Abstract:Rainfall-runoff relationships were developed and comprehensively assessed for five basins located in semi-humid and semi-arid areas. It was shown that a common rainfall-runoff relationship can represent that of three basins far away from one another. The error was allowable and the accuracy was high. Three evaluation metrics, including the similarity index, the relative root mean square error, and the topography index, were employed to quantitatively assess the similarity of the underlying surface in selected basins. Results show that a common rainfall- runoff relationship can describe different basins with similar underlying surface conditions, even though they are far from one another. It was concluded that the relative root mean square error and the distribution curve of the topography index are more suitable for assessing the similarity of the underlying surface in semi-humid and semi-arid basins.

Abstract:Based on 26 single-peak floods between 1965 and 2009 in the Dapoling sub-watershed (or Dapoling Basin) in the upper Huaihe River, the mean basin lag time was calculated. The observed data were delimited by the year 1985 according to the land use change to compare the variation of mean basin lag time, calculate the lag time for different rainfall depths, and analyze the respective relationship of lag time with runoff depth and peak discharge. The results show that the land use change caused a large variation of the mean basin lag time. The lag time from the centroid of the rainfall hydrograph to peak time TLPC decreased from 9.98h to 5.26h after the land use change. The lag time from the centroid of the rainfall hydrograph to the centroid of the discharge hydrograph TLC, the lag time from the beginning of a rainfall event to peak time TLP,and the lag time from the peak rainfall intensity to peak discharge TLPP increased after the land use change. The TLC, TLP, and TLPP values increased from 21.32h to 26.77 h, from 34.64 h to 35.08 h, and from 10.00 h to 11.50 h, respectively. During the periods before and after land use change and the entire period in the Dapoling Basin, there was a certain relationship between the four lag time variables and the rainfall depth, but no relationship was found between lag time and runoff depth or between lag time and peak discharge.

Abstract:In terms of the landscape pattern, this study made an assessment of the landscape ecological health of the Zhangweinan River Basin in three eras (the 1980s, 1990s, and 2000s). This study identified the impact of climate change and human activities on the basis of analysis of the evolution trends of watershed landscape ecological health and also quantitatively determined the contribution of different human activities. The results show that, since the 1980s, the landscape ecological health of the Zhangweinan River Basin has presented a worsening trend. The contributions that climate change and human activities made to the evolution of the landscape ecological health are 13.95% and 86.05%, respectively. As driving factors of human activities, urbanization and the utilization of water resources have negative effects on watershed landscape ecological health evolution, with contribution rates of -37.19% and -34.89%, respectively, while soil and water conservation has positive effects on watershed landscape ecological health evolution, with a contribution rate of 25.72%.

Abstract:In order to strengthen the management of risk sources and guarantee the security of drinking water source areas, the drinking water source area of the Taizhou Third Waterworks was used as a case study. A risk identification system for risk sources (such as plants discharging wastewater without treatment, sewage treatment plants, and wharfs) was developed considering factors including the hazard degree of risk sources themselves, the control mechanisms of risk sources, and the hazards caused by risk accidents. Furthermore, the water environmental integrated risk assessment system for drinking water source areas was improved by enhancing the environmental regulation ability and emergency response capability. Grading standards and weights of indices, as well as risk grade dividing standards of risk sources and drinking water source areas, were obtained from surveys and expert panel acts. On the basis of evaluation systems, the evaluation results were obtained: (a) there are eight middle-risk sources and no high-risk source around the Taizhou Third Waterworks, and (b) the risk level of the water source area of the Taizhou Third Waterworks is low.

Abstract:In order to obtain the strength safety factor of concrete dams in multi-axial stress states, taking concrete gravity dams as an example, the safety factors for multi-axial strength were calculated with the overload factor K1 and the failure distance factor K2. The calculated results show that K1 is slightly less than the safety factor K0 for uniaxial strength in the two-axial tension-compression zone, K1 is greater than K0 in the two-axial compression- compression zone, and K2 is less than K1 and K0 in the two-axial tension-compression zone and compression- compression zone. This indicates that the safety factor for multi-axial strength of concrete dams is significantly different from the safety factor for uniaxial strength. The safety factor for multi-axial strength should be used in the strength design and safety evaluation of concrete dams.

Abstract:Based on densification and surface coating using the electro-migration reaction of silicate ions, the effects of mortar properties, such as the ratio of water to binder, mineral admixture, curing period, and thickness of the specimen, on the surface coating layer thickness, compressive strength, flexural strength, and resistivity of treated mortar specimens were investigated. The results show that the produced coating layer thickness, compressive strength, flexural strength, and resistivity of the specimens increase with the decrease of the ratio of water to binder and the increase of the curing period. The coating layer thicknesses and resistivity of mortar specimens with different admixtures follow an order of silica fume > slag > control (without admixtures) > fly ash. The times corresponding to the appearance of the resistivity peak of the specimens with silica fume and slag are shortened compared with that of the control specimen. The increments of compressive and flexural strength of the mortar specimens with silica fume are higher than those of the control mortar specimen. However, the addition of fly ash exerts little influence on the compressive strength and flexural strength of electrochemically treated specimens. The thickness of mortar specimens has little influence on the properties of electrochemically treated mortar specimens.

Abstract:Ground-penetrating radar (GPR) technology was used to detect the abnormality of a gravel cushion, and the characteristics of GPR response to four abnormal defects, including gravel cushion shedding, gravel cushions with dense and loose interfaces, a gravel cushion with varied thickness, and a gravel cushion filled with loose rock, were studied. Through temporal profile evaluation, drilling data validation, and comparative analysis of a typical single-channel time-domain waveform and its frequency spectrum, the results show the following: the typical single- channel waveform for gravel cushion shedding is characterized by an absence of the event on the profile, the reverse phase of the weak reflection of the interlayer, spectral energy distributed over the whole frequency range, and strong signals appearing in the 550 to 800 MHz bands; the typical single-channel waveform for the gravel cushions with dense and loose interfaces presents the event on the profile, spectrum energy that concentrates in the low-frequency area, and more energy peaks; the typical single-channel waveform for a gravel cushion with varied thickness shows the time difference in reflected waves between the upper and lower interfaces (upward convex event or pull-down event); the typical single-channel waveform for a gravel cushion filled with loose rock shows strong-amplitude complex waves (a random event with a diffraction fringe), significant energy peak superposition, and a higher peak.

Abstract:In order to use the post-install pullout method to test the compressive strength of fiber cement mortar and simulate the status of reinforcement, synthetic fiber (polypropylene fiber and polyvinyl alcohol fiber) cement mortar and steel fiber cement mortar were used to reinforce plain concrete blocks, respectively. After the reinforcement, post-install pullout testing of the reinforced layer was carried out to obtain the pullout force. Based on the relationship between the representative value of the pullout force and the representative value of the corresponding compressive strength of fiber cement mortar test cubes, a fitting strength measurement formula was established using the discrete least squares approximation method. Results show that the accuracy of the strength measurement formula was high and the effectiveness of the strength measurement formula was validated in practice. The incorporation of steel fiber has a better effect on the increase of the pullout force than the synthetic fiber. According to the strength measurement formula, the post-install pullout method can test the fiber cement mortar on-site when the compressive strength ranges from 20 to 90 MPa.

Abstract:Submerging tests with setting water injection holes and sensors, like moisture meters, were set up on a large-thickness self-weight collapsible loess field in Yuci District, in Jinzhong City, Shanxi Province. The results show that the diffusion pattern of the wetting front is rather complicated due to the feature of moisture spreading in test pits from the bottom up, from the top down, and from the center to the two sides because of setting water injection holes. After 52 days of immersion, the whole section of exploratory wells basically reached saturated water content in the test pits. The layout of water injection holes saved a great deal of time and cost of the experiment. The curve of volumetric water content changing with time can be divided into four stages: the early stable stage of volumetric water content, the growth and change stage of volumetric water content, the steady and extended stage of saturated water content, the late and slightly decreasing stage of volumetric water content.

Abstract:Using the contractometer, shrinkage experiments were performed on expansive soil improved with weathered sand through wet-dry cycles to study the variation law of the shrinkage indexes of the improved expansive soil. Based on investigation of the changing characteristics and mechanism of the linear shrinkage rate, volumetric shrinkage rate, shrinkage coefficient, shrinkage limit, and expansion-shrinkage ratio of experimental specimens through wet-dry cycles, a formula for calculation of the shrinkage limit of the improved expansive soil with different numbers of wet-dry cycles was established. Some conclusions are drawn from the test results: the linear shrinkage rate and volumetric shrinkage rate gradually decreased with the increase of the number of wet-dry cycles, and tended to be stable after four wet-dry cycles, with maximal reductions occurring when the mixed amount of weathered sand increased from 0 to 20%; the shrinkage coefficient decreased exponentially with the increase of the number of wet-dry cycles, and tended to be constant after four or five wet-dry cycles; the shrinkage limit increased by a quadratic function with the numbers of wet-dry cycles, and the increment of the shrinkage limit gradually decreased with the increase of the mixed amount of weathered sand through wet-dry cycles; the expansion-shrinkage ratio gradually decreased and tended to be stable with the increase of the number of wet-day cycles, and the value of the expansive soil decreased significantly by mixing with weathered sand, which allowed the expansive soil to meet the standard of embankment filling.

Abstract:A finite element model of a 1.5 MW wind turbine blade was established, and sensitivity analysis of key structural parameters was carried out. The results show that the ply angle has the greatest influence on the structural performance of the blade, with the width and the layer thickness of the spar cap coming second, and that the layer locations of the spar cap and the position of the shear web have the least influence. Based on the sensitivity analysis, an optimization design mathematical model pursued with respect to minimum mass of the blade was developed. The width, layer number, and layer location of the spar cap, and the position of the shear web were employed as the design variables, while the demands of strength, stiffness, and stability of the blade were taken into account as the constraint conditions. The optimization design of the blade was carried out by combining the genetic algorithm and the finite element method. Compared with the original design, the optimization design results achieve a decrease of 9.8% of blade mass, and the strain distribution of the structure is more reasonable, without occurrence of resonance, showing that the method used in this study is efficient.

Abstract:Based on the waveform data of the Jason-2 altimetry satellite from 2008 to 2013, the editing standard, geophysical correction method, and waveform retracking method for satellite altimeter data were studied using Lake Baikal as a case study. The annual and seasonal time series of the abnormal water level of Lake Baikal were calculated using the waveform retracking data, and the seasonal variation rules of the water level were analyzed. The water level of Lake Baikal in October 2013 was predicted using a combined model and compared with the altimeter-derived water level. The results show that the waveform retracking method improves the measurement accuracy of the water level of Lake Baikal, and this is a feasible method of investigating the variation of water level.

Abstract:During the simulation of material mechanical properties of granular materials using the discrete element method(DEM), in order to guarantee the continuity of the generated grading curve for the numerical specimen and the conformity of the generated grading curve with the desired grading curve, a new method based on the probability density function (PDF) was proposed to generate a numerical specimen of the particle flow DEM. A parameter to describe the mismatch of grading was defined to quantify the deviation between the generated grading curve and the original grading curve. A comparison of the proposed method and the existing method of specimen generation was conducted and the influence of the particle number on the generated grading curve was investigated. The results show that the proposed method can generate specimens of an arbitrary grading curve and the generated grading curve has a high degree of continuity and smoothness. Moreover, as the number of generated particles increases, the generated grading curve based on the PDF converges to the original grading curve.

Abstract:In consideration of the size effect of the small-scale cylinder and the obvious lateral friction effect of the square box in a dredged sludge vacuum drainage laboratory test, an instrument for the dredged sludge vacuum drainage laboratory test was developed, with a large-diameter cylinder used as the test container. The instrument consists of seven parts, including the model box, drainage system, pressure system, vacuum pumping system, valve controlling system, tail water collection system, and measurement system. Three groups of comparative experiments for instrument testing under three vacuum conditions show that the test results accord with the basic law of vacuum drainage, and also confirm the existence of the optimal vacuum degree.

Abstract:Based on the complex network theory, the structural vulnerability of a distribution network was assessed from the view of topology of structures. A multi-objective planning model for distribution network optimization was built, with aims to minimize the summation of investment and operation cost, as well as to optimize the structural vulnerability index. An improved minimum-cost spanning tree algorithm was adopted to optimize this planning model. By using the sum of the decrement rate of the economic target and the increment rate of the structural vulnerability target as the objective functions in the iteration process, the multi-objective problem could be solved as a single-objective problem. Results of a sample system with 16 nodes verify the feasibility of the proposed method used for multi-objective structure optimization of the distribution network. The developed planning model can effectively evaluate the structural vulnerability of a distribution network, so as to acquire an optimal planning scheme with a stable structure and with little cost.

Abstract:In order to suppress the fluctuations of the rotor speed and electrical power of the doubly-fed induction generator (DFIG) system when it works at a wind speed greater than the rated value, a new coordinated regulation strategy is proposed using the coordinated passivity techniques, with the pitch angle regulation and excitation voltage control simultaneously considered. First, based on analysis of the characteristics of wind turbines and the basic electromagnetic relationship of DFIGs, a four-order nonlinear model was established for regulation of the pitch angle and control of the excitation voltage of DFIGs. In particular, the formula of the wind power utilization coefficient and pitch angle was fitted with the polynomial function, and the uncertainty of the fitting result was modeled, ensuring the high accuracy of the system model. Secondly, pitch angle control was realized based on design of the former two orders of the robust controller using the Lyapunov techniques, and excitation voltage control was achieved based on the coordinated passivity techniques. Thus, the passive feedback of the whole system was obtained, and the system is both robust and tends to be stable. The simulation results validate the effect of the control strategy. The effectiveness of the present control strategy was also verified by its comparison with other control strategies.