Investigation Into Snap Loading of Cables Used in Moored Breakwaters

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Virginia Tech


A two-dimensional, nonlinear dynamic analysis is conducted on a moored breakwater configuration to investigate snap loads in mooring lines. Breakwaters are structures used to attenuate or eliminate waves and protect shorelines, harbors, and other natural and man-made marine structures from wave damage. The breakwater in this investigation is modeled both as a point mass and as a rigid body. Both models are subjected to free undamped motions and forced undamped wave motion. Energy is dissipated through the use of a coefficient of restitution applied when a mooring line becomes taut (i.e., reaches its natural length). The mooring line is modeled as an inextensible cable with no axial or bending resistance when slack. Snap loading arises when a mooring line transitions suddenly from a slack condition to a taut condition. The analysis was conducted on a breakwater configured upside down and hanging by two mooring lines. The length of the mooring lines, coefficient of restitution, size and shape of the breakwater, initial position of the breakwater, amplitude of wave forcing, ratio of vertical to horizontal forcing, and frequency of forcing were all varied in the analysis. The results show that the rotations of the rigid body and the wave forcing have a significant role in the analysis, indicating that a rigid-body model for a moored breakwater under wave forcing is the more accurate model.



nonlinear dynamics, vibration, snap loading, breakwater, mooring lines