Abstract:The release of nutrientsand microbial enzyme activities were monitored during the decomposition of Hydrilla verticillatum incubated in tanks with sediments or sands. It can be found that the decomposition rates of sediment and sand substrates were 64. 62%and 62. 15%, respectively. And during the plant decomposition, abundant nutrients were released into overlying water, and the dissolved oxygen concentrations and oxidation-reduction potential values decreased while the concentrations of total nitrogen and total phosphorus rapidly increased. At the end of decomposition(146 d), the quality of overlying water was recovered back to the initial level. The aromatic protein was the main dissolved organic matter into overlying water at first, then the humic acid- and fulvic acid-like refractory organic compounds increased gradually. The decomposition process of plant has a relationship with microbial enzyme activities, which is related to the water quality and the characteristics of plant itself. Cellulase and sucrase have a close relationship(r=0. 70, P<0. 05), which is affected by total organic carbon and total nitrogen. Meanwhile, the catalase has a significant correlation between dissolved oxygen and electrical conductivity in overlying water(P<0. 05), while alkaline phosphatase and urease had a negatively correlation with the total phosphorus and the ammonia nitrogen respectively(P<0. 05).

Abstract:The spatial distribution of a basin hydrological network is usually unreasonable, and the network may contain a large number of redundant stations and monitoring blank areas. In this regard, the 4-year and mean daily runoff data from 27 sites of the Lower Illinois River Basin is used in this study to achieve an optimization of hydrological network. Three objective functions, which are joint entropy ratio, redundancy ratio and Nash-Sutcliffe efficiency coefficient(NSE), are constructed to quantitatively evaluate the information of station network, based on three criteria of maximum joint entropy, minimum total correlation and minimum data fluctuation. The results show that a preliminary optimized site combination composed of 11stations can provide the same amount of information as the original station network, and at the same time, the redundant information can be reduced by 74. 2%. The total amount of information and redundant information were increased by 37. 1% and 22. 3% respectively by adding 3 sites on the basis of preliminary optimized site combination. Compared with the original station network, the number of optimized sites is 14, the total amount of information is increased by 37. 1%, and the amount of redundant information is reduced by 68. 5%.

Abstract:In order to study the supply source of widely distributed metasilicate type mineral water in the Changbai Mountain area, based on the information of hydrogeology and geophysics, the water supply of the Changbai Mountain springs from the Qiangtang Basin in Tibet was determined, through the hydrogen and oxygen isotope analysis as well as the water chemical analysis. TDS of the Changbai Mountain spring water is low, but with rich metasilicate, and this phenomenon indicates that the aquifer that water flows through is composed of silicate volcanic rock. Combined with the massive eruption of volcanic basalt in the area of Changbai Mountain, it can be concluded that the groundwater channel is composed of pore basalt. Therefore, the protection of Tibetan glaciers, rivers and lakes should be strengthened to ensure the sustainable development and utilization of high-quality mineral water in the area of Changbai Mountain.

Abstract:To obtain the spatiotemporal characteristics of soil moisture in Anhui Province, the Kriging method was firstly used to interpolate the in-situ observed and multilayer soil moisture to gridded data. Then, the spatiotemporal variability of soil moisture across this region was analyzed. A Back Propagation(BP)neural network optimized by the genetic algorithm was established to retrieve the soil moisture using the brightness temperature measured by the Fengyun 3B satellite. The results show that soil moisture across Anhui Province shows high temporal fluctuations. And, the soil moisture in the Huaibei plain and the Dabie Mountains is lower than the other regions. As depth becomes deeper, soil moisture has a higher value with lower seasonal and horizontal variability. The correlation between retrieved and observed daily gridded values across the five sub-regions is 0. 605, while the corresponding root mean square error is 0. 056 m³/m³. Clearly, the proposed retrieval algorithm is able to capture the spatiotemporal variability of soil moisture in Anhui Province.

Abstract:The thermal conductivity of municipal solid waste(MSW)is the basis of heat accumulation and migration in landfill, but it is lack of researches on the MSW thermal conductivity at present. Therefore, the thermal conductivity under different influence factors, which are water content, void ratio and mass fraction of organic matter, was carried out by the transient method in this study. The research results show that the coefficient of MSW thermal conductivity increases with the increase of saturation degree, while it decreases with the increase of void ratio under a same content of organic component. What’s more, the coefficient of thermal conductivity decreases with the increase of organic content when the void ratio is constant. When the degree of saturation increases from the dry state to the residual degree of saturation, the thermal conductivity coefficient increases quickly. Then, as the saturation continually increases, the conductivity coefficient increases steadily.

Abstract:A new interface element model with embedded spring is proposed to overcome the shortcomings that considers the position of connector in the mesh generation if the connector of steel-concrete composite structure is simulated by the spring element. In this model, the contact between the steel plate and the concrete is simulated by the interface element, and the action of connectors are simulated by the spring that can be located anywhere within the interface element. The model can not only consider various connections at the interface between the steel plate and the concrete reasonably, but also freely generate mesh without the influence from the position of connectors. The numerical simulations of push-out experiment and the arch foot of concrete-filled steel tube arch bridge show that the proposed model is convenient for mesh generation and of high calculating precision, which ensures the element model is suitable for the analysis of practical engineering.

Abstract:In past three years, variable loads of six structures during the construction were investigated in Xi’an and its surrounding areas. Different statistical methods were adopted to analyze the surveyed data, and the change regularities of variable loads during the construction process were obtained. Besides, the difference of variable loads between shear wall structure and frame structure during the construction were analyzed as well. Based on the statistical results of two structure types, recommended standard values of variable loads during construction were given and compared with other researches and current codes. The results show that variable loads during the construction are in accordance with extreme value-I distribution or exponential distribution. The variable loads of a same structural type has the same change regularities during the construction. Meanwhile, the smaller the statistical samples are divided, the greater the value of variable loads is, and the more concentrated the materials stack, the greater the difference among the standard values obtained by different methods is. In the building stage of vertical components, variable loads of a shear wall structure was greater than that of a frame structure, but values are close in other stages. A construction cycle can be divided into four stages, as vertical component construction, support building, horizontal component construction and support demolition, where the recommended values of variable loads are 1. 894 kN/m², 1. 716 kN/m², 1. 295 kN/m², and 1. 998 kN/m², respectively.

Abstract:A test device for the pullout test of reinforced bar in the rockfil has been designed. After that, a series of pullout tests for the ribbed steel bars in rockfill were carried out, and the shear characteristics of contact interface in the reinforced rockfill were studied. The experimental results show that the relationship curves between shear stress and shear displacement of the contact surface is obviously nonlinear, and the shape is similar to the parabola at the lower end. Meanwhile, the influence of overburden pressure on the test results is larger, and the peak and residual shear stress increases with the increase of overburden pressure, while the peak shear displacement decreases gradually. In addition, a damage constitutive model of contact surface is established based on the theory of damage mechanics, which can better simulate the influence of overlying pressure on the shear characteristics of contact surface and the nonlinear characteristics including the strain hardening, the strain softening and the residual state.

Abstract:The influence of the length of downstream pier wall and the width of the neck pier wall on the failure modes of gate slot, and the design method of shear bearing capacity were studied by static experiments on eight scaled gate slot specimens. The results show that the failure mode of the gate slot changes from the tensile failure of the neck pier wall to the shear failure of the downstream pier wall with decreasing the length of downstream pier wall and increasing the width of neck pier wall. The reliability of the stress graphic reinforcement calculating methods applied to the neck pier wall is verified by comparing calculated and actual reinforcement amount. The limit condition to design the shear bearing capacity of the downstream pier wall is given according to the experiment and finite element calculation results, which provides a reference for the revision of Design Specification for Hydraulic Concrete Structures(DL/T 5057—2009).

Abstract:Columnar jointed basalt develops in the arch dam foundation and the dam abutment of Baihetan Hydropower Station. After the water storage in the hydropower station, the head difference between the upstream and the downstream of dam will form a high seepage pressure, and the strength characteristics of rock mass under high osmotic pressure is one of concerned scientific issues in rock engineering. Therefore, artificial material with physical and mechanical characteristics similar to those of in-situ rock mass was used to make the columnar jointed rock mass model samples with the same joint structure. In order to investigate the effect of seepage flow pressure on the failure modes, strength and seepage quantity of jointed rock mass, a series of triaxial tests on the columnar jointed rock mass samples were carried out under different osmotic pressures. The experimental results indicate that the failure mode of columnar jointed rock mass is sliding failure which alongs the joint dip angle under seepage flow pressure. Moreover, the columnar jointed rock mass has a lower strength under seepage, and the peak strength of triaxial compression test is negatively correlated with the osmotic pressure. Furthermore, four stages for the stress-strain curve of columnar jointed rock mass under triaxial compression condition are summarized based on test results, and seepage quantity shows phased characteristics with the stress-strain curve. Additionally, the effect of seepage on columnar jointed rock mass strength and seepage flow is obvious.

Abstract:This study took the Changzhou site as an example, and collected the historical data of meteorological observation during 2000—2017 and the historical data of weather forecast during 2011—2015. We calibrated the Hargreaves-Samani model, the Multiple Regression model and the Fourier analysis model by using the ET₀ calculated by historical meteorological data based on the FAO56-PM formula, and applied these three methods to the daily ET₀ prediction based on the weather forecast for the next one to seven days during the period form April 21, 2016 to October 24, 2017. The results showed that the MR models had the highest prediction accuracy overall with the lowest δ_MAE(0. 751 mm/d)and the highest δ_AAC(87%)during the forecast periods of 1 d, 4 d, and 7 d, except that δ_RMSE was slightly higher than the HAR model during the forecast period of 3 d. In view of the fact that the accuracy of the weather forecast decreases with the increase of forecast period, it is suggested that the forecast period of Changzhou station should not be longer than three days. Further comparison on the accuracy of seasonal scale showed that the prediction accuracy of the MR model during the forecast periods from 1 d to 3 d in each season is higher than those of HAR model and FA model. Overall, the MR model has the highest prediction accuracy and should be used for ET₀ prediction at the Changzhou site.

Abstract:This study analyzed the influence of different test conditions and engineering measures on the distribution characteristics of multistage bifurcations based on the tail physical model of the Ganjiang River, and discussed the linkage responding law of multistage bifurcations. The results indicate that the distribution characteristics is influenced by discharge, branch mouth topography, position of the island head, entrance topography of branch and water surface slope at varying degrees. In addition, when an influence factor in a bifurcation is changed, the water diversion ratio in neighboring bifurcations will change, as well as other bifurcations, which is the linkage responding phenomenon.

Abstract:The influence of floating structure on the downstream flow structure in the finite flowing was studied by using a physical model test. By comparing the floating structure in different positions and under discharge conditions, the distribution of flow velocity, the non-uniform coefficient and the length of recirculation zone of the characteristic cross section are analyzed. The results show that the influence of floating structure position on the velocity distribution and the non-uniform coefficient is clearly observed, and the discharge condition also has a great influence on them. Besides, this effect shows an increasing trend with the increase of flow discharge. Both different positions and discharges have a significant impact on the length of the recirculation zone. In the practical engineering, attention should be paid to the engineering problems caused by the change of the positions and discharge. The change rule of downstream flow structure of floating structures during the process of running is obtained in this study, which can provide references for the design of floating structural stability.

Abstract:Physical experiments were conducted in this study to investigate the flow velocity distribution and the turbulence characteristics in the wake of a horizontal axis tidal stream turbine under the combined action of wave and current. The results show that the existence of wave would contribute to the recovery of flow velocity behind the support structure. Compared with that under pure current, larger velocity deficit was observed within the swept area and slower velocity recovery rate was found in the far wake, when the model turbine operates under the combined action of wave and current. It’s also found that the flow velocity in the downstream of turbine would increase with the increasing of wave height and wave period. Meanwhile, turbulence intensity in the flow field under combined wave and current is generally higher than that under a pure current condition. In addition, turbulence intensity would decrease with the increasing of wave period, while would increase with the increasing of wave height.

Abstract:Flow field of dual buoyant jets in wavy-crossflow environment was measured using the PIV technique. The phase-averaged and time-average velocity field in different conditions were qualitatively described, and the quantitative result of vertical velocity decay at the centerline was given by introducing a characteristic length(l_mb), considering effects of crossflow, wave and buoyancy. The results showed that, the effluent clouds were produced due to the combined effects of wave and current and the interaction of two jets was attenuated under the effect of wave. The buoyancy effect could reduce the jet deflection angle and the lateral width. Based on the dimensional analysis, dimensionless vertical velocity at the centerline could be divided into three regions: the near-field region(z/l_mb<3), the transition region(3<z/l_mb<6), and the far-field region(z/l_mb>6).