Abstract:In order to deeply analyze the hydrological characteristics and the mechanism of runoff generation and concentration in the Niyang River catchment in Southeast Tibet, the precipitation-runoff water balance problem is examined. Based on meteorological and hydrological observation data, such as daily precipitation and flow, at Gongbujiangda, Baheqiao, Gengzhang hydrological stations etc. in the Niyang River catchment, the phenomenon of watershed average precipitation calculated with the traditional Thiessen polygons method being less than the runoff is analyzed. The precipitation-runoff water imbalance problem is described. The method and steps for distributed computing of the watershed average precipitation for the Niyang River catchment considering the topographical features, spatial distribution regularity of precipitation, and distribution of hydrological stations are proposed, and an example calculation is given. The results show that misunderstanding of the spatial distribution of precipitation in the Niyang River catchment and the calculation of watershed average precipitation with the traditional Thiessen polygons method are the main causes of the water imbalance problem. The calculation of the watershed average precipitation should consider the vertical distribution differences of precipitation in the Niyang River catchment.

Abstract:Considering the hydrological calculation and prediction of ungauged basins, a distributed hydrological model, the THREW model, was adopted to study the upper basin of the Brahmaputra River from the Nuxia Hydrological Station. Surface meteorological observation, remote sensing of vegetation cover, snow cover area, and section hydrological monitoring data were used to calibrate the model, and the latest CMIP5 data were used to estimate the runoff evolution. The results showed that, in the upper basin of the Brahmaputra River from the Nuxia Hydrological Station, the Nash-Sutcliffe efficiency coefficient of monthly runoff simulation of the calibration period from 1991 to 1995 was 0. 75, the coefficient of monthly runoff simulation of the validation period from 1996 to 2000 was 0. 76, and the runoff markedly increased when the CO₂ discharge in the AR5 of IPCC was maximal.

Abstract:In order to obtain the operational characteristics of centrifugal pumps in a high-elevation area, the flow field inside a centrifugal pump at different elevations(0 m, 1 000 m, 2 000 m, 3 000 m, 4 000 m, and 5 000 m)was simulated numerically using the MRF model within the Fluent software with the actual operational parameters at an elevation of 3 000 m as input. The change rules of pressure and velocity in the flow field inside the centrifugal pump were examined. The results show that while the elevation is 5 000 m, the average pressure in the flow field inside the centrifugal pump is 47 672. 15 Pa, which is half of the average pressure in plain areas. The influence of the elevation on the velocity field and velocity vector field is small, and can be negligible.

Abstract:In regard to temperature control and crack prevention for concrete dams in plateau areas with high elevation and large temperature differences, a summary was made of research on concrete crack prevention during the construction of the first large concrete gravity dam, with a height of more than 100 meters, in the Tibet Autonomous Region. Based on on-site monitoring data during the dam construction for the Zangmu Hydropower Station, dynamic feedback simulation analysis technology was used to demonstrate the real working condition throughout the construction period. Then, risks that may occur during the later construction period were predicted according to the simulation results, and the related standards and measures for temperature control and crack prevention were adjusted and optimized.

Abstract:Indoor static experiments were conducted to investigate the kinetics and equilibrium processes of phosphorus(P)adsorption and desorption by sediments collected from the midstream of the Huaihe River. The results of the kinetics experiments showed that the kinetics process of the P adsorption and desorption could be divided into a fast stage and a slow stage, and that the fast stage occurred in the first 1. 5 hours, while the adsorption rate was about 16 times of the desorption rate. The results of the equilibrium experiments showed that the amount of the solid phase equilibrium absorption of P by sediments increased with the liquid phase P concentration, and the increasing speed was faster when the liquid phase P concentration was low, but gradually slowed when the liquid phase P concentration further increased. The amount of the solid phase equilibrium desorption of P by sediments increased with the increase of the amount of the solid phase equilibrium absorption of P. The amount of equilibrium adsorption and desorption of P by sediments per unit mass was 16% to 40% of the amount of equilibrium adsorption of P. The adsorbed P could not be completely desorbed, which indicated that the adsorption process and the desorption process were not reversible. There was a linear positive correlation between the P retention capacity by sediments and the amount of solid phase equilibrium adsorption of P by sediments per unit mass, and the retention rate of P by sediments was 0. 847 in the midstream of the Huaihe River.

Abstract:Simulated rainfall experiments were conducted with three slope gradients(11. 3°, 21. 8°, and 35. 0°)and three rainfall intensities(85 mm/h, 110 mm/h, and 125 mm/h)to investigate the rill evolution process on saline soil slopes in coastal reclamation. The evolution process of rill erosion was recorded with a digital camera, and then the image data were analyzed with Image-Pro Plus(IPP)6 software. The results are as follows: (a)Rills formed soon after the runoff occurred and the rill density changed rapidly with different slope gradients and rainfall intensities. The rill number, rill depth, average rill width, and rill density increased with the rainfall duration. (b)At low slope gradients the drop pits developed slowly, and the rill erosion rate was low. With the increase of the slope gradient, water concentrated in the drop pits rapidly, and the erosion rate increased, leading to rapid evolution of rills. (c)The number of rills increased with the rill depth. There were significant linear positive correlations of the slope erosion rate with the average depth of rills and Re at p< 0. 05 and p< 0. 01, respectively.

Abstract:FEM models of two different scales, including the reservoir basin and near-dam area, were established based on study of the method for determining the model boundaries. By extracting the boundary condition of the near-dam area model from deformation results of the reservoir basin model, a reservoir basin effect analysis method is proposed to study the effect of reservoir basin deformation on the deformation behavior of high concrete dams. Calculated results of a typical project show that reservoir basin deformation has a significant effect on the deformation of a high concrete dam with a large reservoir capacity. In the study of the operational performance and back analysis of mechanical parameters and deformation monitoring indices of high concrete dams with measured data, especially for the project with a wide area of water surface in front of it and a large reservoir capacity, the effect of reservoir basin deformation should be taken into consideration so as to fully understand the operational performance of dams, and effectively monitor the dam operation in safe conditions.

Abstract:In order to improve the performance of the biogeography-based optimization(BBO)algorithm applied to optimization design of engineering structures, an improved BBO algorithm was proposed through introduction of a nonlinear model for migrating species and an idea of “elite guidance”. The improved algorithm was then applied to optimization design for structural engineering. Taking classical truss structures with two continuous variables as examples, optimization design of structures with a minimum mass under the constraints was performed. Numerical experiments show that the improved algorithm has faster convergence speed, better stability, and better performance as compared with the BBO algorithm, and can be effectively applied to optimization design of engineering structures.

Abstract:In order to study the effect of leachate recirculation on the pore-water pressure migration in a landfill, a theoretical equation of the pore-water pressure was built under the premise of ignoring the leachate migration in the vertical direction and with consideration of the actual working conditions of leachate recirculation in the landfill, the liquid phase constitutive equation, the water balance condition, and biochemical degradation of organic compounds. The equation was solved under different boundary conditions, and analytical solutions were obtained under two conditions of group-well recirculation and single-well recirculation. The results showed the following: (a)In single-well recirculation, the pore-water pressure was stable after 30 days of recirculation, the pore-water pressure quickly decreased with the distance from the well, and the recirculation effect was greater within 15 m of the well and lesser beyond 20 m of the well. (b)In group-well recirculation, the pore-water pressure increased rapidly at the beginning of recirculation, then, the pore-water pressure in the landfill cells finally reached the recirculation head pressure, and the group-well recirculation had a stronger effect than the single-well recirculation. (c)High pore-water pressure is generated during leachate recirculation in the garbage, so, in practical engineering, the pore-water pressure should be considered when determining the recirculation time and distance.

Abstract:Based on the characteristics of unclassified tailings in the Sijiaying iron mine, experimental research on exploitation of new backfilling cementing materials that can replace the cement was carried out using lime, desulfurization gypsum, slag, and other solid wastes. Using scanning electron microscopy(SEM)and X-ray diffraction(XRD)analysis, the hydration mechanisms of the new backfilling cementing materials were analyzed, and the optimum ratio of activators was determined. The results show that the strength of the new backfilling cementing materials can meet the filling body strength requirements for safe mining in the Sijiaying iron mine when the mass fractions of slurry, lime, and desulfurization gypsum are 68%, 3. 5%, and 16. 0%, respectively, and the cement-sand ratio is 1∶8. The results also show that the new backfilling cementing materials have a more compact structure and coarser occurrence when compared with the cement. The hydration products of the new backfilling cementing materials are mainly AFt crystals and C-S-H gel, which greatly increases the age strength of the new backfilling cementing materials.

Abstract:The influence of different amounts of glass powder substituting for cementitious materials(0, 5%, 8%, and 15% by weight)on the compressive strength and acid corrosion resistance of concrete was studied through experiments. The mass loss and compressive strength loss of various specimens were compared after corrosion in 5% H₂SO₄ solution and 5% CH₃COOH solution for 28 d. The morphology of the specimens after corrosion was analyzed using SEM. The results show that the addition of glass powder can improve the corrosion resistance of concrete to H₂SO₄ and CH₃COOH, and the resistance of concrete to CH₃COOH was worse than the resistance to H₂SO₄. A great deal of gypsum formed on the surface of the specimens corroded by H₂SO₄. The surface of specimens corroded by CH₃COOH became loose, with a large amount of pores and cracks. When the substitution amount of glass powder was 8%, the specimens showed the best corrosion resistance to H₂SO₄ and CH₃COOH.

Abstract:In view of the problem that support vector regression(SVR)cannot provide better porosity prediction because different lithologic reservoirs have different pore types and different porosity structures, a new model for estimating porosity, taking lithology information into account, is proposed. In the model, the lithology information of the sample is converted to attribute values that are closely associated with the lithology information. A method that combines the grid search algorithm for rough screening and intelligent search algorithms(genetic algorithms and particle swarm optimization)for fine filtering was used to optimize the model parameters. The grid search algorithm for rough screening was used to determine the approximate scope of the optimal solution, and intelligent search algorithms for fine filtering were used to determine the optimal solution in a local region. The optimized parameters were used to establish the forecasting model. The predicted results were compared with the measured data. The results show that the prediction accuracy of the model is greatly improved when the lithology information is taken into account, and the prediction accuracy of the intelligent search algorithms for fine filtering is higher than that of traditional methods.

Abstract:Based on the difference of wave impedance between underwater sand strata and rock media, a stratigraphic model of fluctuant strata containing water, fine sand, gravel sand, and conglomerate was established using Tesseral2D software for seismic numerical simulation. Then, the forward calculation with the model was conducted under different channel spacings, least offsets, wavelet frequencies, and wave velocities in rocks. Under normal circumstances with a source frequency of 400 Hz, a least offset of 5 m, and a channel spacing of 1 m or 2 m, the seismic response is significant, with constant phases and less interference waves, which also well reflects the underwater stratum interface. In combination with the geological data from the bridge site area of the Second Nanjing Yangtze River Bridge, a stratigraphic model for underwater sand strata was established, containing water, silty clay, silty sand, gravel pebble, and conglomerate. Forward simulation using Tesseral2D software shows that, with a source frequency of 400 Hz, a channel spacing of 2 m, and a least offset of 5 m, the seismic response can well reflect the underwater interfaces between different rock strata, and determine the thickness and distribution range of underwater sand strata, providing an important theoretical basis for the exploration of underwater sand strata.

Abstract:Based on the Waveform data from Jason-2 and SARAL/AltiKa satellites, a new method of eliminating the gross error of altimetry data was developed. By eliminating the sea surface height that was not in the predetermined trajectory, the gross error in each segment of altimetry data was eliminated according to the sea surface height in each cycle of each Pass file, in order to improve the usability of satellite data in coastal areas. Through crossover adjustment, the time-varying signals for the radial orbit error and sea level were further weakened. The discrete sea surface height with high accuracy, which was obtained with the remove-restore technique, was gridded using the radial basis function method. A mean sea surface height model with grid resolutions of 2. 5′×2. 5′ was established. The root mean square error between the sea surface height data from the established model and the data from tidal stations is ±0. 017 m, and the standard deviation between the established model and MSS-CNES-CLS11 was ±0. 070 m. The results show that the established mean sea surface height model for Zhejiang coastal areas is reliable.

Abstract:Based on forecast data obtained from the China Meteorological Administration, Taiwan Meteorological Center, Japan Meteorological Agency, and Joint Typhoon Warning Center of the USA, 24-hour, 48-hour, and 72-hour ensemble forecasts of typhoon tracks of 31 typhoons over the Northwestern Pacific in 2013 were conducted using the weighted bias-removed ensemble mean method. Error analysis indicates that the results of ensemble forecasts using the fixed training method with a constant weighting factor are quite sensitive to the selection of training samples, showing significant fluctuation of error for different training samples, while the error of ensemble forecasts using the moving training method with a variable weighting factor shows a declining trend with the increase of the number of training samples and tends to be stable when the number reaches 40. Comparisons show that twin typhoons in the training period have a large influence on the forecast accuracy, and the accuracy is significantly increased by removal of the influence of twin typhoons. Based on comprehensive comparisons of forecast results of 2013s typhoon tracks, the moving training method with 40 training samples and without consideration of twin typhoons in the training period is recommended.

Abstract:Based on satellite remote sensing technology, this study used the analytical method of geomorphic feature lines to analyze the geomorphic evolution characteristics of the Jiangjiasha sand ridge, Huangshayang channel, and Kushuiyang channel during the period from 1973 to 2014. The results show that the Jiangjiasha sand ridge, Huangshayang channel, and Kushuiyang channel form an organic whole; the nearshore segment moves from west to east; and the offshore segment moves from north to south. The Kushuiyang channel has retreated significantly in the offshore direction(eastward). This may be related to the southward movement of the moving tidal wave formed by the intersection of the southern and northern tidal wave systems, and reveals the erosion and deposition patters of the seabed in this area.

Abstract:Using the mixing length of sediment-laden flow constructed with data fitting and combining the Prandtl mixing length theory, a new equation describing the velocity distribution of sediment-laden flow was established. Based on this new equation and the analogy of the relationship between the momentum transfer coefficient and mixing length, a new equation describing the vertical distribution of sediment concentration was also established. Through verification with observed data from the flume experiment and field survey, it was found that these two equations can objectively describe the vertical variations of velocity and sediment concentration, showing a higher precision in describing the sediment concentration. The error analysis shows that the error of the near-bottom velocity is large, indicating that the selection and judgment of the bottom boundary layer need further investigation; the error of the sediment concentration close to the surface is large, indicating that the selection of the reference point for the sediment concentration requires further theoretical research, in order to discard the influence of random effects.