Abstract:In order to analyze the complicated water temperature distribution law in the intersection area and the influence mechanism of flow structure on it, the numerical simulation software Fluent was used to simulate the time-mean flow field, turbulence characteristics and water temperature distribution in the river junction area under different conditions by changing the confluence angle and the confluence ratio, and to analyze the relationship between the water temperature distribution characteristics (water temperature non-uniformity index) and the characteristic parameters of the flow structure (turbulence kinetic energy and vorticity) in the intersection area under different working conditions. The influence mechanism of different flow structure on the water temperature distribution was explored. The results show that the flow shear affects the position of the hot mixing layer and the secondary circulation affects the shape of the hot mixing layer. The larger the confluence angle or confluence ratio, the smaller the cross section non-uniformity index and the faster the water temperature mixing. With the change of shear layer location (turbulent kinetic quantization shear), the hot mixing layer is closer to the outer bank wall (intersection to side wall), and the bending degree of the hot mixing layer increases with the increase of secondary circulation strength. It shows a good linear relationship between turbulence kinetic energy and vorticity and section heterogeneity index.

Abstract:This paper conducted systematic research on the mute feed effect caused by the change of project scheduling conditions of flood and waterlogging between three levels of basin, sub-basin and urban in the Taihu Basin. Taking the Taihu Basin and its internal water conservancy districts and towns as an example, different simulation conditions and scheduling scenarios were designed based on the idea of control variables, and the flood movement process in the basin under different flood control project conditions and scheduling schemes at various levels was quantitatively simulated. The mute feed effect of flood and waterlogging was analyzed from the aspect of water level variation at various levels. The results indicate that properly raising the drainage control water level of urban flood protection and waterlogging drainage project can relieve the flood control pressure of basin and sub-basin while ensuring the safety of urban internal flood control and drainage, but with limited effect. Modestly reducing the control water level of sub-basin drainage project along the Yangtze River and Hangzhou Bay can significantly reduce the water level of the Taihu Lake and sub-basins, and can also have a certain effect on the internal water level drop of urban. The capacity of flood discharge of the basin has highly increased with implementation of the flood releasing projects such as the Wusong River, and can also substantially reduce the water level of the Taihu Lake and sub-basins. However, further implementation of the sub-basin flood protection and waterlogging drainage project could only lower the internal water level of sub-basins, with almost no impact on the basin and the urban.

Abstract:In order to improve the accuracy of similarity analysis of precipitation images, a rainfall similarity search method based on daily precipitation images of watershed is proposed. The algorithm first extracts the daily precipitation, precipitation distribution, precipitation center characteristics of the precipitation images, and calculates the similarity distance of each characteristic respectively. Then, an ensemble weighting method of normalized discounted cumulative gain-improved particle swarm optimization is proposed to weight and fuse the three extracted features as the similarity measure of precipitation image. The similarity search experiments of daily precipitation images on the Jialing River Basin illustrate that the method proposed in this paper can better characterize the spatiotemporal characteristics of the precipitation image and quickly discover similar rainfall processes from precipitation images.

Abstract:To solve the problems of rough water-level edge and insufficient detection accuracy in existing algorithms, this paper proposes a high-accuracy water gauge level detection network, called DetSegNet. Unlike traditional methods that use a single network for the water gauge recognition and the water segmentation, DetSegNet innovates in the network structure, loss function, etc., by improving the YOLOv4 and DeepLabv3+ algorithms. It effectively integrates modules for water gauge scale recognition, water area segmentation, waterline detection, and water level calculation, achieving efficient localization and precise segmentation of the interface area between the water gauge and the water body. Experimental results show that DetSegNet surpasses existing algorithms in terms of detection accuracy and speed on water gauge image datasets. Field tests demonstrate that water level detection accuracy of this method is less than 1 cm, meeting the accuracy requirements of hydrological monitoring.

Abstract:To investigate the synergistic purification of photocatalysis and water recycling for nitrogen, phosphorus and imidacloprid pollution, three groups of ecological floating bed systems including the blank control, water circulation and photocatalytic water circulation, and six treatment groups were designed for the purification of two kinds of simulated water(nitrogen-phosphorus (NP) receding water and NP-imidacloprid complex polluted receding water).The experimental results showed that the water circulation enhanced the removal of nitrogen, and the removal rates of ammonia and nitrate nitrogen in the water of the water recirculating floating bed for the receding water purification of nitrogen and phosphorus increased by 5.5% and 27.1%, respectively, compared with the blank control floating bed after 7.d. The addition of photocatalytic purification technology could accelerate the nitrification of ammonia and nitrate nitrogen, and the removal rates of ammonia and nitrate nitrogen in the water of the water recirculating floating bed for the purification of nitrogen and phosphorus retreat water increased by 26.2% and 20.3%, respectively, compared with the blank control floating bed. Imidacloprid affected the purification efficiency of nitrogen and phosphorus in a water circulating floating bed. The TiO2 composite photocatalytic ceramic pellets had a good oxidative degradation effect on imidacloprid and a significant purification effect on the compound pollution of nitrogen, phosphorus and imidacloprid. The photocatalytic water recirculation floating bed purified 58.2% of imidacloprid in the compound polluted return water, and the removal rates of ammonia nitrogen, nitrate nitrogen and phosphate in the water body were increased by 72.4%, 15.0% and 14.8% respectively compared to the water recirculation floating bed without the addition of imidacloprid.

Abstract:By taking the Fuhe Basin and Heihe Basin as studying areas, this study employs the SWAT model driven by four distinct precipitation products (CMORPH CMA, CMFD, CMADS, MSWEP) to simulate the daily flow and evaluate the hydrological performance of these products in both humid and arid regions. Meanwhile, the sensitive parameters of watershed were selected by the adaptive method for factor fixing and subsequently the consistency check was performed to ensure their reliability. The results indicate that all four precipitation products achieved NSE values above 0.7, with CMORPH CMA and CMADS outperforming the rest by achieving 0.82 in the Fuhe Basin, while in the Heihe Basin, they scored 0.76, compared to CMFD and MSWEP which scored 0.72 and 0.74, respectively. Moreover, in the Fuhe Basin, all four precipitation products share the same sensitive parameters, but in the Heihe Basin, CMORPH CMA and CMADS have six shared sensitive parameters, while CMFD and MSWEP have five and eight sensitive parameters, respectively. These findings suggest that all four precipitation products can be successfully applied in both humid and arid basins, but the simulation performance of CMORPH CMA and CMADS is superior to that of CMFD and MSWEP. Additionally, the similarity of precipitation performance will enhance the similarity of selected sensitivity parameters during the model analysis.

Abstract:In order to study the influence of ice sheet on the local scour of composite piers and the distribution of flow field around them, the influence of different flow conditions and pier sizes on the local scour of composite piers was analyzed under different cover conditions based on the scour test of moving bed. The empirical equation for predicting the maximum thrust depth of composite pier under the conditions of open channel flow and overburden flow was established, and the flow field in front of the piers was measured by ADV. The results show that the scour pattern of composite pier is similar to that of tandem pier, and the maximum scour depth always appears in front of the pier. The depth of incoming flow, incoming flow velocity, pier size and ice sheet roughness are positively correlated with the maximum scour depth. In the rough ice-overburden flow condition, the maximum vertical velocity in front of the pier is the highest, resulting in greater maximum scour depth than that of open channel flow and smooth ice flow under the same condition.

Abstract:To study the mechanical and hydrological mechanism of vegetation, the water absorption distribution function of plant root was introduced to describe the water uptake characteristics of different root architectures, and the calculation model considering the hydro-mechanical reinforcement of vegetation was established for the slope stability analysis. The rationality and validity of the model were verified by combining the experimental results. Considering the hydro-mechanical effects of different root architectures, the reinforcement effects of typical sections of bank slope in Hongze Lake embankment was carried out. The results showed that the matric suction of soil was significantly improved by the root water uptake, and the influence range was about 2.5 times the root depth; in the initial stage of root water uptake, the difference between different root architectures was small, but with the gradual increase of time, the difference between different root architectures gradually increased; the hydro-mechanical effects of vegetation can significantly improve the stability of embankment slope, and after 24 hours of rainfall, the factor of safety under root reinforcement is about 1.4 times that of bare soil bank slope.

Abstract:A series of large-scale triaxial tests are conducted on the influence of particle grading and relative density on the strength and deformation characteristics of sandy gravel with high content of particles smaller than 5 mm. It shows that the compaction performance of sandy gravel decreases with the increasing mass fraction of particle less than 5 mm. Strength parameters and deformation parameters increase with the increase of the mass fraction of particles larger than 5 mm P 5 and relative density Dr. The strength parameters, c, φ, φ 0 and Δ φ ,increase linearly with the growth of P 5 and Dr, and there is almost no interaction between influences of P 5 and Dr on strength parameters. The test results also show that the Duncan E-B model parameters K and K b increase with the growth of P 5 and Dr, the effects of Dr on K and K b are greater for sandy gravel with higher content of particles larger than 5 mm, and the effects of P 5 on K and K b are more significant for sandy gravel with higher relative density. The empirical formulas, considering the effects of particle grading and Dr, are proposed to predict mechanical properties and Duncan E-B model parameters, and the formulas have high precision in prediction of mechanical indexes of poorly-graded sandy gravel with high content of fine particles for overburden in Poyang Lake area.

Abstract:In order to study the correlation between bearing capacity of helical piles in sand foundation and oblique tensile angle and burial depth, the finite element model of helical piles in sand is established by ABAQUS. The numerical simulation results and test results of helical piles under vertical and horizontal pull-out are compared to verify the accuracy and feasibility of the numerical model. Considering the influence of oblique tensile angle and burial depth on the ultimate bearing capacity of helical piles, four groups of helical pile models with different burial depths, are set up and different oblique tensile angles are applied respectively. The results suggest that the ultimate bearing capacity of helical piles in sand decreases when the oblique tensile angle increases. When the oblique tensile angle is less than 30°, the relationship curve between the ultimate bearing capacity and the oblique tensile angle is approximately linear. There is a critical burial depth ratio for the ultimate bearing capacity of helical piles. When the burial depth ratio is not less than 4, it does not change with the increase of burial depth ratio. Meanwhile, the ultimate bearing capacity formula of deeply buried helical piles under oblique tensile load is derived. Through verification, the formula can better reflect the rule that the ultimate bearing capacity of helical piles decreases gradually with the increase of oblique tensile angle.

Abstract:In order to explore the sources of surface sediments in sand ridges of the Jiangsu Coast, the lead (Pb) isotope characteristics of acid-insoluble sediments in the sand ridges of the Jiangsu Coast were analyzed. The results showed that the Pb isotope ratios of landward sediments in the offshore sand ridges were similar to those in the onshore sand ridges, indicating a landward migration trend of sediments under the action of tidal waves. Pb and neodymium (Nd) isotope analyses revealed that the sediments of the Yangtze River and surrounding rivers were transported to the seaward area of the offshore sand ridges under the action of the Yangtze River diluted water and the East China Sea coastal current. The sediment input from the Old Yellow River Delta had an impact on the onshore sand ridges and the landward area of offshore sand ridges under the action of the Subei coastal current. On the contrary, the impacts of sediment input from the Modern Yellow River Delta, Jeju Island and Korean rivers were weak on the sand ridges of the Jiangsu Coast.

Abstract:To study the local scour characteristics and flow field features of submerged square piles under the effect of different flow intensity, a series of local scour tests were carried out around the pile foundation with the non-uniform sand, and numerical tests were conducted to analyze the scour topography, change law of scour depth and flow turbulence around the square pile. The flow field around the pile were simulated by OpenFOAM. Thereafter, this study discussed the distribution characteristics of horseshoe vortex at the upstream of pile, backflow and downflow around the pile. The results show that the depth of scouring pits, the height of dunes and their sizes around the piles all increase with the increasing of flow intensity under the clear-water scour condition. In the equilibrium scouring terrain, flow around the pile is very complicated, and the turbulence energy in the scour pit becomes larger with the increasing flow intensity value. When the flow intensity is close to 1.0, the shielding effect of coarse-grained sediment on fine particles affects the maximum scour depth of pile perimeter to some extent; thus, the eddy current intensity in the scour pit in front of pile will be enhanced, resulting in more complicated flow behaviour in the scour pit.