Hydroelastic performance of an ultra-large containership in irregular and freak waves

Ship motions, local wave impact loads on ship bow and global wave-induced structural responses of a 20 000 TEU (twenty-foot equivalent unit) containership are studied in irregular and freak waves. A two-way coupled CFD-MBD (computational fluid dynamics–multi body dynamics) method is adopted for the co-simulation of the interactions between flow field and structure model of an elastic ship beam. The fluid–structure interaction method is validated with experimental measurement in regular waves. It is found that the maximum value of the vertical bending moment response amplitude operator appears in the condition of λ/L=1.0. In the flow field, a potential-viscous flow coupled HOS-CFD (high order spectrum–CFD) method is applied in the simulation of the irregular and freak waves. The freak wave generated by HOS-CFD method shows good agreement with the HOS input data. It is found that the amplitude of pitch motion is most sensitive to the wave height of irregular waves. When the significant wave height of the irregular wave increases by 1.6 times, the VBM, heave, and pitch responses increase by about 2 times, 3.5 times, and 6 times, respectively. In addition, the cumulative distributions of hull motion, VBM amidship, and most sensor pressures are well fitted with Weibull distribution. In high sea states, bow slamming and green water are the main causes of high frequency responses of VBM.