Study Of Parametric Rolling Of C11 Container Ship Based On Wave Group Analysis Method In Head Wave

Ship parametric rolling(PR)is one of the five failure modes of ship stability in waves,which usually occurs when the ship is travelling in head waves or following waves.The occurrence of ship parametric rolling could cause large amplitude roll motion of ships,at the same time it would induce severe vertical ship motions,which threatens the navigation safety of ship.In this paper,the wave group analysis method is used for ship parametric rolling study,which can promote the better understanding of the mechanism of ship parametric rolling.The present work is also beneficial for predicting the dangerous waves that may cause parametric rolling when ship is sailing,and therefore reduce or avoid the occurrence of ship parametric rolling.The model test data of ship parametric rolling in random head seas performed at CSSRC is analyzed.First of all,the statistical analysis of the incident wave and ship roll motions from model test is carried out.The statistical results show that ship roll motion is significantly different under different random waves in the same sea state.Next,wave group method is used to the statistics of random waves.In the wave group analysis method,the minimum wave number in a wave group is set to 3,and the wave group threshold is set to 40% of the significant wave height.By defining the dangerous duration time of ship parametric rolling,the statistical results of roll motion time series segments and characteristic wave groups are obtained,which are used to compare the probability of occurrence and intensity of ship parametric rolling among the random input waves time series from different random seeds number.In addition,the frequency distribution statistics of the selected PR segments are carried out by summarizing and analyzing all selected duration time PR segments at each forward speed.Meanwhile the correlation between the maximum roll amplitude and its duration time,corresponding characteristic wave groups as well is studied.Finally,through model test data,eleven typical wave groups are selected from all characteristic wave group corresponding to the selected PR segments at zero forward speed.The second-order nonlinear wave making theory is used to study the wave group generation method in deep water wave basin.The effectiveness of the second order nonlinear wave making method is validated by comparison the results of the target theoretical wave group and the measured wave elevations.The model test shows that ship parametric rolling can occur only when there is a certain time duration of generated wave in front of the independent target wave group or when duration time of multiple typical wave groups is over 450 s.In the process of ship parametric rolling,the development and evolution of ship parametric rolling will be influenced by the wave in front of the characteristic wave group.The duration time of ship parametric rolling,the growth process of the PR and the maximum rolling amplitude are related to the wave in front of the characteristic wave group.