深水复合锚泊线动力特性比较分析

Comparative analysis on dynamic characteristics of deepwater hybrid mooring line

为了研究复合锚泊线的动力特性,文章对完全相同的两根复合锚泊线,保持其他条件不变,用聚酯纤维系缆代替钢索,使锚泊线顶端张力-静位移特性曲线基本一致,然后采用数值模拟的方法对整根复合锚泊线的动力特性进行比较分析。比较两种复合锚泊线的自振频率、复合刚度和锚泊阻尼。建立复合锚泊线的二维非线性有限元动力分析模型,基于Del Vecchio(1992)提出的经验公式,采用迭代的方法计算复合锚泊线的刚度,比较上部平台分别发生慢漂和波频运动时刚度的变化。锚泊线和海床之间的接触作用基于刚性海床假定,基于Morrison公式计算锚泊线的惯性力和拖曳力荷载,给定上部平台运动时程后在时域范围内进行复合锚泊线的动力分析,通过计算锚泊线从平台运动中吸收的能量,得到锚泊系统的阻尼,比较上部平台分别发生慢漂和波频运动时阻尼的变化。

For study dynamic characteristics of the deepwater hybrid mooring line,considering the two hybrid mooring lines is completely identical while other conditions are kept unchanged,and the top end tension-static offset characteristic curve of the two mooring lines is consistent as much as possible,the polyester rope is as the substitute for the wire,then the method of numerical simulation is adopted to carry on the comparative analysis on dynamic characteristic.And the natural frequency,complex stiffness and mooring-induced damping are compared.After the establishment of two-dimensional nonlinear finite element dynamic model of the hybrid mooring line,the calculation on stiffness of the hybrid mooring line is accomplished through the iterative method based on the empirical formula proposed by Del Vecchio in 1992.When the wave drift motion and wave frequency oscillations of the floating platform are specified,the consequent variations of stiffness are compared respectively.The mooring line and seabed interaction are based on the hypothesis of rigid seabed.The fluid drag force and inertia force on the mooring line are calculated according to the Morrison formula.The dynamic analysis is executed through time-domain nonlinear finite element method accounting for the oscillations of the moored floating platform.The energy absorbed from the oscillation of the floating platform in the mooring line is worked out,and then the mooring-induced damping is achieved.Finally,the wave drift motion and wave frequency oscillations of the floating platform are specified,the consequent variations of the mooring-induced damping are compared.