Nonlinear analysis for ship-generated waves interaction with mooring line/riser systems

A time-domain hybrid finite element-boundary element (FE-BE) method is developed to investigate nonlinear interaction between ship waves and slender structures. The ship waves are modeled in the context of the three-dimensional potential theory including ship steady state motion, and the velocity potential are computed using a higher-order boundary element method (HOBEM). A special global coordinate-based FEM rod model, when using catenary solution as an initial static profile, is employed in the accurate analysis of slender structures. The internal flow is incorporated in the numerical model by adding a new term to the effective tension formulation while both the seabed support and friction effect are performed by using a nonlinear quadratic spring and a Coulomb friction model. The numerical model is verified with the published experimental and numerical results for the ship waves generation and dynamic responses of mooring line/riser. Numerical simulations are executed to determine the dynamic behavior of two example slender structures such as multi-component mooring line and deepwater steel catenary riser under ship waves. Then the coupled analysis program is applied for a truss Spar with its mooring lines subjected to ship waves, wind-generated waves and their combined action, respectively. The dependence of the top node tensions of the slender structures on ship path, ship speed, ship distance, internal flow and seabed friction, is also examined.