Complex Dynamics of Slack Mooring System Under Wave and Wind Excitations

ABSTRACT

In the present study, stability analysis of a multi-point slack moored buoy is performed under the action of wave and wind forces. The effect of non-linearities due to hydrodynamic damping, geometric nonlinearity due to mooring lines, nonlinearity due to restoring force and excitation force have been considered.. The dynamic analysis is done using time domain integration scheme. The wave force has been calculated using the Eatock Taylor and Hung’s approach while the fluctuating wind force has been considered as a sinusoidally varying force the amplitude of which has been obtained in conjunction with IS:875-1987 (Part 3) Code. The approximate response of the system is determined by a two term harmonic balance method [1]. The stability analysis of the approximate solution is then performed using perturbation technique coupled with Hill’s variational equation and Floquet’s theory and the frequency ranges in which instability phenomena can occur are derived. Phase plots are obtained for finding bifurcation of solution like symmetry breaking bifurcation, period doubling bifurcation etc. Results are presented which illustrate the effects of the geometric nonlinearity of the mooring lines on the response of the buoy.