Nonlinear dynamics and stability of spread mooring with riser

The dynamics of a floating vessel with its spread mooring and riser subject ed to environmental excitation from current, wind, and waves is studied to investigate the effect of riser dynamics on the stability and bifurcation s equences of stationkeeping. A design methodology is developed to reveal the dependence of slow motion dynamics of spread mooring systems (SMS) on seve ral design parameters, such as riser location, water depth, length and fair lead of mooring lines, orientation and pretension in the mooring lines. Non linear stability and bifurcation theory are used to produce catastrophe set s in the design space defining regions of qualitatively different dynamics. Limited rime simulations are performed to verify the richness of the non-l inear system dynamics identified in the catastrophe sets. The mathematical model is based on the third-order maneuvering,equations in the horizontal p lane including hydrodynamic memory. The riser dynamics is modeled quasi-sta tically by a nonlinear three-dimensional large deformation finite element m odel. Mooring lines are modeled by deep-water catenaries with drag and touc hdown effect. External excitation consists of time-independent current, win d, and mean wave drift forces. (C) 2001 Elsevier Science Ltd. All rights re served.