Estimation of added mass moment of inertia in roll motion through numerical simulation

Dynamic ship stability is an important subject in the field of Naval Architecture due to lack of understanding may result in extreme roll motion. Direct investigation of dynamic stability modes such as parametric rolling is possible through the CFD analysis but is costly due to the long simulation time, while other numerical methods like panel methods can speed up the process. Success in using these methods depend on the solution of motion’s equation and accurate estimation of each term including mass moment and added mass moment of inertia, damping and restoring moments. At the present time, there is a lack of precise estimation of added mass moment of inertia, which is usually accounted for 10-25% of mass moment of inertia. This paper presents an innovative method to calculate added mass moment of inertia by exciting a ship model through series of harmonic moments using CFD simulations. At maximum roll angle, where the acceleration is maximised and angular velocity is zero (damping moment is negligible), the total moments are measured. By ascertaining the restoring and harmonic excited moments momentarily, the added mass moment of inertia could be determined with greater accuracy. In this investigation and for the purpose of analysis, the influence of forward speeds, coupled heave, pitch and roll motions, and various encounter frequencies are taken into account.