The Analysis Of Parametric Rolling Of Ship And Study On Inhibition Measures

When ships navigate in waves,there will be large amplitude rolling even lead ships to capsizing.The serious phenomena is caused by wind-wave-current and other external parameters of motion.In this paper,using nonlinear theory to analyze the large amplitude rolling phenomena when ships sailing in waves based on C11 container ship.The design of U-type passive anti-roll tanks is used to suppress the parametric roll according to the large-angle parametric roll resonance.In this paper,the rolling motion of ships are mainly studied at different wave heights and encounter frequency in the longitudinal wave.According to the theory of parametric vibration,the study of ship roll motion is used to develop the roll regressive force of ship nonlinearly based on the Mathieu equation.At first,the sudy of the single-degree-of-freedom roll motion of ships is carried out.The three-degree-of-freedom(heave,roll,pitch)coupled motion of ships is studied based on the single degree of freedom.The numerical simulation of three-degree-of-freedom motion of ships are carried out,and then compared with the experimental results.The phenomenon of large amplitude rolling of ships is analyzed.In this paper,the linear theory is not applicable to calculate stability at large inclining angle of ships because of parametric rolling is large angle rolling,so the nonlinear theory is mainly used.As the ship sailing in the waves,the change of instantaneous wet surface of ships because of the relative position of the vessel and wave,which leads to the restoring force of ships has been changing constantly.In this paper,the restoring force of ships is expressed as a function of roll angle and time through the third-order taylor expansion of it.The expressions of the relevant hydrodynamic coefficients are obtained by searching for related literature.The methord of programming and software is used to solve the related hydrodynamic coefficients based on the empirical formula and the expression.It is brought into the coupled motion equations of three-degree-of-freedom when obtaining the relevant hydrodynamic coefficients.The three-degree-of-freedom motion is numerically simulated according to the coupled equations and then compared with the experimental data.For the large angle rolling phenomenon when ships are sailing in the waves,the ships are equipped with anti-roll tanks to inhibit the rolling motion of ships.A various of factors should be comprehensive considered when design the anti-roll tanks.The structure of anti-roll tank is designed according to the relevant parameters of Cll container ship and the anti-rolling efficiency of anti-roll tank is determined by comparing the amplitude of rolling which equipped with tank to amplitude of rolling which has not equipped with tank.The double-tank is designed based on the single-tank and compare the anti-rolling efficiency of double-tank with single-tank.It is found that the anti-rolling efficiency of double-tank is better than that of single-tank.In addition,double-tank has a good role in resistanting pitch motion.