The effects of slowly-varying wave drift forces on the nonlinear dynamics of mooring systems have been studied extensively in the past 30 years. It has been concluded that slowly-varying wave drift may resonate with mooring system natural frequencies. In recent work, we have shown that this resonance phenomenon is only one of several possible nonlinear dynamic responses of mooring systems to slowly-varying wave drift excitation. We were able to reveal new phenomena based on the design methodology developed at the University of Michigan for autonomous mooring systems and treating slowly-varying drift as an external time-varying force. In this paper, the U of M methodology is used systematically to reveal seven phenomena induced by mean and slowly-varying drift forces; one of those is resonance. Conceptually, numerous qualitatively different behaviors may be induced. The next step towards comprehensive identification of such phenomena is taken by introducing the method of harmonic balance to study nonautonomous mooring systems.
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