Abstract:The method of indicators of hydrologic alteration and range of variability approach(IHA/RVA)was used to quantitatively evaluate the change degree of hydrological parameters at representative stations in the mainstream of the Tarim River and ecological effects caused by the operation of reservoirs in the upper reaches of the Tarim River. The results show that the operation of the reservoirs caused a significant change of the eco-hydrological regime of the Tarim River, and the change degrees were all higher than 60%. Significant changes occurred on the average flows in March and June, the annual 1-day and 3-day minimum discharges, the annual 30-day and 90-day maximum discharges, the number of low pulses, and the number of reversals. Reservoir operation significantly affected the ecosystem around the Tarim River. It is urgent to regulate the discharge of the river, in order to achieve the harmonious development of regional economy and ecological environmental protection.

Abstract:To explore the causes for the loess collapse and the mud forest formation in the eastern bank of Dabusu Lake, the source and failure mechanisms for subsurface flow were studied. The results show that, according to the salt content of topsoil larger than that of subsoil, precipitation infiltration cannot recharge the underground water. Isotopic analysis results indicate that Dabusu Lake is mainly recharged by groundwater, and subsurface flow comes from the seepage of surrounding rivers. Leak water of rivers discharges towards Dabusu Lake through the silt layer beneath the loess layer, which is one of the reasons for the development of mud forest. The dust particles of loess above the silt layer are taken into the lake by subsurface flow, forming cavities on the bottom of the loess layer and finally resulting in collapses. Besides, the freeze-thaw action also aggravates the seepage failure. Subsurface flow, fine particle loss, and freeze-thaw action are the main reasons for loess failure, and avoiding fine particle loss, and freeze-thaw action is the key to preventing the development of loess failure.

Abstract:The daily rainfall records for the period of 1979-2014 from two urban and rural representative rain gauges(i. e. , Yangjing and Xiaziwei)in Shanghai City were compared, and factors of precipitation at the two rain gauges were analyzed. The influences of urbanization on local precipitation were revealed based on the investigation of the time variability of precipitation at the two rain gauges before and after the year of 2000 and the difference between the two rainfall series. Results show that, with the acceleration of urbanization in Shanghai City since 2000, the relationship between the precipitation at the two rain gauges presents systematic variation before and after 2000, and their differences have become more significant. Considering that the two rain gauges are both located in the eastern plain of the Taihu Basin, with the similar time variability of typhoon precipitation, the differences between the precipitation at the two rain gauges from 1979 to 2014 are mainly attributed to the urbanization-induced local precipitation enhancement without consideration of the regional differences. The rapid urbanization in Shanghai City since 2000 has significantly enhanced the local precipitation at the urban rain gauge and increased the probability of heavy rainfall events.

Abstract:Based on the rainstorm data from the middle and lower reaches of the Chuhe River in the period from 1959 to 2010 and the tide level data at Xiaguan Station in Nanjing City, a joint distribution function of the annual maximum 1-day, 3-day, and 7-day rainstorms and the corresponding tide levels of the Yangtze River with different return periods was built based on the Copula function. The encounter probabilities of the design rainstorm and different tide level intervals and the encounter probabilities of the design tide level and different rainstorm intervals were calculated. The results are similar to conclusions in the Nanjing Urban Flood Control Planning, indicating that the calculation method is reasonable and feasible and can provide a reference for combined calculation of rainstorm and tide level.

Abstract:Based on discharge, water level, and precipitation data at the Guajingkou Station and water level data at surrounding stations from 1966 to 2014(with data missing from 1989 to 2005), a model for estimation of discharge in Taihu Lake was established with multiple linear regression. The annual sequence matrixes of the impact factors of the discharge were classified using clustering analysis according to the similarity, the years similar to the objective years were determined, and, finally, the regression model parameters were calibrated based on the data from similar years. Compared with the regression model based on the common series data, the regression model based on the data from similar years has a higher accuracy.

Abstract:In order to solve the problem of conductor galloping on ultra-high-voltage transmission lines, a kind of phononic crystal conductor which consists of a conductor, spacers, and spring oscillators is proposed. Based on the vibration differential equation of the conductor and Bloch theory, the transfer matrix method is established to calculate the vibration band structure of the phononic crystal conductor. The calculated results show that the phononic crystal conductor exhibits local resonance band gap characteristics in the frequency range of conductor galloping. In order to verify the band gap characteristics of the phononic crystals conductor, using a four-divided conductor as an example, the finite element method is employed to calculate the amplitude and frequency responses of the finite periodic phononic crystal conductor. The results show that remarkable vibration attenuation of the conductor occurs in the frequency range of band gaps, which may provide a new idea for vibration control of conductor galloping on transmission lines.

Abstract:In view of fewer drilling wells and the difficulty of thin reservoir prediction in the rolling exploration stage in an area in Huizhou, the pre-stack simultaneous inversion technique based on the regularization operator was adopted to solve the problems of the difficulty of determining the lateral boundary of sand using the skewed distribution of drilling. More reasonable variation and variation functions were determined and treated as the key parameter input for geo-statistics inversion. The predicted thickness of the vertical thin reservoir was improved by geo-statistical inversion. The inversion results show that the reservoir in the design well X3 will develop, and data from the new drilling well X3 verify the result. There are three sets of sand bodies in the target zone: A2UP, A2LOW, and A2, which are mutually unconnected.

Abstract:Toppling failure of unstable rocks was analyzed using fracture mechanics. Based on tensile-shear fracture tests of rock samples, fracture initiation and propagation mechanisms under loading were analyzed, and crack propagation during the fracture process was investigated. The effects of the crack length, width, and inclination angle as well as the loading point on the failure mode and stability of unstable rocks were discussed. An overhanging rock, the Taibaiyan unstable rock in Wanzhou District of Chongqing City was used as a case study. The stress state of crack tips under different cracking conditions was calculated using the finite element software ANSYS, the relationship between the complex breaking stress intensity factor and stress state was discussed, and the dynamic process of crack propagation was simulated. Results show that, during the processes of tension, shear, and toppling failures of unstable rocks, tensile stresses were concentrated at creak tips, unstable rock cracking was first induced by tension failures, and shear-compression failures occurred at the bottom. The sensibilities of the factors to the instability of unstable rocks were ranked in an descending order as follows: the loading position, crack length, crack inclination angle, and crack width.

Abstract:The weak form of the extended finite element method(XFEM)with the initial stress field was derived, and was used to numerically simulate the crack in a weld-induced residual stress field. A more accurate stress intensity factor(SIF)was obtained with the interaction integral method. Based on this, the variation of SIF of steam generator safety-end dissimilar metal joints with the crack depth in the weld-induced residual stress field was analyzed. The results show that SIF increases first and then decreases with the continuous propagation of the crack inside the welded joint, indicating that the resistance of a material against crack propagation increases first and then decreases. The method of exerting an initial stress field utilizes the advantage of XFEM in simulation of crack propagation, and avoids the repetitive computation induced by grid updating.

Abstract:Research on the inter-annual and multi-decadal sea level variability which may influence the long-term trend of the sea level change in the tropical Pacific Ocean was reviewed, the effect of two types of El Niñ o events on the inter-annual sea level change in the tropical Pacific Ocean was summarized, and the close relationship of the multi-decadal changes in trade winds and sea level in the tropical Pacific Ocean was revealed. It is pointed out that the pattern of recent sea level change in the tropical Pacific Ocean is determined by the trade wind intensification, and the decrease of strength of El Niñ o events is favorable to this pattern, while the effect of La Nina events needs to be further studied. Data limitation leads to fewer quantitative research achievements of the multi-decadal change, and the heat flux model for study of inter-annual and multi-decadal sea level variability needs to be improved.

Abstract:A three-dimensional(3D)hydrodynamic model was developed based on FLOW-3D. The influences of the lateral spacing and relative installation elevation of the turbines and incoming velocity on the hydrodynamics around two parallel-arranged horizontal-axis tidal stream turbines were investigated. Numerical results show that an increase of the lateral spacing between two turbines leads to a decrease of the maximum fluid force acting on the turbines in the flow direction, with a maximum decrease of 6. 62%, and a decrease of the maximum velocity in the accelerating region of the wake field, with a maximum decrease of 1. 21%. The changes of relative installation elevation of turbines and incoming velocity have significant impacts on the rotating speed of turbines, maximum fluid force acting on turbines, and the velocity distribution within the wake field.

Abstract:A finite element model of bucket foundation embedded in an elastic half-space was established using the finite element software ABAQUS. The accuracy of simulated results of the model was verified by comparing the numerical solution with existing analytical solutions. The influences of different factors on the vertical initial dynamic impedance of bucket foundation and the relationship between initial dynamic impedances of the bucket foundation and shell foundation were studied. The results show that the length-to-diameter ratio and thickness-to-diameter ratio of the bucket foundation, soil Poissons ratio, soil shear modulus, and soil nonhomogeneity have significant influence on the initial impedance, while bucket foundation material has little influence on the initial impedance. The initial impedances of the bucket foundation and shell foundation are nearly the same, and the bucket foundation can be simplified as the shell foundation in simulated calculation.

Abstract:In order to obtain the aeolian vibration property of large cross-sectional conducts JL1X1/G2A-1520/125-481 used for ultra-high voltage(UHV)power transmission, governing equations for aeolian vibration of this type of conduct were constructed. The double amplitude, allowable amplitude, and power dissipation per unit length at 16 equally spaced frequency points in a band of frequencies between 8 Hz and 80 Hz were calculated, and the dynamic bending strain and stress at the suspension point for each frequency point were determined by the maximum amplitude at the antinode. Study shows that, under the self-damping vibration condition, the double amplitude of the conduct increases first and then decreases with the increase of the frequency, with a maximum value at a frequency of near 20 Hz, and the vibration amplitude of the conduct exceeds the allowable value when the vibration frequency ranges from 20 to 40 Hz. The power dissipation per unit length increases first and then decreases with the increase of the frequency, and reaches the peak value at a frequency of 40 Hz. In the band of frequencies between 20 Hz and 40 Hz, the dynamic bending strain and stress of the conduct were greater than their allowable values. Compared with the weakest band of frequencies between10 Hz and 20 Hz of the common cross-sectional conduct, the weakest band of frequencies of large cross-sectional conduct JL1X1/G2A-1520/125-481 is between 20 Hz and 40 Hz, which should be paid more attention in vibration prevention and damping schemes.

Abstract:It is necessary to monitor the state of ZnO arresters to guarantee their safe operation. In order to select a best way to monitor the state of arresters, the advantages, disadvantages, and application of each monitoring method were analyzed. The results show that the harmonic analysis method is the most effective method. The properties of the harmonic analysis method in practical application could be improved by modifying the resistive leakage current and selecting an appropriate window function when conducting fast discrete Fourier transform on the collected signals. Through review of monitoring technologies in China and abroad, it can be found that in the future, the overall development trend of online monitoring methods of ZnO arresters is to develop fully automatic and multi-functional integrated online insulation monitoring systems.