Response of Structure with Air-Backed and Water-Backed Medium Subjected to Underwater Shock Pulse

Underwater explosion (UNDEX) causes devastating effects on offshore structures. Studying its effect on structures is important, especially concerning navy or defense facilities, offshore pipelines and other critical underwater infrastructures. Blast resistant design of such structures requires proper estimation of shock pulses and the effect of the water medium on the structural response. Analytical framework and numerical studies in this area pertain mainly to the response of free-standing structures subjected to the blast wave with water-backed medium and air-backed medium. The response of a submerged structure in water subjected to shock wave is unlike that of the structure in air due to the presence of a fluid medium behind the structure. But, the effect of structure with a water-backed medium is rarely studied and reported. In this study, numerical analysis is performed to simulate the response of a cantilever beam in water when subjected to shock waves. A Coupled Eulerian Lagrangian (CEL) and fluid–structure interaction (FSI) is performed using an explicit finite element analysis software to simulate the shock wave propagation and its interaction with the structure. A shock-tube type framework has been set up to study the structural response and has been replicated through numerical simulations. Multiples analysis are performed to evaluate the structural performance by varying (a) sectional properties of structure (dimensions) and (b) shock wave magnitude. The deformation of the structure, impulse transferred to the structure and its supports, rebound effect and the shock wave transmission behind the structure are studied and summarized from the analyses.