High-density resistivity imaging method is widely used in landslide monitoring.The resistivity of rock and soil is closely related to factors,such as porosity,moisture content,saturation and temperature.In this study,...High-density resistivity imaging method is widely used in landslide monitoring.The resistivity of rock and soil is closely related to factors,such as porosity,moisture content,saturation and temperature.In this study,the resistivity test was designed to investigate the influence of physical factors and pore solution components on the resistivity of landslide soil.Experimental and analytical results find that both moisture content and volumetric water content varies greatly under the same resistivity.At different temperatures,soil resistivity exhibits great changes.Under the same temperature,the ion concentration and species in pore solutions have great influence on soil resistivity.Based on the test results and grey correlation analysis,this study established a resistivity model by considering porosity,saturation,temperature and ion concentration.The study lays a foundation for the high-density resistivity method to measure the moisture content of landslides.展开更多
Lake is an important part of the natural ecosystem, and its morphological characteristics reflect the capacity of lake regulation and storage, the strength of material migration, and the characteristics of shoreline d...Lake is an important part of the natural ecosystem, and its morphological characteristics reflect the capacity of lake regulation and storage, the strength of material migration, and the characteristics of shoreline development. In most existing studies, remote sensing images are used to quantify the morphological characteristics of lakes. However, the extraction accuracy of lake water is greatly affected by cloud cover and vegetation cover, and the inversion accuracy of lake elevation data is poor, which cannot accurately describe the response relationship of lake landscape morphology with water level change. Therefore, this paper takes Tonle Sap Lake as the research object, which is the largest natural freshwater lake in Southeast Asia. DEM is constructed based on high-resolution measured topographic data, and morphological indicators such as lake area, lake shoreline length, perimeter area ratio, longest axis length, maximum width, shoreline development index, lake shape complexity, compactness ratio and form ratio are adopted to researching the evolution law of high water overflows and low water outbursts quantitatively, and clarifying the variation characteristics of landscape morphology with water level gradient in Tonle Sap Lake. The research results have important theoretical significance for the scientific utilization of Tonle Sap Lake water resources and the protection of the lake ecosystem.展开更多
A new blasting approach of combined blastholes with different diameters is proposed to solve the problems of oversize boulders and rock toes in open-pit mine. A non-ideal detonation model and a statistical damage cons...A new blasting approach of combined blastholes with different diameters is proposed to solve the problems of oversize boulders and rock toes in open-pit mine. A non-ideal detonation model and a statistical damage constitutive model are implemented in dynamic finite element analysis to investigate the formation mechanism of oversize boulders and toes. The damage distribution and evolution process of rock blasting fragmentation is simulated, and the scheme is further optimized. Numerical analysis results showed that pocket charges and satellite blastholes can only improve bench top fragmentation, but they cannot reduce the oversize in the middle and bottom of bench as well as the toe problem. The new blasting approach of combined blastholes with different diameters can effectively reduce the oversize boulders and toes as well as the production costs.展开更多
A multiproxy approach including bulk organic carbon, δ^(13) C, lignin phenols, and lipid biomarker analyses were applied to characterize the source and composition of sedimentary organic matter in the head part of Th...A multiproxy approach including bulk organic carbon, δ^(13) C, lignin phenols, and lipid biomarker analyses were applied to characterize the source and composition of sedimentary organic matter in the head part of Three Gorges Reservoir. OM consisted of both natural(autochthonous and allochthonous) and anthropogenic inputs.The natural OM included input from vascular plants,especially non-woody angiosperms. The allochthonous input included plankton and microbial production, likely due to localized eutrophication. Anthropogenic inputs likely derived from petroleum input and/or urban activities.Other anthropogenic inputs were untreated sewage waste.These influences were concluded to be regionally specific point sources of pollution based on relative distributions and on the fact that molecular characteristics of sedimentary OM were not distributed smoothly along a gradient.展开更多
Slope excavation is one of the most crucial steps in the construction of a hydraulic project. Excavation project quality assessment and excavated volume calculation are critical in construction management. The positio...Slope excavation is one of the most crucial steps in the construction of a hydraulic project. Excavation project quality assessment and excavated volume calculation are critical in construction management. The positioning of excavation projects using traditional instruments is inefficient and may cause error. To improve the efficiency and precision of calculation and assessment, three-dimensional laser scanning technology was used for slope excavation quality assessment. An efficient data acquisition, processing, and management workflow was presented in this study. Based on the quality control indices, including the average gradient, slope toe elevation, and overbreak and underbreak,cross-sectional quality assessment and holistic quality assessment methods were proposed to assess the slope excavation quality with laserscanned data. An algorithm was also presented to calculate the excavated volume with laser-scanned data. A field application and a laboratory experiment were carried out to verify the feasibility of these methods for excavation quality assessment and excavated volume calculation. The results show that the quality assessment indices can be obtained rapidly and accurately with design parameters and scanned data, and the results of holistic quality assessment are consistent with those of cross-sectional quality assessment. In addition, the time consumption in excavation quality assessment with the laser scanning technology can be reduced by 70%e90%, as compared with the traditional method. The excavated volume calculated with the scanned data only slightly differs from measured data, demonstrating the applicability of the excavated volume calculation method presented in this study.展开更多
Studying the critical response characteristics of reinforced concrete box culverts with diverse geometrical configurations under seismic excitations is a necessary step to develop a reasonable design method. In this w...Studying the critical response characteristics of reinforced concrete box culverts with diverse geometrical configurations under seismic excitations is a necessary step to develop a reasonable design method. In this work, numerical analysis and assessment of reinforced concrete box culverts for seismic loading in addition to standard static loading from dead and live loads is conducted, aiming to highlight the critical difference in the seismic performances between two and three cell box culverts under near and far-fault ground motion. The results show how and where the seismic loading alters the responses of seismic loading of the models including the effect on safety and failure. The geometrical configurations of the culvert combined with the loading scenarios also significantly influence the magnitude and distribution of the seismic responses. The findings of this work shed light on the critical role of the geometrical configurations and shaking event in the seismic responses of reinforced concrete box culverts and this procedure can be applied as seismic assessment method to any culvert shape, size, and material.展开更多
To investigate the influence of asymmetric tidal mixing(ATM) on sediment dynamics in tidal estuaries, we developed a vertically one-dimensional idealized analytical model, in which the M_2 tidal flow, residual flow an...To investigate the influence of asymmetric tidal mixing(ATM) on sediment dynamics in tidal estuaries, we developed a vertically one-dimensional idealized analytical model, in which the M_2 tidal flow, residual flow and suspended sediment concentration(SSC) are described. Model solutions are obtained in terms of tidallyaveraged, and tidally-varying components(M_2 and M_4) of both hydrodynamics and sediment dynamics. The effect of ATM was considered with a time-varying eddy viscosity and time-varying eddy diffusivity of SSC. For the first time, an analytical solution for SSC variation driven by varying diffusivity could be derived. The model was applied to York River Estuary, where higher(or lower) eddy diffusivity was observed during flood(or ebb) in a previous study. The model results agreed well with the observation in both hydrodynamics and sediment dynamics. The vertical sediment distribution under the influence of ATM was analyzed in terms of the phase lag of the M_2 component of SSC relative to tidal flow. The phase lag increases significantly in estuaries with typical ATM(higher diffusivity during flood and lower diffusivity during ebb) for the case of seaward-directed net bottom shear stress(e.g., strong river discharge). In contrary, the phase lag is reduced by ATM, if the tidally-averaged bottom shear stress is landward(e.g., strong horizontal density gradient). The dynamics of sediment transport was analyzed as a function of ATM phase lag to identify the time of highest sediment diffusivity, as well as a function of the residual flow, to evaluate the relative importance of seaward and landward residual flows. In estuaries with relative strong fresh water discharge or weak tidal forcing(in case of flood season or neap tide), the near bottom SSC could be higher during ebb than during flood, since the bottom shear stress is higher during ebb due to seaward residual flow. However, landward net sediment transport can be expected in these estuaries in case of a typical ATM, because higher diffusivity causes higher SSC and landward transport during the flood period, while both SSC and seaward transport could be lower during ebb. On the contrary, seaward sediment transport can be expected in estuaries with landward tidally mean bottom shear stress in case of a reverse ATM,where sediment diffusivity is higher during the ebb.展开更多
Geological environments of rock mass projects are always very complicated, and further investigations on rock mechanical characteristics are needed. There are considerable distinctions in rock mechanical characteristi...Geological environments of rock mass projects are always very complicated, and further investigations on rock mechanical characteristics are needed. There are considerable distinctions in rock mechanical characteristics under unloading and loading conditions. A series of tests are conducted to study the stress-strain relationship of rock masses under loading and unloading conditions. Also, the anisotropy, the size effect, and the rheological property of unloading rock mass are investigated. The tests presented in the paper include model test and granite rheological test, which are conducted considering geological condition, rock mass structure, in-situ stress field of the permanent shiplock of the Three Gorges Project. The main differences between loading and unloading rock masses are stress paths, yield criteria, deformation and strength parameters, etc.. Different structural plane directions affect unloading rock mass evidently. With increasing size, the tensile strength, the compressive strength, the deformation modulus, the Poisson's ratio and the anisotropy of rock mass all decrease. For sandstone samples with parallel bedding planes, the cohesion c increases but the internal friction angle ? decreases under unloading condition when compared with the values under loading condition. While for samples with vertical bedding planes, the trend is adverse. The rheological property of rocks has close relationship with the tensile stresses of rock masses. When the sandstone samples are tested under high stress condition, their rheological properties are very obvious with the unloading of confining pressure, and three typical rheological stages are shown. Rheological rate changes with the variations in axial stress and confining pressure.展开更多
Since the impoundment of the Three Gorges Reservoir in 2003,algal blooms have frequently been observed in it.The chlorophyll a concentration is an important parameter for evaluating algal blooms.In this study,the chlo...Since the impoundment of the Three Gorges Reservoir in 2003,algal blooms have frequently been observed in it.The chlorophyll a concentration is an important parameter for evaluating algal blooms.In this study,the chlorophyll a concentration in Xiangxi Bay,in the Three Gorges Reservoir,was predicted using HJ-1 satellite imagery.Several models were established based on a correlation analysis between in situ measurements of the chlorophyll a concentration and the values obtained from satellite images of the study area from January 2010 to December 2011.Chlorophyll a concentrations in Xiangxi Bay were predicted based on the established models.The results show that the maximum correlation is between the reflectance of the band combination of B4/(B2+B3) and in situ measurements of chlorophyll a concentration.The root mean square errors of the predicted values using the linear and quadratic models are 18.49 mg/m3 and 18.52 mg/m3,respectively,and the average relative errors are 37.79% and 36.79%,respectively.The results provide a reference for water bloom prediction in typical tributaries of the Three Gorges Reservoir and contribute to large-scale remote sensing monitoring and water quality management.展开更多
Ensuring that water flows smoothly into spillways is the main challenge in spillway design.In order to help avoid the formation of vortices and separation of flow along the guide wall in front of the gates during over...Ensuring that water flows smoothly into spillways is the main challenge in spillway design.In order to help avoid the formation of vortices and separation of flow along the guide wall in front of the gates during overflow through the spillway,an experiment with a physical model of the Yutang Dam bank spillway was carried out.The profile of the guide wall was redesigned to eliminate the formation of vortices and separation of flow.This involves opening up holes in the middle part of the guide wall.The test results show that the design is effective in improving the flow conditions of the inlet,and in ensuring the desired values of water head along the guide wall and discharge capacities of the spillway.展开更多
Conditions for complete and lag synchronizations in drive-response systems are considered under the unified framework of generalized synchronization.The question is addressed that whether the synchronization condition...Conditions for complete and lag synchronizations in drive-response systems are considered under the unified framework of generalized synchronization.The question is addressed that whether the synchronization conditions achieving complete synchronization is still valid for lag synchronization when the time delay of signal transmission between the drive and response systems increases from 0.Theoretical and numerical results show that whether the synchronization conditions is stable for the influence of the time delay of signal transmission depends on a particular form of equilibria of the drive and response systems.Furthermore,it seems that the less the number of the equilibria of the drive system,the more likely the synchronization conditions are stable for the time delay of signal transmission.展开更多
A control scheme named the variable-lateral-force cavitator, which is focused on the control of lift force, drag force and lateral forces for underwater supercavity vehicles was proposed, and the supercavitating flow ...A control scheme named the variable-lateral-force cavitator, which is focused on the control of lift force, drag force and lateral forces for underwater supercavity vehicles was proposed, and the supercavitating flow around the cavitator was investigated numerically using the mixture multiphase flow model. It is verified that the forces of pitching, yawing, drag and lift, as well as the supercavity size of the underwater vehicle can be effectively regulated through the movements of the control element of the variable-lateral-force cavitator in the radial and circumferential directions. In addition, if the control element on either side protrudes to a height of 5% of the diameter of the front cavitator, an amount of forces of pitching and yawing equivalent to 30% of the drag force will be produced, and the supercavity section appears concave inwards simultaneously. It is also found that both the drag force and lift force of the variable-lateral-force cavitator decline as the angle of attack increases.展开更多
This paper introduces an optimization method(SCE-SR)that combines shuffled complex evolution(SCE)and stochastic ranking(SR)to solve constrained reservoir scheduling problems,ranking individuals with both objectives an...This paper introduces an optimization method(SCE-SR)that combines shuffled complex evolution(SCE)and stochastic ranking(SR)to solve constrained reservoir scheduling problems,ranking individuals with both objectives and constrains considered.A specialized strategy is used in the evolution process to ensure that the optimal results are feasible individuals.This method is suitable for handling multiple conflicting constraints,and is easy to implement,requiring little parameter tuning.The search properties of the method are ensured through the combination of deterministic and probabilistic approaches.The proposed SCE-SR was tested against hydropower scheduling problems of a single reservoir and a multi-reservoir system,and its performance is compared with that of two classical methods(the dynamic programming and genetic algorithm).The results show that the SCE-SR method is an effective and efficient method for optimizing hydropower generation and locating feasible regions quickly,with sufficient global convergence properties and robustness.The operation schedules obtained satisfy the basic scheduling requirements of reservoirs.展开更多
A field campaign was carried out to investigate continuous diel methane(CH_4) flux from a subtropical eutrophic pond in November 2016. The diffusive methane flux of a single measurement had a range from2.68 9 10-5 to ...A field campaign was carried out to investigate continuous diel methane(CH_4) flux from a subtropical eutrophic pond in November 2016. The diffusive methane flux of a single measurement had a range from2.68 9 10-5 to 0.028 mmol·m^(-2)·h^(-1) with an average of0.011 ± 0.005 mmol·m^(-2)·h^(-1). The diffusive methane flux of measurements from 9:00 to 10:30 and from 21:00 to22:30 were very close to the average diffusive flux of all measurements. The bubble methane flux at different time measurements had much more variability than the diffusive methane flux. The bubble methane flux of a single measurement had a range from 0 to 0.312 mmol·m^(-2)·h^(-1) with an average of 0.024 ± 0.054 mmol·m^(-2)·h^(-1). For the eutrophic pond, the average bubble and diffusive CH_4 flux were 0.56 ± 0.18 and 0.26 ± 0.04 mmol·m^(-2)·day^(-1),respectively, and the CH_4 ebullition flux accounted for68.23% of the total flux. The maximum of the bubble CH_4 flux was about 4.6 times of the minimum CH_4 ebullition.The maximum of diffusive CH_4 flux was * 1.7 times of the corresponding minimum. The diffusive methane fluxes in daytime and nighttime were almost equal. However, the bubble methane flux in daytime was 0.029 mmol·m^(-2)·h^(-1),which was 1.6 times of that at night. Wind speed, thesurface water temperature, and DO dominate methane effluxes from the pond, and the latter is in nature subjected to the metabolism of algae in the pond. However, key environmental factors which dominate gas flux processes vary with different weather conditions. Wind speed is unimportant when it is extremely low.展开更多
Eichhornia crassipes is a hyperaccumulator of metals and has been widely used to remove metal pollutants from water, but disposal of contaminated plants is problematic.Biochar prepared from plants is commonly used to ...Eichhornia crassipes is a hyperaccumulator of metals and has been widely used to remove metal pollutants from water, but disposal of contaminated plants is problematic.Biochar prepared from plants is commonly used to remediate soils and sequester carbon.Here, the catalytic activity of biochar prepared from plants enriched with iron was investigated as a potentially beneficial use of metal-contaminated plants.In a 30-day hydroponic experiment, E.crassipes was exposed to different concentrations of Fe(Ⅲ)(0, 4, 8, 16, 32 and 64 mg/L), and Fe-biochar(Fe-BC) was prepared by pyrolysis of the plant roots.The biochar was characterized using X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive X-ray spectrometry(EDS), Brunauer–Emmett–Teller(BET) analysis, X-ray photoelectron spectroscopy(XPS) and atomic absorption spectrometry(AAS).The original root morphology was visible and iron was present as γ-Fe2O3 and Fe3O4.The biochar enriched with Fe(Ⅲ) at 8 mg/L(8-Fe-BC) had the smallest specific surface area(SSA, 13.54 m^2/g) and the highest Fe content(27.9 mg/g).Fe-BC catalytic activity was tested in the electrocatalytic reduction of H2O2 using cyclic voltammetry(CV).The largest reduction current(1.82 mA/cm^2) was displayed by 8-Fe-BC, indicating the highest potential catalytic activity.We report here, for the first time, on the catalytic activity of biochar made from iron-enriched plants and demonstrate the potential for reusing metalcontaminated plants to produce a biochar catalyst.展开更多
Tracking and quantifying the moisture sources of precipitation in different drainage basins in the Tibetan Plateau(TP)help to reveal basin-scale hydrological cycle characteristics under the interactions between the we...Tracking and quantifying the moisture sources of precipitation in different drainage basins in the Tibetan Plateau(TP)help to reveal basin-scale hydrological cycle characteristics under the interactions between the westerlies and Indian summer monsoon(ISM) systems and to improve our understanding on the mechanisms of water resource changes in the ‘Asian Water Tower' under climate changes. Based on a Eulerian moisture tracking model(WAM-2) and three atmospheric reanalysis products(ERA-I, MERRA-2, and JRA-55), the contributions of moisture sources to the precipitation in six major sub-basins in the TP were tracked during an approximately 35-year period(1979/1980–2015). The results showed that in the upper Indus(UI),upper Tarim River(UT), and Qaidam Basin(QB), the moisture sources mainly extended westward along the mid-latitude westerlies to the western part of the Eurasian continent. In contrast, in the Yarlung Zangbo River Basin(YB), inner TP(ITP), and the source area of three eastern rivers(TER, including the Nujiang River, Lancang River, and Yangtze River), the moisture sources extended both westward and southward, but mainly southward along the ISM. In winter and spring, all of the sub-basins were dominated by western moisture sources. In summer, the western sources migrated northward with the zonal movement of the westerlies, and simultaneously the southern sources of the YB, ITP, and TER expanded largely toward the Indian Ocean along the ISM. In autumn, the moisture sources of the UI, UT, and QB shrank to the western sources, and the moisture sources of the YB, ITP, and TER shrank to the central-southern TP and the Indian subcontinent. By quantifying the moisture contributions from multiple sources, we found that the terrestrial moisture dominated in all of the sub-basins, particularly in the UT and QB(62–73%). The oceanic contributions were relatively high in the UI(38–42%) and YB(38–41%). In winter, evaporation from the large western water bodies(such as the Mediterranean, Red Sea, and Persian Gulf) was significantly higher than that from the continental areas. This contributed to the peak(valley) values of the oceanic(terrestrial) moisture contributions to all of the subbasins. In summer, the terrestrial moisture contributions to the UI, UT, and QB reached their annual maximum, but the abundant oceanic moisture transported by the ISM restrained the appearance of land source contribution peaks in the YB, ITP, and TER,resulting in almost equal moisture contributions in the YB from the ocean and land.展开更多
This paper is concerned with the minimal wave speed in a diffusive epidemic model with nonlocal delays.We define a threshold.By presenting the existence and the nonexistence of traveling wave solutions for all positiv...This paper is concerned with the minimal wave speed in a diffusive epidemic model with nonlocal delays.We define a threshold.By presenting the existence and the nonexistence of traveling wave solutions for all positive wave speed,we confirm that the threshold is the minimal wave speed of traveling wave solutions,which models that the infective invades the habitat of the susceptible.For some cases,it is proven that spatial nonlocality may increase the propagation threshold while time delay decreases the threshold.展开更多
基金supported by Hubei Provincial Engineering Research Center of Slope Habitat Construction Technique Using Cement-based Materials(China Three Gorges University)No.2022SNJ15。
文摘High-density resistivity imaging method is widely used in landslide monitoring.The resistivity of rock and soil is closely related to factors,such as porosity,moisture content,saturation and temperature.In this study,the resistivity test was designed to investigate the influence of physical factors and pore solution components on the resistivity of landslide soil.Experimental and analytical results find that both moisture content and volumetric water content varies greatly under the same resistivity.At different temperatures,soil resistivity exhibits great changes.Under the same temperature,the ion concentration and species in pore solutions have great influence on soil resistivity.Based on the test results and grey correlation analysis,this study established a resistivity model by considering porosity,saturation,temperature and ion concentration.The study lays a foundation for the high-density resistivity method to measure the moisture content of landslides.
文摘Lake is an important part of the natural ecosystem, and its morphological characteristics reflect the capacity of lake regulation and storage, the strength of material migration, and the characteristics of shoreline development. In most existing studies, remote sensing images are used to quantify the morphological characteristics of lakes. However, the extraction accuracy of lake water is greatly affected by cloud cover and vegetation cover, and the inversion accuracy of lake elevation data is poor, which cannot accurately describe the response relationship of lake landscape morphology with water level change. Therefore, this paper takes Tonle Sap Lake as the research object, which is the largest natural freshwater lake in Southeast Asia. DEM is constructed based on high-resolution measured topographic data, and morphological indicators such as lake area, lake shoreline length, perimeter area ratio, longest axis length, maximum width, shoreline development index, lake shape complexity, compactness ratio and form ratio are adopted to researching the evolution law of high water overflows and low water outbursts quantitatively, and clarifying the variation characteristics of landscape morphology with water level gradient in Tonle Sap Lake. The research results have important theoretical significance for the scientific utilization of Tonle Sap Lake water resources and the protection of the lake ecosystem.
基金supported by Chinese National Natural Science Foundation (No. 51809016 and No. 51979152)Chongqing Municipal Natural Science Foundation (No. cstc2019jcyjmsxmX0645)
文摘A new blasting approach of combined blastholes with different diameters is proposed to solve the problems of oversize boulders and rock toes in open-pit mine. A non-ideal detonation model and a statistical damage constitutive model are implemented in dynamic finite element analysis to investigate the formation mechanism of oversize boulders and toes. The damage distribution and evolution process of rock blasting fragmentation is simulated, and the scheme is further optimized. Numerical analysis results showed that pocket charges and satellite blastholes can only improve bench top fragmentation, but they cannot reduce the oversize in the middle and bottom of bench as well as the toe problem. The new blasting approach of combined blastholes with different diameters can effectively reduce the oversize boulders and toes as well as the production costs.
基金supported by the"100"talent program of Zhejiang University to D.He under the Grant No.188020*194231701/008 and188020-193810201/102NSFC to Y.Sun under the Grant No.41372131
文摘A multiproxy approach including bulk organic carbon, δ^(13) C, lignin phenols, and lipid biomarker analyses were applied to characterize the source and composition of sedimentary organic matter in the head part of Three Gorges Reservoir. OM consisted of both natural(autochthonous and allochthonous) and anthropogenic inputs.The natural OM included input from vascular plants,especially non-woody angiosperms. The allochthonous input included plankton and microbial production, likely due to localized eutrophication. Anthropogenic inputs likely derived from petroleum input and/or urban activities.Other anthropogenic inputs were untreated sewage waste.These influences were concluded to be regionally specific point sources of pollution based on relative distributions and on the fact that molecular characteristics of sedimentary OM were not distributed smoothly along a gradient.
基金supported by the National Natural Science Foundation of China(Grant No.51379109)
文摘Slope excavation is one of the most crucial steps in the construction of a hydraulic project. Excavation project quality assessment and excavated volume calculation are critical in construction management. The positioning of excavation projects using traditional instruments is inefficient and may cause error. To improve the efficiency and precision of calculation and assessment, three-dimensional laser scanning technology was used for slope excavation quality assessment. An efficient data acquisition, processing, and management workflow was presented in this study. Based on the quality control indices, including the average gradient, slope toe elevation, and overbreak and underbreak,cross-sectional quality assessment and holistic quality assessment methods were proposed to assess the slope excavation quality with laserscanned data. An algorithm was also presented to calculate the excavated volume with laser-scanned data. A field application and a laboratory experiment were carried out to verify the feasibility of these methods for excavation quality assessment and excavated volume calculation. The results show that the quality assessment indices can be obtained rapidly and accurately with design parameters and scanned data, and the results of holistic quality assessment are consistent with those of cross-sectional quality assessment. In addition, the time consumption in excavation quality assessment with the laser scanning technology can be reduced by 70%e90%, as compared with the traditional method. The excavated volume calculated with the scanned data only slightly differs from measured data, demonstrating the applicability of the excavated volume calculation method presented in this study.
文摘Studying the critical response characteristics of reinforced concrete box culverts with diverse geometrical configurations under seismic excitations is a necessary step to develop a reasonable design method. In this work, numerical analysis and assessment of reinforced concrete box culverts for seismic loading in addition to standard static loading from dead and live loads is conducted, aiming to highlight the critical difference in the seismic performances between two and three cell box culverts under near and far-fault ground motion. The results show how and where the seismic loading alters the responses of seismic loading of the models including the effect on safety and failure. The geometrical configurations of the culvert combined with the loading scenarios also significantly influence the magnitude and distribution of the seismic responses. The findings of this work shed light on the critical role of the geometrical configurations and shaking event in the seismic responses of reinforced concrete box culverts and this procedure can be applied as seismic assessment method to any culvert shape, size, and material.
基金The National Natural Science Foundation of China under contract Nos U2040220, 52079069, 52009066, 52379069,52009079, 42006156 and U2240220the CRSRI Open Research Program under contract No. CKWV20221003/KY+2 种基金the Open Research Program of Hubei Key Laboratory of Intelligent Yangtze and Hydroelectric Science under contract No. ZH2102000109the Outstanding Young and Middle-aged Scientific and Technological Innovation Team in Universities of Hubei Province under contract No. T2021003the Hubei Province Chutian Scholar Program (granted to Andreas Lorke)。
文摘To investigate the influence of asymmetric tidal mixing(ATM) on sediment dynamics in tidal estuaries, we developed a vertically one-dimensional idealized analytical model, in which the M_2 tidal flow, residual flow and suspended sediment concentration(SSC) are described. Model solutions are obtained in terms of tidallyaveraged, and tidally-varying components(M_2 and M_4) of both hydrodynamics and sediment dynamics. The effect of ATM was considered with a time-varying eddy viscosity and time-varying eddy diffusivity of SSC. For the first time, an analytical solution for SSC variation driven by varying diffusivity could be derived. The model was applied to York River Estuary, where higher(or lower) eddy diffusivity was observed during flood(or ebb) in a previous study. The model results agreed well with the observation in both hydrodynamics and sediment dynamics. The vertical sediment distribution under the influence of ATM was analyzed in terms of the phase lag of the M_2 component of SSC relative to tidal flow. The phase lag increases significantly in estuaries with typical ATM(higher diffusivity during flood and lower diffusivity during ebb) for the case of seaward-directed net bottom shear stress(e.g., strong river discharge). In contrary, the phase lag is reduced by ATM, if the tidally-averaged bottom shear stress is landward(e.g., strong horizontal density gradient). The dynamics of sediment transport was analyzed as a function of ATM phase lag to identify the time of highest sediment diffusivity, as well as a function of the residual flow, to evaluate the relative importance of seaward and landward residual flows. In estuaries with relative strong fresh water discharge or weak tidal forcing(in case of flood season or neap tide), the near bottom SSC could be higher during ebb than during flood, since the bottom shear stress is higher during ebb due to seaward residual flow. However, landward net sediment transport can be expected in these estuaries in case of a typical ATM, because higher diffusivity causes higher SSC and landward transport during the flood period, while both SSC and seaward transport could be lower during ebb. On the contrary, seaward sediment transport can be expected in estuaries with landward tidally mean bottom shear stress in case of a reverse ATM,where sediment diffusivity is higher during the ebb.
基金Supported by the National Natural Science Foundation of China (90610029, 50679079, 50909052)
文摘Geological environments of rock mass projects are always very complicated, and further investigations on rock mechanical characteristics are needed. There are considerable distinctions in rock mechanical characteristics under unloading and loading conditions. A series of tests are conducted to study the stress-strain relationship of rock masses under loading and unloading conditions. Also, the anisotropy, the size effect, and the rheological property of unloading rock mass are investigated. The tests presented in the paper include model test and granite rheological test, which are conducted considering geological condition, rock mass structure, in-situ stress field of the permanent shiplock of the Three Gorges Project. The main differences between loading and unloading rock masses are stress paths, yield criteria, deformation and strength parameters, etc.. Different structural plane directions affect unloading rock mass evidently. With increasing size, the tensile strength, the compressive strength, the deformation modulus, the Poisson's ratio and the anisotropy of rock mass all decrease. For sandstone samples with parallel bedding planes, the cohesion c increases but the internal friction angle ? decreases under unloading condition when compared with the values under loading condition. While for samples with vertical bedding planes, the trend is adverse. The rheological property of rocks has close relationship with the tensile stresses of rock masses. When the sandstone samples are tested under high stress condition, their rheological properties are very obvious with the unloading of confining pressure, and three typical rheological stages are shown. Rheological rate changes with the variations in axial stress and confining pressure.
基金supported by the National Natural Science Foundation of China(Grants No.51009080 and 51179095)the Research Innovation Fund for Postgraduates in China Three Gorges University(Grant No.2012CX012)
文摘Since the impoundment of the Three Gorges Reservoir in 2003,algal blooms have frequently been observed in it.The chlorophyll a concentration is an important parameter for evaluating algal blooms.In this study,the chlorophyll a concentration in Xiangxi Bay,in the Three Gorges Reservoir,was predicted using HJ-1 satellite imagery.Several models were established based on a correlation analysis between in situ measurements of the chlorophyll a concentration and the values obtained from satellite images of the study area from January 2010 to December 2011.Chlorophyll a concentrations in Xiangxi Bay were predicted based on the established models.The results show that the maximum correlation is between the reflectance of the band combination of B4/(B2+B3) and in situ measurements of chlorophyll a concentration.The root mean square errors of the predicted values using the linear and quadratic models are 18.49 mg/m3 and 18.52 mg/m3,respectively,and the average relative errors are 37.79% and 36.79%,respectively.The results provide a reference for water bloom prediction in typical tributaries of the Three Gorges Reservoir and contribute to large-scale remote sensing monitoring and water quality management.
文摘Ensuring that water flows smoothly into spillways is the main challenge in spillway design.In order to help avoid the formation of vortices and separation of flow along the guide wall in front of the gates during overflow through the spillway,an experiment with a physical model of the Yutang Dam bank spillway was carried out.The profile of the guide wall was redesigned to eliminate the formation of vortices and separation of flow.This involves opening up holes in the middle part of the guide wall.The test results show that the design is effective in improving the flow conditions of the inlet,and in ensuring the desired values of water head along the guide wall and discharge capacities of the spillway.
基金supported by the National Natural Science Foundation of China(11002103 and 11032009)Shanghai Leading Academic Discipline(B302)
文摘Conditions for complete and lag synchronizations in drive-response systems are considered under the unified framework of generalized synchronization.The question is addressed that whether the synchronization conditions achieving complete synchronization is still valid for lag synchronization when the time delay of signal transmission between the drive and response systems increases from 0.Theoretical and numerical results show that whether the synchronization conditions is stable for the influence of the time delay of signal transmission depends on a particular form of equilibria of the drive and response systems.Furthermore,it seems that the less the number of the equilibria of the drive system,the more likely the synchronization conditions are stable for the time delay of signal transmission.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51379108 and 51609125)the Open Foundation of Engineering Research Center of Eco-environment in Three Gorges Reservoir Region,Ministry of Education(Grant No.2015KF-03)the University Scientific Research and Application Project of Yichang(Grant No.A16-302-a13)
文摘A control scheme named the variable-lateral-force cavitator, which is focused on the control of lift force, drag force and lateral forces for underwater supercavity vehicles was proposed, and the supercavitating flow around the cavitator was investigated numerically using the mixture multiphase flow model. It is verified that the forces of pitching, yawing, drag and lift, as well as the supercavity size of the underwater vehicle can be effectively regulated through the movements of the control element of the variable-lateral-force cavitator in the radial and circumferential directions. In addition, if the control element on either side protrudes to a height of 5% of the diameter of the front cavitator, an amount of forces of pitching and yawing equivalent to 30% of the drag force will be produced, and the supercavity section appears concave inwards simultaneously. It is also found that both the drag force and lift force of the variable-lateral-force cavitator decline as the angle of attack increases.
基金supported by the National Key Research and Development Program of China(Grant No.2016YFC0401702)the Fundamental Research Funds for the Central Universities(Grant No.2018B11214)the National Natural Science Foundation of China(Grants No.51379059 and 51579002)
文摘This paper introduces an optimization method(SCE-SR)that combines shuffled complex evolution(SCE)and stochastic ranking(SR)to solve constrained reservoir scheduling problems,ranking individuals with both objectives and constrains considered.A specialized strategy is used in the evolution process to ensure that the optimal results are feasible individuals.This method is suitable for handling multiple conflicting constraints,and is easy to implement,requiring little parameter tuning.The search properties of the method are ensured through the combination of deterministic and probabilistic approaches.The proposed SCE-SR was tested against hydropower scheduling problems of a single reservoir and a multi-reservoir system,and its performance is compared with that of two classical methods(the dynamic programming and genetic algorithm).The results show that the SCE-SR method is an effective and efficient method for optimizing hydropower generation and locating feasible regions quickly,with sufficient global convergence properties and robustness.The operation schedules obtained satisfy the basic scheduling requirements of reservoirs.
基金financially supported by the National Science of China (Nos. 41273110, 91647207, and 51509086)Natural Science Foundation of Hubei Province, China (2014CFB672)
文摘A field campaign was carried out to investigate continuous diel methane(CH_4) flux from a subtropical eutrophic pond in November 2016. The diffusive methane flux of a single measurement had a range from2.68 9 10-5 to 0.028 mmol·m^(-2)·h^(-1) with an average of0.011 ± 0.005 mmol·m^(-2)·h^(-1). The diffusive methane flux of measurements from 9:00 to 10:30 and from 21:00 to22:30 were very close to the average diffusive flux of all measurements. The bubble methane flux at different time measurements had much more variability than the diffusive methane flux. The bubble methane flux of a single measurement had a range from 0 to 0.312 mmol·m^(-2)·h^(-1) with an average of 0.024 ± 0.054 mmol·m^(-2)·h^(-1). For the eutrophic pond, the average bubble and diffusive CH_4 flux were 0.56 ± 0.18 and 0.26 ± 0.04 mmol·m^(-2)·day^(-1),respectively, and the CH_4 ebullition flux accounted for68.23% of the total flux. The maximum of the bubble CH_4 flux was about 4.6 times of the minimum CH_4 ebullition.The maximum of diffusive CH_4 flux was * 1.7 times of the corresponding minimum. The diffusive methane fluxes in daytime and nighttime were almost equal. However, the bubble methane flux in daytime was 0.029 mmol·m^(-2)·h^(-1),which was 1.6 times of that at night. Wind speed, thesurface water temperature, and DO dominate methane effluxes from the pond, and the latter is in nature subjected to the metabolism of algae in the pond. However, key environmental factors which dominate gas flux processes vary with different weather conditions. Wind speed is unimportant when it is extremely low.
基金supported by supported by the National Natural Science Foundation of China (Nos.21677086 and 21577078)Hubei Innovation Group Project (No.2015CFA021)+1 种基金the Hubei Foreign Science and Technology Cooperation Project (No.2018AHB020)Three Gorges University Master’s Thesis Training Fund (No.2018SSPY143).
文摘Eichhornia crassipes is a hyperaccumulator of metals and has been widely used to remove metal pollutants from water, but disposal of contaminated plants is problematic.Biochar prepared from plants is commonly used to remediate soils and sequester carbon.Here, the catalytic activity of biochar prepared from plants enriched with iron was investigated as a potentially beneficial use of metal-contaminated plants.In a 30-day hydroponic experiment, E.crassipes was exposed to different concentrations of Fe(Ⅲ)(0, 4, 8, 16, 32 and 64 mg/L), and Fe-biochar(Fe-BC) was prepared by pyrolysis of the plant roots.The biochar was characterized using X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive X-ray spectrometry(EDS), Brunauer–Emmett–Teller(BET) analysis, X-ray photoelectron spectroscopy(XPS) and atomic absorption spectrometry(AAS).The original root morphology was visible and iron was present as γ-Fe2O3 and Fe3O4.The biochar enriched with Fe(Ⅲ) at 8 mg/L(8-Fe-BC) had the smallest specific surface area(SSA, 13.54 m^2/g) and the highest Fe content(27.9 mg/g).Fe-BC catalytic activity was tested in the electrocatalytic reduction of H2O2 using cyclic voltammetry(CV).The largest reduction current(1.82 mA/cm^2) was displayed by 8-Fe-BC, indicating the highest potential catalytic activity.We report here, for the first time, on the catalytic activity of biochar made from iron-enriched plants and demonstrate the potential for reusing metalcontaminated plants to produce a biochar catalyst.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program (Grant Nos. 2019QZKK0201 & 2019QZKK020705)the National Natural Science Foundation of China (Grant Nos. 41988101 & 41871057)"Strategic Priority Research Program" of Chinese Academy of Sciences (Grant No. XDA20060202)。
文摘Tracking and quantifying the moisture sources of precipitation in different drainage basins in the Tibetan Plateau(TP)help to reveal basin-scale hydrological cycle characteristics under the interactions between the westerlies and Indian summer monsoon(ISM) systems and to improve our understanding on the mechanisms of water resource changes in the ‘Asian Water Tower' under climate changes. Based on a Eulerian moisture tracking model(WAM-2) and three atmospheric reanalysis products(ERA-I, MERRA-2, and JRA-55), the contributions of moisture sources to the precipitation in six major sub-basins in the TP were tracked during an approximately 35-year period(1979/1980–2015). The results showed that in the upper Indus(UI),upper Tarim River(UT), and Qaidam Basin(QB), the moisture sources mainly extended westward along the mid-latitude westerlies to the western part of the Eurasian continent. In contrast, in the Yarlung Zangbo River Basin(YB), inner TP(ITP), and the source area of three eastern rivers(TER, including the Nujiang River, Lancang River, and Yangtze River), the moisture sources extended both westward and southward, but mainly southward along the ISM. In winter and spring, all of the sub-basins were dominated by western moisture sources. In summer, the western sources migrated northward with the zonal movement of the westerlies, and simultaneously the southern sources of the YB, ITP, and TER expanded largely toward the Indian Ocean along the ISM. In autumn, the moisture sources of the UI, UT, and QB shrank to the western sources, and the moisture sources of the YB, ITP, and TER shrank to the central-southern TP and the Indian subcontinent. By quantifying the moisture contributions from multiple sources, we found that the terrestrial moisture dominated in all of the sub-basins, particularly in the UT and QB(62–73%). The oceanic contributions were relatively high in the UI(38–42%) and YB(38–41%). In winter, evaporation from the large western water bodies(such as the Mediterranean, Red Sea, and Persian Gulf) was significantly higher than that from the continental areas. This contributed to the peak(valley) values of the oceanic(terrestrial) moisture contributions to all of the subbasins. In summer, the terrestrial moisture contributions to the UI, UT, and QB reached their annual maximum, but the abundant oceanic moisture transported by the ISM restrained the appearance of land source contribution peaks in the YB, ITP, and TER,resulting in almost equal moisture contributions in the YB from the ocean and land.
基金The second author was supported by the National Key Research and DevelopmentProgram of China (No. 2016YFC0402502)。
文摘This paper is concerned with the minimal wave speed in a diffusive epidemic model with nonlocal delays.We define a threshold.By presenting the existence and the nonexistence of traveling wave solutions for all positive wave speed,we confirm that the threshold is the minimal wave speed of traveling wave solutions,which models that the infective invades the habitat of the susceptible.For some cases,it is proven that spatial nonlocality may increase the propagation threshold while time delay decreases the threshold.
