Numerical study on 6-DOF motions of ships advancing in oblique waves by frequency-domain higher-order Rankine source method

In order to predict the 6-DOF motions of ships advancing in oblique waves, the frequency-domain higher-order Rankine source method was adopted to solve the diffraction and radiation including steady flow effects, and a multi-degree-of-freedom computational model was established. In this model, the influence of fluid viscosity on roll motion was considered by introducing additional viscous roll damping coefficient, which was solved by using the energy method to deal with the free rolling decay curve obtained based on the computational fluid dynamics theory, into the motion equations in frequency domain. On the basis of the above method, a computer code was developed. Numerical simulations were first conducted on the heave, roll and pitch motions of S175 in bow oblique waves (β=150°). By comparing the present results with the experimental data and numerical solutions obtained from the methods using the translating-pulsating Green's function, it is found that the present method is of better stability and has a higher prediction precision near the resonant frequency due to its consideration of steady flow effects. Then further investigations were conducted on the 6-DOF motions of S175 and a full formed bulk carrier S-Cb84 with different headings. The good agreement between numerical results and experimental data shows that the present method can be applied to various ship types at different heading angles. © 2022, Editorial Board of Journal of Ship Mechanics. All right reserved.