Global response of submerged floating tunnel against underwater explosion

초록

Submerged floating tunnels (SFT) for transportation must be designed to secure passengers’ safety in case of accidental events. Underwater explosion is the most critical event to long submerged structures. It generates shock waves propagating into the surrounding fluid to conflict impulse loading to SFTs. Extreme impulse loading makes critical damage to the body of SFT and may break it into several pieces. To design a safe SFT against underwater explosion, its behavior must be investigated and clarified. In this paper, first, shock waves and impulse pressures generated by an explosive away from the SFT are expressed by the formulas coming from the experimental results. Second, the SFT tethered by mooring lines and anchors is modeled as a simply supported uniform beam with continuous elastic springs. Finite element analysis for the beam model subjected to the impulse loading from the experimental formulas is conducted by using a commercial code so that the response of the SFT can be investigated. For design purpose, theoretical analysis is also conducted for the same model. Impulse loading along the SFT is assumed as piecewise linear, whose initial peak decays linearly. Based on this assumption, simple equations to show the response of the SFT due to underwater explosion attack were deduced. Time dependent displacements were calculated by these equations. The calculated results were compared with the previous numerical results and proved to give good agreement with them. Theoretical analysis using the simple equations yields solutions so rapidly that they can be applied for parametric study of the response of SFT against underwater explosion during initial design stage. Also guidelines for design of SFT can be proposed