规则波中内转塔式FPSO艏摇失稳研究

Research on Yaw Instability of Turret Moored FPSO in Regular Waves

研究规则波中内转塔浮式生产储卸油平台(FPSO)的艏摇失稳现象。采用SESAM软件建立船舶水动力模型并计算水动力系数。考虑平均漂移力,建立了FPSO艏摇单自由度非线性动力学方程。应用Lyapunov稳定性定理分析平衡艏摇角随波长-船长比的叉形分岔现象,并与模型试验进行对比,结果吻合较好,验证了理论分析的正确性。分析了横摇和纵摇阻尼、内转塔位置和载况对FPSO艏摇失稳的影响。考虑一阶波浪力和平均漂移力,建立了FPSO的6自由度全耦合动力学方程并数值求解,研究艏摇失稳时FPSO的6自由度运动响应,分析艏摇初始条件的影响。计算结果表明,初始条件的细微差异会导致不同的运动响应,艏摇失稳会显著增大横摇响应幅值。

In this paper,research on yaw instability of the turret moored FPSO in regular waves is carried.A ship hydrodynamic model is established by using software SESAM and the hydrodynamic coefficients are calculated.A nonlinear dynamic equation of FPSO yaw motion with one degree of freedom is established.The pitchfork bifurcation of equilibrium yaw angle with the wave length-ship length ratio is analyzed by Lyapunov stability theorem,and fits well with the model test.Influence of the roll and pitch damping,position of the turret and load condition on the heading instability are studied.A full coupled equation considering mean drift forces and first order wave forces is established to solve the motion responses of FPSO.Influence of initial conditions of yaw on the numerical result is analyzed.The results indicate that a slight difference in initial conditions will lead to quite different motion responses.Occurrence of yaw instability will significantly increase the response amplitude of roll motion.