This letter reports traffic flow sensitivity to visco-elasticity, with the traffic flow modeling briefly described at first and then used to do traffic flow simulations whose results can reflect the properties of spat...This letter reports traffic flow sensitivity to visco-elasticity, with the traffic flow modeling briefly described at first and then used to do traffic flow simulations whose results can reflect the properties of spatial-temporal evolution of ring traffic flow. It reveals that visco-elasticity plays crucial role in formation of traffic flow patterns, implying that self-organization of traffic flow is crucial in determining traffic flow status.展开更多
The pressure-sensitive effect on the pore structure of sandstone was investigated using X-ray computed micro-tomography and QEMSCAN quantitative mineral analysis. In a physical simulation study, we extracted the pore ...The pressure-sensitive effect on the pore structure of sandstone was investigated using X-ray computed micro-tomography and QEMSCAN quantitative mineral analysis. In a physical simulation study, we extracted the pore network model from digital cores at different confining pressures and evaluated the effect of pressure sensitivity on the multiphase displacement process. In both the pore network model and QEMSCAN scanning, the pore structure was observed to be damaged under a high confining pressure. Due to their different scales, the pores and throats exhibited inhomogeneous changes; further, the throats exhibited a significant variation compared to that exhibited by the pores. Meanwhile, the heterogeneity of the pore structure under the two aforementioned activities was aggravated by the elastic-plastic deformation of the pore structure.The pressure-sensitive effect increased the proportion of mineral particles, such as quartz(the main component of the core skeleton), and reduced the proportion of clay minerals. The clay minerals were originally attached to the pore walls or interspersed in the pores; however, as the pressure increased, the clay minerals accumulated in the pores resulting in blockage of the pores. While simulating the multiphase displacement process, increasing the confining pressure was observed to severely restrict the flowability of oil and water. This study promises to improve the efficiency of reservoir development in terms of oil and gas exploitation.展开更多
Affected by external environmental factors and evolution of dam performance, dam seepage behavior shows nonlinear time-varying characteristics. In this study, to predict and evaluate the long-term development trend an...Affected by external environmental factors and evolution of dam performance, dam seepage behavior shows nonlinear time-varying characteristics. In this study, to predict and evaluate the long-term development trend and short-term fluctuation of the dam seepage behavior, two monitoring models were developed, one for the base flow effect and one for daily variation of dam seepage elements. In the first model, to avoid the influence of the time lag effect on the evaluation of seepage variation with the time effect component of seepage elements, the base values of the seepage element and the reservoir water level were extracted using the wavelet multi-resolution analysis method, and the time effect component was separated by the established base flow effect monitoring model. For the development of the daily variation monitoring model for dam seepage elements, all the previous factors, of which the measured time series prior to the dam seepage element monitoring time may have certain influence on the monitored results, were considered. Those factors that were positively correlated with the analyzed seepage element were initially considered to be the support vector machine(SVM) model input factors, and then the SVM kernel function-based sensitivity analysis was performed to optimize the input factor set and establish the optimized daily variation SVM model. The efficiency and rationality of the two models were verified by case studies of the water level of two piezometric tubes buried under the slope of a concrete gravity dam.Sensitivity analysis of the optimized SVM model shows that the influences of the daily variation of the upstream reservoir water level and rainfall on the daily variation of piezometric tube water level are processes subject to normal distribution.展开更多
A modified cellular automaton model for traffic flow on highway is proposed with a novel concept about the variable security gap. The concept is first introduced into the original Nagel-Schreckenberg model, which is c...A modified cellular automaton model for traffic flow on highway is proposed with a novel concept about the variable security gap. The concept is first introduced into the original Nagel-Schreckenberg model, which is called the non-sensitive driving cellular automaton model. And then it is incorporated with a sensitive driving NaSch model,in which the randomization brake is arranged before the deterministic deceleration. A parameter related to the variable security gap is determined through simulation. Comparison of the simulation results indicates that the variable security gap has different influence on the two models. The fundamental diagram obtained by simulation with the modified sensitive driving NaSch model shows that the maximumflow are in good agreement with the observed data, indicating that the presented model is more reasonable and realistic.展开更多
In this paper,the proposed is a quasi-flow constitutive model with strain-rate sen- sitivity for elastic plastic large deformation.The model is based on the Quasi-flow Corner theory, and is suitable for the sheet meta...In this paper,the proposed is a quasi-flow constitutive model with strain-rate sen- sitivity for elastic plastic large deformation.The model is based on the Quasi-flow Corner theory, and is suitable for the sheet metal forming process simulation with a variable punch machine velocity. Uniaxial tensile tests and deep-drawing tests of a circular blank with square punch are carried out and numerically simulated.The consistency between the experimental and the numerically simulated results shows the validity of the present new constitutive model.展开更多
Based on model tests of earthen dam breach due to piping failure, a numerical model was developed.A key difference from previous research is the assumption that the cross-section of the pipe channel is an arch, with a...Based on model tests of earthen dam breach due to piping failure, a numerical model was developed.A key difference from previous research is the assumption that the cross-section of the pipe channel is an arch, with a rectangle at the bottom and a semicircle at the top before the collapse of the pipe roof, rather than a rectangular or circular cross-section.A shear stress-based erosion rate formula was utilized, and the arched pipe tunnel was assumed to enlarge along its length and width until the overlying soil could no longer maintain stability.Orifice flow and open channel flow were adopted to calculate the breach flow discharge for pressure and free surface flows, respectively.The collapse of the pipe roof was determined by comparing the weight of the overlying soil and the cohesion of the soil on the two sidewalls of the pipe.After the collapse, overtopping failure dominated, and the limit equilibrium method was adopted to estimate the stability of the breach slope when the water flow overtopped.In addition, incomplete and base erosion, as well as one-and two-sided breaches were taken into account.The USDAARS-HERU model test P1, with detailed measured data, was used as a case study, and two artificially filled earthen dam failure cases were studied to verify the model.Feedback analysis demonstrates that the proposed model can provide satisfactory results for modeling the breach flow discharge and breach development process.Sensitivity analysis shows that the soil erodibility and initial piping position significantly affect the prediction of the breach flow discharge.Furthermore, a comparison with a well-known numerical model shows that the proposed model performs better than the NWS BREACH model.展开更多
Implementation of an opposing jet in design of a hypersonic blunt body significantly modifies the external flowfield and yields a considerable reduction in the aerodynamic drag.This study aims to investigate the effec...Implementation of an opposing jet in design of a hypersonic blunt body significantly modifies the external flowfield and yields a considerable reduction in the aerodynamic drag.This study aims to investigate the effects of flowfield modeling parameters of injection and freestream on the flow structure and aerodynamics of a blunt body with an opposing jet in hypersonic flow.Reynolds-Averaged Navier-Stokes(RANS)equations with a Shear Stress Transport(SST)turbulence model are employed to simulate the intricate jet flow interaction.Through utilizing a Non-Intrusive Polynomial Chaos(NIPC)method to construct surrogates,a functional relation is established between input modeling parameters and output flowfield and aerodynamic quantities in concern.Sobol indices in sensitivity analysis are introduced to represent the relative contribution of each parameter.It is found that variations in modeling parameters produce large variations in the flow structure and aerodynamics.The jet-to-freestream total-pressure ratio,jet Mach number,and freestream Mach number are the major contributors to variation in surface pressure,demonstrating an evident location-dependent behavior.The penetration length of injection,reattachment angle of the shear layer,and aerodynamic drag are also most sensitive to the three crucial parameters above.In comparison,the contributions of freestream temperature,freestream density,and jet total temperature are nearly negligible.展开更多
Flooding is a common natural disaster that causes enormous economic, social, and human losses. Of various flood routing methods, the dynamic wave model is one of the best approaches for the prediction of the character...Flooding is a common natural disaster that causes enormous economic, social, and human losses. Of various flood routing methods, the dynamic wave model is one of the best approaches for the prediction of the characteristics of floods during their propagations in natural rivers because all of the terms of the momentum equation are considered in the model. However, no significant research has been conducted on how the model sensitivity affects the accuracy of the downstream hydrograph. In this study, a comprehensive analysis of the input parameters 9f the dynamic wave model was performed through field applications in natural rivers and routing experiments in artificial channels using the graphical multi-parametric sensitivity analysis (GMPSA). The results indicate that the effects of input parameter errors on the output results are more significant in special situations, such as lower values of Manning's roughness coefficient and/or a steeper bed slope on the characteristics of a design hydrograph, larger values of the skewness factor and/or time to peak on the channel characteristics, larger values of Manning's roughness coefficient and/or the bed slope on the space step, and lower values of Manning's roughness coefficient and/or a steeper bed slope on the time step and weighting factor.展开更多
Experiments of saturated water flow and heat transfer were conducted for a meter-scale model of regularly fractured granite.The fractured rock model(height 1502.5 mm,width 904 mm,and thickness 300 mm),embedded with tw...Experiments of saturated water flow and heat transfer were conducted for a meter-scale model of regularly fractured granite.The fractured rock model(height 1502.5 mm,width 904 mm,and thickness 300 mm),embedded with two vertical and two horizontal fractures of pre-set apertures,was constructed using 18 pieces of intact granite.The granite was taken from a site currently being investigated for a high-level nuclear waste repository in China.The experiments involved different heat source temperatures and vertical water fluxes in the embedded fractures either open or filled with sand.A finite difference scheme and computer code for calculation of water flow and heat transfer in regularly fractured rocks was developed,verified against both the experimental data and calculations from the TOUGH2 code,and employed for parametric sensitivity analyses.The experiments revealed that,among other things,the temperature distribution was influenced by water flow in the fractures,especially the water flow in the vertical fracture adjacent to the heat source,and that the heat conduction between the neighboring rock blocks in the model with sand-filled fractures was enhanced by the sand,with larger range of influence of the heat source and longer time for approaching asymptotic steady-state than those of the model with open fractures.The temperatures from the experiments were in general slightly smaller than those from the numerical calculations,probably due to the fact that a certain amount of outward heat transfer at the model perimeter was unavoidable in the experiments.The parametric sensitivity analyses indicated that the temperature distribution was highly sensitive to water flow in the fractures,and the water temperature in the vertical fracture adjacent to the heat source was rather insensitive to water flow in other fractures.展开更多
The paper studies the methodologies of the cargo flow study and projections in Tumen River Economic Development Area(TREDA) that some governments and international scholars used. The authors consider that, in order to...The paper studies the methodologies of the cargo flow study and projections in Tumen River Economic Development Area(TREDA) that some governments and international scholars used. The authors consider that, in order topromote investment, facilitation of cross-border trade and infrastructure in the region, the basic methodology should bebased on the regional economic growth of pertinent Northeast Asian countries and regions to make projections of the situations of regional cargo flows, and then analyzing the cargo flow trend. Based on the above, the authors utilize the routescomparing model and gravity model to forecast the cargo flows through the ports and related routes in TREDA (2000 -2020). The authors also inquire into the main obstacles which affect the cargo flows of the region, analyze the influenceson cargo flows if the obstacles change with sensitivity analyses and try to find the way to sole the obstacles.展开更多
In this paper,after the successful applications to open water propeller performance estimations,the influence of transition sensitive and modified mass transfer models tuned to account for the laminar flow in the pred...In this paper,after the successful applications to open water propeller performance estimations,the influence of transition sensitive and modified mass transfer models tuned to account for the laminar flow in the prediction of the cavitation inception of marine propulsors is investigated from the point of view of the unsteady functioning and induced pressure pulses.The VP1304(also known as PPTC)test case,for which dedicated data were collected during several workshops,is considered first.After preliminary analyses using RANS,also Detached Eddy Simulations(DES)are included to better account for the vortex dynamics and its influence on pressure pulses.Similarly to what observed in uniform inflow,results show a better agreement with the available measurements of propeller performances and confirm the reliability of the proposed approaches for unsteady,non-cavitating,model scale propeller predictions.The overall cavitation pattern is improved too by the application of the transition sensitive correction to the mass transfer model,but the complex dynamics of bubble cavitation observed in experiments prevents quantitatively better predictions in terms of thrust/torque breakdown and induced pressure pulses levels regardless the use of RANS or DES methods.展开更多
基金support of Russian Foundation for Basic Research (RFBR 13-01-12056)National Natural Science Foundation of China (10972212)
文摘This letter reports traffic flow sensitivity to visco-elasticity, with the traffic flow modeling briefly described at first and then used to do traffic flow simulations whose results can reflect the properties of spatial-temporal evolution of ring traffic flow. It reveals that visco-elasticity plays crucial role in formation of traffic flow patterns, implying that self-organization of traffic flow is crucial in determining traffic flow status.
文摘The pressure-sensitive effect on the pore structure of sandstone was investigated using X-ray computed micro-tomography and QEMSCAN quantitative mineral analysis. In a physical simulation study, we extracted the pore network model from digital cores at different confining pressures and evaluated the effect of pressure sensitivity on the multiphase displacement process. In both the pore network model and QEMSCAN scanning, the pore structure was observed to be damaged under a high confining pressure. Due to their different scales, the pores and throats exhibited inhomogeneous changes; further, the throats exhibited a significant variation compared to that exhibited by the pores. Meanwhile, the heterogeneity of the pore structure under the two aforementioned activities was aggravated by the elastic-plastic deformation of the pore structure.The pressure-sensitive effect increased the proportion of mineral particles, such as quartz(the main component of the core skeleton), and reduced the proportion of clay minerals. The clay minerals were originally attached to the pore walls or interspersed in the pores; however, as the pressure increased, the clay minerals accumulated in the pores resulting in blockage of the pores. While simulating the multiphase displacement process, increasing the confining pressure was observed to severely restrict the flowability of oil and water. This study promises to improve the efficiency of reservoir development in terms of oil and gas exploitation.
基金supported by the National Natural Science Foundation of China(Grant No.51709021)the Open Foundation of the State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering(Grant No.2016491111)
文摘Affected by external environmental factors and evolution of dam performance, dam seepage behavior shows nonlinear time-varying characteristics. In this study, to predict and evaluate the long-term development trend and short-term fluctuation of the dam seepage behavior, two monitoring models were developed, one for the base flow effect and one for daily variation of dam seepage elements. In the first model, to avoid the influence of the time lag effect on the evaluation of seepage variation with the time effect component of seepage elements, the base values of the seepage element and the reservoir water level were extracted using the wavelet multi-resolution analysis method, and the time effect component was separated by the established base flow effect monitoring model. For the development of the daily variation monitoring model for dam seepage elements, all the previous factors, of which the measured time series prior to the dam seepage element monitoring time may have certain influence on the monitored results, were considered. Those factors that were positively correlated with the analyzed seepage element were initially considered to be the support vector machine(SVM) model input factors, and then the SVM kernel function-based sensitivity analysis was performed to optimize the input factor set and establish the optimized daily variation SVM model. The efficiency and rationality of the two models were verified by case studies of the water level of two piezometric tubes buried under the slope of a concrete gravity dam.Sensitivity analysis of the optimized SVM model shows that the influences of the daily variation of the upstream reservoir water level and rainfall on the daily variation of piezometric tube water level are processes subject to normal distribution.
文摘A modified cellular automaton model for traffic flow on highway is proposed with a novel concept about the variable security gap. The concept is first introduced into the original Nagel-Schreckenberg model, which is called the non-sensitive driving cellular automaton model. And then it is incorporated with a sensitive driving NaSch model,in which the randomization brake is arranged before the deterministic deceleration. A parameter related to the variable security gap is determined through simulation. Comparison of the simulation results indicates that the variable security gap has different influence on the two models. The fundamental diagram obtained by simulation with the modified sensitive driving NaSch model shows that the maximumflow are in good agreement with the observed data, indicating that the presented model is more reasonable and realistic.
基金The project supported by the Scientific Foundation of National Outstanding Youth of China (10125208),the National Natural Science Foundation of China (19832020),and the National Education Committee of China
文摘In this paper,the proposed is a quasi-flow constitutive model with strain-rate sen- sitivity for elastic plastic large deformation.The model is based on the Quasi-flow Corner theory, and is suitable for the sheet metal forming process simulation with a variable punch machine velocity. Uniaxial tensile tests and deep-drawing tests of a circular blank with square punch are carried out and numerically simulated.The consistency between the experimental and the numerically simulated results shows the validity of the present new constitutive model.
基金supported by the National Key Research and Development Program of China(Grant No.2017YFC0404805)the National Natural Science Foundation of China(Grants No.51779153 and 51539006)+1 种基金the Central Public-interest Scientific Institution Basal Research Fund(Grant No.Y717012)the Natural Science Foundation of Jiangsu Province(Grant No.BK20161121)
文摘Based on model tests of earthen dam breach due to piping failure, a numerical model was developed.A key difference from previous research is the assumption that the cross-section of the pipe channel is an arch, with a rectangle at the bottom and a semicircle at the top before the collapse of the pipe roof, rather than a rectangular or circular cross-section.A shear stress-based erosion rate formula was utilized, and the arched pipe tunnel was assumed to enlarge along its length and width until the overlying soil could no longer maintain stability.Orifice flow and open channel flow were adopted to calculate the breach flow discharge for pressure and free surface flows, respectively.The collapse of the pipe roof was determined by comparing the weight of the overlying soil and the cohesion of the soil on the two sidewalls of the pipe.After the collapse, overtopping failure dominated, and the limit equilibrium method was adopted to estimate the stability of the breach slope when the water flow overtopped.In addition, incomplete and base erosion, as well as one-and two-sided breaches were taken into account.The USDAARS-HERU model test P1, with detailed measured data, was used as a case study, and two artificially filled earthen dam failure cases were studied to verify the model.Feedback analysis demonstrates that the proposed model can provide satisfactory results for modeling the breach flow discharge and breach development process.Sensitivity analysis shows that the soil erodibility and initial piping position significantly affect the prediction of the breach flow discharge.Furthermore, a comparison with a well-known numerical model shows that the proposed model performs better than the NWS BREACH model.
文摘Implementation of an opposing jet in design of a hypersonic blunt body significantly modifies the external flowfield and yields a considerable reduction in the aerodynamic drag.This study aims to investigate the effects of flowfield modeling parameters of injection and freestream on the flow structure and aerodynamics of a blunt body with an opposing jet in hypersonic flow.Reynolds-Averaged Navier-Stokes(RANS)equations with a Shear Stress Transport(SST)turbulence model are employed to simulate the intricate jet flow interaction.Through utilizing a Non-Intrusive Polynomial Chaos(NIPC)method to construct surrogates,a functional relation is established between input modeling parameters and output flowfield and aerodynamic quantities in concern.Sobol indices in sensitivity analysis are introduced to represent the relative contribution of each parameter.It is found that variations in modeling parameters produce large variations in the flow structure and aerodynamics.The jet-to-freestream total-pressure ratio,jet Mach number,and freestream Mach number are the major contributors to variation in surface pressure,demonstrating an evident location-dependent behavior.The penetration length of injection,reattachment angle of the shear layer,and aerodynamic drag are also most sensitive to the three crucial parameters above.In comparison,the contributions of freestream temperature,freestream density,and jet total temperature are nearly negligible.
文摘Flooding is a common natural disaster that causes enormous economic, social, and human losses. Of various flood routing methods, the dynamic wave model is one of the best approaches for the prediction of the characteristics of floods during their propagations in natural rivers because all of the terms of the momentum equation are considered in the model. However, no significant research has been conducted on how the model sensitivity affects the accuracy of the downstream hydrograph. In this study, a comprehensive analysis of the input parameters 9f the dynamic wave model was performed through field applications in natural rivers and routing experiments in artificial channels using the graphical multi-parametric sensitivity analysis (GMPSA). The results indicate that the effects of input parameter errors on the output results are more significant in special situations, such as lower values of Manning's roughness coefficient and/or a steeper bed slope on the characteristics of a design hydrograph, larger values of the skewness factor and/or time to peak on the channel characteristics, larger values of Manning's roughness coefficient and/or the bed slope on the space step, and lower values of Manning's roughness coefficient and/or a steeper bed slope on the time step and weighting factor.
基金Project (No 50778014) supported by the National Natural Science Foundation of China
文摘Experiments of saturated water flow and heat transfer were conducted for a meter-scale model of regularly fractured granite.The fractured rock model(height 1502.5 mm,width 904 mm,and thickness 300 mm),embedded with two vertical and two horizontal fractures of pre-set apertures,was constructed using 18 pieces of intact granite.The granite was taken from a site currently being investigated for a high-level nuclear waste repository in China.The experiments involved different heat source temperatures and vertical water fluxes in the embedded fractures either open or filled with sand.A finite difference scheme and computer code for calculation of water flow and heat transfer in regularly fractured rocks was developed,verified against both the experimental data and calculations from the TOUGH2 code,and employed for parametric sensitivity analyses.The experiments revealed that,among other things,the temperature distribution was influenced by water flow in the fractures,especially the water flow in the vertical fracture adjacent to the heat source,and that the heat conduction between the neighboring rock blocks in the model with sand-filled fractures was enhanced by the sand,with larger range of influence of the heat source and longer time for approaching asymptotic steady-state than those of the model with open fractures.The temperatures from the experiments were in general slightly smaller than those from the numerical calculations,probably due to the fact that a certain amount of outward heat transfer at the model perimeter was unavoidable in the experiments.The parametric sensitivity analyses indicated that the temperature distribution was highly sensitive to water flow in the fractures,and the water temperature in the vertical fracture adjacent to the heat source was rather insensitive to water flow in other fractures.
文摘The paper studies the methodologies of the cargo flow study and projections in Tumen River Economic Development Area(TREDA) that some governments and international scholars used. The authors consider that, in order topromote investment, facilitation of cross-border trade and infrastructure in the region, the basic methodology should bebased on the regional economic growth of pertinent Northeast Asian countries and regions to make projections of the situations of regional cargo flows, and then analyzing the cargo flow trend. Based on the above, the authors utilize the routescomparing model and gravity model to forecast the cargo flows through the ports and related routes in TREDA (2000 -2020). The authors also inquire into the main obstacles which affect the cargo flows of the region, analyze the influenceson cargo flows if the obstacles change with sensitivity analyses and try to find the way to sole the obstacles.
文摘In this paper,after the successful applications to open water propeller performance estimations,the influence of transition sensitive and modified mass transfer models tuned to account for the laminar flow in the prediction of the cavitation inception of marine propulsors is investigated from the point of view of the unsteady functioning and induced pressure pulses.The VP1304(also known as PPTC)test case,for which dedicated data were collected during several workshops,is considered first.After preliminary analyses using RANS,also Detached Eddy Simulations(DES)are included to better account for the vortex dynamics and its influence on pressure pulses.Similarly to what observed in uniform inflow,results show a better agreement with the available measurements of propeller performances and confirm the reliability of the proposed approaches for unsteady,non-cavitating,model scale propeller predictions.The overall cavitation pattern is improved too by the application of the transition sensitive correction to the mass transfer model,but the complex dynamics of bubble cavitation observed in experiments prevents quantitatively better predictions in terms of thrust/torque breakdown and induced pressure pulses levels regardless the use of RANS or DES methods.