In this paper, a close relationship between the intraseasonal variation of subtropical high over East Asia and the convective activities around the South China Sea and the Philippines is analysed from OLR data.This re...In this paper, a close relationship between the intraseasonal variation of subtropical high over East Asia and the convective activities around the South China Sea and the Philippines is analysed from OLR data.This relationship is studied by using the theory of wave propagating in a slowly varying medium and by using a quasi-geoslrophic, linear, spherical model and the IAP-GCM, respectively. The results show that when the SST is warming around the western tropical Pacific or the Philippines, the convective activities are intensified around the Philippines. As a consequence, the subtropical high will be intensified over East Asia. The computed results also show that when the anomaly of convective activities are caused around the Philippines, a teleconnection pattern of circulation anomalies will be caused over South Asia, East Asia and North America.展开更多
This paper presents the concept of a Dielectric-lined Multiwave Cerenkov Generator producing high power millimeter waves, which has been investigated with a two and onehalf dimensional electromagnetic relativistic Par...This paper presents the concept of a Dielectric-lined Multiwave Cerenkov Generator producing high power millimeter waves, which has been investigated with a two and onehalf dimensional electromagnetic relativistic Particle-in-Cell (PIC) plasma simulation code. Themodified device can operate in a lower diode-voltage regime with much higher radiation efficiencyand slight downshift of operation frequency. There exist the optima for the permittivity of thedielectric liner and for the magnitude of the guiding magnetic field. The required intensity of theguiding field is reduced by the introduction of the liner. The enhanced propagation of the electronbeam is studied in the presence of the liner.展开更多
The computer simulation of Al three-dimensional crystallite containing grain boundary of special type was carried out and its behaviour under high rate loading was investigated. The molecular dynamics method was used ...The computer simulation of Al three-dimensional crystallite containing grain boundary of special type was carried out and its behaviour under high rate loading was investigated. The molecular dynamics method was used and interaction betwen atoms was described based on pseudopotential method. Vortical character of the atom movements in the grain boundary region is realized under shear loading in certain directions. Back and forth movements of atoms in the direction which is perpendicular to the shear also arise. Amplitude of such movements is approximately equal to an interplanar distance in this direction.展开更多
A Lagrangian-Eulerian hybrid scheme to solve unsteady N-S equation in two-dimensional incompressible fluid at high Reynolds numbers is presented in this paper. A random walk is imposed to simulate the viscous diffusio...A Lagrangian-Eulerian hybrid scheme to solve unsteady N-S equation in two-dimensional incompressible fluid at high Reynolds numbers is presented in this paper. A random walk is imposed to simulate the viscous diffusion, the vortex-in-cell method is used to obtain the convection velocity, and nascent vortices are created on a cylinder to satisfy the zero-slip condition. The impulsively started flow around a circular cylinder and the separation induced by a pair of incident vortices symmetrically approaching a circular cylinder have been successfully simulated by the hybrid scheme. The impulsively started flow from rest has been computed at Reynolds numbers 3000 and 9500. Comparisons are made with those results of finite-difference method, vortex method and flow visualization. Agreement is good. The particular attention has been paid to the evolutions of flow pattern. A topological analysis has been proposed in the region of the near wake. The bulge, isolated secondary vortex, a pair of secondary vortices, ' forewake phenomenon and other patterns are simulated numerically. The separation induced by a pair of incident vortices approaching a circular cylinder has been investigated by using the same scheme. The rebounding phenomenon of the incident vortex is observed and is attributed to the effect of the secondary vortex. In particular, we have found that a tertiary vortex can be formed near the surface; this phenomenon has been verified by flow visualization reported recently.展开更多
A flexible flat torque converter was proposed to fulfill the requirement of miniaturization and power density maximization for automobiles.Constructed by two arcs joined by lines,the torus was designed directly from d...A flexible flat torque converter was proposed to fulfill the requirement of miniaturization and power density maximization for automobiles.Constructed by two arcs joined by lines,the torus was designed directly from design path.The influence of flatness on the performance of the torque converter was evaluated.The software CFX and standard k-ε model were adopted to simulate the internal flow fields of the torque converter under different flatness ratios.The results indicated that the performance of the torque converter got worse as the flatness declined,but the capacity of pump increased.The efficiency and the torque ratio dropped slightly as the flatness ratio decreased.So the torque converter could be squashed appropriately to get high power density without too much efficiency sacrifice.But when the flatness ratio was below 0.2,there was a significant drop in the efficiency.展开更多
To enhance the fidelity and accuracy of the simulation of communication networks,hardware-in-the-loop(HITL) simulation was employed.HITL simulation methods was classified into three categories,of which the merits an...To enhance the fidelity and accuracy of the simulation of communication networks,hardware-in-the-loop(HITL) simulation was employed.HITL simulation methods was classified into three categories,of which the merits and shortages were compared.Combing system-in-the-loop(SITL) simulation principle with high level architecture(HLA),an HITL simulation model of asynchronous transfer mode(ATM) network was constructed.The throughput and end-to-end delay of all-digital simulation and HITL simulation was analyzed,which showed that HITL simulation was more reliable and effectively improved the simulation credibility of communication network.Meanwhile,HLA-SITL method was fast and easy to achieve and low-cost during design lifecycle.Thus,it was a feasible way to research and analyze the large-scale network.展开更多
The yaw effect of the side flow around a high-speed train is studied by means of large eddy simulation at two typical yaw angles of φ= 30° and 60°, respectively. Both the mean and fluctuating values of lift...The yaw effect of the side flow around a high-speed train is studied by means of large eddy simulation at two typical yaw angles of φ= 30° and 60°, respectively. Both the mean and fluctuating values of lift force and side force coefficients increase obviously as the yaw angle increases. The spectral analysis indicates that the time-dependent aerodynamic forces are dominated by several energetic frequencies and the frequency range is broadened to a higher extent for the large yaw angle. To have a better understanding of the train aerodynamic behaviors, the dedicate three-dimensional vortical structures are analyzed for the flow at the two yaw angles. Moreover, the time-averaged flow patterns, turbulent statistics, and the surface forces are also studied on sectional planes along the train.展开更多
The influence of high temperature effects on the protrusion of Mach stem in strong shock reflection over a wedge was numerically investigated. A two-dimensional inviscid solver applies finite volume method and unstruc...The influence of high temperature effects on the protrusion of Mach stem in strong shock reflection over a wedge was numerically investigated. A two-dimensional inviscid solver applies finite volume method and unstructured quadrilateral grids were employed to simulate the flow. Theoretical analysis was also conducted to understand the phenomenon. Both numerical and theoretical results indicate a wall-jet penetrating forward is responsible for the occurrence of Mach stem protrusion. The protrusion degree seems to depend on the thermal energy buffer capacity of the testing gas. Approaches to increase the energy buffer capacity, such as vibrational relaxation, molecular dissociation, and increase of frozen heat caoacitv, all tend to escalate the orotrusion effect.展开更多
In recent years, microstrip antennas have been more widely applied in satellite communications, mobile phones, unmanned aerial vehicle (UAV), and weapons. A micro-electro-mechanical systems-based (MEMS-based) high...In recent years, microstrip antennas have been more widely applied in satellite communications, mobile phones, unmanned aerial vehicle (UAV), and weapons. A micro-electro-mechanical systems-based (MEMS-based) high-resistance silicon C-band microstrip antenna array has been designed for the intelligent ammunition. The center frequency is 4.5 GHz. A cavity has been designed in substrate to reduce the dielectric constant of silicon and high-resistance silicon has been used as the material of substrate to improve the gain of antenna. It is very easy to be manufactured by using MEMS technology because of the improved structure of the antenna. The results show that the gain of the antenna is 8 dB and voltage standing wave ratio (VSWR) is less than 2 by the analysis and simulation in high freauencv structure simulator (HFSS).展开更多
Presented here is a compact explicit difference scheme of high accuracy for solving the extended Boussinesq equations. For time discretization, a three-stage explicit Runge-Kutta method with TVD property is used at pr...Presented here is a compact explicit difference scheme of high accuracy for solving the extended Boussinesq equations. For time discretization, a three-stage explicit Runge-Kutta method with TVD property is used at predicting stage, a cubic spline function is adopted at correcting stage, which made the time discretization accuracy up to fourth order; For spatial discretization, a three-point explicit compact difference scheme with arbitrary order accuracy is employed. The extended Boussinesq equations derived by Beji and Nadaoka are solved by the proposed scheme. The numerical results agree well with the experimental data. At the same time, the comparisons of the two numerical results between the present scheme and low accuracy difference method are made, which further show the necessity of using high accuracy scheme to solve the extended Boussinesq equations. As a valid sample, the wave propagation on the rectangular step is formulated by the present scheme, the modelled results are in better agreement with the experimental data than those of Kittitanasuan.展开更多
The high frequency (HF) channel simulators with time-varying parameters based on the Watterson model are analyzed. The methods of simulating the HF channel with time-varying parameters are proposed. The linearly time-...The high frequency (HF) channel simulators with time-varying parameters based on the Watterson model are analyzed. The methods of simulating the HF channel with time-varying parameters are proposed. The linearly time-varying delay spread is introduced into the channel simulators to simulate the transition states between two channel modes of CCIR520-1. Two signals, including a 500 Hz and a 1 000 Hz bandwidth signal are respectively input into the standard Watterson HF channel model and the proposed channel model with time-varying parameters. Some simulation results prove that the proposed HF channel model with time-varying parameters can reflect the time-varying characteristics of frequency selected fading of HF channel.展开更多
In this paper,using a nonlinear low-order barotropic system with orography and momentum forcing as well as dissipation,we have theoretically calculated the two kinds of curves for the seasonal northward movement of su...In this paper,using a nonlinear low-order barotropic system with orography and momentum forcing as well as dissipation,we have theoretically calculated the two kinds of curves for the seasonal northward movement of subtropical highs.It has been shown that the theoretical results resemble basically with the analysed results of wave spectrum data.展开更多
This study concerns the precipitation induced by a tropical cyclone (TC) before the TC arrives, which will be referred to as TC remote precipitation (TRP). Based on the distribution characteristics of the non-rota...This study concerns the precipitation induced by a tropical cyclone (TC) before the TC arrives, which will be referred to as TC remote precipitation (TRP). Based on the distribution characteristics of the non-rotational wind and the divergent-wind vertical circulation related to TC, the subtropical high, and TRP of 45 TRP events during June, July, and August of 2000-2009, the relationships among these three entities (TC, subtropical high, and TRP) can be categorized into four patterns. The first pattern accounts for the highest proportion of the TRP events (59%), and a conceptual model is then provided for this pattern. The primary characteristics of this model are as follows: TC, the subtropical high, and TRP can interact with each other through the divergent-wind secondary circulation at both sides of the ridge line of the subtropical high (between the subtropical high and TC, and between the subtropical high and TRP). At the upper level (150 or 200 hPa), the northward non-rotational wind from the TC converged toward the subtropical high ridge line and subsided, and at 950 hPa the divergent wind from the ridge line of the subtropical high converged toward TC; these constructed the secondary circulation between TC and the subtropical high. In the meantime, the southward non- rotational wind at the upper level (150 or 200hPa) from TRP and the divergent wind at 950hPa from the subtropical high ridge line toward TRP constructed the secondary circulation between TRP and the subtropical high. As TC and TRP interacted with each other, the subtropical high ridge line was usually under the down- draft area of the whole atmosphere. The other three patterns are different from the first pattern mainly in terms of the intensity and position of the non-rotational-wind secondary circulation. The numerical simulation of the Beijing 7.21 rainstorm confirmed the relationship amongTC, the subtropical high, and TRP, indicating that when the interaction weakened, the TRP also weakened.展开更多
Genetic algorithm(GA)is utilized to design microstrip patch antenna shapes for broad bandwidth.A new project based on GA and high frequency simulation software(HFSS)is proposed to perform optimization.Reasonable agree...Genetic algorithm(GA)is utilized to design microstrip patch antenna shapes for broad bandwidth.A new project based on GA and high frequency simulation software(HFSS)is proposed to perform optimization.Reasonable agreement between simulated results and measured results of the GA-optimized design is obtained.The optimized patch design exhibits a three-fold enhancement in bandwidth when contrasted with a standard square microstrip antenna,showing the validity of this project.展开更多
文摘In this paper, a close relationship between the intraseasonal variation of subtropical high over East Asia and the convective activities around the South China Sea and the Philippines is analysed from OLR data.This relationship is studied by using the theory of wave propagating in a slowly varying medium and by using a quasi-geoslrophic, linear, spherical model and the IAP-GCM, respectively. The results show that when the SST is warming around the western tropical Pacific or the Philippines, the convective activities are intensified around the Philippines. As a consequence, the subtropical high will be intensified over East Asia. The computed results also show that when the anomaly of convective activities are caused around the Philippines, a teleconnection pattern of circulation anomalies will be caused over South Asia, East Asia and North America.
文摘This paper presents the concept of a Dielectric-lined Multiwave Cerenkov Generator producing high power millimeter waves, which has been investigated with a two and onehalf dimensional electromagnetic relativistic Particle-in-Cell (PIC) plasma simulation code. Themodified device can operate in a lower diode-voltage regime with much higher radiation efficiencyand slight downshift of operation frequency. There exist the optima for the permittivity of thedielectric liner and for the magnitude of the guiding magnetic field. The required intensity of theguiding field is reduced by the introduction of the liner. The enhanced propagation of the electronbeam is studied in the presence of the liner.
文摘The computer simulation of Al three-dimensional crystallite containing grain boundary of special type was carried out and its behaviour under high rate loading was investigated. The molecular dynamics method was used and interaction betwen atoms was described based on pseudopotential method. Vortical character of the atom movements in the grain boundary region is realized under shear loading in certain directions. Back and forth movements of atoms in the direction which is perpendicular to the shear also arise. Amplitude of such movements is approximately equal to an interplanar distance in this direction.
文摘A Lagrangian-Eulerian hybrid scheme to solve unsteady N-S equation in two-dimensional incompressible fluid at high Reynolds numbers is presented in this paper. A random walk is imposed to simulate the viscous diffusion, the vortex-in-cell method is used to obtain the convection velocity, and nascent vortices are created on a cylinder to satisfy the zero-slip condition. The impulsively started flow around a circular cylinder and the separation induced by a pair of incident vortices symmetrically approaching a circular cylinder have been successfully simulated by the hybrid scheme. The impulsively started flow from rest has been computed at Reynolds numbers 3000 and 9500. Comparisons are made with those results of finite-difference method, vortex method and flow visualization. Agreement is good. The particular attention has been paid to the evolutions of flow pattern. A topological analysis has been proposed in the region of the near wake. The bulge, isolated secondary vortex, a pair of secondary vortices, ' forewake phenomenon and other patterns are simulated numerically. The separation induced by a pair of incident vortices approaching a circular cylinder has been investigated by using the same scheme. The rebounding phenomenon of the incident vortex is observed and is attributed to the effect of the secondary vortex. In particular, we have found that a tertiary vortex can be formed near the surface; this phenomenon has been verified by flow visualization reported recently.
基金Supported by the National Natural Science Foundation of China (50905016)
文摘A flexible flat torque converter was proposed to fulfill the requirement of miniaturization and power density maximization for automobiles.Constructed by two arcs joined by lines,the torus was designed directly from design path.The influence of flatness on the performance of the torque converter was evaluated.The software CFX and standard k-ε model were adopted to simulate the internal flow fields of the torque converter under different flatness ratios.The results indicated that the performance of the torque converter got worse as the flatness declined,but the capacity of pump increased.The efficiency and the torque ratio dropped slightly as the flatness ratio decreased.So the torque converter could be squashed appropriately to get high power density without too much efficiency sacrifice.But when the flatness ratio was below 0.2,there was a significant drop in the efficiency.
基金Supported by the National Natural Science Foundation of China (61101129)Specialized Research Fund for the Doctoral Program of Higher Education(20091101110019)
文摘To enhance the fidelity and accuracy of the simulation of communication networks,hardware-in-the-loop(HITL) simulation was employed.HITL simulation methods was classified into three categories,of which the merits and shortages were compared.Combing system-in-the-loop(SITL) simulation principle with high level architecture(HLA),an HITL simulation model of asynchronous transfer mode(ATM) network was constructed.The throughput and end-to-end delay of all-digital simulation and HITL simulation was analyzed,which showed that HITL simulation was more reliable and effectively improved the simulation credibility of communication network.Meanwhile,HLA-SITL method was fast and easy to achieve and low-cost during design lifecycle.Thus,it was a feasible way to research and analyze the large-scale network.
基金supported by the Knowledge Innovation Project of the Chinese Academy of Sciencesthe National Natural Science Foundation of China (11402261)the Fundamental Research Funds for the Central Universities (2013)
文摘The yaw effect of the side flow around a high-speed train is studied by means of large eddy simulation at two typical yaw angles of φ= 30° and 60°, respectively. Both the mean and fluctuating values of lift force and side force coefficients increase obviously as the yaw angle increases. The spectral analysis indicates that the time-dependent aerodynamic forces are dominated by several energetic frequencies and the frequency range is broadened to a higher extent for the large yaw angle. To have a better understanding of the train aerodynamic behaviors, the dedicate three-dimensional vortical structures are analyzed for the flow at the two yaw angles. Moreover, the time-averaged flow patterns, turbulent statistics, and the surface forces are also studied on sectional planes along the train.
文摘The influence of high temperature effects on the protrusion of Mach stem in strong shock reflection over a wedge was numerically investigated. A two-dimensional inviscid solver applies finite volume method and unstructured quadrilateral grids were employed to simulate the flow. Theoretical analysis was also conducted to understand the phenomenon. Both numerical and theoretical results indicate a wall-jet penetrating forward is responsible for the occurrence of Mach stem protrusion. The protrusion degree seems to depend on the thermal energy buffer capacity of the testing gas. Approaches to increase the energy buffer capacity, such as vibrational relaxation, molecular dissociation, and increase of frozen heat caoacitv, all tend to escalate the orotrusion effect.
基金supported by the Chinese PLA General Armament Department under Grant No.51318020305
文摘In recent years, microstrip antennas have been more widely applied in satellite communications, mobile phones, unmanned aerial vehicle (UAV), and weapons. A micro-electro-mechanical systems-based (MEMS-based) high-resistance silicon C-band microstrip antenna array has been designed for the intelligent ammunition. The center frequency is 4.5 GHz. A cavity has been designed in substrate to reduce the dielectric constant of silicon and high-resistance silicon has been used as the material of substrate to improve the gain of antenna. It is very easy to be manufactured by using MEMS technology because of the improved structure of the antenna. The results show that the gain of the antenna is 8 dB and voltage standing wave ratio (VSWR) is less than 2 by the analysis and simulation in high freauencv structure simulator (HFSS).
基金The project was financially supported by the National Natural Science Foundation of China (Grant No50479053)
文摘Presented here is a compact explicit difference scheme of high accuracy for solving the extended Boussinesq equations. For time discretization, a three-stage explicit Runge-Kutta method with TVD property is used at predicting stage, a cubic spline function is adopted at correcting stage, which made the time discretization accuracy up to fourth order; For spatial discretization, a three-point explicit compact difference scheme with arbitrary order accuracy is employed. The extended Boussinesq equations derived by Beji and Nadaoka are solved by the proposed scheme. The numerical results agree well with the experimental data. At the same time, the comparisons of the two numerical results between the present scheme and low accuracy difference method are made, which further show the necessity of using high accuracy scheme to solve the extended Boussinesq equations. As a valid sample, the wave propagation on the rectangular step is formulated by the present scheme, the modelled results are in better agreement with the experimental data than those of Kittitanasuan.
文摘The high frequency (HF) channel simulators with time-varying parameters based on the Watterson model are analyzed. The methods of simulating the HF channel with time-varying parameters are proposed. The linearly time-varying delay spread is introduced into the channel simulators to simulate the transition states between two channel modes of CCIR520-1. Two signals, including a 500 Hz and a 1 000 Hz bandwidth signal are respectively input into the standard Watterson HF channel model and the proposed channel model with time-varying parameters. Some simulation results prove that the proposed HF channel model with time-varying parameters can reflect the time-varying characteristics of frequency selected fading of HF channel.
文摘In this paper,using a nonlinear low-order barotropic system with orography and momentum forcing as well as dissipation,we have theoretically calculated the two kinds of curves for the seasonal northward movement of subtropical highs.It has been shown that the theoretical results resemble basically with the analysed results of wave spectrum data.
基金This research was jointly supported by the National Basic Research Program of China (Nos. 2009CB421503 and 2013CB430103) and the National Natural Science Foundation of China (Grant Nos. 40975037 and 41375058).
文摘This study concerns the precipitation induced by a tropical cyclone (TC) before the TC arrives, which will be referred to as TC remote precipitation (TRP). Based on the distribution characteristics of the non-rotational wind and the divergent-wind vertical circulation related to TC, the subtropical high, and TRP of 45 TRP events during June, July, and August of 2000-2009, the relationships among these three entities (TC, subtropical high, and TRP) can be categorized into four patterns. The first pattern accounts for the highest proportion of the TRP events (59%), and a conceptual model is then provided for this pattern. The primary characteristics of this model are as follows: TC, the subtropical high, and TRP can interact with each other through the divergent-wind secondary circulation at both sides of the ridge line of the subtropical high (between the subtropical high and TC, and between the subtropical high and TRP). At the upper level (150 or 200 hPa), the northward non-rotational wind from the TC converged toward the subtropical high ridge line and subsided, and at 950 hPa the divergent wind from the ridge line of the subtropical high converged toward TC; these constructed the secondary circulation between TC and the subtropical high. In the meantime, the southward non- rotational wind at the upper level (150 or 200hPa) from TRP and the divergent wind at 950hPa from the subtropical high ridge line toward TRP constructed the secondary circulation between TRP and the subtropical high. As TC and TRP interacted with each other, the subtropical high ridge line was usually under the down- draft area of the whole atmosphere. The other three patterns are different from the first pattern mainly in terms of the intensity and position of the non-rotational-wind secondary circulation. The numerical simulation of the Beijing 7.21 rainstorm confirmed the relationship amongTC, the subtropical high, and TRP, indicating that when the interaction weakened, the TRP also weakened.
基金This work was supported by the Specialized Research Fund for the Doctoral Program of Higher Education(No.200700130046)the National Natural Science Foundation of China(Grant Nos.60771060 and 60971078).
文摘Genetic algorithm(GA)is utilized to design microstrip patch antenna shapes for broad bandwidth.A new project based on GA and high frequency simulation software(HFSS)is proposed to perform optimization.Reasonable agreement between simulated results and measured results of the GA-optimized design is obtained.The optimized patch design exhibits a three-fold enhancement in bandwidth when contrasted with a standard square microstrip antenna,showing the validity of this project.