Nonlinear Dynamics Research Of The Ship Pitching And Rolling Coupled Motions

In the study of the ship's sea-keeping, the waves of the sea and the ship itself have had an effect on the ship's motions, which is led to complex six degrees of freedom swaying motions of the ship. These swaying motions and its dynamic effects will reduce the stability and safety of the vessel to a certain extent. Ship rolling and pitching motion have had the largest impact on ship's swaying motions in six degrees of freedom movement of the ship hull coordinate system. Therefore, in the study of ship motions, it is a very important work to grasp all kinds of nonlinear dynamic characteristics of ship rolling and pitching motions accurately. To study the nonlinear dynamic behaviors of ship rolling and pitching motions is one of the key issues of investigating ship's stability. For this purpose, the thesis has carried out the following works:(1) Establish the kinetic model of ship rolling and pitching coupled motionsThe article takes the ship system which is in a free mode under the horizontal constraint as research object, assumes that the ship is upright floating in the initial state and there is no speed. On this basis, the thesis adopts Euler angles in describing the swaying motions of ship. After analyzing the force condition of ship under the action of regular wave, respectively derived the expression of kinetic energy, potential energy, damping torque, wave force and disturbance torque of regular wave in ship system. Finally based on the Lagrange equation, the article set up the mathematical model of ship rolling and pitching coupled motions under the ship parameters.(2) Analyze the dynamical characteristics of vessel's rolling and pitching motion of one DOFOn the basis of the dynamical model derived from the front article, The article adopts classic runge-kutta method in the numerical calculation of the equation set. Then, the article discuss the effect of different amplitudes, initial phase-angles, wave frequencies and angel control parameters of regular wave's torque disturbance on the dynamic characteristics of ship's rolling and pitching motion of one DOF.(3) Analyze the dynamical characteristics of vessel's rolling and pitching coupled motionsThe article discuss the effect of different amplitudes, wave frequencies and angel control parameters of regular wave's torque disturbance on the dynamic characteristics of ship's rolling and pitching coupled motions through the method of numerical calculation.