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[MAG33-P05] Development of Numerical Model of Explosion to Reproduce the "Black Rain"
Keywords:black rain, Explosion model
This paper outlines the explosion modeling for the present simulation. The method of performing the computation as a uniform gas sphere with a radius of several tens of meters at high temperature and high pressure, using the conditions after a certain period of time immediately after explosion as the initial values for the explosion reproduction, is described in the Los Alamos laboratory report by Bethe et al. (LA-1020). The combined LA-1020 and LA-1021 document is now published as LA-2000. In this paper, a system to calculate the amount of state after explosion mainly following the method described in LA-2000 was created in Excel software and used as the initial value for the explosion simulation. The TNT equivalent value of the Hiroshima A-bomb has been considered to be 16 kt, but in this report, 10 kt is used as the detonation energy taking into account the explosive pressure on the surrounding area.
The formation of the mushroom cloud is simulated seamlessly from immediately after explosion until the plume rises, referring the method used for volcanic plumes. In this paper, two types of dust in the mushroom cloud are treated: dust originating from the bomb itself and dust originating from buildings on the ground.
During the ascent process of the mushroom cloud after explosion, a strong updraft creates a torus-like, three-dimensional vortex. The position of the vortex is tracked with time, and the cloud growth process is verified by comparing similar past simulations with nuclear data. The simulation results are in good agreement with the experimental data when the initial value of 10 kt is used.
In order to verify the prediction accuracy of the explosion scale, a comparison of the overpressure caused by the shock wave propagating on the ground was conducted, and it was confirmed that setting the explosion energy to 10 kt is in better agreement with the overpressure on the ground in Hiroshima. Based on the above verification, we visualized the dust concentration distribution on the central cross section through the explosion point. These results show that the fireball expands to near the ground surface, but the spherical concentration fraction is deformed by a strong updraft in the middle of the expansion and then begins to rise.
The formation of the mushroom cloud is simulated seamlessly from immediately after explosion until the plume rises, referring the method used for volcanic plumes. In this paper, two types of dust in the mushroom cloud are treated: dust originating from the bomb itself and dust originating from buildings on the ground.
During the ascent process of the mushroom cloud after explosion, a strong updraft creates a torus-like, three-dimensional vortex. The position of the vortex is tracked with time, and the cloud growth process is verified by comparing similar past simulations with nuclear data. The simulation results are in good agreement with the experimental data when the initial value of 10 kt is used.
In order to verify the prediction accuracy of the explosion scale, a comparison of the overpressure caused by the shock wave propagating on the ground was conducted, and it was confirmed that setting the explosion energy to 10 kt is in better agreement with the overpressure on the ground in Hiroshima. Based on the above verification, we visualized the dust concentration distribution on the central cross section through the explosion point. These results show that the fireball expands to near the ground surface, but the spherical concentration fraction is deformed by a strong updraft in the middle of the expansion and then begins to rise.