三阶摄动对锚泊线动力分析的影响

The Effect of Third -Order Perturbation on the Result of the Mooring Line Dynamic Analysis

本文研究了作用在锚泊线上的水动力表达式中三阶项对锚泊线动力分析的影响。由于慢荡运动的特性，可以认为对于系泊结构物，二阶摄动已经包含运动的主要部分。但水动力的表达式对其平衡位置反对称，在表达式中只有线性项存在。为了研究水动力的非线性是否对锚泊线的动力产生影响，本文推导了三阶摄动方程，并用推导的三阶理论进行了理论研究。对计算结果的分析，可以发现三阶摄动在低频范围内对锚泊线的动力分析影响不大。

This paper investigates the effect of third-order terms of the expression of hydrodynamic force acting on the mooring line on the result of perturbation method used in the mooring line dynamic analysis. It is believed that for a moored structure second order perturbation can predict the main part of the oscillation. But the expression of hydrodynamic force acting on the mooring line is anti-symmetrical to its equilibrium position, so only linear terms of the polynomials fitted to the expression remain in the second order perturbation equations. In order to make it clear how the non-linearity of the hydrodynamic force affects the dynamics of the moorning line, the third-order perturbation equations are derived and solved. From the results obtained, we found that the third-order perturbation contributes a minor quantity in the range of low frequency.