A Modular Methodology for the Estimation of the Ship Roll Response under the Action of Stochastic Wind and Waves

A combined analytical/numerical approach is proposed to address the problem of the ship roll motion under the combined action of wind and waves. The approach is modular allowing an easy update of the methodology on the basis of new research outcomes. Realistic environmental conditions regarding both wind and waves are considered. The spatial correlation of wind gusts is taken into account by means of an “aerodynamic admittance” function. The proposed analytical procedure allows obtaining approximate statistical averages of the roll motion without necessarily resorting to time consuming Monte Carlo simulations. On the basis of the results obtained, an estimation of the capsize probability can be carried out. It seems that the effect of wind gustiness could be considered negligible when compared to the effect of waves and of mean wind speed if the ship roll period is not too large. Finally, the presented approach moves towards the concept of “performance based analysis”, recently introduced at IMO as the basis for future developments of Intact Stability, in a clear and formal way.