanced.

When the source-based reduction facilities cannot be carried out during the construction of sponge city, the stormwater control measures (SCM) are usually set up at the terminal drainage outlets to achieve the goal of runoff control and pollutant reduction. Because there is usually large drop between the drainage outlet and the waterfront zone in mountain city, resulting in a high flow rate of water from the drainage outlets, it is easy to cause strong hydraulic erosion to the SCM and may adversely affect their normal operation. Based on the falling-sill dissipation facility installed according to the high drop topographic features of drainage outlets in Chongqing urban, the numerical model with FULENT software was constructed to simulate the hydraulic process of different energy dissipation configurations in this study. The results show that the solid-baffle typed falling-sill dissipation facility has out-performance energy dissipation, and the energy dissipation rate was as high as 90%, and the outlet velocity of the end of facilities was irrelevant to the inlet flow, while only related to single drop height. The higher the single drop height, the water flow was susceptible to form a hydraulic vortex in the backwater area of falling-sill under the influence of potential energy, which can lead the greatest extent of turbulence kinetic energy dissipation, and finally result in a gradual decrease of the maximum pressure of water flow in the horizontal direction to achieve the targeted hydraulic energy dissipation.