The Ho3＋/yb3＋ co-doped a-NaYF4 single crystal was grown successfully for the first time by a modified Bridgman method in which KF was used as assisting flux and a large temperature gradient （70-90℃ /cm） of solid-...The Ho3＋/yb3＋ co-doped a-NaYF4 single crystal was grown successfully for the first time by a modified Bridgman method in which KF was used as assisting flux and a large temperature gradient （70-90℃ /cm） of solid-liquid interface was adopted. Upconversion emissions at green -544 nm, red -657 and -751 nm were obtained under 980 nm laser diode excitation. The intensity at -544 nm was much stronger than those of -657 and -751 nm. The mechanisms of the upconversion emissions were investigated by studying the relationship between the upconversion intensity and pump power. The optimized Yb3＋ concentration was about 8.08moi% when Ho3＋ concentration was hold at about 1.0mol%. The results showed that Ho3＋/yb3＋ doped α-NaYF4 single crystal was a possible candidate upconversion material for the green solid-state laser.展开更多
As supercavitating projectiles move at high speed, the periodic impacts ("tail-slap") on the interior surface of the cavity generally occur due to disturbances. The interactions between the projectile and th...As supercavitating projectiles move at high speed, the periodic impacts ("tail-slap") on the interior surface of the cavity generally occur due to disturbances. The interactions between the projectile and the water/cavity interface are the sources of structural vibrations, which affect the guidance of the vehicle and undermine the structural reliability. The Fluid/Structure Interaction calculation procedure of the tail-slaps of supercavitating projectile is established, and the dynamic behaviours of the projectile operating in tail-slap conditions with and without considering Fluid/Structure Interaction are obtained and compared. The responses of the projectile riding a reducing cavity are studied, and the effect of Fluid/Structure Interaction is also analyzed. The results show that the angular velocity of projectile increases as the body slowing down, and the amplitude of the elastic displacement response decreases at the beginning and increases when the cavity size is close to the diameter of the tail of projectile. The effect of Fluid/Structure Interaction reduces the amplitudes and frequencies of the impact loads and the vibration responses of the body, and when the speed is higher, the effect is more apparent.展开更多
Dear Editor,Phosphorus (P) is essential and often a limiting nutrient for biological production on land and in the seas (Elser et al., 2007). The biologically available P to terrestrial and aquatic ecosystems ultimate...Dear Editor,Phosphorus (P) is essential and often a limiting nutrient for biological production on land and in the seas (Elser et al., 2007). The biologically available P to terrestrial and aquatic ecosystems ultimately derives from the continental weathering of rocks on the surface of the earth (F?llmi, 1996;Ruttenberg, 2003).展开更多
A localized flexible airfoil at low Reynolds numbers is modeled and the aerodynamic performance is analyzed numerically.With characteristic based split scheme,a fluid solver for two dimensional incompressible Navier-S...A localized flexible airfoil at low Reynolds numbers is modeled and the aerodynamic performance is analyzed numerically.With characteristic based split scheme,a fluid solver for two dimensional incompressible Navier-Stokes equations is developed under the ALE framework,coupled with the theory of shallow arch,which is approximated by Galerkin method.Further,the interactions between the unsteady flow and the shallow arch are studied in detail.In particular,the effect of the selfexcited vibration of the structure on aerodynamic performance of the airfoil is investigated deeply at various angles of attack.The results show that the lift-to-drag ratio has been increased greatly compared with the rigid airfoil.Finally,the relationship between the self-excited vibration and the evolution of the flow is analyzed using FFT tools.展开更多
The unsteady flow separation of airfoil with a local flexible structure(LFS)is studied numerically in Lagrangian frames in detail,in order to investigate the nature of its high aerodynamic performance.For such aeroela...The unsteady flow separation of airfoil with a local flexible structure(LFS)is studied numerically in Lagrangian frames in detail,in order to investigate the nature of its high aerodynamic performance.For such aeroelastic system,the characteristicbased split(CBS)scheme combined with arbitrary Lagrangian-Eulerian(ALE)framework is developed firstly for the numerical analysis of unsteady flow,and Galerkin method is used to approach the flexible structure.The local flexible skin of airfoil,which can lead to self-induced oscillations,is considered as unsteady perturbation to the flow.Then,the ensuing high aerodynamic performances and complex unsteady flow separation at low Reynolds number are studied by Lagrangian coherent structures(LCSs).The results show that the LFS has a significant influence on the unsteady flow separation,which is the key point for the lift enhancement.Specifically,the oscillations of the LFS can induce the generations of moving separation and vortex,which can enhance the kinetic energy transport from main flow to the boundary layer.The results could give a deep understand of the dynamics in unsteady flow separation and flow control for the flow over airfoil.展开更多
基金This work was supported by the National Natural Science Foundation of China （No.51472125, No.51272109） and K. C. Wong Magna Fund in Ningbo University.
文摘The Ho3＋/yb3＋ co-doped a-NaYF4 single crystal was grown successfully for the first time by a modified Bridgman method in which KF was used as assisting flux and a large temperature gradient （70-90℃ /cm） of solid-liquid interface was adopted. Upconversion emissions at green -544 nm, red -657 and -751 nm were obtained under 980 nm laser diode excitation. The intensity at -544 nm was much stronger than those of -657 and -751 nm. The mechanisms of the upconversion emissions were investigated by studying the relationship between the upconversion intensity and pump power. The optimized Yb3＋ concentration was about 8.08moi% when Ho3＋ concentration was hold at about 1.0mol%. The results showed that Ho3＋/yb3＋ doped α-NaYF4 single crystal was a possible candidate upconversion material for the green solid-state laser.
基金Sponsored by the Fundamental Research Funds for the Central Universities(Grant No.HIT.NSRIF.201159)the National Natural Science Foundation of China(Grant No.51149003)
文摘As supercavitating projectiles move at high speed, the periodic impacts ("tail-slap") on the interior surface of the cavity generally occur due to disturbances. The interactions between the projectile and the water/cavity interface are the sources of structural vibrations, which affect the guidance of the vehicle and undermine the structural reliability. The Fluid/Structure Interaction calculation procedure of the tail-slaps of supercavitating projectile is established, and the dynamic behaviours of the projectile operating in tail-slap conditions with and without considering Fluid/Structure Interaction are obtained and compared. The responses of the projectile riding a reducing cavity are studied, and the effect of Fluid/Structure Interaction is also analyzed. The results show that the angular velocity of projectile increases as the body slowing down, and the amplitude of the elastic displacement response decreases at the beginning and increases when the cavity size is close to the diameter of the tail of projectile. The effect of Fluid/Structure Interaction reduces the amplitudes and frequencies of the impact loads and the vibration responses of the body, and when the speed is higher, the effect is more apparent.
基金supported by the National Oceanic and Atmospheric Administration (NOAA) Ocean and Atmospheric Research, USA。
文摘Dear Editor,Phosphorus (P) is essential and often a limiting nutrient for biological production on land and in the seas (Elser et al., 2007). The biologically available P to terrestrial and aquatic ecosystems ultimately derives from the continental weathering of rocks on the surface of the earth (F?llmi, 1996;Ruttenberg, 2003).
基金This research is supported by Program for New Century Excellent Talents in University in China,No.NCET-07-0685.
文摘A localized flexible airfoil at low Reynolds numbers is modeled and the aerodynamic performance is analyzed numerically.With characteristic based split scheme,a fluid solver for two dimensional incompressible Navier-Stokes equations is developed under the ALE framework,coupled with the theory of shallow arch,which is approximated by Galerkin method.Further,the interactions between the unsteady flow and the shallow arch are studied in detail.In particular,the effect of the selfexcited vibration of the structure on aerodynamic performance of the airfoil is investigated deeply at various angles of attack.The results show that the lift-to-drag ratio has been increased greatly compared with the rigid airfoil.Finally,the relationship between the self-excited vibration and the evolution of the flow is analyzed using FFT tools.
基金the National Fundamental Research Program of China(973 Program),No.2012CB026002the National High Technology Research Program of China(863 Program),No.2012AA052303.
文摘The unsteady flow separation of airfoil with a local flexible structure(LFS)is studied numerically in Lagrangian frames in detail,in order to investigate the nature of its high aerodynamic performance.For such aeroelastic system,the characteristicbased split(CBS)scheme combined with arbitrary Lagrangian-Eulerian(ALE)framework is developed firstly for the numerical analysis of unsteady flow,and Galerkin method is used to approach the flexible structure.The local flexible skin of airfoil,which can lead to self-induced oscillations,is considered as unsteady perturbation to the flow.Then,the ensuing high aerodynamic performances and complex unsteady flow separation at low Reynolds number are studied by Lagrangian coherent structures(LCSs).The results show that the LFS has a significant influence on the unsteady flow separation,which is the key point for the lift enhancement.Specifically,the oscillations of the LFS can induce the generations of moving separation and vortex,which can enhance the kinetic energy transport from main flow to the boundary layer.The results could give a deep understand of the dynamics in unsteady flow separation and flow control for the flow over airfoil.
