Abstract

The study of roll damping is one of the most fundamental subjects of ship hydrodynamic performance. Based on the unsteady Reynolds-averaged Navier-Stokes equations, simulation of a typical 14000 TEU container ship model (DTC) with predicted roll decay motion in calm water is performed. The simulation is achieved by the method which involves higher-order upwind scheme, a blended k–ω/k–? two-equation turbulence model, free surface tracking approach, structured overset grid and 6 degrees of freedom motion method. The resulting roll period is 1.74% shorter than the experimental data and the roll damping is 21.12% larger than that. The variation of hull surface pressure and vortices shedding induced by the roll decay motion in a period are also studied.

Introduction

Based on assumptions of small amplitude motions and potential flow, potential theory has been well developed but it is hard to predict roll motion because the theory just takes account of the wave radiation damping but fails to account for the viscous damping, flow separation, and vortex generation. And roll motion of ships is strongly related to viscosity effects and is extremely sensitive to viscosity-induced flow separations. Prediction of roll damping has been mainly depended on semi-empirical formulas and physical tank tests for a long time. Generally speaking, roll damping is classified by wave damping, lift damping, friction damping, eddy making damping and bilge keel damping. Only the wave damping may be obtained based on assumptions of potential flow theory. Other components of roll damping are determined by empirical formulas or experiments. Ikeda (1977) and Himeno (1981) developed an empirical method to predict the roll damping according to a series of model experiments. And different roll damping assessments via decay model testing were proposed (Fernandes, 2009). Meanwhile numerical methods have been developed to study roll motion damping. Nonlinear formulation was proposed by Yeung (2001) to compute the problems involving bodies with sharp edges or appendages. Bangun (2010) developed a solver that accounts for the non-linear free-surface condition to determine the hydrodynamic forces on a rolling barge with bilge keels. Avalos (2014) implemented a two-dimensional numerical code to study the roll damping decay of a FPSO with bilge keel.

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