LS-DYNA Applications in Shipbuilding

Authors: Hervé Le Sourne, Nicolas Couty, François Besnier, Cyrille Kammerer, Hervé Legavre Principa Marine, Nantes, France DCN Ingénierie, Cherbourg, France Ship and submarine structures have long been studied thanks to finite element methods. Their large dimension and complexity, the coupling with heavy fluid and the presence of a free surface raise numerical problems on the field of dynamic analysis. This is particularly true for extreme or accidental situations such as collision and grounding, underwater explosion and severe fluid impact. This paper describes first numerical methods and tools developed in LS-DYNA and used in the simulation of ship-submarine collisions, with a focus on the outer collision dynamics, i.e. global motion of the impacted structure. Using a new version of the rigid body dynamic program MCOL included in LS-DYNA, the influence of hydrodynamic effects is highlighted in ship-submarine collisions and in military surface ship collisions. The second part of this paper is dedicated to dynamic response analysis of surface ship or submarines submitted to underwater explosions (UNDEX). Coupled with the Underwater Shock Analysis (USA) code, LS-DYNA is a powerful tool used to simulate the response of ships or submarines to both the shock wave induced by the detonation and the bubble gas effects. Through some examples of 3D numerical models of military vessels, the paper presents the capabilities of the LS-DYNA/USA tool and some difficulties encountered in such an analysis. Impulse loads with high pressure peaks may occur when a ship bottom hits the water with a high velocity. This is often called "slamming”. Sometimes ships suffer from local damage from the impact load or large buckling on the deck. In the last part of this paper, LS-DYNA is used to simulate such water-entries. Interaction between lagrangian bodies and multi-materials eulerian fluids (air and water) is taken into account thanks to a penalty coupling method.