The hydrodynamic behavior in a high-density downer reactor was studied. A two-fluid model based on the kinetic theory of granular flow with a k-ε turbulent model was developed to simulate the flow behavior in the sys...The hydrodynamic behavior in a high-density downer reactor was studied. A two-fluid model based on the kinetic theory of granular flow with a k-ε turbulent model was developed to simulate the flow behavior in the system. This simulation achieved an averaged solid fraction in the bed as high as 18% in this operating regime. The flow development in high-density downer consists of 3 regions, which are first acceleration, second acceleration, and fully developed regions. In the fully developed region, the lateral distribution of the solid volume fraction is low and almost uniform in the center region with a high density peak near the wall region. Gas and solid velocities gradually increase toward the wall and form a peak near the wall region. In addition, the solid volume fraction, gas and solid velocities increase with solid circulation rate.展开更多
The purpose of this study was to describe the roles of microstructure types and grain boundary characteristics in fatigue crack propagation behavior in ferrite-pearlite steel and ferrite-bainite steel.The ferrite-bain...The purpose of this study was to describe the roles of microstructure types and grain boundary characteristics in fatigue crack propagation behavior in ferrite-pearlite steel and ferrite-bainite steel.The ferrite-bainite dual-phase steel was obtained by intermediate heat treatment conducted on ferrite-pearlite low carbon steel.This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy(SEM),electron backscattering diffraction(EBSD) and fatigue fractography analysis.Microscopic images arrested by in-situ SEM showed that the second hard bainite phase distributed in the soft ferrite matrix had a significant effect on preventing the cracks opening compared with pearlite,and that the cracks in ferrite-bainite steel were "locked" in the second hard bainite phase while the crack propagation path in ferrite-pearlite steel was more tortuous.Moreover,the fatigue fracture surface analysis and the coincidence site lattice(CSL) obtained by EBSD indicated that low-CSL grain boundaries in ferrite-bainite steel distributed more uniformly,which has a more significant effect on the resistance of crack propagation.It was revealed that ferrite-bainite dual-phase microstructures could inhibit the fatigue crack propagation more effectively than ferrite-pearlite microstructures.展开更多
Deformation behaviors of bicrystalline and nano-polycrystalline structures of various tilt angles and inclination angles in two dimensions are investigated in detail using a two-mode phase field crystal model.The inte...Deformation behaviors of bicrystalline and nano-polycrystalline structures of various tilt angles and inclination angles in two dimensions are investigated in detail using a two-mode phase field crystal model.The interaction between grain boundary(GB)and dislocation is also examined in bicrystals and nano-polycrystals that both contain asymmetric and symmetric tilt GBs,with energy analysis being carried out to analyze these processes.During deformation simulations,we assume the volume of each simulation cell at every time step is coincident with that of the initial state just before deformation.Our simulation results show that the behaviors of symmetric and asymmetric GBs in bicrystals and nano-polycrystals differ from each other depending on tilt angle and inclination angle.A new dislocation emission mechanism of interest is observed in bicrystals which contain low angle symmetric tilt GBs.Low angle GB has a higher mobility relative to high angle GB in both bicrystalline and nano-polycrystalline structures,as does asymmetric GB to symmetric GB.The generation,motion,pileup and annihilation of dislocations,grain rotation and grain coalescence are observed,which is consistent with the simulation results obtained by molecular dynamics.These simulation results can provide strong guidelines for experimentation.展开更多
A competitive system on the n-rectangle： {x ∈ Rn： 0 ≤ xi ≤ li, i = 1,... ,n} was con- sidered, each species of which, in isolation, admits logistic growth with the hyperbolic structure saturation. It has an （n ...A competitive system on the n-rectangle： {x ∈ Rn： 0 ≤ xi ≤ li, i = 1,... ,n} was con- sidered, each species of which, in isolation, admits logistic growth with the hyperbolic structure saturation. It has an （n - 1）-dimensional invariant surface called carrying simplex E as a globe attractor, hence the long term dynamics of the system is com- pletely determined by the dynamics on E. For the three-dimensional system, the whole dynamical behavior was presented. It has a unique positive equilibrium point and any limit set is either an equilibrium point or a limit cycle. The system is permanent and it is proved that the number of periodic orbits is finite and non-periodic oscillation the May Leonard phenomenon does not exist. A criterion for the positive equilibrium to be globally asymptotically stable is provided. Whether there exist limit cycles or not remains open.展开更多
文摘The hydrodynamic behavior in a high-density downer reactor was studied. A two-fluid model based on the kinetic theory of granular flow with a k-ε turbulent model was developed to simulate the flow behavior in the system. This simulation achieved an averaged solid fraction in the bed as high as 18% in this operating regime. The flow development in high-density downer consists of 3 regions, which are first acceleration, second acceleration, and fully developed regions. In the fully developed region, the lateral distribution of the solid volume fraction is low and almost uniform in the center region with a high density peak near the wall region. Gas and solid velocities gradually increase toward the wall and form a peak near the wall region. In addition, the solid volume fraction, gas and solid velocities increase with solid circulation rate.
文摘The purpose of this study was to describe the roles of microstructure types and grain boundary characteristics in fatigue crack propagation behavior in ferrite-pearlite steel and ferrite-bainite steel.The ferrite-bainite dual-phase steel was obtained by intermediate heat treatment conducted on ferrite-pearlite low carbon steel.This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy(SEM),electron backscattering diffraction(EBSD) and fatigue fractography analysis.Microscopic images arrested by in-situ SEM showed that the second hard bainite phase distributed in the soft ferrite matrix had a significant effect on preventing the cracks opening compared with pearlite,and that the cracks in ferrite-bainite steel were "locked" in the second hard bainite phase while the crack propagation path in ferrite-pearlite steel was more tortuous.Moreover,the fatigue fracture surface analysis and the coincidence site lattice(CSL) obtained by EBSD indicated that low-CSL grain boundaries in ferrite-bainite steel distributed more uniformly,which has a more significant effect on the resistance of crack propagation.It was revealed that ferrite-bainite dual-phase microstructures could inhibit the fatigue crack propagation more effectively than ferrite-pearlite microstructures.
基金supported by the National Natural Science Foundation of China(Grant Nos.51274167 and 51174168)the Northwestern Polytechnical University Foundation for the Fundamental Research(Grant No.JC20120222)
文摘Deformation behaviors of bicrystalline and nano-polycrystalline structures of various tilt angles and inclination angles in two dimensions are investigated in detail using a two-mode phase field crystal model.The interaction between grain boundary(GB)and dislocation is also examined in bicrystals and nano-polycrystals that both contain asymmetric and symmetric tilt GBs,with energy analysis being carried out to analyze these processes.During deformation simulations,we assume the volume of each simulation cell at every time step is coincident with that of the initial state just before deformation.Our simulation results show that the behaviors of symmetric and asymmetric GBs in bicrystals and nano-polycrystals differ from each other depending on tilt angle and inclination angle.A new dislocation emission mechanism of interest is observed in bicrystals which contain low angle symmetric tilt GBs.Low angle GB has a higher mobility relative to high angle GB in both bicrystalline and nano-polycrystalline structures,as does asymmetric GB to symmetric GB.The generation,motion,pileup and annihilation of dislocations,grain rotation and grain coalescence are observed,which is consistent with the simulation results obtained by molecular dynamics.These simulation results can provide strong guidelines for experimentation.
文摘A competitive system on the n-rectangle： {x ∈ Rn： 0 ≤ xi ≤ li, i = 1,... ,n} was con- sidered, each species of which, in isolation, admits logistic growth with the hyperbolic structure saturation. It has an （n - 1）-dimensional invariant surface called carrying simplex E as a globe attractor, hence the long term dynamics of the system is com- pletely determined by the dynamics on E. For the three-dimensional system, the whole dynamical behavior was presented. It has a unique positive equilibrium point and any limit set is either an equilibrium point or a limit cycle. The system is permanent and it is proved that the number of periodic orbits is finite and non-periodic oscillation the May Leonard phenomenon does not exist. A criterion for the positive equilibrium to be globally asymptotically stable is provided. Whether there exist limit cycles or not remains open.
