Coupled dynamic analysis of FOWT (floating offshore wind turbine) with partially broken blade
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Increasing numbers of FOWT (floating offshore wind turbines) are planned in the coming years due to their high potential in massive generation of clean energy from ocean-wind. In the present study, a numerical prediction tool has been used for the fully coupled dynamic analysis of an offshore floating wind turbine system in time domain including aero-loading, blade-rotor dynamics and control, tower elasticity, mooring dynamics, and platform motions so that the influence of partially broken blade on the system's global performance can be assessed. A mono-column tension leg platform (TLP) type FOWT with 5MW turbine is selected as an example. The blades are 62.6m-long LM fiberglass blades, which are properly modified by NREL. The time-domain analysis is carried out with a sudden break of a tip portion of blade in the middle of simulation, and the dynamic responses of FOWT including transient effects are observed. Through this study, it is seen that the imbalance of rotor due to partially broken blade may induce appreciable loads on the entire wind turbine system, including blades, tower, floater, and tethers, especially in highfrequency range. In particular, due to the rotational imbalance with damage, the 1P, 2P, and 3P excitations and responses are more pronounced in the tower and blade dynamics compared to the intact case. The developed technology and numerical tool are readily applicable to the design of new FOWTs regardless of floater types and environments. The present approach can directly be applied to the development of remote structural health monitoring system for future FOWTs in detecting partial component failure by measuring tower or platform responses. Copyright 2013 by the International Society of Offshore and Polar Engineers (ISOPE).