For the ultra-high water-cut reservoirs,after long-term water injection exploitation,the physical properties of the reservoir change and the heterogeneity of the reservoir becomes increasingly severe,which further agg...For the ultra-high water-cut reservoirs,after long-term water injection exploitation,the physical properties of the reservoir change and the heterogeneity of the reservoir becomes increasingly severe,which further aggravates the spatial difference of the flow field.In this study,the displacement experiments were employed to investigate the variations in core permeability,porosity,and relative permeability after a large amount of water injection.A relative permeability endpoint model was proposed by utilizing the alternating conditional expectation(ACE)transformation to describe the variation in relative permeability based on the experimental data.Based on the time dependent models for permeability and relative permeability,the traditional oil-water two-phase model was improved and discretized using the mimetic finite difference method(MFD).The two cases were launched to confirm the validation of the proposed model.The impact of time-varying physical features on reservoir production performance was studied in a real water flooding reservoir.The experimental results indicate that the overall relative permeability curve shifts to the right as water injection increases.This shift corresponds to a transition towards a more hydrophilic wettability and a decrease in residual oil saturation.The endpoint model demonstrates excellent accuracy and can be applied to time-varying simulations of reservoir physics.The impact of variations in permeability and relative permeability on the reservoir production performance yields two distinct outcomes.The time-varying permeability of the reservoir results in intensified water channeling and poor development effects.On the other hand,the time-varying relative permeability enhances the oil phase seepage capacity,facilitating oil displacement.The comprehensive time-varying behavior is the result of the combined influence of these two parameters,which closely resemble the actual conditions observed in oil field exploitation.The time-varying simulation technique of reservoir physical properties proposed in this paper can continuously and stably characterize the dynamic changes of reservoir physical properties during water drive development.This approach ensures the reliability of the simulation results regarding residual oil distribution.展开更多
Due to the complex high-temperature characteristics of hydrocarbon fuel,the research on the long-term working process of parallel channel structure under variable working conditions,especially under high heat-mass rat...Due to the complex high-temperature characteristics of hydrocarbon fuel,the research on the long-term working process of parallel channel structure under variable working conditions,especially under high heat-mass ratio,has not been systematically carried out.In this paper,the heat transfer and flow characteristics of related high temperature fuels are studied by using typical engine parallel channel structure.Through numeri⁃cal simulation and systematic experimental verification,the flow and heat transfer characteristics of parallel chan⁃nels under typical working conditions are obtained,and the effectiveness of high-precision calculation method is preliminarily established.It is known that the stable time required for hot start of regenerative cooling engine is about 50 s,and the flow resistance of parallel channel structure first increases and then decreases with the in⁃crease of equivalence ratio(The following equivalence ratio is expressed byΦ),and there is a flow resistance peak in the range ofΦ=0.5~0.8.This is mainly caused by the coupling effect of high temperature physical proper⁃ties,flow rate and pressure of fuel in parallel channels.At the same time,the cooling and heat transfer character⁃istics of parallel channels under some conditions of high heat-mass ratio are obtained,and the main factors affect⁃ing the heat transfer of parallel channels such as improving surface roughness and strengthening heat transfer are mastered.In the experiment,whenΦis less than 0.9,the phenomenon of local heat transfer enhancement and deterioration can be obviously observed,and the temperature rise of local structures exceeds 200℃,which is the risk of structural damage.Therefore,the reliability of long-term parallel channel structure under the condition of high heat-mass ratio should be fully considered in structural design.展开更多
This paper aims to numerically explore the characteristics of unsteady cavitating flow around a NACA0015 hydrofoil,with a focus on vorticity attributes.The simulation utilizes a homogeneous mixture model coupled with ...This paper aims to numerically explore the characteristics of unsteady cavitating flow around a NACA0015 hydrofoil,with a focus on vorticity attributes.The simulation utilizes a homogeneous mixture model coupled with a filter-based density correction turbulence model and a modified Zwart cavitation model.The study investigates the dynamic cavitation features of the thermal fluid around the hydrofoil at various incoming flow velocities.It systematically elucidates the evolution of cavitation and vortex dynamics corresponding to each velocity condition.The results indicate that with increasing incoming flow velocity,distinct cavitation processes take place in the flow field.展开更多
Gas-liquid flow(GLF),especially slug and annular flows in oil and gas gathering and transportation pipelines,become particularly complex inside elbows and can easily exacerbate pipeline corrosion and damage.In thisstu...Gas-liquid flow(GLF),especially slug and annular flows in oil and gas gathering and transportation pipelines,become particularly complex inside elbows and can easily exacerbate pipeline corrosion and damage.In thisstudy,FLUENT was used to conduct 3D simulations of slug and annular flow in elbows for different velocitiesto assess the ensuing changes in terms of pressure.In particular,the multifluid VOF(Volume of Fraction)modelwas chosen.The results indicate that under both slug and annular flow conditions,the pressure inside the elbow islower than the outside.As the superficial velocity of liquid and gas increase,the pressure and liquid flow velocityat different positions of the elbow also increase,while the secondary flow weakens.Under annular flow conditions,the liquid film on the outer side of the elbow is thicker than that on the inner side,and the liquid velocityin the main liquid film zone is the lowest.展开更多
The third-order flow Gerdjikov–Ivanov(TOFGI)equation is studied,and the Darboux transformation(DT)is used to obtain the determinant expression of the solution of this equation.On this basis,the soliton solution,ratio...The third-order flow Gerdjikov–Ivanov(TOFGI)equation is studied,and the Darboux transformation(DT)is used to obtain the determinant expression of the solution of this equation.On this basis,the soliton solution,rational solution,positon solution,and breather solution of the TOFGI equation are obtained by taking zero seed solution and non-zero seed solution.The exact solutions and dynamic properties of the Gerdjikov–Ivanov(GI)equation and the TOFGI equation are compared in detail under the same conditions,and it is found that there are some differences in the velocities and trajectories of the solutions of the two equations.展开更多
As the proportion of newenergy increases,the traditional cumulant method(CM)produces significant errorswhen performing probabilistic load flow(PLF)calculations with large-scale wind power integrated.Considering the wi...As the proportion of newenergy increases,the traditional cumulant method(CM)produces significant errorswhen performing probabilistic load flow(PLF)calculations with large-scale wind power integrated.Considering the wind speed correlation,a multi-scenario PLF calculation method that combines random sampling and segmented discrete wind farm power was proposed.Firstly,based on constructing discrete scenes of wind farms,the Nataf transform is used to handle the correlation between wind speeds.Then,the random sampling method determines the output probability of discrete wind power scenarios when wind speed exhibits correlation.Finally,the PLF calculation results of each scenario areweighted and superimposed following the total probability formula to obtain the final power flow calculation result.Verified in the IEEE standard node system,the absolute percent error(APE)for the mean and standard deviation(SD)of the node voltages and branch active power are all within 1%,and the average root mean square(AMSR)values of the probability curves are all less than 1%.展开更多
Smelting with oxygen bottom blowing is one of the main methods used in the frame of copper pyrometallurgy.With this approach,feed materials and oxygen-enriched air are introduced in reversed order to enhance multiphas...Smelting with oxygen bottom blowing is one of the main methods used in the frame of copper pyrometallurgy.With this approach,feed materials and oxygen-enriched air are introduced in reversed order to enhance multiphaseflow within the furnace.Understanding the flow structure and temperature distribution in this setup is crucial foroptimizing production.In this study,gas-liquid interactions,and temperature profiles under varying air-injectionconditions are examined by means of numerical simulation for a 3.2 m×20 m furnace.The results indicate that thehigh-velocity regions are essentially distributed near the lance within the reaction region and the flue gas outlet,while low-velocity regions are located close to the furnace walls on both side of the reaction region.Dead regionsappear in the sedimentation region,with gas velocities surpassing those of the molten phase.As the injection rateincreases from 0.50 to 0.80 Nm3/s,the stabilization time of the average liquid surface velocity decreases from 2.6 sto 1.9 s,exhibiting a similar trend to the gas holdup.During stabilization,the average liquid surface velocity risesfrom 0.505 to 0.702 m/s.The average turbulent kinetic energy(TKE)of the fluid in the molten bath increases from0.095 to 0.162 m^(2)/s^(2).The proportion of the area distribution with TKE greater than 0.10 m^(2)/s^(2) and the gas holdupat steady state both rise with an increase in the injection quantity.The maximum splashing height of the melt growsfrom approximately 0.756 to 1.154 m,with the affected area expanding from 14.239 to 20.498 m^(2).Under differentworking conditions with varying injection quantities,the average temperature changes in melt zone and flue gaszone of the furnace are small.The temperature in the melt and in the flue-gas zone spans the interval 1200℃–1257℃,and 1073℃–1121℃,respectively.The temperature distribution of the melt and flue gas reveals a patterncharacterized by elevated temperatures in the reaction zone,gradually transitioning to lower temperatures in thesedimentation region.展开更多
Nanotechnology holds immense importance in the biomedical field due to its ability to revolutionize healthcare on a molecular scale.Motivated by the imperative of enhancing patient outcomes,a comprehensive numerical s...Nanotechnology holds immense importance in the biomedical field due to its ability to revolutionize healthcare on a molecular scale.Motivated by the imperative of enhancing patient outcomes,a comprehensive numerical simulation study on the dynamics of blood flow in a stenosed artery,focusing on the effects of copper and alumina nanoparticles,is conducted.The study employs a 2-dimensional Newtonian blood flow model infused with copper and alumina nanoparticles,considering the influence of a magnetic field,thermal radiation,and various flow parameters.The governing differential equations are first non-dimensionalized to facilitate analysis and subsequently solved using the 4th order collocation method,bvp4c module in MATLAB.This approach obtains velocity and temperature profiles,revealing the impact of relevant parameters crucial in the biomedical field.The findings of this study underscore the significance of understanding blood flow dynamics in stenosed arteries and the potential benefits of utilizing copper and alumina nanoparticles in treatment strategies.The incorporation of nanoparticles introduces novel avenues for enhancing therapeutic interventions,particularly in mitigating the effects of stenosis.The elucidation of velocity and temperature profiles provides valuable insights into the behavior of blood flow under different conditions,thereby informing the development of targeted biomedical applications.The arterial curvature flow parameter influences temperature profiles,with increased parameters promoting more efficient heat dissipation.The elevated values of Prandtl number and thermal radiation parameter showcase the diminished temperature profiles,indicating stronger dominance of momentum diffusion over thermal diffusion and radiative heat transfer mechanism.Sensitivity analysis of the pertinent physical parameters reveals that the Prandtl number has the most significant impact on blood flow dynamics.A statistical analysis of the present results and existing literature has also been included in the study.Overall,this research contributes to advancing our understanding of vascular health and lays the groundwork for innovative approaches in stenosis treatment and related biomedical fields.展开更多
With the widespread implementation of distributed generation(DG)and the integration of soft open point(SOP)into the distribution network(DN),the latter is steadily transitioning into a flexible distribution network(FD...With the widespread implementation of distributed generation(DG)and the integration of soft open point(SOP)into the distribution network(DN),the latter is steadily transitioning into a flexible distribution network(FDN),the calculation of carbon flow distribution in FDN is more difficult.To this end,this study constructs a model for low-carbon optimal operations within the FDN on the basis of enhanced carbon emission flow(CEF).First,the carbon emission characteristics of FDNs are scrutinized and an improved method for calculating carbon flow within these networks is proposed.Subsequently,a model for optimizing low-carbon operations within FDNs is formulated based on the refined CEF,which merges the specificities of DG and intelligent SOP.Finally,this model is scrutinized using an upgraded IEEE 33-node distribution system,a comparative analysis of the cases reveals that when DG and SOP are operated in a coordinated manner in the FDN,with the cost of electricity generation was reduced by 40.63 percent and the cost of carbon emissions by 10.18 percent.The findings indicate that the judicious optimization of areas exhibiting higher carbon flow rates can effectively enhance the economic efficiency of DN operations and curtail the carbon emissions of the overall network.展开更多
This paper presents a copula technique to develop time-variant seismic fragility curves for corroded bridges at the system level and considers the realistic time-varying dependence among component seismic demands. Bas...This paper presents a copula technique to develop time-variant seismic fragility curves for corroded bridges at the system level and considers the realistic time-varying dependence among component seismic demands. Based on material deterioration mechanisms and incremental dynamic analysis, the time-evolving seismic demands of components were obtained in the form of marginal probability distributions. The time-varying dependences among bridge components were then captured with the best fitting copula function, which was selected from the commonly used copula classes by the empirical distribution based analysis method. The system time-variant fragility curves at different damage states were developed and the effects of time-varying dependences among components on the bridge system fragility were investigated. The results indicate the time-varying dependence among components significantly affects the time-variant fragility of the bridge system. The copula technique captures the nonlinear dependence among component seismic demands accurately and easily by separating the marginal distributions and the dependence among them.展开更多
For low-speed underwater vehicles, the ocean currents has a great influence on them, and the changes in ocean currents is complex and continuous, thus whose impact must be taken into consideration in the path planning...For low-speed underwater vehicles, the ocean currents has a great influence on them, and the changes in ocean currents is complex and continuous, thus whose impact must be taken into consideration in the path planning. There are still lack of authoritative indicator and method for the cooperating path planning. The calculation of the voyage time is a difficult problem in the time-varying ocean, for the existing methods of the cooperating path planning, the computation time will increase exponentially as the autonomous underwater vehicle（AUV） counts increase, rendering them unfeasible. A collaborative path planning method is presehted for multi-AUV under the influence of time-varying ocean currents based on the dynamic programming algorithm. Each AUV cooperates with the one who has the longest estimated time of sailing, enabling the arrays of AUV to get their common goal in the shortest time with minimum timedifference. At the same time, they could avoid the obstacles along the way to the target. Simulation results show that the proposed method has a promising applicability.展开更多
基金supported by Research project of Shengli Oifield Exploration and Development Research Institute (Grant No.30200018-21-ZC0613-0125)。
文摘For the ultra-high water-cut reservoirs,after long-term water injection exploitation,the physical properties of the reservoir change and the heterogeneity of the reservoir becomes increasingly severe,which further aggravates the spatial difference of the flow field.In this study,the displacement experiments were employed to investigate the variations in core permeability,porosity,and relative permeability after a large amount of water injection.A relative permeability endpoint model was proposed by utilizing the alternating conditional expectation(ACE)transformation to describe the variation in relative permeability based on the experimental data.Based on the time dependent models for permeability and relative permeability,the traditional oil-water two-phase model was improved and discretized using the mimetic finite difference method(MFD).The two cases were launched to confirm the validation of the proposed model.The impact of time-varying physical features on reservoir production performance was studied in a real water flooding reservoir.The experimental results indicate that the overall relative permeability curve shifts to the right as water injection increases.This shift corresponds to a transition towards a more hydrophilic wettability and a decrease in residual oil saturation.The endpoint model demonstrates excellent accuracy and can be applied to time-varying simulations of reservoir physics.The impact of variations in permeability and relative permeability on the reservoir production performance yields two distinct outcomes.The time-varying permeability of the reservoir results in intensified water channeling and poor development effects.On the other hand,the time-varying relative permeability enhances the oil phase seepage capacity,facilitating oil displacement.The comprehensive time-varying behavior is the result of the combined influence of these two parameters,which closely resemble the actual conditions observed in oil field exploitation.The time-varying simulation technique of reservoir physical properties proposed in this paper can continuously and stably characterize the dynamic changes of reservoir physical properties during water drive development.This approach ensures the reliability of the simulation results regarding residual oil distribution.
文摘Due to the complex high-temperature characteristics of hydrocarbon fuel,the research on the long-term working process of parallel channel structure under variable working conditions,especially under high heat-mass ratio,has not been systematically carried out.In this paper,the heat transfer and flow characteristics of related high temperature fuels are studied by using typical engine parallel channel structure.Through numeri⁃cal simulation and systematic experimental verification,the flow and heat transfer characteristics of parallel chan⁃nels under typical working conditions are obtained,and the effectiveness of high-precision calculation method is preliminarily established.It is known that the stable time required for hot start of regenerative cooling engine is about 50 s,and the flow resistance of parallel channel structure first increases and then decreases with the in⁃crease of equivalence ratio(The following equivalence ratio is expressed byΦ),and there is a flow resistance peak in the range ofΦ=0.5~0.8.This is mainly caused by the coupling effect of high temperature physical proper⁃ties,flow rate and pressure of fuel in parallel channels.At the same time,the cooling and heat transfer character⁃istics of parallel channels under some conditions of high heat-mass ratio are obtained,and the main factors affect⁃ing the heat transfer of parallel channels such as improving surface roughness and strengthening heat transfer are mastered.In the experiment,whenΦis less than 0.9,the phenomenon of local heat transfer enhancement and deterioration can be obviously observed,and the temperature rise of local structures exceeds 200℃,which is the risk of structural damage.Therefore,the reliability of long-term parallel channel structure under the condition of high heat-mass ratio should be fully considered in structural design.
文摘This paper aims to numerically explore the characteristics of unsteady cavitating flow around a NACA0015 hydrofoil,with a focus on vorticity attributes.The simulation utilizes a homogeneous mixture model coupled with a filter-based density correction turbulence model and a modified Zwart cavitation model.The study investigates the dynamic cavitation features of the thermal fluid around the hydrofoil at various incoming flow velocities.It systematically elucidates the evolution of cavitation and vortex dynamics corresponding to each velocity condition.The results indicate that with increasing incoming flow velocity,distinct cavitation processes take place in the flow field.
基金supported by the Ministry of Industry and Information Technology High Tech Ship Special Project(Grant No.CBG3N21-2-6).
文摘Gas-liquid flow(GLF),especially slug and annular flows in oil and gas gathering and transportation pipelines,become particularly complex inside elbows and can easily exacerbate pipeline corrosion and damage.In thisstudy,FLUENT was used to conduct 3D simulations of slug and annular flow in elbows for different velocitiesto assess the ensuing changes in terms of pressure.In particular,the multifluid VOF(Volume of Fraction)modelwas chosen.The results indicate that under both slug and annular flow conditions,the pressure inside the elbow islower than the outside.As the superficial velocity of liquid and gas increase,the pressure and liquid flow velocityat different positions of the elbow also increase,while the secondary flow weakens.Under annular flow conditions,the liquid film on the outer side of the elbow is thicker than that on the inner side,and the liquid velocityin the main liquid film zone is the lowest.
基金Project supported by the National Natural Science Foundation of China(Grant No.12201329)the Zhejiang Provincial Natural Science Foundation of China(Grant No.LY24A010002)the Natural Science Foundation of Ningbo(Grant No.2023J126)。
文摘The third-order flow Gerdjikov–Ivanov(TOFGI)equation is studied,and the Darboux transformation(DT)is used to obtain the determinant expression of the solution of this equation.On this basis,the soliton solution,rational solution,positon solution,and breather solution of the TOFGI equation are obtained by taking zero seed solution and non-zero seed solution.The exact solutions and dynamic properties of the Gerdjikov–Ivanov(GI)equation and the TOFGI equation are compared in detail under the same conditions,and it is found that there are some differences in the velocities and trajectories of the solutions of the two equations.
基金supported by Basic Science Research Program through the National Natural Science Foundation of China(Grant No.61867003).
文摘As the proportion of newenergy increases,the traditional cumulant method(CM)produces significant errorswhen performing probabilistic load flow(PLF)calculations with large-scale wind power integrated.Considering the wind speed correlation,a multi-scenario PLF calculation method that combines random sampling and segmented discrete wind farm power was proposed.Firstly,based on constructing discrete scenes of wind farms,the Nataf transform is used to handle the correlation between wind speeds.Then,the random sampling method determines the output probability of discrete wind power scenarios when wind speed exhibits correlation.Finally,the PLF calculation results of each scenario areweighted and superimposed following the total probability formula to obtain the final power flow calculation result.Verified in the IEEE standard node system,the absolute percent error(APE)for the mean and standard deviation(SD)of the node voltages and branch active power are all within 1%,and the average root mean square(AMSR)values of the probability curves are all less than 1%.
基金Supported by Yunnan Fundamental Research Projects(Nos.202301AT070469,202301AT070275)Supported by Yunnan Major Scientific and Technological Projects(No.202202AG050002).
文摘Smelting with oxygen bottom blowing is one of the main methods used in the frame of copper pyrometallurgy.With this approach,feed materials and oxygen-enriched air are introduced in reversed order to enhance multiphaseflow within the furnace.Understanding the flow structure and temperature distribution in this setup is crucial foroptimizing production.In this study,gas-liquid interactions,and temperature profiles under varying air-injectionconditions are examined by means of numerical simulation for a 3.2 m×20 m furnace.The results indicate that thehigh-velocity regions are essentially distributed near the lance within the reaction region and the flue gas outlet,while low-velocity regions are located close to the furnace walls on both side of the reaction region.Dead regionsappear in the sedimentation region,with gas velocities surpassing those of the molten phase.As the injection rateincreases from 0.50 to 0.80 Nm3/s,the stabilization time of the average liquid surface velocity decreases from 2.6 sto 1.9 s,exhibiting a similar trend to the gas holdup.During stabilization,the average liquid surface velocity risesfrom 0.505 to 0.702 m/s.The average turbulent kinetic energy(TKE)of the fluid in the molten bath increases from0.095 to 0.162 m^(2)/s^(2).The proportion of the area distribution with TKE greater than 0.10 m^(2)/s^(2) and the gas holdupat steady state both rise with an increase in the injection quantity.The maximum splashing height of the melt growsfrom approximately 0.756 to 1.154 m,with the affected area expanding from 14.239 to 20.498 m^(2).Under differentworking conditions with varying injection quantities,the average temperature changes in melt zone and flue gaszone of the furnace are small.The temperature in the melt and in the flue-gas zone spans the interval 1200℃–1257℃,and 1073℃–1121℃,respectively.The temperature distribution of the melt and flue gas reveals a patterncharacterized by elevated temperatures in the reaction zone,gradually transitioning to lower temperatures in thesedimentation region.
基金funded by Universiti Teknikal Malaysia Melaka and Ministry of Higher Education(MoHE)Malaysia,grant number FRGS/1/2024/FTKM/F00586.
文摘Nanotechnology holds immense importance in the biomedical field due to its ability to revolutionize healthcare on a molecular scale.Motivated by the imperative of enhancing patient outcomes,a comprehensive numerical simulation study on the dynamics of blood flow in a stenosed artery,focusing on the effects of copper and alumina nanoparticles,is conducted.The study employs a 2-dimensional Newtonian blood flow model infused with copper and alumina nanoparticles,considering the influence of a magnetic field,thermal radiation,and various flow parameters.The governing differential equations are first non-dimensionalized to facilitate analysis and subsequently solved using the 4th order collocation method,bvp4c module in MATLAB.This approach obtains velocity and temperature profiles,revealing the impact of relevant parameters crucial in the biomedical field.The findings of this study underscore the significance of understanding blood flow dynamics in stenosed arteries and the potential benefits of utilizing copper and alumina nanoparticles in treatment strategies.The incorporation of nanoparticles introduces novel avenues for enhancing therapeutic interventions,particularly in mitigating the effects of stenosis.The elucidation of velocity and temperature profiles provides valuable insights into the behavior of blood flow under different conditions,thereby informing the development of targeted biomedical applications.The arterial curvature flow parameter influences temperature profiles,with increased parameters promoting more efficient heat dissipation.The elevated values of Prandtl number and thermal radiation parameter showcase the diminished temperature profiles,indicating stronger dominance of momentum diffusion over thermal diffusion and radiative heat transfer mechanism.Sensitivity analysis of the pertinent physical parameters reveals that the Prandtl number has the most significant impact on blood flow dynamics.A statistical analysis of the present results and existing literature has also been included in the study.Overall,this research contributes to advancing our understanding of vascular health and lays the groundwork for innovative approaches in stenosis treatment and related biomedical fields.
基金supported in part by National Natural Science Foundation of China under Grant 52007026.
文摘With the widespread implementation of distributed generation(DG)and the integration of soft open point(SOP)into the distribution network(DN),the latter is steadily transitioning into a flexible distribution network(FDN),the calculation of carbon flow distribution in FDN is more difficult.To this end,this study constructs a model for low-carbon optimal operations within the FDN on the basis of enhanced carbon emission flow(CEF).First,the carbon emission characteristics of FDNs are scrutinized and an improved method for calculating carbon flow within these networks is proposed.Subsequently,a model for optimizing low-carbon operations within FDNs is formulated based on the refined CEF,which merges the specificities of DG and intelligent SOP.Finally,this model is scrutinized using an upgraded IEEE 33-node distribution system,a comparative analysis of the cases reveals that when DG and SOP are operated in a coordinated manner in the FDN,with the cost of electricity generation was reduced by 40.63 percent and the cost of carbon emissions by 10.18 percent.The findings indicate that the judicious optimization of areas exhibiting higher carbon flow rates can effectively enhance the economic efficiency of DN operations and curtail the carbon emissions of the overall network.
基金Natural Science Foundation of China under Grant No.51808376
文摘This paper presents a copula technique to develop time-variant seismic fragility curves for corroded bridges at the system level and considers the realistic time-varying dependence among component seismic demands. Based on material deterioration mechanisms and incremental dynamic analysis, the time-evolving seismic demands of components were obtained in the form of marginal probability distributions. The time-varying dependences among bridge components were then captured with the best fitting copula function, which was selected from the commonly used copula classes by the empirical distribution based analysis method. The system time-variant fragility curves at different damage states were developed and the effects of time-varying dependences among components on the bridge system fragility were investigated. The results indicate the time-varying dependence among components significantly affects the time-variant fragility of the bridge system. The copula technique captures the nonlinear dependence among component seismic demands accurately and easily by separating the marginal distributions and the dependence among them.
基金supported by the National Natural Science Foundation of China(5110917951179156+2 种基金5137917661473233)the Natural Science Basic Research Plan in Shaanxi Province of China(2014JQ8330)
文摘For low-speed underwater vehicles, the ocean currents has a great influence on them, and the changes in ocean currents is complex and continuous, thus whose impact must be taken into consideration in the path planning. There are still lack of authoritative indicator and method for the cooperating path planning. The calculation of the voyage time is a difficult problem in the time-varying ocean, for the existing methods of the cooperating path planning, the computation time will increase exponentially as the autonomous underwater vehicle（AUV） counts increase, rendering them unfeasible. A collaborative path planning method is presehted for multi-AUV under the influence of time-varying ocean currents based on the dynamic programming algorithm. Each AUV cooperates with the one who has the longest estimated time of sailing, enabling the arrays of AUV to get their common goal in the shortest time with minimum timedifference. At the same time, they could avoid the obstacles along the way to the target. Simulation results show that the proposed method has a promising applicability.
