Owing to the unique advantages in flight altitude,dwelling time and wide coverage area,stratospheric airships provide permanent monitoring and surveillance for both civil and military applications.Here we propose a se...Owing to the unique advantages in flight altitude,dwelling time and wide coverage area,stratospheric airships provide permanent monitoring and surveillance for both civil and military applications.Here we propose a semi-rigid stratosphere airship design with circumferential high-pressure inflatable rings and a longitudinal carbon fiber skeleton supported inside.We perform numerical simulations to analyze the deformation characteristics during the whole ascending and descending process.An equivalent internal gradient pressure model of helium is established based on the capsule shape and buoyancy-weight equilibrium conditions.The implicit dynamic method is used to deal with the large deformation of the airship capsule under a low negative pressure condition.Deformation and load-bearing performance of the airship capsule,inflatable ring,skeleton,and suspension line are obtained under different working conditions.The results show that the airship,supported with the inflatable rings and the suspension lines,effectively maintains the shape and ensures the stiffness during the ascending,dwelling,and descending stages,especially suffering from negative pressure.展开更多
To evaluate the effect of actual cooling rate of liquid steel in the ladle on the metallurgical performances of a tundish, a transient and coupled computational model was developed to reveal the flow fields, temperatu...To evaluate the effect of actual cooling rate of liquid steel in the ladle on the metallurgical performances of a tundish, a transient and coupled computational model was developed to reveal the flow fields, temperature fields, residence time distribution of the molten steel and the inclusion removal efficiency in a typical single-strand tundish with given geometry and process parameters. The results showed that, with the decrease of the ladle stream cooling rate, the temperature difference of bulk flow at the outlet of tundish over a normal casting period decreased from 11.3 to 2.6 K, and the dead volume fraction of the tundish decreased from 17.58% to 14. 35%, while the inclusion removal efficiency was increased especially for the inclusions with the diameter less than 50 μm, whose removal ratio could be increased by 20.62%. When the cooling rate was less than 0.3 K · min-1 , however, the variation rates of the three evaluation criterions above declined significantly, which suggested that a critical value existed for the effect of the cooling rate of ladle stream on the tundish performances. The establishment of the critical ladle stream cooling rate should be very important to achieve persistent metallurgical properties of tundish over the whole casting stage, together with the reasonable ladle insulation design.展开更多
基金support from the National Natural Science Foundation of China(No.11872160).
文摘Owing to the unique advantages in flight altitude,dwelling time and wide coverage area,stratospheric airships provide permanent monitoring and surveillance for both civil and military applications.Here we propose a semi-rigid stratosphere airship design with circumferential high-pressure inflatable rings and a longitudinal carbon fiber skeleton supported inside.We perform numerical simulations to analyze the deformation characteristics during the whole ascending and descending process.An equivalent internal gradient pressure model of helium is established based on the capsule shape and buoyancy-weight equilibrium conditions.The implicit dynamic method is used to deal with the large deformation of the airship capsule under a low negative pressure condition.Deformation and load-bearing performance of the airship capsule,inflatable ring,skeleton,and suspension line are obtained under different working conditions.The results show that the airship,supported with the inflatable rings and the suspension lines,effectively maintains the shape and ensures the stiffness during the ascending,dwelling,and descending stages,especially suffering from negative pressure.
文摘To evaluate the effect of actual cooling rate of liquid steel in the ladle on the metallurgical performances of a tundish, a transient and coupled computational model was developed to reveal the flow fields, temperature fields, residence time distribution of the molten steel and the inclusion removal efficiency in a typical single-strand tundish with given geometry and process parameters. The results showed that, with the decrease of the ladle stream cooling rate, the temperature difference of bulk flow at the outlet of tundish over a normal casting period decreased from 11.3 to 2.6 K, and the dead volume fraction of the tundish decreased from 17.58% to 14. 35%, while the inclusion removal efficiency was increased especially for the inclusions with the diameter less than 50 μm, whose removal ratio could be increased by 20.62%. When the cooling rate was less than 0.3 K · min-1 , however, the variation rates of the three evaluation criterions above declined significantly, which suggested that a critical value existed for the effect of the cooling rate of ladle stream on the tundish performances. The establishment of the critical ladle stream cooling rate should be very important to achieve persistent metallurgical properties of tundish over the whole casting stage, together with the reasonable ladle insulation design.
