Papers by Author: Yoshio Nakayama

Abstract: A subsurface magazine has an explosive storage chamber, a horizontal passageway, and a vertical shaft for vent. It was proposed and legislated in Japan. The authors found that small amount of water on the floor of its storage chamber mitigated the blast pressure remarkably. The mechanism of the mitigation has been studied, however, it is not still well understood. In this study, the explosion in a transparent, square cross section, and straight tube was carried out to examine the mechanism of blast-wave mitigation by water. The arrangement and amount of water in the tube were varied for five ways. The dependence of mitigation effect on the arrangement and amount of water was evaluated by measuring the blast pressures in the tube and outside the tube. The results of this study concluded that the mitigation of blast wave by water is mainly due to the interaction between the explosion and the water very near the explosion point. On the contrary, the water at other part of the tube was found to strengthen the blast pressure.

Abstract: This paper investigates explosions in a straight square tube in order to understand the mitigation effect of water on blast waves that emerge outside. Numerical simulations are used to assess the effect of water that is put inside the tube. The water reduces the peak overpressure outside, which agrees well with the experimental data. The increases in the kinetic and internal energies of the water are estimated, and the internal energy transfer at the air/water interface is shown to be an important factor in mitigating the blast wave in the present numerical method.

Abstract: To reduce safe distance such as inhabited building distance (IBD), a new type magazine, which is referred to as a subsurface magazine, has been proposed and the explosion effects have been discussed. We have conducted explosive tests by using relatively large scale models (23 kg and 78 kg in mass) and examined mass effect (scale effect) of blast waves caused by explosion of high explosives. The magazines were composed of a arch-type explosive storage room with a line hinge along the top of the roof of the wall, a square passage way to ground which will release the blast wave. Explosion hazards from the explosion of subsurface magazines were collected to understand the characteristics of airblast, fragments, and ground shocks. Safety criteria for the subsurface magazine are discussed based on the experimental results.