Influence of linear springing on the fatigue damage of ultra large ore carriers

Abstract

Springing occurs more frequently to ultra large ships, as their natural frequencies are relatively low and approaches the spectral peak of the wave energy spectrum in certain sea states. Springing is a resonance phenomenon between the waves and the ship hull, and this high frequency vibration has a significant influence on the fatigue damage of hull structures. This paper deals with the influence of springing on the fatigue damage of ultra large ore carriers. The springing responses of ultra large ore carriers are calculated by a three-dimensional linear hydroelasticity method in the frequency domain. A fatigue damage calculation method accounting for the springing effect is applied that is based on the fatigue spectrum analysis method and the approximation method of joint narrowband. The fatigue damage of the deck and bottom longitudinals in the deck and bottom of ultra large ore carriers of various sizes has been calculated by this method. The influences of ship size, structural damping, sea state, wave heading, navigational speed, and loading condition on the structure fatigue damage ratio of ultra large ore carrier are analyzed.