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Nonlinear hydrodynamic forces acting on an offshore structure n waves

波浪作用在海上结构上的非线性水动力

基本信息

批准号：
07455401
负责人：
KINOSHITA Takeshi
金额：
$ 4.54万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1997
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07455401/
关键词：
wave drift force wave drift damping slow drift motion springing ringing

项目摘要

Offshore structures moored in waves often undergo slow drift motions. Because the restoring force offered by the mooring system is weak, the natural period is long enough to match up with the slowly varying nonlinear wave excitaion, which will cause resonance with large amplitude of horizontal excursion. It is critical for the design of the mooring devices to predict these drift motions precisely. It is well konown that the slow drift damping plays a key role to determine the amplitude of the drift motions when the resonamce is triggered. Previous works show that the so-colled wave drift damping makes an important contribution sometimes even dominant compared with the other components of the slow drift damping such as viscous damping and mooring damping.First of all concerning this topic, the probelm of a single circular cylinder freely oscillating in both waves and slow current was considered. Series calculations of wave drift damping were made to show the effects of cylinder draft an … More d water depth. Then the ineraction among multiple circular cylinders was considered. The comparison of calculated results with the experimental data were presented. In these works, the method of eigenfunction expansion was used to solve the boundary value problem. It has a limitation to be applied to bodies with arbitrary shapes.On the other hand, the boundary element method is also used to solve the problem of floating structures in both waves and slow current. The method is applied to a circular cylinder. Calculated results are compared with those by the semi-analytical method to validate the method. Then a series calculation are carried out on ellipsoids with various breadth and draft to examine the effects of body shape on the wave drift damping.High-frequency nonlinear wave excitation is also studied. Double frequency and triple frequency excitations in regular wave trains are computed by an eigenfunction expansion method. They may cause springing and ringing phenomena of a tension leg pratform. Less

在波浪中停泊的近海结构物通常会经历缓慢的漂移运动。由于系泊系统提供的恢复力较弱，其固有周期足够长，足以与缓慢变化的非线性波浪激励相匹配，从而引起水平漂移幅度较大的共振。准确预测这些漂移运动对系泊装置的设计至关重要。众所周知，当共振被触发时，慢漂移阻尼对决定漂移运动的幅度起着关键作用。前人的工作表明，与慢漂移的其他成分如粘性阻尼器和系泊阻尼器相比，所谓的波浪漂移阻尼器具有重要的贡献，有时甚至占主导地位。进行了波浪漂移阻尼的系列计算，以显示圆柱体吃水和…的影响更大的水深。然后考虑了多个圆柱体之间的惯性作用。给出了计算结果与实验数据的比较。在这些工作中，使用了特征函数展开的方法来求解边值问题。对于任意形状的物体，边界元方法也有其局限性。另一方面，边界元方法也被用来解决波浪和慢流中的浮体问题。将该方法应用于圆柱体的计算。计算结果与半解析法的计算结果进行了比较，验证了该方法的有效性。然后对不同宽度和吃水的椭球体进行了一系列计算，考察了船体形状对波浪漂移衰减的影响，并研究了高频非线性波浪激励。用特征函数展开法计算了规则波列中的倍频和三频激励。它们可能会导致紧张腿的弹跳和响铃现象。较少