THE PREDICTION OF WAVE-INDUCED MOTION AND MOORING FORCES FOR FLOATING OFFSHORE STRUCTURES

本文对浮式结构物在不规则波浪中的慢漂运动和系泊缆力进行了一系列的理论和实验研究。（1）在二阶势流理论的框架内，提出了一种精确模拟海洋浮式结构物慢漂运动和系缆力的方法。该方法已被应用于了解慢漂移行为的结构，如铰接柱和系泊半潜式平台。它被证实，半潜式的慢漂移运动的模拟时间历程是在相当好的协议与模型试验中的测量，如果粘性阻尼项进行适当的评估，比如通过Morison公式。(2)研制了一种用于随机强迫振动试验的专用仪器，用于测量铰接柱模型在低频运动中的水动力。在dateil中研究了柱的高频运动和入射波对水动力的影响。试验结果表明：（1）铰接柱在低频运动时的流体动力阻尼主要是由粘性效应引起的;（B）这种阻尼力受柱的高频运动和来波的强烈影响。由于测量数据数量较少，观察到其显著分散。在现阶段很难定量地预测在低频运动中作用在柱上的流体动力。这将是今后研究的问题。

A series of theoretical and experimental investigations have been conducted to predict the slow drift motion and mooring line forces for floating structures in irregular sea waves. The resluts obtained from this project are summarized as follows:(1) An exact method for simulating the slow drift motion and mooring line forces for floating offshore structures has been proposed within the framework of the second order potential flow theory. The method has been applied to understand the slow drift behaviour of such structures as an articulated column and a moored semi-submersible. It was confirmed that the simulated time histories of the slow drift motion of the semi-submersible are in fairly good agreement with the measured ones in model tests, if the viscous damping term is evaluated appropriately, say by means of the Morison formula.(2) A specific instrument for the random forced oscillation test has been manufactured to measure the hydrodynamic forces on an articulated column model in the low frequency motion. The effects of the high frequency motion of the column and the incoming waves on the hydrodynamic forces have been investigated in dateil. The conclusions arising from the test are listed in the following:a) The hydrodynamic damping of the articulated column in the low frequency motion is mainly due to viscous effects.b) Such damping forces are strongly influenced by the presence of the high frequency motion of the column as well as the incoming waves. Due to small number of the measured data their significant scatter observed. it is difficult at the present stage to predict quantitatively the hydrodynamic forces on the column in the low frequency motion. This will be a matter for future research.