| Summary: | 博士 === 國防大學理工學院 === 國防科學研究所 === 103 === The objectives of this study are under the condition of underground command center subjected to near-field explosion to investigate the propagation mechanism of blast pressure and the effects of blast pressure attenuation inside the tunnel system by using both experimental and numerical methods. Experiments are conducted in a small scale and are divided into three categories: (1) Free field tests, (2) Tests with different tunnel types, (3) Tests with decompression modules. The results of experiments are used to validate the accuracy of the numerical models. In the numerical simulation, the Arbitrary-Lagrangian-Eulerian (ALE) algorithm of fluid-structure interaction and mapping technique are adopted to evaluate the effects of blast pressure propagation. In order to be further applied for the underground command center for the needs of the pressure protection, a large scale numerical model is used for analyses and discussions.
The study shows that the results by using Ls-Dyna mapping technique are consistent with experimental results in blast pressure attenuation and provide a reasonable response in terms of the blast pressure.
Based on the results of explosion tests, two empirical formulas that are individually used to predict the overpressure for the near surface burst and the overpressure decay ratio inside a straight tunnel are proposed. In addition, from straight tunnel explosion tests, the blast pressure at the portal of the tunnel due to the confinement effect increases about 32% in comparison with that of the near surface burst. This increased ratio combined with the proposal empirical formulas can easily be used to provide a reasonable and fast overpressure prediction inside the tunnel.
Three different types of the tunnel are investigated in the study. There are Elbow-type, T-type and Branch-type tunnels. The results show that the blast propagation mechanism inside the tunnel is various, in particular, the overpressure on both sides of the wall is different. Based on the experimental and numerical analyses, 7 formulas used to predict the ratio of transmitted overpressure are also proposed.
The designs of decompression modules (expansion chamber, one-orifice plate attenuator, double-orifice plate attenuator) by changing the tunnel cross-section are studied. It shows that the use of the decompression modules does have the positive effect on the pressure attenuation. Also it indicates that a double-orifice plate attenuator is the best of all, followed by a one-orifice plate attenuator, and then followed by an expansion chamber. The results are served as the basis for the further design of the protective facility.
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