Abstract:To improve the simulation accuracy in the Chinese semi-humid watershed, this study took the Chenhe Catchment in the semi-humid area as the study area and selected 6 parameters including ZSOILFAC, GWEXP, REFKDT, RETDEPRTFAC, OVROUGHRTFAC and MANNFAC for the sensitivity analysis of WRF-Hydro model parameters. The sensitivity of these parameters was qualitatively analyzed by studying the influence of different parameter value in the reasonable range on the flood simulation and each evaluation index, and the modified Morris screening method was used to quantitatively determine the sensitivity of each parameter. The results show that ZSOILFAC, REFKDT and MANNFAC are very sensitive, and it is suggested to take the value within 0.1 to 1.0, 0.0 to 1.0 and 0.5 to 1.5 respectively.

Abstract:In order to analyze the impacts of water level changes on the ecological structure of water-level-fluctuating zone in the reservoir and improve the accuracy of the calculation of the inundation frequency, an analysis method of inundation frequency is proposed based on GF-1 satellite data. Firstly, the GF-1 WFV satellite imageries are preprocessed and a buffer zone is set up to extract the water body through multiple iterations. Then, the spatial distribution characteristics of the inundation frequency are obtained by geographical registration and inundation frequency calculated from the proposed method. Finally, the reliability of the inundation frequency is verified by the accuracy of water body distribution simulated from the method. The application in Sanhekou Reservoir show that the proposed analysis method of the inundation frequency can accurately reflect the spatiotemporal variation characteristics of the water body information. The overall classification accuracy and Kappa coefficient of simulated water body results reach 86.5% and 73% respectively, which can accurately reproduce the water body changes during the impoundment period of reservoir and improve the accuracy of inundation frequency calculation.

Abstract:Based on the documents on drinking-water source evaluation included in Web of Science (WOS), the knowledge domain map of drinking-water source evaluation was established by the comprehensive use of bibliometrics tools and traditional literature review methods, the historical development and evolution process was analyzed, and the future development trend was also given. The results show that this field has experienced three stages of early accumulation, sustained development and rapid expansion, showing a trend of multi-disciplinary integration with environmental science, environmental engineering and water resources as the core. The research topics are abundant, showing a trend of continuous expansion, but the heat distribution of the topics generally show a continuous concentration trend. The preference of different countries or regions for drinking-water source evaluation research is mainly determined by the major type of drinking-water sources and the main pollution stress that they face. At present, the important research frontiers and hot spots involve 9 aspects, such as the harm of emerging pollutants, the effect of pollutant removal process, the eutrophication of lakes and reservoirs, water quality assessment methods, human health risks of water pollution, new technologies for pollutant detection, the impact of climate change on drinking-water source, the relationship of industrial or agricultural production and drinking-water safety, and the ecosystem health in drinking-water source. In the future, it is necessary to fully summarize the system characteristics of different types of drinking-water sources and establish an intelligence-integrated technology system of monitoring, assessment, forecasting, early-warning and response for drinking-water sources. Particular attention should be paid to the quantitative characterization, evolution modes and driving mechanism of drinking-water source system health.

Abstract:To address the problem that the existing water-level detection method based on the gray image segmentation is susceptible to complex illumination conditions such as water surface flaring and reflection, and the problem of large measurement errors caused by the entanglement of floating objects during high flood periods, a deep-learning-based intelligent water-level monitoring method for staff gauge is designed. This method uses the three-class sample images of staff gauge,water surface, and floating objects, which are collected under different conditions and accurately labeled manually, to construct the data set, and then trains the deep fully convolutional neural network to perform the pixel-by-pixel classification prediction of staff gauge images. Finally, the pixel position of water line is detected in the semantic segmentation image, and transformed into the actual water level value. The test results show that the method can overcome the shortcoming of traditional methods in the image feature extraction, improve the adaptability of image segmentation to complex changing environments in the field, realize the recognition of measurement effectiveness, and achieve the purpose of intelligent monitoring of water level with the comprehensive uncertainty of measurement less than 3 cm.

Abstract:In order to study the sensitivity of water quality parameters of different underlying surface types under various rainfall scenarios, the modified Morris screening method was used to analyze the overall characteristics of water quality parameters sensitivity of the SWMM, clarify the influence degree of different rainfall intensity and underlying surface types on water quality parameter sensitivity, and reveal the differentiation characteristics of highly sensitive parameters of each water quality index. The results show that the number of highly sensitive and sensitive parameters and sensitivity increase with increasing rainfall intensity, and the sensitivity level of water quality parameters for road and grassy area significantly elevated under rainstorm condition, however, the time lag of rainfall peak will reduce the sensitivity of some highly sensitive water quality parameters. In terms of sensitivity, the parameters are runoff index, maximum accumulation, washoff coefficient, rate constant and half-saturation constant in descending order. The significance tests show that the influence degree of underlying surface types on the number of highly sensitive and sensitive parameters is higher than that of rainfall conditions. The number of sensitivity parameters and their sensitivity for roof are generally large, mainly affected by the area proportion and permeability of underlying surfaces. The sensitivities of runoff exponents of ammonia nitrogen for farmland are significantly higher than COD, TP and TN, which is related to the process of fertilizer hydrolysis and ammonia nitrogen loss.

Abstract:To analyze the relationship between different outflows from Three Gorges Reservoir (TGR) during the drawdown period and the weighted usable area (WUA) of sedentary fish spawning habitat in Dongting Lake, the water depth and flow velocity were selected as the key influencing factors of sedentary fish spawning habitat, and the habitat suitable curves were established. This study quantitatively assessed the spatial variation characteristics of fish spawning habitat suitability based on the physical habitat simulation model (PHABSIM), and quantified the suitable ecological flow required for the fish spawning. The results show that the increase of outflow from TGR during the drawdown period has a certain effect on the water level and flow velocity of Dongting Lake. The effect on East Dongting Lake is obvious, but the effects on South Dongting Lake and West Dongting Lake are less. With the increase of outflow, the WUA of sedentary fishes spawning habitats in the lake area first increased and then decreased, whilst the difference is that the WUA of East Dongting Lake shows a gradual upward trend, the WUA of South Dongting Lake has a small overall increase with a double-peak curve, and the WUA of West Dongting Lake shows a trend of decreasing after increasing. The suitable ecological flow range of sedentary fishes spawning habitat was 18 500-24 500 m³/s, and the optimum ecological flow is 22 500 m³/s.

Abstract:According to the relevant requirements of smart water conservancy and digital twin engineering construction, by integrating the modern artificial intelligence and water dispatching professional knowledge, the definition and basic functions of smart water dispatching for the South-to-North Water Diversion Middle Route Project are tentatively proposed in this paper combined with the tasks and responsibilities of water transportation scheduling. Through analyzing the logical relationship between intelligence and wisdom, this paper systematically discusses the key technologies, existing shortcomings, and improvement suggestions for the smart water transportation and dispatching in the middle route from the perspectives of perceptual intelligence, cognitive intelligence, and decision-making intelligence. With respect to the perception intelligence, it should be a combination of non-contact and contact measurement, a mixture of machine vision and traditional sensors, and an integration of automatic monitoring and manual inspection. Data cleaning technology is required to support the multi-source data fusion. In the cognition intelligence, a framework is suggested by integrating mechanism studying and data mining. From the perspective of prediction, early warning, rehearsal and emergency plan, the key technologies and modeling requirements of water dispatching were comprehensively analyzed, and the regulation strategy model, simulation model, prediction and early warning model, Self-adaptive model, and so on should be constructed. In terms of intelligent decision-making for the dispatch of the middle route, a regulation approach based on simulation deduction as feedforward and real-time monitoring as feedback is proposed. An automated water dispatching regulation strategy based on rolling decision correction and real-time response is established, and a multi-objective optimization dispatch model should be constructed.

Abstract:In order to adapt to the new requirements of large-scale photovoltaic output connected to the Wujiang River Basin and jointed dispatching and bundled transmission with cascade hydropower stations, the staged generation strategy of cascaded hydropower stations under the Hydro-PV complementary mode was proposed based on the actual energy storage control mode of the basin, and the reasonable range of energy storage at the beginning of the flood season and the end of the year was determined, so as to draw the Hydro-PV complementary cascade energy storage dispatching diagram to guide the medium and long-term Hydro-PV complementary dispatching. The case verification results show that, compared with the actual power generation of cascade hydropower stations in the basin, the Hydro-PV complementary cascade energy storage dispatching diagram can increase the system power generation by 70 million to 210 million kW·h. The drawing of Hydro-PV complementary cascade energy storage dispatching diagram is simple and reasonable, and the optimal dispatching results are in line with the reality, which can be used for the medium and long-term Hydro-PV complementary optimal dispatching in the Wujiang River Basin.

Abstract:To solve the dispatching problem of water-light complementary base, a new drawing method of reservoir dispatching diagram is proposed according to the frequency group of incoming water, and the application strategy of reservoir dispatching diagram is provided. Taking the Xizang section of the upper reaches of Lancang River as an example, the results obtained by the proposed method meet the practical requirements of the project, benefit the stable operation of the power grid, and improve the efficiency of the power station.

Abstract:The influence mechanism of foam fluid on the seepage in the embankment foundation and the development of embankment seepage failure are unclear. In this study, the seepage failure experiment without foam fluid and the seepage failure experiment with foam fluid are carried out to investigate the characteristics of seepage in soil during the development of seepage failure and the influence of foam fluid on soil seepage. The experimental results show that foam fluid has a significant impact on the seepage in soil. The flow resistance greatly increased by the foam bubble trapped in pores, while the soil is turned to unsaturated state, which leads to the enhanced impervious performance. Besides, the flow path becomes longer due to the existence of foam fluid, which reduces the hydraulic gradient, and in turn significantly restrains the development of seepage failure of the embankment foundation.

Abstract:In order to study the influence of sisal fiber and interface roughness on the shear mechanical properties of soil-rock interface, concrete modules with rough surface were used as the rock surface similar material and a series of indoor shear tests were carried out. Combined with the SEM test, the mechanism of sisal fiber participating in the strengthening of the interface is further analyzed. The results show that sisal fiber can improve the shear mechanical properties of soil-concrete interface by improving the cohesion. The addition of 0.8% by weight increases the interfacial bond strength of soil-cement interface by 0.8-5 times and the internal friction angle by 0.1-0.2 times. The interface roughness mainly enhances the shear mechanical performance of the interface by improving the bond strength. For an interface roughness of 6.5 mm, the increase of interfacial bond strength ranges from 7 kPa to 15.5 kPa, resulting in an improvement of 0.2-3 times. The enhancement of roughness on the shear mechanical performance of the soil-cement interface exhibits two distinct patterns for the plain soil interface and the fiber-reinforced interface. Regarding the relationship between interfacial bond strength and roughness for the fiber-reinforced interface, the optimal value of roughness appears within a smaller range (0-2.5 mm).

Abstract:To study the influence of corridor frame on the vortex-induced vibration performance of bridge, by taking a footbridge with corridor frame as the engineering example, the rigid segment model with three different corridor frame size was made, and the wind tunnel test of corresponding segment model was carried out to analyze the influence of corridor frame on the vortex-induced vibration performance of girder. In order to consider the effect of space frame size variation on the aerodynamic characteristics of the whole bridge, the displacement response of girder at the span and 1/4 span in the uniform and turbulent flow field was analyzed through the wind tunnel test for the aeroelastic model of whole bridge. It revealed that: Corridor frame significantly changes the vortex-induced vibration performance of the bridge, and there is a large amplitude of vortex-induced vibration in the non-corridor frame state. Vortex-induced vibration performance of the small corridor frame and middle corridor frame is worse than that of non-corridor frame, while vortex-induced vibration performance of large corridor frame is better than that of non-corridor frame. Compared with the three different states, the vortex-induced vibration performance improves with the increase of corridor frame size, and except for the small-amplitude vortex-induced vibration in some operating conditions, there is no vortex-induced vibration in other operating conditions for the state of large corridor frame. If the upwind side of beam is different, the vortex-induced vibration response can be different. The maximum amplitude of the non-corridor frame, small corridor frame and middle corridor frame at the wide windward side is reduced by 49.72%, 27.57%, and 23.21%, compared with those at the narrow windward side, respectively. Combined with the fact that there is no vortex-induced vibration under the uniform and turbulent flow field in the aeroelastic test of the whole bridge, the space corridor frame overall improves the vortex-induced vibration performance of the bridge.

Abstract:Based on the state of rock before failure in the working face of TBM, the double concentrated-force model is established for the working face under the thrust action of TBM disc cutters. Analytical expression of the stress distribution of rock under the coordinated action of double disc cutters is given by using the Boussinesq solution for the elastic half-space problem and the superposition principle. Based on the characteristics of stress distribution and the requirements for TBM rock breaking, necessary conditions for TBM rock breaking have been proposed, and the prediction formulas for the rock breaking thrust of disc cutter are provided using the uniaxial strength theory and the multi-axial strength theory, respectively. The engineering example shows that the rock breaking thrust of disc cutter predicted based on the multi-axial strength criterion proposed in this paper agrees well with the actual thrust during the TBM operation.

Abstract:In order to investigate the effects of end anchorage method and prestressing level on the flexural behavior of reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP) plates, an experiment was carried out on six large-scale T-beams. The failure mode, load-deflection curve, characteristic load, CFRP strain, CFRP utilization rate and ductility were analyzed. The results indicate that the anchorage method has a significant effect on the ultimate load of RC beams, whereas it has little effect on the cracking and yielding loads. With an increase of prestressing level from 0 to 0.5, the failure mode changes from the concrete crushing to the CFRP fracture and the cracking and yielding loads are increased by 75.0%-237.5% and 13.6%-50.9%, respectively, compared with the unstrengthened specimen. The ultimate load increases gradually in the concrete crushing mode but is affected limitedly in the CFRP fracture mode with an increase of prestressing level. The use of a reliable end anchorage can increase the CFRP utilization rate in the ultimate load; however, applying the prestress can considerably increase the CFRP utilization rate in the whole loading state.

Abstract:In order to study the influence of dry-wet cycles on the mechanical properties and microstructure of clay, a series of unconfined compressive strength tests and CT scanning tests were carried out to reveal the deterioration mechanism of clay caused by dry-wet cycles from macroscopic and microscopic perspectives. The following conclusions were drawn: With the increase of the times of dry-wet cycles, the compressive strength of clay maintained an exponential decline trend. After 4 cycles, the compressive strength lost about 40%, and after 8 cycles, the compressive strength basically reached the stable state. It can be seen that from the cross-section of CT scanning, during the dry-wet cycle, cracks start to develop around the sample and gradually expand inward. The width and length of cracks continue to increase, and the continuity also improves. With the increase of the times of dry-wet cycles, the porosity of each layer of the sample increased significantly and the porosity of the interface between different layers increased more significantly. The cracks between layers developed first, and vertical cracks also developed on the surface of sample. Besides, the number of connected pores increases while the number of isolated pores decreases. There is a negative exponential relationship between porosity and compressive strength of clay under different dry-wet cycles and when the number of dry-wet cycles reaches 4 times, the increase of porosity has less effect on the decrease of compressive strength.

Abstract:In order to achieve the remote, cost-effective, and efficient evaluation of the metering performance of DC charging piles, a DNN model for calculating accumulated electric energy of DC charging piles is established based on deep neural network (DNN) and a large amount of data of on-site electric vehicles charging on DC charging piles. A method of remote metering performance verification for DC charging piles is proposed, and the correlation between variables and accumulated electric energy during charging is analyzed. The instance verification results show that the state of charge has the greatest influence on the calculation of accumulated electric energy, and the current has the least influence. The established DNN model can accurately calculate the “actual” output energy of the pile to be measured, and the absolute value of the difference between the indication error of model calculation result and the actual verification indication error is less than 1%. Therefore, the proposed method can achieve an efficient metering performance evaluation.

Abstract:For the effective suppression of ultra-low frequency oscillation in Northwest power grid with a large proportion of hydro power in China, it is crucial to simultaneously optimize multi-stage frequency control parameters of speed governing system and local control unit. To address this problem, a parameter optimization method for the multi-stage frequency control of hydropower is proposed to suppress the ultra-low frequency oscillation in this study. Based on the multi-stage frequency control model, the security region of joint control parameters for suppressing ultra-low frequency oscillation is theoretically analyzed. Moreover, with the goal of minimizing the absolute value of comprehensive deviation multiplied by the time integral in the security region, the multi-stage control parameters are optimized through particle swarm optimization using the Matlab/Simulink platform. Finally, the time-domain simulation based on the PSCAD/EMTDC platform verifies the effectiveness of theoretical analysis and optimization method of multi-stage frequency control parameters for suppressing the ultra-low frequency oscillation of hydropower.