On secular terms which appear in perturbation problems of non-linear wave forces acting on offshore structures, and solutions of the problems compared with model tests

本文采用摄动法对非线性波浪荷载进行了分析。由于高阶问题中出现的长期项，没有得到三阶波浪激励和波浪漂移附加质量等高阶非线性水动力，而可以获得二阶波浪激励和波浪漂移阻尼等较低的水动力。因此，即使我们使用纯数值方法，如有限差分法来计算完全的非线性问题，我们也没有基准可供比较以确保其精度。本研究提出了解决这些长期问题的新的分析方法和实验测量方法，以验证新的分析方法的解。第一年，我们用特征函数展开法求解了波浪和水流中的垂直圆柱体问题，并将自由面高程与Swan等人的测量数据进行了比较。第二年，我们将我们的方法推广到从圆柱接触到底部的浮动垂直圆柱问题。第三，也是去年，我们发展了一种近场边界元(BEM)和远场特征函数展开法相结合的混合方法。提出了一种利用平面运动机构(PMM)在波浪中测量机动水动力导数的方法。这些导数验证了这一新分析的解决方案。

This research analyzes nonlinear wave loads using perturbation method. Higher order nonlinear hydrodynamic forces such as third order wave excitation and wave drift added mass had not been obtained due to secular terms which appear in higher order problems, whilst lower hydrodynamic forces such as second order wave excitation and wave drift damping can be obtained. Therefore even if we calculate full nonlinear problem using pure numerical method such as a finite difference method, we have no bench marks to be compared to assure its accuracy. This research presents new analysis method of solution to these secular term problems, as well as measurement method of experiment to verify the solutions of this new analysis.First year we solved the problem of a vertical circular cylinder in both wave and current by the eigenfunction expansion method, and compared free surface elevation with the measured date by Swan et al. Second year we extended our method to the problem of floating vertical cylinder from the cylinder touching to the bottom. Third and the last year we developed a hybrid method combining near field boundary element method (BEM) and far field eigenfunction expansion method. We obtained wave drift added mass of a spheroids.We developed a measurement method to obtain maneuvering hydrodynamic force derivatives by Planar Motion Mechanism (PMM) in waves. These derivatives verify the solutions of this new analysis.