波浪作用下缆船拖带系统非线性运动数值模拟

Numerical simulation of nonlinear dynamic movement of towed cable-ship

基于船舶操纵性运动方程和拖缆的三维动力学运动方程,提出了被拖点位置匹配的方法,建立了拖船—拖缆—被拖船系统整体非线性拖带动力学模型。为了考察被拖船航向稳定性与横向稳性的关系以及波浪载荷作用的影响,被拖船采用水平面四自由度运动方程,并引入了波浪的作用力和力矩。拖船采用PD控制方法较真实地模拟了拖船航向改变的运动过程。对一个拖船—拖缆—被拖船系统(5 000 t的拖船和3 000 t的被拖船)在时域内进行了规则波浪作用下拖带运动的模拟,计算结果表明被拖带船舶在波浪中运动呈现运动稳定、不稳定和临界状态3种可能的特性。根据模拟计算结果,认为波浪中拖带航向稳定是被拖带船舶保持稳性的必要条件。

Based on the equations governing the motion of the ship and three dimensions equations of the towed cable system, the nonlinear towing system dynamic model of the towing ship and towed ship connected with cable is established by matching both the positions of the towed point of ship and the end point of cable. For evaluating the relationship between course stability and transverse stability of the towed ship, the four degree equations of the towed ship is used in the towing system dynamic model, For the research on regular waves influence on the motions of the towed ship, the wave action force and moment on the ship is also introduced. The towing ship motion is simulated by steering rudder using control rule of PD, so the motion of towing ship under steering rudder is calculated tntly for simulation. For one towed system that includes one towing ship of 5 000 tons and one towed ship of 3 000 tons connected by towing cable, its motions are simulated by using the nonlinear towing system dynamic model established in this research. The motion characteristics of the towed ship shows three states： stable, instable and critical under regular wave simulation. From the results of the simulation, one can see that for keeping transverse stability of the towed ship, the course stability of the towed ship must be kept.