Nonlinear Stochastic Ship Motion Stability in Different Wave Regimes A.V. BOUKHANOVSKY * , A.B. DEGTYAREV ** St.Petersburg State Marine Technical University deg@mtu-mic.spb.su CRF’96 Conference: 3-9 June 1996, St.Petersburg, Russia Abstract The ship motion stability is investigated by means of motion simulation in irregular seawaves. The method combines nonlinear simulations of the roll and heave motions that are described by system of differential equations with deterministic coefficients and stochastic simulation of external forces excitation. The stability on parametric resonance regimes is investigated. Numerous motion simulations for diverse waves regimes are performed, including wind waves, wind waves with swell systems. Influence of group wave structure on peculiarities of ship parametric excitation is investigated. Comparison of results of such simulation is fulfilled. 1 Introduction Catastrophic phenomena such as ship capsizing are often associated with loss of oscillation stability. Parametric resonance is one of the conditions that may result in loss of stability. This phenomenon emerges if we consider coupling heaving and rolling oscillations. If correlation between excitation frequency and natural frequency of rolling is related as 2:1, unstable oscillation regimes can be observed. The cause of parametric resonance appearance is reciprocity influence of heaving and rolling. So we cannot consider only one equation that describes rolling. We have to analyse the system containing at least two coupling equations that describe rolling and heaving. Professor V.V.Lugovsky proposed the following simplest mathematical model for parametric resonance phenomenon describing [1]: * Post-graduate, Mgr. ** Associate Professor, Ph.D.