In this paper,the failure caused by HRAM loads which were generated by high-speed projectile penetration,and protection technology of the fluid-filled structure were explored.A bubble was preset on the projectile traj...In this paper,the failure caused by HRAM loads which were generated by high-speed projectile penetration,and protection technology of the fluid-filled structure were explored.A bubble was preset on the projectile trajectory in a fluid-filled structure.Based on the reflection and transmission phenomena of pressure waves at the gas-liquid interface and the compressibility characteristics of gases,a numerical analysis was conducted on the influence of preset bubble on projectile penetration and structural failure characteristics.The results indicate that the secondary water-entry impact phenomenon occurs when a preset bubble exists on the projectile trajectory,leading to the secondary water entry impact loads.The rarefaction waves reflected on the surface of the preset bubble cause the attenuation ratio of the initial impact pressure peak to reach 68.8%and the total specific impulse attenuation ratio to reach 48.6%.Furthermore,the larger the bubble,the faster the projectile,and the more obvious the attenuation effect.Moreover,due to the compressibility of the bubble,the global deformation attenuation ratio of the front and rear walls can reach over 80%.However,the larger the bubble size,the faster the projectile velocity,the smaller the local deformation attenuation effect of the rear wall,and the more severe the failure at the perforation of the rear wall.展开更多
Tailor rolled blank （TRB） is a type of emerging material to produce lightweight vehicle parts. Transitional zoners shape is an important parameter for tailor rolled blank. It not only affects mold design and the loc...Tailor rolled blank （TRB） is a type of emerging material to produce lightweight vehicle parts. Transitional zoners shape is an important parameter for tailor rolled blank. It not only affects mold design and the local carrying capacity of the stamping parts, but also determines the maximum value and variation characteristics of rolling force. How to get the best transitional zone＇s shape is a key problem for production of tailor rolled blank. A double power function is put forward using for transitional curve, which is continuous and smooth at all connection points inde- pendent of its parameters, so the sudden change of mechanical parameters during rolling and forming process can be avoided. At the same time, the velocity formula and restriction for arbitrary transitional curve are derived to preset vertical velocity of the roller and judge whether the curve can be rolled successfully or not. Then, the finite element method （FEM） is used to verify the precision of velocity formula and study the mechanical characteristics of different curves. Finally, a method to obtain the optimal curve equation is put forward and verified.展开更多
Two experimental satellites, Chuangxin 1-03 and Shiyan Satellite 4, were put into orbit on a LM-2D launch vehicle from the Jiuquan Satellite Launch Center (JSLC) in northwest China's Gansu Province on November 20.
The instantaneous angle of attack on the blade has a significant effect on the hydrodynamic performance of a vertical-axis tidal-current turbine with straight blades. This paper investigates the influence of different...The instantaneous angle of attack on the blade has a significant effect on the hydrodynamic performance of a vertical-axis tidal-current turbine with straight blades. This paper investigates the influence of different preset angles of attack on the hydrodynamic performance of a three-bladed, vertical-axis, tidal-current turbine both experimentally and numerically. Experiments are carried out in a towing tank. This tested turbine＇s solidity is 0.1146. The preset angles of attack on the blade are -3°, 0°, 3°, and 5°, in the experiments. Experimental results show that with the increase of the preset angle of attack from -3°, to 5°, the hydrodynamic performance of the turbine is improved significantly with the power coefficients being increased from 15.3% to 34.8%, respectively. Compared to the result of a 0° preset angle of attack, the performance of the turbine with positive preset angles of attack is experimentally demonstrated to be beneficial. This performance improvement is also shown by numerical simulations based on the Unsteady Reynolds Averaged Navier-Stokes （URANS） equations. In addition, the numerical results show that the optimal positive preset angle of attack is 7° for the turbine studied. The corresponding power coefficient is 38%. Beyond this optimal preset angle of attack, the hydrodynamic performance of the turbine decreases. Therefore, due to the dynamic stall phenomenon, an optimal preset angle of attack exists for any vertical-axis turbine. This value should be considered in the design of a vertical-axis tidal-current turbine. words：展开更多
This work presents the design and implementation of a 2.4 GHz low power fast-settling frequency-presetting PLL frequency synthesizer in the 0.18μm CMOS process.A low power mixed-signal LC VCO,a low power dual mode pr...This work presents the design and implementation of a 2.4 GHz low power fast-settling frequency-presetting PLL frequency synthesizer in the 0.18μm CMOS process.A low power mixed-signal LC VCO,a low power dual mode prescaler and a digital processor with non-volatile memory are developed to greatly reduce the power consumption and the setting time.The digital processor can automatically calibrate the presetting frequency and accurately preset the frequency of the VCO under process variations.The experimental results demonstrate that the power consumption of the synthesizer is about 4 mA @ 1.8 V and that the typical setting time of the synthesizer is less than 3μs.展开更多
文摘In this paper,the failure caused by HRAM loads which were generated by high-speed projectile penetration,and protection technology of the fluid-filled structure were explored.A bubble was preset on the projectile trajectory in a fluid-filled structure.Based on the reflection and transmission phenomena of pressure waves at the gas-liquid interface and the compressibility characteristics of gases,a numerical analysis was conducted on the influence of preset bubble on projectile penetration and structural failure characteristics.The results indicate that the secondary water-entry impact phenomenon occurs when a preset bubble exists on the projectile trajectory,leading to the secondary water entry impact loads.The rarefaction waves reflected on the surface of the preset bubble cause the attenuation ratio of the initial impact pressure peak to reach 68.8%and the total specific impulse attenuation ratio to reach 48.6%.Furthermore,the larger the bubble,the faster the projectile,and the more obvious the attenuation effect.Moreover,due to the compressibility of the bubble,the global deformation attenuation ratio of the front and rear walls can reach over 80%.However,the larger the bubble size,the faster the projectile velocity,the smaller the local deformation attenuation effect of the rear wall,and the more severe the failure at the perforation of the rear wall.
基金Item Sponsored by National Science and Technology Support Program of China(2011BAF15B02)Natural Science Foundation of Hebei Province of China(E2012203108)+2 种基金Science and Technology Research Program of the Colleges and Universities in Hebei of China(ZD2014034)Independent Research Project of Yanshan University of China(14LGA003)Open Project of National Engineering Research Center for Equipment and Technology of Cold Rolling Strip of China(NECSR-201206)
文摘Tailor rolled blank （TRB） is a type of emerging material to produce lightweight vehicle parts. Transitional zoners shape is an important parameter for tailor rolled blank. It not only affects mold design and the local carrying capacity of the stamping parts, but also determines the maximum value and variation characteristics of rolling force. How to get the best transitional zone＇s shape is a key problem for production of tailor rolled blank. A double power function is put forward using for transitional curve, which is continuous and smooth at all connection points inde- pendent of its parameters, so the sudden change of mechanical parameters during rolling and forming process can be avoided. At the same time, the velocity formula and restriction for arbitrary transitional curve are derived to preset vertical velocity of the roller and judge whether the curve can be rolled successfully or not. Then, the finite element method （FEM） is used to verify the precision of velocity formula and study the mechanical characteristics of different curves. Finally, a method to obtain the optimal curve equation is put forward and verified.
文摘Two experimental satellites, Chuangxin 1-03 and Shiyan Satellite 4, were put into orbit on a LM-2D launch vehicle from the Jiuquan Satellite Launch Center (JSLC) in northwest China's Gansu Province on November 20.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.DUT13JN10)the Doctoral Starting Up Funds of Liaoning Province(Grant No.20111029)
文摘The instantaneous angle of attack on the blade has a significant effect on the hydrodynamic performance of a vertical-axis tidal-current turbine with straight blades. This paper investigates the influence of different preset angles of attack on the hydrodynamic performance of a three-bladed, vertical-axis, tidal-current turbine both experimentally and numerically. Experiments are carried out in a towing tank. This tested turbine＇s solidity is 0.1146. The preset angles of attack on the blade are -3°, 0°, 3°, and 5°, in the experiments. Experimental results show that with the increase of the preset angle of attack from -3°, to 5°, the hydrodynamic performance of the turbine is improved significantly with the power coefficients being increased from 15.3% to 34.8%, respectively. Compared to the result of a 0° preset angle of attack, the performance of the turbine with positive preset angles of attack is experimentally demonstrated to be beneficial. This performance improvement is also shown by numerical simulations based on the Unsteady Reynolds Averaged Navier-Stokes （URANS） equations. In addition, the numerical results show that the optimal positive preset angle of attack is 7° for the turbine studied. The corresponding power coefficient is 38%. Beyond this optimal preset angle of attack, the hydrodynamic performance of the turbine decreases. Therefore, due to the dynamic stall phenomenon, an optimal preset angle of attack exists for any vertical-axis turbine. This value should be considered in the design of a vertical-axis tidal-current turbine. words：
基金Project supported by the National High-Tech Research and Development Program of China(Nos.2008AA010703,2009AA011606).
文摘This work presents the design and implementation of a 2.4 GHz low power fast-settling frequency-presetting PLL frequency synthesizer in the 0.18μm CMOS process.A low power mixed-signal LC VCO,a low power dual mode prescaler and a digital processor with non-volatile memory are developed to greatly reduce the power consumption and the setting time.The digital processor can automatically calibrate the presetting frequency and accurately preset the frequency of the VCO under process variations.The experimental results demonstrate that the power consumption of the synthesizer is about 4 mA @ 1.8 V and that the typical setting time of the synthesizer is less than 3μs.
