HYDRODYNAMIC MEMORY EFFECT ON STABILITY, BIFURCATION, AND CHAOS OF 2-POINT MOORING SYSTEMS

The stability properties of two-point mooring systems governed by thei r stow horizontal motions are studied theoretically. The often-neglect ed memory effect due to hydrodynamic wave loads change-in some cases c ritically-the stability boundaries in the system design space. The thi rd-order maneuvering equations and a nonlinear elastic spring model ar e used to describe the dynamics of the moored vessel and the mooring l ines, respectively. The resulting model accurately represents a two-po int mooring system and can be used for stability analysis in the sense of Lyapunov. The stability charts of mooring systems with memory effe cts exhibit considerable differences from systems without memory in lo cal regions of bifurcation diagrams. Further, the pattern of these cha nges of stability boundaries varies with the hydrodynamic properties o f the moored vessel and/or the environmental conditions. The findings of this study suggest that the number of influencing design parameters can be much more than the present stability theory of dynamical syste ms can handle. They prove, however, that neglecting the memory effect may result in selecting unsafe configurations of two-point mooring sys tems.