Nonlinear Dynamic Response of a Fixed Offshore Platform Subjected to Underwater Explosion at Different Distances

In this paper, the dynamic response of a fixed offshore platform subjected to the underwater explosion (UNDEX) and probable events following it have been investigated. The pressure load due to UNDEX in a specified depth has been applied with a model that considers the effect of blast bubble fluctuations into account. The effect of water on the natural frequency and Fluid-Structure interaction has been modeled as equivalent added mass formulation. The effect of explosion distance on platform response is studied. In this regard, three cases of near, medium, and far-distance explosions are considered. For a case study, a real fixed offshore jacket platform, installed in the Persian Gulf, has been examined. Only the UNDEX pressure load is considered and other dynamic loads such as surface water waves and winds have been neglected. Dead loads, live loads and hydrostatic pressure has been considered in the static case based on the design codes. The results indicated that in near-distance explosions, the UNDEX pressure load can locally damage parts of the platform that are located at the same level as that of explosive material and it can destabilize the platform. In the medium to far distance explosion, a very large base shear was applied to the platform because more elements were exposed to the UNDEX load compared to the near-distance explosion. Therefore, precautionary measures against UNDEX such as risk assessment according to design codes are necessary. As a result of this, member strengthening against explosion may be required.