Hydrodynamic Modeling of a Catenary-Moored Floating Offshore Wind Turbine using the Moving Frame Method.

Abstract

Floating offshore wind turbines are seen as vital to harnessing the greater power potential of higher wind speeds offshore, in deep water. Since offshore turbines are coupled with mooring lines, an advanced model of mooring system is often required. In this project, a novel approach of mathematical modelling of mooring system is presented. It bases on Moving Frame Method, extensively utilizing Cartan's concept of Moving Frames, theory of Lie Groups, especially Special Euclidean SE(3) and Special Orthogonal SO(3) groups, combined with concise notation derived by Frankel. By means of these principles, the multi-segmented model of mooring line has been developed. Hydrodynamic loads have been extended by second order forces, in the form of sum- and difference frequency forces. Equation of motion have been obtained via Principles of Virtual Work and Hamilton's Principle. The resulting equation is then solved numerically using a fourth-order Runge-Kutta method and generalized coordinates are obtained. The overall dynamic response of FOWT is analysed in frequency domain and both wave frequency range (WF) and low frequency range (LF) are investigated. As a larger goal, this project aims to establish a strong base for utilizing MFM in more advanced analyses that can handle intricate influences. While main focus of MFM is kinetics and robotics, this study has ambiguous idea to open the doors for MFM theory to the world of mooring line systems, enhancing also the latter one. Advantages of both world should meet in one project , and therefore a new, advanced dynamics can cooperate with hydrodynamics.