The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. Ho...The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. However, the above problems are not well solved currently because of having the difficulties in how to determine the multi-contact, to preciously present the changeable profiles of the rails and to establish an accurate spatial turnout system dynamics model. Based on a high-speed vehicle-turnout coupled model in which the track is modeled as flexible with rails and sleepers represented by beams, the line tracing extreme point method is introduced to investigate the wheel-rail multiple contact conditions and the key sections of the blade rail, longer nose rail, shorter rail in the switch and nose rail area are discretized to represent the varying profiles of rails in the turnout. The dynamic interaction between the vehicle and turnout is simulated for cases of the vehicle divergently passing the turnout and the multi-point contact is obtained. The tracks of the contact patches on the top of the rails are presented and the wheel-rail impact forces are offered in comparison with the contact patches transference on the rails. The numerical simulation results indicate that the length of two-point contact occurrence of a worn wheel profile and rails is longer than that of the new wheel profile and rails; The two-point contact definitely occurs in the switch and crossing area. Generally, three-point contact doesn’t occur for the new rail profile, which is testified by the wheel-rails interpolation distance and the first order derivative function of the tracing line extreme points. The presented research is not only helpful to optimize the structure of the turnout, but also useful to lower the dynamics of the high speed vehicle-turnout system.展开更多
Carbonate gas reservoirs with edge and bottom water contain abundant reserves,making them key production targets in the Tarim Basin,Sichuan Basin,Ordos Basin,and other petroleum provinces.Water invasion may occur in t...Carbonate gas reservoirs with edge and bottom water contain abundant reserves,making them key production targets in the Tarim Basin,Sichuan Basin,Ordos Basin,and other petroleum provinces.Water invasion may occur in the middle and late development stages of such reservoirs,leading to reduction of gas displacement efficiency and gas recovery.In this paper,a pore-scale water-gas immiscible flow model is established by coupling the fluid flow equation and the gas-water contact(GWC)tracking equation.The process of gas displacement with water is simulated in the heterogeneous porous media generated by the quartet structure generation set(QSGS).Finally,the mechanisms of remaining gas distribution and formation are analyzed,and the variation mechanism of microscopic gas displacement efficiency is discussed.The results are obtained in three aspects.First,the remaining gas is distributed at the blind end,in the pore-throat and as clusters,with their proportions and scales jointly controlled by microscopic pore structures,wettability and capillary number.The remaining gas can be further produced by changing the production pressure differential to disturb the original pressure system and gas expansion,so as to improve the microscopic gas displacement efficiency.Second,the microscopic gas displacement efficiency is closely related to the gas flow process.Formation or expansion of each water flow path may cause rapid increase of water cut and slows down the increase of gas displacement efficiency.Third,the microscopic pore structure and wettability are the inherent features of the gas reservoir,so the capillary number can be optimized to change the mode of GWC advancement,and then to effectively improve the microscopic gas displacement efficiency.It is concluded that for real gas wells,the evolution of mechanical mechanisms of GWC advancement should be revealed depending upon the microscopic pore structure and wettability of the reservoir,and then the optimal capillary number can be determined.Furthermore,clarifying the pore-scale water-gas flow characteristics and physical mechanism of microscopic gas displacement provides guidance for the planning of enhanced gas recovery.展开更多
Normalized interventions were implemented in different cities in China to contain the outbreak of COVID-19 before December 2022.However,the differences in the intensity and timeliness of the implementations lead to di...Normalized interventions were implemented in different cities in China to contain the outbreak of COVID-19 before December 2022.However,the differences in the intensity and timeliness of the implementations lead to differences in final size of the infections.Taking the outbreak of COVID-19 in three representative cities Xi'an,Zhengzhou and Yuzhou in January 2022,as examples,we develop a compartmental model to describe the spread of novel coronavirus and implementation of interventions to assess concretely the effectiveness of Chinese interventions and explore their impact on epidemic patterns.After applying reported human confirmed cases to verify the rationality of the model,we apply the model to speculate transmission trend and length of concealed period at the initial spread phase of the epidemic(they are estimated as 10.5,7.8,8.2 days,respectively),to estimate the range of basic reproduction number(2.9,0.7,1.6),and to define two indexes(transmission rate vt and controlled rate vc)to evaluate the overall effect of the interventions.It is shown that for Zhengzhou,vc is always more than v t with regular interventions,and Xi'an take 8 days to achieve vc>v t twice as long as Yuzhou,which can interpret the fact that the epidemic situation in Xi'an was more severe.By carrying out parameter values,it is concluded that in the early stage,strengthening the precision of close contact tracking and frequency of large-scale nucleic acid testing of non-quarantined population are the most effective on controlling the outbreaks and reducing final size.And,if the close contact tracking strategy is sufficiently implemented,at the late stage largescale nucleic acid testing of non-quarantined population is not essential.展开更多
基金supported by National Natural Science Foundation of China (Grant Nos. 51175032, U1134201)National Basic Research Program of China (973 Program, Grant No. 2011CD711104)
文摘The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. However, the above problems are not well solved currently because of having the difficulties in how to determine the multi-contact, to preciously present the changeable profiles of the rails and to establish an accurate spatial turnout system dynamics model. Based on a high-speed vehicle-turnout coupled model in which the track is modeled as flexible with rails and sleepers represented by beams, the line tracing extreme point method is introduced to investigate the wheel-rail multiple contact conditions and the key sections of the blade rail, longer nose rail, shorter rail in the switch and nose rail area are discretized to represent the varying profiles of rails in the turnout. The dynamic interaction between the vehicle and turnout is simulated for cases of the vehicle divergently passing the turnout and the multi-point contact is obtained. The tracks of the contact patches on the top of the rails are presented and the wheel-rail impact forces are offered in comparison with the contact patches transference on the rails. The numerical simulation results indicate that the length of two-point contact occurrence of a worn wheel profile and rails is longer than that of the new wheel profile and rails; The two-point contact definitely occurs in the switch and crossing area. Generally, three-point contact doesn’t occur for the new rail profile, which is testified by the wheel-rails interpolation distance and the first order derivative function of the tracing line extreme points. The presented research is not only helpful to optimize the structure of the turnout, but also useful to lower the dynamics of the high speed vehicle-turnout system.
基金Project supported by the National Natural Science Foundation Projects of China(NSFC)“Dynamic wetting mechanism and transport characteristics of waterdisplacing-gas in nano-pores of unconventional reservoirs”(No.52174041)“Research on fracturing fluid invasion/flowback/retentionmechanisms in shale reservoirs and their impacts on gas well productivity”(No.52104051)+1 种基金“Research on cross scale coupling flow and production law of effective shale gas reservoir pores”(No.51874319)the Natural Science Foundation Project of Beijing“Simulation study on the transfer mechanismand transfer of oil inmicro-nanopores of tight/shale reservoirs”(No.2204093).
文摘Carbonate gas reservoirs with edge and bottom water contain abundant reserves,making them key production targets in the Tarim Basin,Sichuan Basin,Ordos Basin,and other petroleum provinces.Water invasion may occur in the middle and late development stages of such reservoirs,leading to reduction of gas displacement efficiency and gas recovery.In this paper,a pore-scale water-gas immiscible flow model is established by coupling the fluid flow equation and the gas-water contact(GWC)tracking equation.The process of gas displacement with water is simulated in the heterogeneous porous media generated by the quartet structure generation set(QSGS).Finally,the mechanisms of remaining gas distribution and formation are analyzed,and the variation mechanism of microscopic gas displacement efficiency is discussed.The results are obtained in three aspects.First,the remaining gas is distributed at the blind end,in the pore-throat and as clusters,with their proportions and scales jointly controlled by microscopic pore structures,wettability and capillary number.The remaining gas can be further produced by changing the production pressure differential to disturb the original pressure system and gas expansion,so as to improve the microscopic gas displacement efficiency.Second,the microscopic gas displacement efficiency is closely related to the gas flow process.Formation or expansion of each water flow path may cause rapid increase of water cut and slows down the increase of gas displacement efficiency.Third,the microscopic pore structure and wettability are the inherent features of the gas reservoir,so the capillary number can be optimized to change the mode of GWC advancement,and then to effectively improve the microscopic gas displacement efficiency.It is concluded that for real gas wells,the evolution of mechanical mechanisms of GWC advancement should be revealed depending upon the microscopic pore structure and wettability of the reservoir,and then the optimal capillary number can be determined.Furthermore,clarifying the pore-scale water-gas flow characteristics and physical mechanism of microscopic gas displacement provides guidance for the planning of enhanced gas recovery.
基金supported by Fund Program for the Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province(20210009)the National Natural Science Foundation of China under Grant(11801398)+1 种基金the 1331 Engineering Project of Shanxi Province,Key Projects of Health Commission of Shanxi Province(No.2020XM18)the Key Research and Development Project in Shanxi Province(202003D31011/GZ).
文摘Normalized interventions were implemented in different cities in China to contain the outbreak of COVID-19 before December 2022.However,the differences in the intensity and timeliness of the implementations lead to differences in final size of the infections.Taking the outbreak of COVID-19 in three representative cities Xi'an,Zhengzhou and Yuzhou in January 2022,as examples,we develop a compartmental model to describe the spread of novel coronavirus and implementation of interventions to assess concretely the effectiveness of Chinese interventions and explore their impact on epidemic patterns.After applying reported human confirmed cases to verify the rationality of the model,we apply the model to speculate transmission trend and length of concealed period at the initial spread phase of the epidemic(they are estimated as 10.5,7.8,8.2 days,respectively),to estimate the range of basic reproduction number(2.9,0.7,1.6),and to define two indexes(transmission rate vt and controlled rate vc)to evaluate the overall effect of the interventions.It is shown that for Zhengzhou,vc is always more than v t with regular interventions,and Xi'an take 8 days to achieve vc>v t twice as long as Yuzhou,which can interpret the fact that the epidemic situation in Xi'an was more severe.By carrying out parameter values,it is concluded that in the early stage,strengthening the precision of close contact tracking and frequency of large-scale nucleic acid testing of non-quarantined population are the most effective on controlling the outbreaks and reducing final size.And,if the close contact tracking strategy is sufficiently implemented,at the late stage largescale nucleic acid testing of non-quarantined population is not essential.
