Abstract:Based on information regarding the excavation progress, support progress, and newly outcropped geology at the construction site of a large-scale underground cavern group, a three-dimensional numerical simulation model, which can be updated in real time and reflect the practical process of construction, was established. Using the techniques of uniform design and artificial neural networks and the mixed programming technique of C#. NET+Python, the secondary development of ABAQUS proceeded, and a method of real-time dynamic inversion of surrounding rock mechanical parameters was developed for a large-scale underground cavern group during the construction period. Using the Huangdeng Hydropower Station as an example, real-time dynamic inversion of surrounding rock mechanical parameters during the construction of a large-scale underground cavern group was conducted. The results show that the variations of calculated displacement and measured displacement of measuring points with construction time showed the same pattern of change in different construction periods and were in good agreement. The average error was only 5. 5% in the fifth construction period. This good inversion result verifies the rationality and maneuverability of this method.

Abstract:In order to simulate the movement and dynamic response of adjacent blocks in an underground cavern group under seismic loads, a dynamic anti-sliding model, considering the bond strength between the blocks, was established. The effectiveness of the anti-sliding model in comparison to other models was analyzed using a numerical model. In the practical engineering examples, the calculated root mean square values of horizontal displacement in the X direction of two adjacent blocks of type I were 2. 16 cm and 2. 02 cm when the classical anti-sliding model was used, and 2. 00 cm and 1. 94 cm when the modified anti-sliding model was used throughout the earthquake process. The corresponding simulated results of two adjacent blocks of type II were 3. 68 cm and 3. 65 cm when the classical model was used and 3. 55 cm and 3. 54 cm when the modified model was used. Hence, it is demonstrated that adjacent blocks considering bonding characteristics show much better stability, and the proposed model has high application value.

Abstract:In order to avoid large amounts of computation with the elastic compensation method, the incremental elastic finite element iterative method(IEFEIM)is proposed for solution of the ultimate load of complex structures, based on the advantages of elastic-plastic analysis and plastic limit analysis. With the load factor β as a variable, and by using the self-adaptive increment adjustment technique, the maximum load factor β_max satisfying the equilibrium and yield conditions is obtained by iteration and approximation. In contrast to the elastic-plastic analysis method, the IEFEIM only requires the strength criterion of materials and does not require the constitutive relationship of materials after yielding and failure; in contrast to the plastic limit analysis method, the IEFEIM obtains the maximum load factor by directional search and approximation, without using the programming algorithm for large-scale search; and in contrast to the elastic compensation method, the IEFEIM generates the global stiffness matrix for only one time, without any need of generating the global stiffness matrix for each step, effectively decreasing the amount of computation in iterations. Practical application in engineering projects shows that the IEFEIM can obtain the ultimate load of high dams effectively and provide the structural characteristics close to the ultimate state.

Abstract:Aiming at the crack phenomenon in a hydraulic turbine runner blade, from the perspective of the influence of the start-up law of the turbine governor on the runner, an electro-hydraulic servo system model considering nonlinear parts and a hydraulic turbine model based on comprehensive characteristic curves were established. The closed-loop start-up characteristics for hydraulic turbines whose rising curve of the expected rotation speed shows a straight line rule were analyzed. Considering the deviation of working head and other factors, a comprehensive index is proposed. The start-up process of a Francis hydraulic turbine in China was simulated. The results show that the closed-loop start-up process based on the comprehensive index can obtain a strong dynamic performance and reduce the impacts of the start-up laws on the runner.

Abstract:In order to quantitatively investigate the pattern of change of the surface asperity of textured geomembrane, a new apparatus for measuring surface asperity was developed. Interface shear tests of textured geomembrane with nonwoven geotextile under different normal stresses and corresponding tests on the surface asperity of textured geomembrane were conducted. The results show that the interface shear strength of textured geomembrane with nonwoven geotextile is caused by the embedding and pulling actions between textured points of geomembrane and geotextile fabric. The peak interface shear friction coefficient is mainly influenced by normal stress. When the interface shear strength tends to be residual strength, the damage to textured points of geomembrane tends to be stable and the fabric orientation of geotextile is fully achieved.

Abstract:The discrete element program PFC^3D was used for numerical simulation of a model experiment, which was carried out on an indoor vibration table, in order to study the fluidization of iron concentrate ore in bulk under dynamic loads. The evolution and internal mechanism of the iron concentrate ore fluidization was studied from a mesoscopic perspective. With consideration of the unsaturation during the fluidization process, the water was simulated with small granules and the matrix suction was simulated by setting a bond model between fine granules of ore. The change and development of the displacement field, water particle migration, and mesoscopic fabric were observed during the fluidization process. The results of numerical simulation were compared with those of the model experiment. It was found that the main cause of iron concentrate ore fluidization is the increase of the water level. The mesoscopic mechanisms of fluidization are as follows: under dynamic loads, the fine particles move downwards through the spaces between coarse particles, and the water between the particles that becomes water film flows upwards.

Abstract:In order to investigate concrete cracking characteristics, the traditional average method was modified based on meso-mechanics theory and used in cracking zones. Using different average methods, concrete specimens with different sizes but the same grading and size distributions were analyzed, and cracking characteristics and mechanisms of cracking size dependency were studied. The results show that cracking stress-strain curves obtained with the cracking zone average method are size independent, and they can represent the entire cracking process and determine important cracking parameters. It is also shown that when the specimen size varies, the area and mechanical characteristics of local nonlinear cracking zones are barely affected by the specimens size change, while the area and mechanical characteristics of linear elastic zones are highly affected by the specimens size change, making the global average mechanical characteristics change a lot, thus the cracking size dependency occurs.

Abstract:Based on the three-dimensional Biot consolidation theory, the soft ground consolidation process under negative pressure was calculated with the three-dimensional finite element method by means of ABAQUS software, in which the modified Cam-clay model and the homogenization method of hydraulic conductivity were used and the smear effect was considered. The numerical results with different loading methods and varying hydraulic conductivity and depths of sealing were compared. It was found that the three-dimensional finite element method can reflect the consolidation process under negative pressure more accurately, and the calculated results with nodal loading in the sand cushion agree with the measured data. When the variation of hydraulic conductivity with the void ratio is considered, the results of surface settlement, settlement trend, and the degree of consolidation are closer to the actual conditions. The optimal effective depth of sealing is about 3 m.

Abstract:A large number of basins in China are facing problems such as the degradation of ecosystems and decline of biological resources. This paper is devoted to illustrating the influence of large water conservancy and hydropower projects on major aquatic species in rivers, and demonstrating key technologies for control and regulation, which could help to provide technical support for aquatic ecological civilization construction and ecological conservation. With focuses placed on large rivers in China, such as the Yangtze River, this paper provides a review of the current status and trends of four major Chinese carp and the Chinese sturgeon influenced by large water conservancy and hydropower projects. Based on analysis of the stress effects of these projects on the habitats of major aquatic species, the regulation potential for natural reproduction of the aquatic species as well as possible approaches are discussed. Using a large water conservancy and hydropower project as a case study, the key technologies for optimal regulation of the project in order to increase the natural reproduction of major aquatic species and the applicability of these technologies are discussed.

Abstract:Based on precipitation data and field investigation, we used the Mann-Kendall test and the standard precipitation index(SPI)method to analyze the trends of drought in Xuzhou City at different temporal scales and tried to determine the reasons for the drought disasters in recent years. The precipitation trend analysis showed that the precipitation over Xuzhou City gradually decreased during the period from 1951 to 2013, especially in the spring, autumn, and winter. The annual SPI analysis showed that the drought severity had significantly increased over the study area. Through analysis of the seasonal SPI, we found that the drought severity showed an increasing trend on the whole in the spring, autumn, and winter, while the situation was opposite in the summer and the trend was not significant. The monthly SPI over the period from 2009 to 2013 in Xuzhou City was calculated, and the results showed that there was a moderate drought in the year 2011 and mild droughts in other years. The water demand of wheat growth cannot be satisfied by natural rainfall alone; it requires compensation from irrigation water. Some counties and townships are facing problems such as insufficient farmland water infrastructure and inefficient irrigation techniques, which are among the main factors aggravating the agricultural drought in the city.

Abstract:Based on the hydrogeological conditions of the Huahai irrigation area in the Shule River Basin, and focusing on the relationships between groundwater recharge, runoff, and discharge, a hydrogeological model and a groundwater numerical model were established. The models were identified and calibrated through fitting of the groundwater levels over the past ten years. On this basis, the trend of groundwater level changes in the forthcoming 20 years and the influencing factors were predicted. According to the results, the groundwater level slightly increases under an exploitation intensity of 3. 505 2 million cubic meters per year, and significantly decreases under an exploitation intensity of 20. 098 6 million cubic meters per year, with the greatest decreased level being six meters. Intense exploitation of groundwater can lead to the continuous decline of the groundwater level in the irrigation area. The southeastern part of the study area in particular will be significantly affected, which will cause a series of ecological and environmental problems.

Abstract:In order to study the effect of acceleration-skewed waves on the bottom boundary layer, a numerical model was developed to reproduce the velocity profiles, turbulent intensity, and bottom shear stress as measured in a physical model experiment. Based on this, the hydrodynamic characteristics of the boundary layer under the acceleration-skewed waves were examined. Numerical results show that greater flow acceleration in the positive accelerating stage within a wave crest half-cycle leads to quicker development of the boundary layer, a larger velocity gradient, and greater turbulent intensity, resulting in positive period-averaged bottom shear stress. These features become more pronounced when the degree of acceleration skewness increases. In the oscillating water tunnel, the time-averaged current velocities are positive and negative in the upper and lower regions of the boundary layer, respectively, and the negative near-bed current velocity increases with the degree of acceleration skewness. In the open sea, the time-averaged current velocity is positive over the whole boundary layer, velocity over-shooting is found in the lower region, the velocity is uniform in the upper region, and the positive near-bed current velocity decreases with the increase of the degree of acceleration skewness.

Abstract:In order to study the flow structure in a spur dike field of the North Passage in the Yangtze Estuary, a two-dimensional large-scale coupling model for tidal current and water quality was established using the finite volume method(FVM)and unstructured grids. Based on model verification, the flow structure and pollutant diffusion in the spur dike field of the North Passage during flood tides and ebb tides were studied. The following conclusions are drawn: the high tide level in the north spur dike field in the middle-upper reach of the North Passage is significantly higher than that in the main channel, while the high tide level in the lower reach of the North Passage is close to that in the main channel; the high tide level in the south spur dike field is mostly higher than that in the main channel, and the low tide levels in the north and south spur dike fields are close to that in the main channel; the rate of pollutant diffusion in the south spur dike field is higher than that in the north spur dike field, with a relatively high rate of diffusion during ebb tides; the rate of pollutant diffusion in the spur dike field is higher during spring tides than during neap tides, with a relatively high rate of pollutant diffusion outside the spur dike field in contrast to that inside the spur dike field; after release of pollutants in the spur dike field, the pollutants are transported within the spur dike field and the main channel following flood tides and ebb tides, and lesser amounts enter into the waterway in a short period.

Abstract:In order to obtain the operation state of transmission lines, comprehensive evaluation of the lines is needed. This paper proposes a dynamic comprehensive evaluation model for overhead transmission lines based on the integrated weighting method. The evaluation processis as follows: first, the order relation method is used to determine the subjective weight of each index according to the importance of each index; second, the scatter degree method is used to calculate the objective weight of each index and the comprehensive evaluation function value of the line; finally, the operation state of the overhead transmission line is evaluated according to the comprehensive evaluation function value. The model was applied to evaluation of an overhead transmission line, and the evaluation results are compared with the actual results. The results showthatthe model is effective and feasible.

Abstract:In order to reduce the rotor unbalance load caused by wind shear, tower shadow, and turbulent wind, an individual pitch control strategy based on the combined feedback of the azimuth angle and load is proposed according to a wind model considering the wind shear, tower shadow, and turbulence. In the individual pitch control strategy, the azimuth angle weight coefficient assignment module and the module of blade root flapwise load fed back to the PID controller are used to adjust the pitch angle of each blade and achieve rotor load reduction. The simulated results of the GH Bladed software show that, compared with the collective pitch control strategy, the proposed individual pitch control strategy can significantly reduce the rotor unbalance load, and it is not only effective in alleviating the load fluctuation caused by wind shear and tower shadow, but also able to achieve good load reduction performance under turbulent conditions.