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

本研究以摄动法分析非线性波浪荷载。由于高阶问题中存在长期项，高阶非线性水动力（如三阶波浪激励和波浪漂移附加质量）不能得到，而低阶水动力（如二阶波浪激励和波浪漂移阻尼）可以得到。因此，即使我们使用纯数值方法（如有限差分法）计算完全非线性问题，我们也没有基准来进行比较以确保其精度。本研究提出了求解这些长期项问题的新的分析方法，以及验证新的分析方法的实验测量方法。第一年我们用本征函数展开法求解了波流共同作用下的垂直圆柱问题，第二年，我们将我们的方法从自由面高程推广到浮立圆柱的问题，圆柱体接触底部。第三，也是去年，我们发展了一种结合近场边界元法和远场本征函数展开法的混合方法。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。这些导数验证了新分析的解。

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.