Tomoharu Matsumura

Quantitative Visualization of Open-Air Explosions by Using Background-Oriented Schlieren with Natural Background

This paper describes application of a background oriented schlieren (BOS) technique in order to obtain quantitative measurements of shock waves from explosions by processing high speed digital video recordings. To illustrate the technique we present results from analysis of two explosions, one by C-4, the other by emulsion explosives (EMX). The experimentswere performed at theMinistry of Defense Test field, and carried out by the Ministry of Economy, Trade and Industry (METI). The objective of this paper is to show that the shock wave overpressures in a field explosion test can be predicted quantitatively by means of this technique.

REDUCTION OF EXPLOSION DAMAGE USING SAND OR WATER LAYER

The attenuation of blast waves and fragment velocity caused by an explosion was examined. The blast wave was attenuated by covering an explosive with water based material or sand. The relation between density of the materials for covering the explosive and the attenuation of peak pressure and impulse of the blast wave was studied to reduce the volume and weight of the material. The attenuation effect of the blast wave depended not only on the weight of the barrier materials, but also on the porosity. Reduction of fragment velocity accelerated by a high explosive using a sand or water layer was also evaluated.

TEMPORAL CHANGE OF RAMAN SPECTRA OF CARBON TETRACHLORIDE UNDER LASER‐DRIVEN SHOCK COMPRESSION

Nanosecond time‐resolved Raman spectroscopy has been performed to study a molecular response of carbon tetrachloride under laser‐driven shock compression at laser power density of about 5 GW/cm2. Intense Raman peaks of CCl4 at 213, 314, and 459 cm−1 in the Stokes and anti‐Stokes region were clearly observed simultaneously at single‐shot experiment. These peaks showed a blue shift (high frequency shift) and became broad under compression. The intensity of these peaks increased along with the propagation of shock wave. The temporal change of frequency shift and full width at half‐maximum (FWHM) of peaks showed the different behavior depending on each vibrational mode. The anti‐Stokes and Stokes ratio for each peak increased during shock compression due to the shock induced temperature rise. The temporal change of temperature estimated by Raman spectroscopy showed agreement with that of calculated temperature within present experimental resolution.Nanosecond time‐resolved Raman spectroscopy has been performed to study a molecular response of carbon tetrachloride under laser‐driven shock compression at laser power density of about 5 GW/cm2. Intense Raman peaks of CCl4 at 213, 314, and 459 cm−1 in the Stokes and anti‐Stokes region were clearly observed simultaneously at single‐shot experiment. These peaks showed a blue shift (high frequency shift) and became broad under compression. The intensity of these peaks increased along with the propagation of shock wave. The temporal change of frequency shift and full width at half‐maximum (FWHM) of peaks showed the different behavior depending on each vibrational mode. The anti‐Stokes and Stokes ratio for each peak increased during shock compression due to the shock induced temperature rise. The temporal change of temperature estimated by Raman spectroscopy showed agreement with that of calculated temperature within present experimental resolution.

Dependence of Blast Attenuation on Weight of Barrier Materials

The attenuation effect of barrier materials, which covers an explosive completely, on blast waves was studied. The density of the barrier materials was examined to make the barrier materials light and low in volume. Water gel, small spheres of foam polystyrene, and mixtures of these two materials were used as the barrier materials, and the density of the mixture was varied from 0.12 g•cm-3 to 1.0 g•cm-3 by changing the mixed volume ratio. Natural silica sand was also tested for comparison. A spherical PMMA container was filled with the barrier materials and a spherical pentolite (100 g) was ignited at the center of container. The blast pressure around the container was measured. The mixture of the density of approximately 0.55 g•cm-3 maximized the attenuation of the blast wave for the same volume. The attenuation effect depends not only on the weight of the barrier materials but also on the porosity. A mixture of a density of approximately 0.13 g•cm-3 maximized the attenuation of the blast wave for the same weight. Using porous materials, relatively light barrier materials can attenuate the blast wave effectively, if the volume is not restricted. The attenuation effect of sand was greater than that of water gel and a mixture for the same volume.

Blast Wave Mitigation from the Straight Tube by Using Water Part II - Numerical Simulation

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.

Blast Wave Effects from Internal Explosion of Subsurface Explosive Storage Facility

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.

Background-Oriented Schlieren for Large-Scale and High-Speed Aerodynamic Phenomena (Invited)

Visualization of the flow field around a generic re-entry capsule in subsonic flow and shock wave visualization with cylindrical explosives have been conducted to demonstrate sensitivity and applicability of background-oriented schlieren (BOS) for field experiments. The wind tunnel experiment suggests that BOS with a fine-pixel imaging device has a density change detection sensitivity on the order of 10(sup -5) in subsonic flow. In a laboratory setup, the structure of the shock waves generated by explosives have been successfully reconstructed by a computed tomography method combined with BOS.

Particle velocity history of pentaerythritol tetranitrate shocked along [110] crystal orientation by laser-accelerated miniature flyer impactc

We performed miniature flyer impact experiments to investigate the thermodynamic and optical properties of shocked single-crystal pentaerythritol tetranitrate (PETN). A thin metal plate was accelerated by irradiating it with pulse from a tabletop laser, and impacted on a single crystal of PETN along the [110] axis. The particle velocity history of the laser-accelerated flyer was measured using an optically recording velocity interferometer system. The relationship between the actual particle velocity and the particle velocity measured by the velocity interferometer was obtained by analyzing the particle velocities immediately before and after the flyer collided with the PETN [110] single crystal. The change in the refractive index of the shocked PETN [110] immediately after a shock wave had propagated was also studied.

Card Gap Test of Tri-n-Butyl Phosphate/Fuming Nitric Acid Mixture

For safety research in spent nuclear fuel reprocessing, the study of the potential explosion hazards of TBP (tri-n-butyl phosphate)/nitric acid mixture was conducted. A worst condition of the mixture was assumed with the using of fuming nitric acid (FNA) and a shock ignition stimulus. The shock initiation sensitivity of the TBP/FNA mixture was investigated by the card gap test, which is based on the Japan Explosive Society standard. Separately, photographs using a streak camera and framing camera measured the shock passing time through a PMMA gap, and then, a pressure calibration curve was determined. From the card gap test, it was found that the shock initiation sensitivity of TBP/FNA depends on the mixture ratio. By using the pressure calibration curve, a critical shock pressure was estimated. The shock initiation sensitivity of TBP/FNA at stoichiometry was estimated three or four times higher than that of nitromethane.

Explosion interaction with water in a tube

As proposed and legislated in Japan, subsurface magazines have an explosive storage chamber, a horizontal passageway, and a vertical shaft for a vent. The authors found that a small amount of water on the floor of the storage chamber mitigated blast pressure remarkably. The mitigation mechanism has been examined more closely. To examine the effect of water, the present study assesses explosions in a transparent, square cross section, and a straight tube. A high-speed camera used to observe the tube interior. Blast pressure in and around the tube was also measured. Images obtained using the high-speed camera revealed that water inside the tube did not move after the explosion. Differences between cases of tubes without water and with water were unclear. Along with blast pressure measurements, these study results suggest that blast pressure mitigation by water occurs because of interaction between the explosion and the water near the explosion point.