浮体与系泊系统的耦合动力分析

摘要

浮体与系泊系统的耦合动力分析对各种新型海洋平台和海洋结构物的应用具有重要意义。在浮体和系泊系统的时域耦合分析中，研究并提出了一种预报浮体和系泊系统非线性运动响应和缆索张力的分析技术。考虑瞬时物面变化引起的各种非线性因素，在时域内建立浮体的非线性运动方程并求解，其中，入射波力和静恢复力按瞬时物面条件计算，辐射力和绕射力按浮体在瞬时平均湿表面为平衡位置做简谐振荡运动来计算；考虑系泊缆索受到的非线性流体动力及大位移，采用三维弹性梁理论将缆索模型化，把缆索看作是等拉伸、等弯曲刚度的细长结构，并采用非线性有限元法对缆索的运动方程进行求解；将浮体的分析方法和系泊缆索的分析方法结合，建立了浮体和系泊系统非线性运动响应和缆索张力的耦合计算方法；对缆索，使用高阶单元，只需要较少的单元就可以得到收敛解；对耦合动力分析方程，采用隐式、显式混合的数值格式，最终将方程化为显式格式进行求解，并且合理排列和控制求解次序，这样大大提高了计算效率。对系泊浮体的固有周期、各种工况下大幅非线性运动、缆索张力等进行了计算，并进行对比研究，可以看出，该文的方法既适用于缆索小变形条件下，也适用于缆索大变形条件下浮体与系泊系统的耦合动力分析。%The analysis of the coupled floating body/mooring system is very important for the applying of new type of ocean structure. In time domain analysis of the coupled floating body/mooring system, a coupled analysis technology is developed for the forecasting of nonlinear motion responses and wave loads of float-ing body and mooring system. Considering the nonlinear factors resulting from considering the changing of transient body wetted surface, the nonlinear motion equations are built and solved in time domain. The in-cident wave force and hydrostatic restoring are calculated in transient body surface condition, while the diffraction force and radiation forces are calculated on the assume that the floating body oscillates around the balance situation which is the transient body wetted surface. The applied force on the rod comes from the nonlinear hydrodynamic force from surrouding fluid, and the geometric nonlinearity is considered. A three-dimensional elastic rod theory, which is extended to include the line stretching, is chosen to model-ing the mooring lines and risers. Finite element method is used to interpret the theory in a munerical form. Combining the analysis method for floating body and that for mooring lines, the coupled calculating method of nonlinear motion responses and mooring line tension for floating body and mooring lines is made. For the mooring lines, the higher-order element is used so that the quantity of elements is reduced greatly. For dy-namic analysis of the coupled system, in order to improve the computing efficiency, the integration, which is a mixture of implicit and explicit scheme, is developed, and so that the equations without explicit scheme is obtained, and the reasonable steps of computation are adopted. For the mooring floating body, all kinds of calculations are carried out, such as the natural periods, large amplitude nonlinear motion in all kinds of sea condition, mooring line tension, and so on, and at the same time comparisons among the results show that the analysis methods in this paper are fit not only for small amplitude motion but also large amplitude motion in time domain.