ABSTRACT
This paper presents a simplified method to assess the whipping response of a surface ship subjected to underwater explosions (UNDEX), without modeling explicitly the surrounding water nor the actual structure of the ship, using LS-DYNA/USA. The ship structure is represented using equivalent beam elements based on sections described in girder strength models such as MARS2000, with inertia and area measurements for each section. These elements are then individually connected to the corresponding sections of the hull modelled by means of surface elements. These surface sections are independent from each other allowing the USA code to take into account the fluid-structure interactions, without disturbing the global mechanical behavior of the system. The relevance of this model is evaluated by comparison with a full 3D model through two test cases: a simplified model, and a real case. The validation process first consists in the comparison of natural frequencies and mode shapes, then in the analysis of the whipping response for both approaches. In particular, focus is made on deflections and bending moments.
