ON WAVE INTERACTION WITH FLOATING STRUCTURES WITH DRAGGED MOORINGS

摘要

This study developed an analytical solution in the frequency domain that considers the interactions among waves, floating structures, and mooring lines. The proposed solution was applied to investigate a problem involving a moored floating structure subjected to incident waves. The floating structure was considered as moving with three degrees of freedom, namely surge, heave, and roll. The mooring lines were simplified as springs, and the springs were assumed to be subjected to a Morison-type wave force. In the proposed solution, the wave field is first expressed as a problem involving a superposition of scattering and radiation waves. The wave field to be solved is expressed in terms of unknown structural motions, and wave forces acting on the floating structure and mooring springs are expressed in terms of the unknown wave fields. The solution to the coupling problem is obtained by solving the equations of motion of the floating structure with moorings. The proposed solution was simplified for evaluating cases without moorings, and its results are consistent with those of a solution in the literature. The presented solution was also used to investigate the effects of the mooring springs with added wave forces on wave fields and structural motions. The resonant amplitudes associated with the structure's motion decreased, and the peaks of resonant frequencies shifted slightly toward lower frequencies. The added mass and radiation damping coefficients versus dimensionless wave frequencies are also presented.