2020 年 81 巻 5 号 p. 128-136
The present study describes the propagation characteristics of shock waves discharged from the open end of circular tubes that have obstacles placed in front of the open end. These circular tubes with obstacles were used as simplified models of underground magazines that have dikes installed in front of the open end to prevent blast waves and fragments from directly hitting the surrounding area in case of any accidents. The propagation characteristics of shock waves were analyzed with time-resolved visualized images. The background-oriented schlieren (BOS) technique with a high-speed camera was used for the visualization because of the physical limitation of installing ordinary systems, including schlieren, within the explosion chamber. Model configurations were assessed with three different length/diameter ratios for the tube and three types of obstacles. An explosive, pentaerythritol tetranitrate (PETN) pellet (1.0 g) was ignited inside the model tubes to generate shock waves. R-t diagrams were reconstructed from visualized images and peak overpressure was estimated from the diagrams to allow for comparison with overpressure history, which had previously been obtained. The results showed that while the presence of an obstacle diminished the shock strength, the obstacle size did not have a significant effect on the propagation of shock waves behind the dike model.
