Abstract:A method for dividing watershed by grid inlaid in watershed basic unit is discussed. As big data can precisely describe space distribution of rainfall and spatial variability of underlying surface, a calculation method based on big data, considering effects of space distribution of rainfall and spatial variability of underlying surface on runoff yield and confluence, is proposed. Through an introduction of “grid drop”, the physical nature of watershed instantaneous unit hydrograph is revealed, and the theory of geomorphologic instantaneous unit hydrograph by Rodriguez-Iturbe and Valdes is supplemented. In addition, the limitations of the isochronism line method and the unit hydrograph method are investigated. It can be concluded that the proposed theory of runoff yield and confluence by grid inlaid overcomes the disadvantage and assimilates the advantages of the two methods mentioned above, and provides a possibility of unifying the two methods.

Abstract:The distribution of patterns of large alluvial rivers in China and the reason for their formation were analyzed based on remote sensing images, field survey data, hydrological data, and sediment data. Alluvial reaches of rivers in China are mainly meandering and braided reaches, while some local reaches are anabranching and anastomosing reaches. With the general and special characteristics of the distribution of river patterns taken into account, three critical factors are considered to be the main reasons for the formation of river patterns; the relative sediment transport rate(the ratio of the incoming sediment load to the sediment transport capacity), the relative riverbank erosion shear stress(the ratio of near-bank flow shear stress to the critical erosion-resistant shear stress of the river bank), and control of valley terrain(e. g. , the valley node and channel width).

Abstract:Based on Landsat TM remote sensing images of Liaoning Province in 2014, the characteristics of evapotranspiration for different land use types from the perspectives of time and space were analyzed by calculating the actual evapotranspiration for different land use types and using the discretization function of the ArcGIS software. The results show that the actual evapotranspiration was significantly affected by the land use types, and the intra-annual variation characteristics of actual evapotranspiration varied for different land use types. The contribution of the evapotranspiration depends on the size of the land with a certain land-use type. There is a high degree of consistency between the spatial distribution of evapotranspiration and land use types, indicating that evapotranspiration is closely linked to land use types.

Abstract:Based on measured data of the dam breach of Tangjiashan Barrier Lake, the process of the dam breach was analyzed using the BREACH model and the DB-IWHR model developed by the China Institute of Water Resources and Hydropower Research. A sensitivity analysis of the two models to different parameters was also performed. Results show that, using the parameters of the dam, the two models can both reflect the flooding process induced by the dam breach; the calculated results of the peak flow are more sensitive to the input parameters of the downstream slope and porosity in the BREACH model; the DB-IWHR model improves the calculation of the erosion parameter and downstream water depth, resulting in calculated results less sensitive to the input parameters; and the DB-IWHR model provides software in the Excel format, with a high stability in numerical analysis, which is transparent, self-explanatory, and friendly to practitioners.

Abstract:In order to investigate the characteristics of flow fields around circular cylinders, a numerical model was developed by combing large eddy simulation(LES)with the characteristic-based operator-splitting finite element method. The model was used to simulate flow fields around a circular cylinder and two circular cylinders in tandem arrangement, and the obtained results agree with the existing results. The simulation results show that, for the flow around a circular cylinder, with the increase of the Reynolds number, the vortexes occurring at the top and bottom surfaces alternatively in the near-wake region gradually approach each other and pass along the horizontal line through the geometric center of the cylinder, and the location of vortex shedding gradually approach the cylinder; for the two circular cylinders in tandem arrangement, with Re=1000, the critical space between the two circular cylinders is 2.25 to 2.50 times their diameters; when the space between the two circular cylinders is smaller than the critical space, vortex shedding does not occur at the rear of the upstream cylinder, and the pressure in the space between the two circular cylinders is stable; when the space between the two circular cylinders is larger than the critical space, vortex shedding occurs, and strong negative pressure regions occur at the top and bottom surfaces alternatively in the near-wake region of the upstream cylinder.

Abstract:In order to explore the factors influencing the hydrodynamic performance of an H-type straight-blade tidal turbine, based on theoretical analysis, a three-dimensional model of an H-type straight-blade tidal turbine was established using large-scale modeling software UG, and three-dimensional numerical simulations were carried out using the Fluent software and the sliding mesh method. Under the conditions with the same airfoil type of H-type turbine blade and the same turbine solidity, the hydrodynamic performance of the tidal turbine was analyzed by changing the number of runner blades and inflow velocity. The results show that the number of blades has a significant effect on the hydrodynamic performance of the H-type straight-blade tidal turbine. The greater the number of blades, the smaller the output torque is. When the number of blades is three and the tip speed ratio is 1.63, the highest turbine power coefficient is 31.21%.

Abstract:The characteristics of the cohesive zone at crack tips throughout the fracture process were studied based on the initial fracture toughness(IFT)criterion and cohesive crack model. Single-edge notched beams with different sizes, subjected to three-point bending, were used as specimens, and the length of the cohesive zone at crack tips, the cohesive stress of concrete, and the crack opening displacement(COD)were calculated. The calculated results were verified with the results from tests and the finite element method(FEM). Results show that the maximum and critical lengths of the cohesive zone increase with the size of specimens; the maximum length of the cohesive zone is influenced by the tensile softening curve, while the whole fracture process is slightly affected by the tensile softening curve; after the peak load is reached, the COD is approximately linearly distributed; and the distribution of cohesive stresses depends on the tensile softening curve.

Abstract:A three-dimensional numerical model for debris flow was established with the particle discrete element method(DEM), and the movement characteristics of debris flow were analyzed from the full and local aspects. The results show that the movement process of debris flow can be divided into three stages, including starting acceleration, high-speed sliding, and reduced-speed deposit. When the bottom of the slope is flat, large particles are found on the surface of the deposition body, but small particles are in the middle and low areas. The velocity and energy loss of debris flow is significantly influenced by the contacts and collisions between particles. The maximum speeds of different parts of the debris flow are almost the same, and the time required to reach the speed peak is related to the initially horizontal position of particles, but not related to the deposit depth. Area division is distinct in the deposition body, and the particles of the deposition body are arranged according to their initially horizontal positions. The maximum deposit height is at the slope toe, and the deposit height gradually decreases towards both sides. Significant lateral movement occurs in the debris flow in the early and late stages, which can expand the scope of a disaster.

Abstract:In order to meet the refined management demand of optimal operation of large-scale cascaded reservoirs and solve the problems of long running time and low computational efficiency, a parallel method based on the Fork/Join multi-core parallel framework is proposed for optimal operation of large-scale cascaded reservoirs. A parallel discrete differential dynamic programming(PDDDP)was designed to describe the parallelization scheme for optimal operation of cascaded reservoirs based on the Fork/Join framework. The long-term power generation optimal operation of large-scale cascaded reservoirs on the Hongshui River was used as a case study. The testing results show that the parallel method can make full use of the acceleration performance of the multi-core processor, significantly reducing the computation time, and improving the computational efficiency. Moreover, the choice of the reasonable scale control threshold of the Fork/Join framework is critical to taking full advantage of parallel computation.

Abstract:Based on the principles of fairness and efficiency, an index system and a projection pursuit(PP)model were constructed for water allocation in Wenshan Zhuang and Miao Autonomous Prefecture. The novel bat algorithm(NBA)was integrated into the PP model to solve the problem of the difficulty in determining the optimal projection direction. The established NBA-PP model was used for water allocation in eight counties in Wenshan. Five typical testing functions were used to validate the results of the NBA algorithm. The simulation results were compared with the results from the basic bat algorithm(BA), the artificial bee colony algorithm(ABC), the cuckoo search algorithm(CS), and the differential evolution algorithm(DE). The results show that the NBA algorithm can effectively balance the global search and local development abilities by introducing habitat selection strategy and the self-adaptive echo-Doppler effect mechanism. Compared with the DE, CS, ABC, and BA algorithms, the NBA algorithm performs better in optimization, and it shows a higher convergence rate, higher precision, better convergence stability, and better convergence reliability. The water allocation results using the NBA-PP model are more scientific and objective than using other classification methods.

Abstract:To investigate the effects of permeability and thickness of materials under different loads on the pollution prevention capacity of a cutoff wall, contaminant transport was calculated based on analysis of the engineering properties of the soil-bentonite cutoff wall, and the breakthrough time of the cutoff wall was analyzed under different pressures and boundary conditions. Results indicate that soil-bentonite has a moderate level of compressibility, and the difference between the hydraulic conductivities at the top and bottom of the cutoff wall may reach one order of magnitude. There is a large difference in the breakthrough time calculated with two standards, i. e. , the relative pollutant concentration reaching 10% and the stable pollutant flux reaching 5%, with the ratio of calculated breakthrough time ranging from 1.42 to 2.21. The pollutant flux and relative concentration downstream of the cutoff wall calculated with parameters of the bottom of the cutoff wall are less than those calculated with the initial parameters, and the corresponding breakthrough time of the former is longer than that of the latter. According to the results obtained with the parameters under the maximum pressure, the designed cutoff wall will be dangerous.

Abstract:Based on annual maximum 1-day and 3-day rainfall data from the Changzhou precipitation station from 1951 to 2015, a joint distribution function was constructed using the Copula function, and the corresponding co-occurrence return period and risk of rainstorm combination were calculated. Then, the function was used to evaluate the probable return period and risk of a rainstorm in Changzhou City on June 26, 2015. The results show that the co-occurrence return period when the annual maximum 1-day and 3-day rainfall according to a certain design standard encounter is larger than the respective return periods of annual maximum 1-day and 3-day rainfall. The risk when two rainstorms with the same design frequency encounter is higher, and will decrease with the increase of the corresponding return period. The co-occurrence return period of the rainstorm in Changzhou on June 26 is 218 years, when the co-occurrence risk is only 17.4%, indicating that this rainstorm is special and rare. Flood control in Changzhou City still faces severe issues in the future.

Abstract:To reduce the uncertainty in calculation of unsteady flows, a multivariate alternate updating method is proposed based on the ensemble Kalman filter. This method updates water stage and discharge data alternately to calibrate unsteady flow, using the observed information without the large matrix calculating; meanwhile, scaling transformation is used in order to improve the water level filter precision. Numerical experiments emphatically investigate the effects of measurement accuracy and water level transformation coefficient on forecast precision of the method. The results show that the forecast error increases as the measurement accuracy decreases; the water level transformation coefficient can obviously improve the effect of the multivariate alternate updating method, the larger the water level transformation coefficient is, the higher the forecast precision will be; the multivariate alternate updating method has good calibrating performance and can improve forecast accuracy of unsteady flows in open channel.

Abstract:In order to solve the anti-sliding stability problem of the high-fill revetment along the Yangzte River, the vibro-replacement method was used to treat the deep overburden foundation of high-fill revetment. The results show that the design of the range of vibration stone columns, pile spacing, and pile length should be matched with the terrain and geological conditions. The vibro-substitution method combined with other foundation treatment methods can achieve better treatment effects. Through vibro-replacement, the anti-sliding stability of the revetment can meet the requirements of specifications. Using the vibration stone column to replace the soft foundation replacement to form a composite foundation, the problems of sand liquefaction, bearing capacity, and shear strength of the foundation can be solved effectively.

Abstract:In order to evaluate the performance of magnesium phosphate cement for rapid repair objectively and effectively, ordinary Portland cement mortar was used as a reference mortar, and comparative tests were conducted on the performances of the two kinds of cement mortar for rapid repair with 28d compressive strength. Test results show that, compared with the ordinary Portland cement mortar, magnesium phosphate cement mortar, as a rapid repair material, shows superior performance. The fresh mortar has a high fluidity and the property of rapid setting and hardening, with a setting time of less than 20min; the hardened mortar has good mechanical properties in the early stage, with 3h compressive strength and bonding strength of 42.5MPa and 1.45MPa, respectively; the elastic modulus of the magnesium phosphate cement mortar is low, with 28d static compressive elastic modulus and tensile elastic modulus decreasing by 13.5% and 8.9%, respectively; the tensile strain is high, with 28d ultimate tensile strain increasing by 38.8%; with the excellent durability, 56d dry shrinkage strain of the magnesium phosphate cement mortar decreases by 86.4%, with a value of 118μm/m, while 28d abrasion resistance strength increases by 45.8%.

Abstract:An analysis of the bearing and deformation mechanism of a composite foundation reinforced with geogrid-encased stone columns is presented in order to obtain its bearing characteristic and settlement calculation method. The composite foundation is divided into three parts: the reinforced section, the unreinforced section, and the underlying stratum. Based on the Hooke’s law of space problem and layer summation method, the settlement of the reinforced section is calculated with the layered iteration method in view of the relative slip displacement between the pile and soil of the reinforced section without a plastic zone. The compatibility of vertical and radial deformation of the unreinforced section is analyzed based on the pile-soil element model. The settlement of the underlying stratum is calculated by the layer summation method. Therefore, the calculation formula can be derived for a composite foundation reinforced with geogrid-encased stone columns. The results of engineering examples show that the settlement result obtained from this method is close to the measured one. Furthermore, the method is more feasible and can be applied in engineering practice, whereas the results calculated with other available methods are more dangerous.