From the view point of launch safety caused by fracture of propellant charge,this paper points out that the safety criterion of pressure wave is inadequate to evaluate the launch safety of propellant charge based on t...From the view point of launch safety caused by fracture of propellant charge,this paper points out that the safety criterion of pressure wave is inadequate to evaluate the launch safety of propellant charge based on the initial negative differential pressure and sensitivity tests.Generally,the maximum barrel pressure does not depend upon the intensity of pressure wave correspondingly.The pressure wave intensity can not describe the fracture degree of propellant charge in chamber and reflect the mechanical environment of propellant charge fracturing exactly and wholly.The evaluation criterion for launch safety of propellant charge should be built on the basis of depicting the fracture degree of propellant bed.展开更多
One wedge-shaped microchannel was established,and the hydrodynamic properties of the wedge-shaped gas film were comprehensively investigated.The Navier-Stokes equations coupled with the full energy equation were adopt...One wedge-shaped microchannel was established,and the hydrodynamic properties of the wedge-shaped gas film were comprehensively investigated.The Navier-Stokes equations coupled with the full energy equation were adopted to mainly analyze the lubrication hydrodynamics of the gas film,as the horizontal plate was viewed as the adiabatic wall or the horizontal plate temperature was equal to the tilt plate temperature.A higher gas film temperature strengthened the rarefaction effect,and the more rarefied gas weakened the squeeze.Meanwhile,the vertical flow across the gas film could indicate the relation between the velocity vector and the gas film squeeze and expansion.The adiabatic horizontal plate could resist the heat conduction and enhance the rarefaction effect,and thus the direction of motion of the gas molecules was easier to be changed.展开更多
The collision process of a flying bird and the aircraft windshield was simulated by using movable cellular automata ( MCA) method to improve the structure design of aircrafts. The simulation results show that the whol...The collision process of a flying bird and the aircraft windshield was simulated by using movable cellular automata ( MCA) method to improve the structure design of aircrafts. The simulation results show that the whole strike process is performed in 4. 8 ms,the critical strike velocity for an aeronautic glass windshield is 360 km/h,the windshield vibrates and deforms in the collision,and after absorbing the kinetic energy,its temperature increases. The simulation results coincide with the experiment data better. It is clear that MCA method has more advantages than the usual methods of continuum mechanics.展开更多
Although opportunistic maintenance strategies are widely used for multi-component systems, all opportunistic mainte- nance strategies only consider economic dependence and do not take structural dependence into accoun...Although opportunistic maintenance strategies are widely used for multi-component systems, all opportunistic mainte- nance strategies only consider economic dependence and do not take structural dependence into account. An opportunistic main- tenance strategy is presented for a multi-component system that considers both structural dependence and economic dependence. The cost relation and time relation among components based on structural dependence are developed. The maintenance strategy for each component of a multi-component system involves one of five maintenance actions, namely, no-maintenance, a minimal maintenance action, an imperfect maintenance action, a perfect maintenance action, and a replacement action. The maintenance action is determined by the virtual age of the component, the life expectancy of the component, and the age threshold values. Monte Carlo simulation is designed to obtain the optimal oppor- tunistic maintenance strategy of the system over its lifetime. The simulation result reveals that the minimum maintenance cost with a strategy that considers structural dependence is less than that with a strategy that does not consider structural dependence. The availability with a strategy that considers structural dependence is greater than that with a strategy that does not consider structural dependence under the same conditions.展开更多
To meet the requirements of safety, concealment, and timeliness of trajectory planning during the unmanned aerial vehicle(UAV) penetration process, a three-dimensional path planning algorithm is proposed based on impr...To meet the requirements of safety, concealment, and timeliness of trajectory planning during the unmanned aerial vehicle(UAV) penetration process, a three-dimensional path planning algorithm is proposed based on improved holonic particle swarm optimization(IHPSO). Firstly, the requirements of terrain threat, radar detection, and penetration time in the process of UAV penetration are quantified. Regarding radar threats, a radar echo analysis method based on radar cross section(RCS)and the spatial situation is proposed to quantify the concealment of UAV penetration. Then the structure-particle swarm optimization(PSO) algorithm is improved from three aspects.First, the conversion ability of the search strategy is enhanced by using the system clustering method and the information entropy grouping strategy instead of random grouping and constructing the state switching conditions based on the fitness function.Second, the unclear setting of iteration numbers is addressed by using particle spacing to create the termination condition of the algorithm. Finally, the trajectory is optimized to meet the intended requirements by building a predictive control model and using the IHPSO for simulation verification. Numerical examples show the superiority of the proposed method over the existing PSO methods.展开更多
基金Sponsored by National Defence Prestudy Foundation of China(40406010401)
文摘From the view point of launch safety caused by fracture of propellant charge,this paper points out that the safety criterion of pressure wave is inadequate to evaluate the launch safety of propellant charge based on the initial negative differential pressure and sensitivity tests.Generally,the maximum barrel pressure does not depend upon the intensity of pressure wave correspondingly.The pressure wave intensity can not describe the fracture degree of propellant charge in chamber and reflect the mechanical environment of propellant charge fracturing exactly and wholly.The evaluation criterion for launch safety of propellant charge should be built on the basis of depicting the fracture degree of propellant bed.
基金National Science Foundation of China(51605447)Applied Basic Research Programs of Shanxi Province in China(201801D221370)
文摘One wedge-shaped microchannel was established,and the hydrodynamic properties of the wedge-shaped gas film were comprehensively investigated.The Navier-Stokes equations coupled with the full energy equation were adopted to mainly analyze the lubrication hydrodynamics of the gas film,as the horizontal plate was viewed as the adiabatic wall or the horizontal plate temperature was equal to the tilt plate temperature.A higher gas film temperature strengthened the rarefaction effect,and the more rarefied gas weakened the squeeze.Meanwhile,the vertical flow across the gas film could indicate the relation between the velocity vector and the gas film squeeze and expansion.The adiabatic horizontal plate could resist the heat conduction and enhance the rarefaction effect,and thus the direction of motion of the gas molecules was easier to be changed.
文摘The collision process of a flying bird and the aircraft windshield was simulated by using movable cellular automata ( MCA) method to improve the structure design of aircrafts. The simulation results show that the whole strike process is performed in 4. 8 ms,the critical strike velocity for an aeronautic glass windshield is 360 km/h,the windshield vibrates and deforms in the collision,and after absorbing the kinetic energy,its temperature increases. The simulation results coincide with the experiment data better. It is clear that MCA method has more advantages than the usual methods of continuum mechanics.
基金supported by the Postdoctoral Science Foundation of China(20080431380)
文摘Although opportunistic maintenance strategies are widely used for multi-component systems, all opportunistic mainte- nance strategies only consider economic dependence and do not take structural dependence into account. An opportunistic main- tenance strategy is presented for a multi-component system that considers both structural dependence and economic dependence. The cost relation and time relation among components based on structural dependence are developed. The maintenance strategy for each component of a multi-component system involves one of five maintenance actions, namely, no-maintenance, a minimal maintenance action, an imperfect maintenance action, a perfect maintenance action, and a replacement action. The maintenance action is determined by the virtual age of the component, the life expectancy of the component, and the age threshold values. Monte Carlo simulation is designed to obtain the optimal oppor- tunistic maintenance strategy of the system over its lifetime. The simulation result reveals that the minimum maintenance cost with a strategy that considers structural dependence is less than that with a strategy that does not consider structural dependence. The availability with a strategy that considers structural dependence is greater than that with a strategy that does not consider structural dependence under the same conditions.
基金supported by the National Natural Science Foundation of China (61502522)Hubei Provincial Natural Science Foundation(2019CFC897)。
文摘To meet the requirements of safety, concealment, and timeliness of trajectory planning during the unmanned aerial vehicle(UAV) penetration process, a three-dimensional path planning algorithm is proposed based on improved holonic particle swarm optimization(IHPSO). Firstly, the requirements of terrain threat, radar detection, and penetration time in the process of UAV penetration are quantified. Regarding radar threats, a radar echo analysis method based on radar cross section(RCS)and the spatial situation is proposed to quantify the concealment of UAV penetration. Then the structure-particle swarm optimization(PSO) algorithm is improved from three aspects.First, the conversion ability of the search strategy is enhanced by using the system clustering method and the information entropy grouping strategy instead of random grouping and constructing the state switching conditions based on the fitness function.Second, the unclear setting of iteration numbers is addressed by using particle spacing to create the termination condition of the algorithm. Finally, the trajectory is optimized to meet the intended requirements by building a predictive control model and using the IHPSO for simulation verification. Numerical examples show the superiority of the proposed method over the existing PSO methods.
