Quantitative description of desorption stages of coalbed methane is an important basis to objectively understand the production of coalbed methane well,to diagnose the production state,and to optimize the management o...Quantitative description of desorption stages of coalbed methane is an important basis to objectively understand the production of coalbed methane well,to diagnose the production state,and to optimize the management of draining and collection of coalbed methane.A series of isothermal adsorption experiments were carried out with 12 anthracite samples from 6 coalbed methane wells located in the south of the Qinshui Basin,based on the results of isothermal adsorption experiments,and an analytical model was developed based on the Langmuir sorption theory.With the model,a numerical method that adopts equivalent desorption rate and its curve was established,which can be used to characterize the staged desorption of coalbed methane.According to the experimental and numerical characterizations,three key pressure points determined by the equivalent desorption rate curvature that defines pressure-declining desorption stage,have been proposed and confirmed,namely,start-up pressure,transition pressure and sensitive pressure.By using these three key pressure points,the process of coalbed methane desorption associated with isothermal adsorption experiments can be divided into four stages,i.e.,zero desorption stage,slow desorption stage,transition desorption stage,and sensitive desorption stage.According to analogy analysis,there are differences and similarities between the processes of coalbed methane desorption identified by isothermal adsorption experiments and observed in gas production.Moreover,it has been found that larger Langmuir volume and ratio of Langmuir constants are beneficial to earlier advent of steady production stage,whereas it is also possible that the declining production stage may occur ahead of schedule.展开更多
Flash boiling atomization(FBA)is a promising approach for enhancing spray atomization,which can generate a fine and more evenly distributed spray by increasing the fuel injection temperature or reducing the ambient pr...Flash boiling atomization(FBA)is a promising approach for enhancing spray atomization,which can generate a fine and more evenly distributed spray by increasing the fuel injection temperature or reducing the ambient pressure.However,when the outlet speed of the nozzle exceeds 400 m/s,investigating high-speed flash boiling atomization(HFBA)becomes quite challenging.This difficulty arises fromthe involvement ofmany complex physical processes and the requirement for a very fine mesh in numerical simulations.In this study,an HFBA model for gasoline direct injection(GDI)is established.This model incorporates primary and secondary atomization,as well as vaporization and boilingmodels,to describe the development process of the flash boiling spray.Compared to lowspeed FBA,these physical processes significantly impact HFBA.In this model,the Eulerian description is utilized for modeling the gas,and the Lagrangian description is applied to model the droplets,which effectively captures the movement of the droplets and avoids excessive mesh in the Eulerian coordinates.Under various conditions,numerical solutions of the Sauter mean diameter(SMD)for GDI show good agreement with experimental data,validating the proposed model’s performance.Simulations based on this HFBA model investigate the influences of fuel injection temperature and ambient pressure on the atomization process.Numerical analyses of the velocity field,temperature field,vapor mass fraction distribution,particle size distribution,and spray penetration length under different superheat degrees reveal that high injection temperature or low ambient pressure significantly affects the formation of small and dispersed droplet distribution.This effect is conducive to the refinement of spray particles and enhances atomization.展开更多
In a structural system reliability analysis that lacks probabilistic information, calculating the numerical characteristics of the state functions, especially the first four moments of the state functions, is necessar...In a structural system reliability analysis that lacks probabilistic information, calculating the numerical characteristics of the state functions, especially the first four moments of the state functions, is necessary. Based on that, the structural system reliability is analyzed with a fourth-order moment method. The reliability sensitivity is required to conduct the differential operation of the numerical characteristic functions. A reliability sensitivity analysis formula is then derived in combination with the relation of the differential operation. Based on the matrix theory and Kronecker algebra, this paper systematically derives a matrix expression of the first four moments of the state functions, and establishes the matrix relation between the first four moments of the state functions and those of the basic random variables. On this basis, a differential operation formula of the first four moments of the state functions is further derived against the first four moments of the basic random variables. The vector relation between the state functions and the multidimensional basic random variables is described by means of the matrix operation to extend the operation method. Finally, a concise and intuitive formula is obtained to explore the inherent essential relation between the numerical characteristics of the state functions and those of the basic random variables, leading to a universal equation for the two kinds of numerical characteristics.展开更多
In east China, almost all the old fields have stepped into high water cut stage, with main development blocks into phase of super high water\|cut and high ratio of total oil produced to OOIP. Because of the complicate...In east China, almost all the old fields have stepped into high water cut stage, with main development blocks into phase of super high water\|cut and high ratio of total oil produced to OOIP. Because of the complicated distribution of remaining oil and great difficulties of potential excavation, effective succeed development methods are in urgent. Through physical modeling in lab, field experiments and industrial deployment, a set of necessary industrialized technology is posted, which is suitable for terrestrial fluvial delta reservoirs during super high water bearing stage, including the detailed description of major reservoir, remaining oil monitoring, fine potential exploitation by water flooding and IOR technology by chemical flooding. This technology has been applied to Shengli, Zhongyuan and Henan oilfields with remarkable benefits and social effects.展开更多
In modern processing of conducting materials, such as steel,the time-varying electromagnetic field plays a key role in obtaining the desired microstructure or eliminating solidification defects such as porosity and se...In modern processing of conducting materials, such as steel,the time-varying electromagnetic field plays a key role in obtaining the desired microstructure or eliminating solidification defects such as porosity and segregation in cast billets. Up to now,few studies on the induced electromagnetic force （also called the Lorentz force） field in liquid metal have been reported. Compared with the magnetic field, the induced force field is the real and only direct cause for flow control. The electromagnetic force is comprised of two components. One is time-independent and the other is time- dependent. The time-dependent component varies with time in both amplitude and direction. When it reaches the extreme value,it can be one dozen times larger than the time-independent component. In this paper, a new method to quantitatively describe the induced electromagnetic force in liquid metal under a harmonic electromagnetic field,including both its time- independent and dependent components, was proposed based on the formula derivation from the data of amplitude and phase angle. Through this method ,the features of the time-dependent component were discussed, including the directions of rotation and the long axis. As a result, the force pattern was described. With two example calculations, the method was explained in detail. The results of both examples show that the force field in liquid metal can be divided into several regions with different force features. Example 1 shows the effect of coil position on the evolution of the force field pattern in liquid metal. Example 2 is a kind of stirring by the travelling magnetic field ,whose results present the sub-structures in metal and show that most of them have almost the same rotating direction.展开更多
基金supported by National KeyBasic Research Program of China (Grant No. 2009CB219605)Key Project of National Natural Science Foundation of China (Grant No.40730422)Grand Science and Technology Special Project of China(Grant No. 2011ZX05034-04)
文摘Quantitative description of desorption stages of coalbed methane is an important basis to objectively understand the production of coalbed methane well,to diagnose the production state,and to optimize the management of draining and collection of coalbed methane.A series of isothermal adsorption experiments were carried out with 12 anthracite samples from 6 coalbed methane wells located in the south of the Qinshui Basin,based on the results of isothermal adsorption experiments,and an analytical model was developed based on the Langmuir sorption theory.With the model,a numerical method that adopts equivalent desorption rate and its curve was established,which can be used to characterize the staged desorption of coalbed methane.According to the experimental and numerical characterizations,three key pressure points determined by the equivalent desorption rate curvature that defines pressure-declining desorption stage,have been proposed and confirmed,namely,start-up pressure,transition pressure and sensitive pressure.By using these three key pressure points,the process of coalbed methane desorption associated with isothermal adsorption experiments can be divided into four stages,i.e.,zero desorption stage,slow desorption stage,transition desorption stage,and sensitive desorption stage.According to analogy analysis,there are differences and similarities between the processes of coalbed methane desorption identified by isothermal adsorption experiments and observed in gas production.Moreover,it has been found that larger Langmuir volume and ratio of Langmuir constants are beneficial to earlier advent of steady production stage,whereas it is also possible that the declining production stage may occur ahead of schedule.
基金supported by the National Natural Science Foundation of China(Project Nos.12272270,11972261).
文摘Flash boiling atomization(FBA)is a promising approach for enhancing spray atomization,which can generate a fine and more evenly distributed spray by increasing the fuel injection temperature or reducing the ambient pressure.However,when the outlet speed of the nozzle exceeds 400 m/s,investigating high-speed flash boiling atomization(HFBA)becomes quite challenging.This difficulty arises fromthe involvement ofmany complex physical processes and the requirement for a very fine mesh in numerical simulations.In this study,an HFBA model for gasoline direct injection(GDI)is established.This model incorporates primary and secondary atomization,as well as vaporization and boilingmodels,to describe the development process of the flash boiling spray.Compared to lowspeed FBA,these physical processes significantly impact HFBA.In this model,the Eulerian description is utilized for modeling the gas,and the Lagrangian description is applied to model the droplets,which effectively captures the movement of the droplets and avoids excessive mesh in the Eulerian coordinates.Under various conditions,numerical solutions of the Sauter mean diameter(SMD)for GDI show good agreement with experimental data,validating the proposed model’s performance.Simulations based on this HFBA model investigate the influences of fuel injection temperature and ambient pressure on the atomization process.Numerical analyses of the velocity field,temperature field,vapor mass fraction distribution,particle size distribution,and spray penetration length under different superheat degrees reveal that high injection temperature or low ambient pressure significantly affects the formation of small and dispersed droplet distribution.This effect is conducive to the refinement of spray particles and enhances atomization.
基金Project supported by the National Natural Science Foundation of China(Nos.51135003 and U1234208)the Major State Basic Research Development Program of China(973 Program)(No.2014CB046303)
文摘In a structural system reliability analysis that lacks probabilistic information, calculating the numerical characteristics of the state functions, especially the first four moments of the state functions, is necessary. Based on that, the structural system reliability is analyzed with a fourth-order moment method. The reliability sensitivity is required to conduct the differential operation of the numerical characteristic functions. A reliability sensitivity analysis formula is then derived in combination with the relation of the differential operation. Based on the matrix theory and Kronecker algebra, this paper systematically derives a matrix expression of the first four moments of the state functions, and establishes the matrix relation between the first four moments of the state functions and those of the basic random variables. On this basis, a differential operation formula of the first four moments of the state functions is further derived against the first four moments of the basic random variables. The vector relation between the state functions and the multidimensional basic random variables is described by means of the matrix operation to extend the operation method. Finally, a concise and intuitive formula is obtained to explore the inherent essential relation between the numerical characteristics of the state functions and those of the basic random variables, leading to a universal equation for the two kinds of numerical characteristics.
文摘In east China, almost all the old fields have stepped into high water cut stage, with main development blocks into phase of super high water\|cut and high ratio of total oil produced to OOIP. Because of the complicated distribution of remaining oil and great difficulties of potential excavation, effective succeed development methods are in urgent. Through physical modeling in lab, field experiments and industrial deployment, a set of necessary industrialized technology is posted, which is suitable for terrestrial fluvial delta reservoirs during super high water bearing stage, including the detailed description of major reservoir, remaining oil monitoring, fine potential exploitation by water flooding and IOR technology by chemical flooding. This technology has been applied to Shengli, Zhongyuan and Henan oilfields with remarkable benefits and social effects.
文摘In modern processing of conducting materials, such as steel,the time-varying electromagnetic field plays a key role in obtaining the desired microstructure or eliminating solidification defects such as porosity and segregation in cast billets. Up to now,few studies on the induced electromagnetic force （also called the Lorentz force） field in liquid metal have been reported. Compared with the magnetic field, the induced force field is the real and only direct cause for flow control. The electromagnetic force is comprised of two components. One is time-independent and the other is time- dependent. The time-dependent component varies with time in both amplitude and direction. When it reaches the extreme value,it can be one dozen times larger than the time-independent component. In this paper, a new method to quantitatively describe the induced electromagnetic force in liquid metal under a harmonic electromagnetic field,including both its time- independent and dependent components, was proposed based on the formula derivation from the data of amplitude and phase angle. Through this method ,the features of the time-dependent component were discussed, including the directions of rotation and the long axis. As a result, the force pattern was described. With two example calculations, the method was explained in detail. The results of both examples show that the force field in liquid metal can be divided into several regions with different force features. Example 1 shows the effect of coil position on the evolution of the force field pattern in liquid metal. Example 2 is a kind of stirring by the travelling magnetic field ,whose results present the sub-structures in metal and show that most of them have almost the same rotating direction.
