Numerical study on the vertical response of LNG carrier in abnormal waves generated with different mechanisms

Abstract

To investigate the response difference of a ship encountering the same temporal abnormal waves formed with different physical mechanisms, three abnormal waves are generated with both linear and nonlinear focusing methods. These waves have the same crest height and trough-to-trough period as the New Year Wave. And the induced vertical responses of a LNG carrier are comparatively studied when these three abnormal waves focus at different sections of the ship hull moving with various speeds. Although the temporal profiles of abnormal waves are almost identical, their spatial profiles at the instant of focusing can be different, resulting in the distinct hydrodynamic characteristics between the linear and nonlinear focused abnormal waves. Consequently, the responses of LNG carrier are different, mainly due to the discrepancy in the Froude-Krylov forces. Besides, the focal location and ship forward speed can also significantly influence the peak response of LNG carrier for the given abnormal waves. Finally, some parameters associated with the spatial profile of abnormal wave seem to be more promising to work as indices to illustrate the corresponding generation mechanism and hydrodynamic property, as well as potentially induced extreme ship responses.