Mooring Drag Effects in Interaction Problems of Waves and Moored Underwater Floating Structures

Abstract

In contrast to either considering structures with full degrees of freedom but with wave force on mooring lines neglected or with wave scattering and radiation neglected, in this paper, a new analytic solution is presented for wave interaction with moored structures of full degrees of freedom and with wave forces acting on mooring lines considered. The linear potential wave theory is applied to solve the wave problem. The wave fields are expressed as superposition of scattering and radiation waves. Wave forces acting on the mooring lines are calculated using the Morison equation with relative motions. A coupling formulation among water waves, underwater floating structure, and mooring lines are presented. The principle of energy conservation, as well as numerical results, are used to verify the present solution. With complete considerations of interactions among waves and moored structures, the characteristics of motions of the structure, the wave fields, and the wave forces acting on the mooring lines are investigated.

Numerical Modelling for Synthetic Fibre Mooring Lines Taking Elongation and Contraction into Account

“…M A1 nijkl has the origin in the same term in Equation ( 8) and can be loosely referred to as the added mass. This matrix is a direct consequence of the simplification based on the Taylor series expansion where the inconvenient involvement of the axial deformation ε in hydrodynamic loads is resolved (see Equations ( 21), (23), and ( 24)). More precisely, it is the second term of the Taylor series from Equation (20), i.e., −2ε, that causes M A1 nijkl to be populated with non-zero elements.…”

“…In this study, the water particle acceleration and the water particle velocity due to the incoming waves were accounted for, i.e., the inertial and drag part of the direct wave loads were included. For an underwater floating structure with moorings, the magnitudes of the wave forces acting on the mooring lines could reach up to 12% of the incident wave forces [23].…”