Coupled analysis of floater motion and mooring dynamics for a turret-moored ship

Abstract

Traditional global response analyses of moored floating structures are calculated in two separated steps: calculations of floater motions; and dynamic response analysis of moorings and risers using the top end motions estimated in the first step. Typical shortcomings in the traditional separated approach are neglection or simplification of current forces and low frequency damping contribution from moorings and risers. In a coupled analysis procedure where floater motions and mooring and riser dynamics are calculated simultaneously, these drawbacks are avoided. Motions and mooring line tensions from model tests and simulations using coupled and separated analysis procedures are compared. Illustrations are given by extensive case studies of a turret-moored ship operating in 150 m, 330 m and 2000 m water depth. The main conclusions are that the traditional separated approach may be severely inaccurate, especially for floating structures operating in deep waters. Coupled analysis should be applied for deep water concepts, at least as a check of important design cases. The agreement between model test results and results from coupled analysis is very good.