Research On Parametric Rolling Motion Of A Ship Based On Variable Damping Coefficient

Under the action of parameter excitation,the ship is likely to produce a large angle roll,which leads to a sea accident.Through the study of the cases in recent years,it is found that the container ship is more prone to the phenomenon of parameter rolling.Aiming at the research of ship parameter roll,it will provide some guidance for ship design and optimization,so as to provide guarantee for normal operation and safety of life and property at sea.In this paper,based on computational fluid dynamics,we simulate the ro ll motion of C11 container ship at different amplitudes,periods and speeds by simulating the forced roll motion of three dimensional hull.Comparing the calculated rolling damping coefficient with the simplified Ikeda method,the difference degree between the two methods is analyzed,and the cause of the damping coefficient variation is analyzed from the perspective of vortices field.Then,based on the CFD method,the roll damping coefficient of the first item plus the three item is solved.By using the stochastic nonlinear dynamic method,the steady-state probability density function of ship's single degree of freedom motion under random sea waves under different sea conditions is calculated,and the influence of damping on rolling response is discussed.Finally,change the existing form of the bilge keel,compared with the initial C11 hull structure and bare hull structure,analysis of the bilge keel in roll damping in the contribution degree.Research shows that the roll damping coefficients with rolling motion frequency,amplitude,and speed increases,the empirical formula and CFD calculat ion results in different conditions of the same trend,but the empirical formula is safe;the motion cycle is small,the larger the amplitude,the higher the speed is,the bilge keel around the vortices field numerical value is greater,the obtained under the condition of roll damping is bigger.Considering the roll damping with speed,the probability of large angle rolling is reduced obviously,and the influence of damping coefficient on rolling response gradually decreases as the sea condition becomes more dangerous.When the speed increases to a certain level,the influence of speed effect tends to a constant value.Intermittent bilge keel structure is improved in this paper,under different working conditions are calculated the probability of rolling angle greater than 10° and the original structure are small.Considering the comprehensive factors such as structural strength and economy,the structure can be applied in practice.Compared to shorten the bilge keel and bare hull structure,proved that the t wo kinds of structure with the original hull roll suppression ability is far.The more dangerous in the sea,the bilge keel structure roll characteristic difference is small.