Based on the elastic-plastic large deformation finite element formulation as well as the shell element combined discrete Kirchhoff theoretical plate element (DKT) with membrane square element, deep-drawing bending spr...Based on the elastic-plastic large deformation finite element formulation as well as the shell element combined discrete Kirchhoff theoretical plate element (DKT) with membrane square element, deep-drawing bending springback of typical U-pattern is studied. At the same time the springback values of the drawing of patterns' unloading and trimming about the satellite aerial reflecting surface are predicted and also compared with those of the practical punch. Above two springbacks all obtain satisfactory results, which provide a kind of effective quantitative pre-prediction of springback for the practical engineers.展开更多
Robert Frost is one of the best poets in the 20th century.His philosophical poem "Fire and Ice" is to be discussed as a piece representing modernity.By analyzing some specific elements,this essay tries to co...Robert Frost is one of the best poets in the 20th century.His philosophical poem "Fire and Ice" is to be discussed as a piece representing modernity.By analyzing some specific elements,this essay tries to convince that the poem is a perfect example of Frost's unique style-traditional forms combined with modern thoughts.展开更多
For application to exploration under the surface of icy objects in the solar system, the penetration of an impact probe into an icy target was experimentally simulated by using the ballistic range. Slender projectiles...For application to exploration under the surface of icy objects in the solar system, the penetration of an impact probe into an icy target was experimentally simulated by using the ballistic range. Slender projectiles with a cylindrical body and various nose shapes were tested at the impact velocity 130 - 420 m/s. The motion of the penetrator, fragmentation of ice and crater forming were observed by the high-speed camera. It revealed that the crown-shaped ejection was made for a short time after the impact and then the outward normal jet-like stream of ice pieces continued for much longer time. The concave shape of the crater was successfully visualized by pouring the plaster into it. The two-stage structure, the pit and the spall, was clearly confirmed. The rim was not formed around the crater. Observation of the crater surface and the ice around the trace of the penetrator shows that both crushing into smaller ice pieces and recompression into ice blocks are caused by the forward motion of the penetrator. In case of a body with a flow-through duct, ice pieces entering the inlet at the nose tip were ejected from the tail, resulting in relaxation of the impact force. The correlation of the penetration distance and the crater diameter with the impact velocity was investigated.展开更多
The investigation of mechanisms of nucleation of ice crystals by aerodynamic cooling produced by supersonic airflow is carried out. Three processes are considered to be the principal causes for aerodynamic cooling and...The investigation of mechanisms of nucleation of ice crystals by aerodynamic cooling produced by supersonic airflow is carried out. Three processes are considered to be the principal causes for aerodynamic cooling and nucleation of ice crystals. They are f adiabatic cooling in supersonic airflow. cooling at the cores of vortices around the edge of airflow and entrainment of ambient stationary air into supersonic airflow. It is thcrmodynamically confirmed that the temperature lowering in supersonic flow depends on the Mach number M there and stagnant pressure Po at a certain stagnant temperature To The temperature will decrease by more than 6℃ asM increases by 0.1. The influence of Po on cooling is shown through the variation of mass flow rates, which increase with Po Experiments in laboratory have shown that ice forming rate Pi produced by supersonic airflow increases from 1011 to 1012/g as M increases from 1.10 to 1.84 at Po=5 and 6 atm, and Pi increases from 4.3×1011 to 10.3×1012/g as the mass flow rate increases from 3.5 to 5.7 g/s and Po increases from 1.5 to 5.0 atm at M=1.80 and To=25℃. In field experiments the ice concentrations of 50 to 200 per liter in about 2000 m3 were measured when air of about 0.5 g were spurted at a Mach number of M=1.80 into supercooled fog with temperatures between -0.5℃ and -4.6℃.These results are compatible with the prediction of aerodynamics.The snapshot taken in experiments represents the detailed structures of vortex motion around a supersonic airflow.展开更多
基金This project is supported by National Natural Science Foundation of China (No.19832020)Provincial Natural Science Foundation of Jilin (No.20000519)
文摘Based on the elastic-plastic large deformation finite element formulation as well as the shell element combined discrete Kirchhoff theoretical plate element (DKT) with membrane square element, deep-drawing bending springback of typical U-pattern is studied. At the same time the springback values of the drawing of patterns' unloading and trimming about the satellite aerial reflecting surface are predicted and also compared with those of the practical punch. Above two springbacks all obtain satisfactory results, which provide a kind of effective quantitative pre-prediction of springback for the practical engineers.
文摘Robert Frost is one of the best poets in the 20th century.His philosophical poem "Fire and Ice" is to be discussed as a piece representing modernity.By analyzing some specific elements,this essay tries to convince that the poem is a perfect example of Frost's unique style-traditional forms combined with modern thoughts.
文摘For application to exploration under the surface of icy objects in the solar system, the penetration of an impact probe into an icy target was experimentally simulated by using the ballistic range. Slender projectiles with a cylindrical body and various nose shapes were tested at the impact velocity 130 - 420 m/s. The motion of the penetrator, fragmentation of ice and crater forming were observed by the high-speed camera. It revealed that the crown-shaped ejection was made for a short time after the impact and then the outward normal jet-like stream of ice pieces continued for much longer time. The concave shape of the crater was successfully visualized by pouring the plaster into it. The two-stage structure, the pit and the spall, was clearly confirmed. The rim was not formed around the crater. Observation of the crater surface and the ice around the trace of the penetrator shows that both crushing into smaller ice pieces and recompression into ice blocks are caused by the forward motion of the penetrator. In case of a body with a flow-through duct, ice pieces entering the inlet at the nose tip were ejected from the tail, resulting in relaxation of the impact force. The correlation of the penetration distance and the crater diameter with the impact velocity was investigated.
文摘The investigation of mechanisms of nucleation of ice crystals by aerodynamic cooling produced by supersonic airflow is carried out. Three processes are considered to be the principal causes for aerodynamic cooling and nucleation of ice crystals. They are f adiabatic cooling in supersonic airflow. cooling at the cores of vortices around the edge of airflow and entrainment of ambient stationary air into supersonic airflow. It is thcrmodynamically confirmed that the temperature lowering in supersonic flow depends on the Mach number M there and stagnant pressure Po at a certain stagnant temperature To The temperature will decrease by more than 6℃ asM increases by 0.1. The influence of Po on cooling is shown through the variation of mass flow rates, which increase with Po Experiments in laboratory have shown that ice forming rate Pi produced by supersonic airflow increases from 1011 to 1012/g as M increases from 1.10 to 1.84 at Po=5 and 6 atm, and Pi increases from 4.3×1011 to 10.3×1012/g as the mass flow rate increases from 3.5 to 5.7 g/s and Po increases from 1.5 to 5.0 atm at M=1.80 and To=25℃. In field experiments the ice concentrations of 50 to 200 per liter in about 2000 m3 were measured when air of about 0.5 g were spurted at a Mach number of M=1.80 into supercooled fog with temperatures between -0.5℃ and -4.6℃.These results are compatible with the prediction of aerodynamics.The snapshot taken in experiments represents the detailed structures of vortex motion around a supersonic airflow.
