The techniques of pressurized mining and hydraulic fracturing are often used to improve gas well productivity at the later development stage of low-permeability carbonate gas reservoirs,but reservoirs are watered out ...The techniques of pressurized mining and hydraulic fracturing are often used to improve gas well productivity at the later development stage of low-permeability carbonate gas reservoirs,but reservoirs are watered out and a great number of micro fractures are produced.Therefore,one of the key factors for underground gas storages(UGS)rebuilt from low-permeability fractured gas reservoirs with CO_(2) as the cushion gas is how to expand storage capacity effectively by injecting CO_(2) to displace water and to develop control strategies for the stable migration of gas-water interface.In this paper,a mathematical model was established to simulate the gas-water flow when CO_(2) was injected into dual porosity reservoirs to displace water.Then,the gas-water interface migration rules while CO_(2) was injected in the peripheral gas wells for water displacement were analyzed with one domestic UGS rebuilt from fractured gas reservoirs as the research object.And finally,discussion was made on how CO_(2) dissolution,bottom hole flowing pressure(BHFP),CO_(2) injection rate and micro fracture parameters affect the stability of gas-water interface in the process of storage capacity expansion.It is shown that the speed of capacity expansion reaches the maximum value at the fifth cycle and then decreases gradually when UGS capacity is expanded in the pattern of more injection and less withdrawal.Gasewater interface during UGS capacity expansion is made stable due to that the solubility of CO_(2) in water varies with the reservoir pressure.When the UGS capacity is expanded at constant BHFP and the flow rate,the expansion speed can be increased effectively by increasing the BHFP and the injection flow rate of gas wells in the central areas appropriately.In the reservoir areas with high permeability and fracture-matrix permeability ratio,the injection flow rate should be reduced properly to prevent gas-water interface fingering caused by a high-speed flow.Furthermore,it is necessary to monitor strictly the migration of gas-water interface by using observation wells to prevent gas escape through the edge water or water breakthrough at high-permeability zones.These research results provide a technical and theoretical support for water displacement and capacity expansion of UGS rebuilt from low-permeability fractured gas reservoirs with CO_(2) as the cushion gas.展开更多
The change of impervious surface area(ISA) can effectively reveal the gradual process of urbanization and act as a key index for monitoring urban expansion. Experiencing rapid growth of the built environment in the 20...The change of impervious surface area(ISA) can effectively reveal the gradual process of urbanization and act as a key index for monitoring urban expansion. Experiencing rapid growth of the built environment in the 2000 s, urban expansion of Beijing has not been fully characterized through ISA. In this study, Landsat TM images of Beijing in 2001 and 2009 were obtained, and the eight-year urban expansion process in Beijing was analyzed using the ISA extracted by means of the vegetation-imperious surface-soil(V-I-S) model. From the spatial variation in ISA, the ring structure of urban expansion in Beijing was significant during the study period, with decreasing urban density from the city center to the periphery. In the ring road analysis, the most dramatic changes of ISA were found between the fifth ring and the sixth ring. This area has experienced the most new residential development, and is currently the main source of urban expansion. The typical profile lines revealed the directional characteristics of urban expansion. The east-west profile was the most urbanized axes in Beijing, while ISA change in the east-north profile was more significant than in the other five profiles. Moreover, the transition matrix of ISA levels revealed an increase in urban density in the low density built areas; the Moran′s I index showed a clear expansion of the central urban area, which spread contiguously; and the standard deviational ellipse indicated the northeast was the dominant direction of urban expansion. These findings can provide important spatial control guidelines in the next round of national economic and social development planning, overall urban and rural planning, and land use planning.展开更多
In order to improve the output power and increase the lifetime of laser diodes,expansion-matched submounts were investigated by finite element analysis.The submount was designed as sandwiched structure.By varying the ...In order to improve the output power and increase the lifetime of laser diodes,expansion-matched submounts were investigated by finite element analysis.The submount was designed as sandwiched structure.By varying the vertical structure and material of the middle layer,the thermal expansion behavior on the mounting surface was simulated to obtain the expansion-matched design.In addition,the thermal performance of laser diodes packaged by different submounts was compared.The numerical results showed that,changing the thickness ratio of surface copper to middle layer will lead the stress and junction temperature to the opposite direction.Thus compromise needs to be made in the design of the vertical structure.In addition,the silicon carbide（SiC） is the most promising material candidate for the middle layer among the materials discussed in this paper.The simulated results were aimed at providing guidance for the optimal design of sandwich-structure submounts.展开更多
To clarify the effects of the vertical angle of a conical punch on stretch flangeability, hole expansion forming tests were conducted. Test results showed that the hole expansion ratio becomes larger as the vertical a...To clarify the effects of the vertical angle of a conical punch on stretch flangeability, hole expansion forming tests were conducted. Test results showed that the hole expansion ratio becomes larger as the vertical angle decreases.Results also showed that the fracture strain at the fracture location on the hole edge was constant and independent of the vertical angle. This is because the hole expansion ratio was controlled not only by the fracture strain, which is independent of the vertical angle, but also by deformation uniformity along the hole edge. From the result of numerical analyses, it was determined that deformation uniformity depends on the gradient of circumferential stress along the radius direction. When the vertical angle is sharp, the circumferential stress showed a steep decline and the deformation localization was suppressed. Consequently, the hole edge deformed more uniformly and the hole expansion ratio became larger. It is concluded that in order to improve stretch flangeability of high strength steel, it is important to uniformly deform the hole edge by applying a conical punch with a sharp vertical angle.展开更多
For the multi-frequency acoustic analysis, a series expansion method has been introduced to reduce the computation time of the frequency-independent parts, but the Runge phenomenon will arise when this method is emplo...For the multi-frequency acoustic analysis, a series expansion method has been introduced to reduce the computation time of the frequency-independent parts, but the Runge phenomenon will arise when this method is employed in high frequency band. Therefore, this method is improved by analyzing the application condition and proposing the selection principle of the series truncation number. The argument interval can be adjusted with the wavenumber factor. Therefore, the problem of unstable numeration and poor precision can be solved, and the application scope of this method is expanded. The numerical example of acoustic radiation shows that the improved method is correct for acoustic analysis in wider frequency band with less series truncation number and computation amount.展开更多
Liquid-solid fluidized beds are used in mineral processing industries to separate particles based on parti- cle size, density, and shape. Understanding the expanded fluidized bed is vital for accurately assessing its ...Liquid-solid fluidized beds are used in mineral processing industries to separate particles based on parti- cle size, density, and shape. Understanding the expanded fluidized bed is vital for accurately assessing its performance. Expansion characteristics of the fluidized bed were studied by performing several experi- ments with iron ore, chromite, quartz, and coal samples. Using water as liquid medium, experiments were conducted to study the effects of particle size, particle density, and superficial velocity on fluidized bed expansion. The experimental data were utilized to develop an empirical mathematical model based on dimensional analysis to estimate the expansion ratio of the fluidized bed in terms of particle character- istics, operating and design parameters. The predicted expansion ratio obtained from the mathematical model is in good agreement with the experimental data.展开更多
In this paper,a simplified lattice Boltzmann method(SLBM)without evolution of the distribution function is developed for simulating incompressible viscous flows.This method is developed from the application of fractio...In this paper,a simplified lattice Boltzmann method(SLBM)without evolution of the distribution function is developed for simulating incompressible viscous flows.This method is developed from the application of fractional step technique to the macroscopic Navier-Stokes(N-S)equations recovered from lattice Boltzmann equation by using Chapman-Enskog expansion analysis.In SLBM,the equilibrium distribution function is calculated from the macroscopic variables,while the non-equilibrium distribution function is simply evaluated from the difference of two equilibrium distribution functions.Therefore,SLBM tracks the evolution of the macroscopic variables rather than the distribution function.As a result,lower virtual memories are required and physical boundary conditions could be directly implemented.Through numerical test at high Reynolds number,the method shows very nice performance in numerical stability.An accuracy test for the 2D Taylor-Green flow shows that SLBM has the second-order of accuracy in space.More benchmark tests,including the Couette flow,the Poiseuille flow as well as the 2D lid-driven cavity flow,are conducted to further validate the present method;and the simulation results are in good agreement with available data in literatures.展开更多
文摘The techniques of pressurized mining and hydraulic fracturing are often used to improve gas well productivity at the later development stage of low-permeability carbonate gas reservoirs,but reservoirs are watered out and a great number of micro fractures are produced.Therefore,one of the key factors for underground gas storages(UGS)rebuilt from low-permeability fractured gas reservoirs with CO_(2) as the cushion gas is how to expand storage capacity effectively by injecting CO_(2) to displace water and to develop control strategies for the stable migration of gas-water interface.In this paper,a mathematical model was established to simulate the gas-water flow when CO_(2) was injected into dual porosity reservoirs to displace water.Then,the gas-water interface migration rules while CO_(2) was injected in the peripheral gas wells for water displacement were analyzed with one domestic UGS rebuilt from fractured gas reservoirs as the research object.And finally,discussion was made on how CO_(2) dissolution,bottom hole flowing pressure(BHFP),CO_(2) injection rate and micro fracture parameters affect the stability of gas-water interface in the process of storage capacity expansion.It is shown that the speed of capacity expansion reaches the maximum value at the fifth cycle and then decreases gradually when UGS capacity is expanded in the pattern of more injection and less withdrawal.Gasewater interface during UGS capacity expansion is made stable due to that the solubility of CO_(2) in water varies with the reservoir pressure.When the UGS capacity is expanded at constant BHFP and the flow rate,the expansion speed can be increased effectively by increasing the BHFP and the injection flow rate of gas wells in the central areas appropriately.In the reservoir areas with high permeability and fracture-matrix permeability ratio,the injection flow rate should be reduced properly to prevent gas-water interface fingering caused by a high-speed flow.Furthermore,it is necessary to monitor strictly the migration of gas-water interface by using observation wells to prevent gas escape through the edge water or water breakthrough at high-permeability zones.These research results provide a technical and theoretical support for water displacement and capacity expansion of UGS rebuilt from low-permeability fractured gas reservoirs with CO_(2) as the cushion gas.
基金Under the auspices of Key Project of National Natural Science Foundation of China(No.41130534)
文摘The change of impervious surface area(ISA) can effectively reveal the gradual process of urbanization and act as a key index for monitoring urban expansion. Experiencing rapid growth of the built environment in the 2000 s, urban expansion of Beijing has not been fully characterized through ISA. In this study, Landsat TM images of Beijing in 2001 and 2009 were obtained, and the eight-year urban expansion process in Beijing was analyzed using the ISA extracted by means of the vegetation-imperious surface-soil(V-I-S) model. From the spatial variation in ISA, the ring structure of urban expansion in Beijing was significant during the study period, with decreasing urban density from the city center to the periphery. In the ring road analysis, the most dramatic changes of ISA were found between the fifth ring and the sixth ring. This area has experienced the most new residential development, and is currently the main source of urban expansion. The typical profile lines revealed the directional characteristics of urban expansion. The east-west profile was the most urbanized axes in Beijing, while ISA change in the east-north profile was more significant than in the other five profiles. Moreover, the transition matrix of ISA levels revealed an increase in urban density in the low density built areas; the Moran′s I index showed a clear expansion of the central urban area, which spread contiguously; and the standard deviational ellipse indicated the northeast was the dominant direction of urban expansion. These findings can provide important spatial control guidelines in the next round of national economic and social development planning, overall urban and rural planning, and land use planning.
文摘In order to improve the output power and increase the lifetime of laser diodes,expansion-matched submounts were investigated by finite element analysis.The submount was designed as sandwiched structure.By varying the vertical structure and material of the middle layer,the thermal expansion behavior on the mounting surface was simulated to obtain the expansion-matched design.In addition,the thermal performance of laser diodes packaged by different submounts was compared.The numerical results showed that,changing the thickness ratio of surface copper to middle layer will lead the stress and junction temperature to the opposite direction.Thus compromise needs to be made in the design of the vertical structure.In addition,the silicon carbide（SiC） is the most promising material candidate for the middle layer among the materials discussed in this paper.The simulated results were aimed at providing guidance for the optimal design of sandwich-structure submounts.
文摘To clarify the effects of the vertical angle of a conical punch on stretch flangeability, hole expansion forming tests were conducted. Test results showed that the hole expansion ratio becomes larger as the vertical angle decreases.Results also showed that the fracture strain at the fracture location on the hole edge was constant and independent of the vertical angle. This is because the hole expansion ratio was controlled not only by the fracture strain, which is independent of the vertical angle, but also by deformation uniformity along the hole edge. From the result of numerical analyses, it was determined that deformation uniformity depends on the gradient of circumferential stress along the radius direction. When the vertical angle is sharp, the circumferential stress showed a steep decline and the deformation localization was suppressed. Consequently, the hole edge deformed more uniformly and the hole expansion ratio became larger. It is concluded that in order to improve stretch flangeability of high strength steel, it is important to uniformly deform the hole edge by applying a conical punch with a sharp vertical angle.
基金supported by the National Natural Science Foundation of China(51379083,51479079,51579109)the Specialized Research Fund for the Doctoral Program of Higher Education of China(20120142110051)
文摘For the multi-frequency acoustic analysis, a series expansion method has been introduced to reduce the computation time of the frequency-independent parts, but the Runge phenomenon will arise when this method is employed in high frequency band. Therefore, this method is improved by analyzing the application condition and proposing the selection principle of the series truncation number. The argument interval can be adjusted with the wavenumber factor. Therefore, the problem of unstable numeration and poor precision can be solved, and the application scope of this method is expanded. The numerical example of acoustic radiation shows that the improved method is correct for acoustic analysis in wider frequency band with less series truncation number and computation amount.
基金the financial support given by CSIRthrough a network project(NWP-31)to carry out this study
文摘Liquid-solid fluidized beds are used in mineral processing industries to separate particles based on parti- cle size, density, and shape. Understanding the expanded fluidized bed is vital for accurately assessing its performance. Expansion characteristics of the fluidized bed were studied by performing several experi- ments with iron ore, chromite, quartz, and coal samples. Using water as liquid medium, experiments were conducted to study the effects of particle size, particle density, and superficial velocity on fluidized bed expansion. The experimental data were utilized to develop an empirical mathematical model based on dimensional analysis to estimate the expansion ratio of the fluidized bed in terms of particle character- istics, operating and design parameters. The predicted expansion ratio obtained from the mathematical model is in good agreement with the experimental data.
文摘In this paper,a simplified lattice Boltzmann method(SLBM)without evolution of the distribution function is developed for simulating incompressible viscous flows.This method is developed from the application of fractional step technique to the macroscopic Navier-Stokes(N-S)equations recovered from lattice Boltzmann equation by using Chapman-Enskog expansion analysis.In SLBM,the equilibrium distribution function is calculated from the macroscopic variables,while the non-equilibrium distribution function is simply evaluated from the difference of two equilibrium distribution functions.Therefore,SLBM tracks the evolution of the macroscopic variables rather than the distribution function.As a result,lower virtual memories are required and physical boundary conditions could be directly implemented.Through numerical test at high Reynolds number,the method shows very nice performance in numerical stability.An accuracy test for the 2D Taylor-Green flow shows that SLBM has the second-order of accuracy in space.More benchmark tests,including the Couette flow,the Poiseuille flow as well as the 2D lid-driven cavity flow,are conducted to further validate the present method;and the simulation results are in good agreement with available data in literatures.
