应用两次展开法求解系泊柱体慢漂运动方程

Large drift motion of mooring cylinder by applying twice expansion method

在深海中系泊的海洋平台,如Spar平台,水下部分为带有系泊的圆柱结构,其水平方向运动响应往往具有较低的自振频率,容易在低频波浪力(源于非线性的差频效应)作用下发生共振响应,使结构发生大幅水平慢漂。当浮体的瞬时位置大幅偏离初始位置时,基于初始平衡位置的摄动展开法会存在较大误差。针对这一问题,采用两次展开方法,对大幅慢漂运动开展时域模拟研究。对双色波作用下自由漂浮圆柱的大幅运动响应问题进行数值分析,并与采用基于初始平衡位置的摄动展开法的计算结果进行了对比。结果表明,采用新的两次展开法可以计算出波浪遭遇频率的变化和波浪漂移阻尼,而这无法从基于初始平衡位置的常规摄动展开法中得到,体现了两次展开法在分析大幅慢漂问题上的优势。

Large drift phenomenon of Spar platform is often observed in deep sea,whose natural frequency in horizontal direction is very low because the difference frequency of the nonlinear wave is close to the natural frequency of the structure. There is a large error if the perturbation expansion based on the initial equilibrium location is adopted when the floater is far away from the initial equilibrium position. For this reason,a twice-expansion time domain method is employed in this paper to study the problem. Using this method,the motion response of a free cylinder is evaluated,and the results are compared with those by perturbation expansion method based on initial equilibrium location. The comparisons show that the twice-expansion method demonstrates the performance on calculating the change of encountering frequency between waves and structures as well as the wave drift damping,while the original method does not.This shows the advantages of the twice-expansion method in solving the large drift problem.