Wave Loads Investigation of a VLCC by Experimental and Theoretical Methods

On the large scale the commercial ship development trend indicates that the length of ship becomes longer and longer whilst its hull girder turns into much more flexible than that of small and medium-sized ships. This results in a ship sustaining both springing and slamming responses when travelling at sea. A VLCC is introduced in this paper to study its low and high frequency wave load responses in both full loaded and ballast condition. Experimental and theoretical methods were used to investigate the characteristic of this VLCC’s wave loads. A segmental model with its length more than six meters being connected by two non-uniform beams was used to get the vertical bending moments at each measured cut. A 2D nonlinear theory and a 3D hydroelastic theory were both employed to predict the wave loads responses. The results had been compared between experimental and theoretical methods. It was shown that springing phenomenon was prone to appear when wave amplitude was low and its period was short, especially when wave encounter frequency was an integral multiple of the basic vibration frequency of the ship hull girder. Slamming happened when the wave amplitude was high. However, it was difficult to distinguish slamming or springing or their combination from the wave-induced vibrations because of the small damping ratio in total vibrations. Loading condition has a great influence on wave loads responses especially on the springing behavior. It was found that springing behavior is much more severe in ballast condition than in full loaded condition. The mechanism of it which mentioned in other reference was reconfirmed in this paper.