Hydroelastic Analysis of the Bending-Torsional Coupling Vibrations of an Ultra-Large Container Ship

Abstract

Springing is a resonance phenomenon between the waves and the ship hull, and the high frequency vibration will threaten the safety of hull structures. With the development of economy, the size of ultra large container ships has been increasing, and the resulting springing and whipping response and their effects has been paid more and more attention. The structure of an ultra large container ship is essentially U-shaped with a low shear center, which results in strong coupling between horizontal bending and torsion. On the other hand, the actual response of hull structures will have an apparently dynamic amplification phenomenon under the effect of springing. In this paper, the wave-induced loads on the hull structure is estimated in the framework of the 3D linear hydroelastic theory, which coupling horizontal and torsional vibration. The vibration characteristics are investigated by using finite element method (FEM), which can get a better calculation accuracy than the simplified calculation method such as the Transfer Matrix Method. And the mode shape of displacement and section loads of the whole ship can be obtained and processed, which is needed for the analysis of hydroelasticity. Finally, in order to consider the effect of the dynamic amplification effect, the dynamic response analysis approach is used for the stress calculation. A 21000TEU is calculated by this method, and the difference between wave-induced and springing-induced section load in frequency domain is shown. Then the results of the frequency response analysis is compared with the quasi-static methods. And the effect of the springing and the dynamic magnification is analyzed.