A numerical study of the motion and structural responses of interlinked spars in irregular waves

Abstract

A numerical analysis has been made of the motion characteristics and structural responses of interlinked spars of three different arrays in irregular waves. The goal of the study is to clarify the behavior of the interlinked structure as a new type of platform for offshore wind turbines and to establish its design criteria. The numerical model used herein includes the connectors and taut/catenary mooring lines, but aerodynamics and rotor-dynamics are not considered. Both the connectors and the mooring lines are modeled by elastic beams. The minimum energy principle and Lagrange multiplier method are applied to formulate the governing equation for the dynamics of the connectors and mooring lines. Numerical solutions are obtained by using an in-house finite element method (FEM) code. Meanwhile, hydrodynamic coefficients are calculated by using an in-house code based on the nine-node higher-order boundary element method. The performances of three different arrays of the interlinked spars are evaluated and compared in terms of the motion of the structure and the tensile force and bending moment of the connectors. It is found that the three arrays considered in this work show motion behavior and structural responses similar to those of a single spar. Therefore, the arrayed structures can be considered positively as a new type of offshore wind farm, because the construction cost for mooring lines, power cables, and installation can be largely reduced, and the hydrodynamic and elastic behavior is favorable. ？ 2014. The International Society of Offshore and Polar Engineers.