EFFECT OF MOORING LINE ARRANGEMENT ON THE DYNAMICS OF SPREAD MOORING SYSTEMS

A design methodology is formulated to reveal the dependence of nonline ar slow-motion dynamics of spread mooring systems (SMS) on mooring lin e arrangement. For a given SMS configuration, catastrophe sets are dev eloped in the parametric design space showing the dependence of stabil ity boundaries and singularities of bifurcations on design variables. This approach eliminates the need for nonlinear simulations. For gener al SMS design, however, the designer relies on experience rather than scientific understanding of SMS nonlinear dynamics, due to the high nu mber of design variables. Several numerical applications are used to d emonstrate counterintuitive ways of improving SMS dynamics. The SMS de sign methodology formulated in this paper aims at providing fundamenta l understanding of the effects of mooring line arrangement and pretens ion on SMS horizontal plane dynamics. Thus, the first guidelines are d eveloped to reduce trial and error in SMS design. The methodology is i llustrated by comparing catastrophe sets for various SMS configuration s with up to three mooring lines. Numerous examples for a barge and a tanker SMS which exhibit qualitatively different nonlinear dynamic beh avior are provided.