Dynamic analysis of the coupled floating body/mooring system

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 floating 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 incident 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 modeling 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 dynamic 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.