Investigation on time-domain simulation and experiment of harmonic rolling of ultra-large container ship in waves

When an accident due to harmonic rolling occurs, loss will be huge, especially for ultra-large container ships (ULCS). In the paper, the time-domain method is adopted to study and analyze the occurrence of non-linear harmonic rolling phenomenon of ULCS and subsequent motion behaviors. Under the weakly scattering hypothesis, six-degree-of freedom(6-DOF) time-domain ship motion equation is established by employing impulse response function. The incidental wave force and the restoring force are obtained by pressure integrating on instantaneous wet surface, while the roll damping coefficient is obtained by experiment. An ULCS navigating in regular waves of various frequencies is numerically simulated and investigated by model tests. The characteristics and mechanism of harmonic rolling of the ship with different metacenter-heights, which sails in head and following waves of different periods, are studied and analyzed. The result comparison shows that the time-domain method used in the paper can predict the occurrence and motion amplitude of the harmonic rolling very well. Although the seaworthiness of ULCS is generally better than smaller ships, there is still the possibility of triggering the problem of harmonic rolling in real sea navigation. Thus, it is necessary to study and analyze during ship design.