The role of Uncoupled Eulerian-Lagrangian approach in UNDEX investigations for ship-like structures

Understanding the dynamic response of submerged structures under pressure loads is crucial for naval shipbuilding and offshore engineering. Among these loads, underwater explosions (UNDEX) are particularly critical, directly affecting the safety and performance of structures such as submarines, drilling platforms, and military vessels. Advancements in numerical methods have made simulations the primary tool for addressing UNDEX events. Numerical approaches for UNDEX typically employ coupled or decoupled techniques. Coupled methods resolve the fluid-structure interaction (FSI) problem by directly and simultaneously modelling the interaction between the explosion-induced pressure wave and the ship’s dynamic response. Uncoupled (or decoupled) methods use a 2-step numerical procedure considering before the time-domain loads on a rigid structure and then their structural dynamic effect. Coupled models are highly accurate for UNDEX scenarios but time-consuming, while decoupled models offer computational efficiency and easier implementation but with less predictive accuracy due to the lack of consideration for FSI. Despite its importance, there is a lack of comprehensive studies comparing coupled and uncoupled approaches for UNDEX modelling. This work addresses this gap by evaluating the structural response of a floating ship-like structure under an UNDEX scenario using the two approaches. It employs a Coupled Eulerian-Lagrangian (CEL) method to account for FSI, and a two-step Uncoupled Eulerian-Lagrangian (UEL) approach for the decoupled analysis, excluding seabed or surface reflection effects. The study highlights the key results of both strategies, comparing their advantages, limitations, and applications in marine and naval engineering.