Wet Deck Slamming Analysis of Twin-Hulled Offshore Ship in Irregular Sea Waves

Abstract

In ship hull design, it is important to predict the seakeeping parameters like ship motions, vertical accelerations, wave impact loads, deck wetness, etc. when the ship is subjected to waves. According to the ABS Guide for Building and Classing High Speed Naval Craft (HSNC 2007) slamming impact load is one of the most critical factors for the scantling design of hull structures[7]. Accurate prediction of wave impact loads requires solution of three problems. First one is the prediction of wave kinematics, second one is the prediction of the pressure and viscous forces and the third one is the prediction of ship motion during the wave impact.This paper focuses on the wet deck slamming analysis of twin-hulled offshore ship in irregular sea waves and proposes a Computational Fluid Dynamics (CFD) solution using Volume of Fluid (VOF) method and Six Degrees of Freedom Model (6DOF). Irregular waves were modeled using JONSWAP wave spectrum. The wave profile obtained from the numerical simulation was validated with analytical results. The wave impact load and the hull motions depend on many factors, such as sea state, ship speed, draft, wave heading angle, hull structure, ship loading condition etc. In this paper, we have analyzed the wet deck slamming for a survival condition with sea state of significant wave height of 9m with two different ship loadings and two different ship speeds. CFD analyses were also carried out for calm sea conditions with different ship loadings. The heave and pitch motion of the ship in wave conditions are compared with calm sea conditions. The ship motions, vertical accelerations, pitch velocities and the wet deck slamming pressures are compared for the two ship loadings and two ship speeds. This paper describes these results in detail.