A full time-domain analysis program is developed for the coupled dynamic analysis of offshore structures. For the hydrodynamic loads, a time domain second order method is developed. In this approach, Taylor series expansions are applied to the body surface boundary condition and the free surface boundary condition, and Stokes perturbation procedure is then used to establish corresponding boundary value problems with time-independent boundaries. A higher-order boundary element method (HOBEM) is developed to calculate the velocity potential of the resulting flow field at each time stepIn the coupled dynamic analysis, the motion equation for the hull and dynamic equations for mooring-lines/risers/tendons are solved simultaneously using Newmark method. The coupled analysis program is applied for a TLP motion response simulation. Numerical results including motions, tensions at the top of the tendons are presented, and some significant conclusions are derived.
Floating platforms, such as Spar, TLP, and FPSO, have been widely used for oil and gas production in deep water. With the increase of water depth, the mass and damping of mooring lines and risers become nontrivial and the surface-platform motions can be appreciably affected by them. Therefore, it is important to include dynamic interactions between surface vessels and lines. Ma et al. (2000), Lee and Flory (1999), Lee and Devlin (2000) and Kim et al. (2001a, b) showed that the conventional uncoupled or quasi-static analysis might produce unreliable results when deepwater condition is considered.
In this case, an integrated approach is the coupled-dynamic analysis so that all the interactions among platforms, mooring lines/tendons, and risers, can be fully evaluated. Previous studies on the coupling effects between a moored structure and its mooring system in general followed the similar approach (de Kat and Dercksen (1994); Ran and Kim (1997); Ormberg and Larsen (1997); Ran et al. (1998); Ormberg et al., 1998).
