Research Of Ship Parametric Rolling Occurrence Interval And Amplitude Distribution

Ship parametric rolling was considered to be one of the five different stability failure modes with the development of the second generation intact stability criteria by the IMO (International Maritime Organization) due to its incidence rate and huge hazard. Taking the voyage of C11 container ship in regular waves as research subject, the numerical simulation of its parametric rolling in all heading angles has been done. Meanwhile, the numerical results of ship parametric rolling with consideration to wind loads are obtained. The contrastive analysis of the simulation results is shown for these two conditions (with or without wind loads). The analytical solutions of parametric-roll-motions (with or without wind loads) are obtained by using multiple scales method.Make sure that the roll natural frequency is half of the encounter frequency, on the premise of it, the critical areas for parametric rolling of C11 container ship are obtained through the wave frequency solution to the equation of the encounter frequency under a series of speeds and heading angles, and combined with specific relation of wave length and ship length. Choosing several combinations of sea conditions, using the AQWA-NAUT program to calculate the three degrees of freedom ship motions. All through these simulations, the instantaneous change of wet surface would be taken into account, and the nonlinear damping coefficients are used, with fixed speed and head angle. According to the simulation results, the time history of rolling angle and its amplitude-frequency spectrum are plotted, through which the characteristics of ship parametric rolling in different heading angles and speeds are summarized. The study shows that the critical areas for parametric rolling of C11 container ship are accurate to some extent. On the premise of frequency condition, with specified speed and wave amplitude, parametric rolling would occur in both longitudinal waves and oblique waves, what’s more, it might happen even in beam seas. The roll amplitude will increase when the head angle approaches to 0 degree or 180 degree. When parametric rolling occurs, roll amplitude component due to wave forced excitation is very small in oblique waves and it is almost zero in longitudinal waves. Besides, the change about wave amplitude will make the roll excitation form switch between forced excitation and parametric excitation.Researching ship parametric rolling with consideration to wind loads is the first try. Wind loads coefficients are calculated by using Fujiwara wind load derivation. When comparing the numeric results of two conditions (with or without wind loads), the effect of wind loads on ship parametric rolling can be found. The steady wind loads to the ship provides a constant bias and changes the strength of parametric excitation, which will change the ship’s resonance state.Single degree of freedom equations of ship parametric rolling with or without wind loads are established and analytically solved by using multiple scales method respectively. At last, contrastive analysis of numeric results and analytical results has been done.