Ship responses to abnormal waves simulated by the nonlinear Schrödinger equation

This paper studies the behaviour of an LNG carrier and a chemical tanker encountering different long-crested nonlinear water waves produced numerically by the nonlinear Schrödinger equation, which is capable of representing the modulational instability and of generating abnormal waves. The corresponding performance are also compared with those to the linear waves in the same sea state characterized by JONSWAP spectra, mainly focusing on the aspects of heave, pitch and vertical bending moment obtained in three typical cases. The results show that, with the increased nonlinearity, the presence of a large set of abnormal waves apparently leads to larger ship motions which are very similar for these two types of ships, but gives rise to totally different vertical bending moments due to the different ratio of dominant wave length to ship length, demonstrating that also in this case the ship responses are not only determined by the wave height but also depend on the relative wave length.