Transient response reduction of floating offshore wind turbine subjected to sudden mooring line failure

Abstract

Floating offshore wind turbine (FOWT) is subjected to different dynamic loads during its lifetime. It is essential to ensure the safety of FOWT against these loads to avoid the economic losses. In the past, a majority of the studies focused on reducing the effect of dynamic loads due to wind and waves. This paper explores the application of a tuned mass damper (TMD) for reducing the transient response of FOWT during the mooring line failure. The FOWT is subjected to sudden loads when there is a mooring line breakage. The response control of FOWT during such an event is of immense importance to avoid the catastrophic failure. Although TMD is usually designed for vibration reduction in a steady state, this work focuses on transient response reduction. The investigations are carried out for a case where TMD is placed in the nacelle of FOWT. A reduced-order model is used for the TMD design. An optimum TMD is obtained by minimizing the H∞ norm of the system response when subjected to external disturbances. The designed TMD performance is assessed by carrying out a coupled nonlinear dynamic analysis using aero-hydro-servo-elastic code, OpenFAST. Three different environmental conditions corresponding to below-rated, near-rated, and near-cut-out wind speeds are considered for the analysis. The effectiveness of the TMD is assessed for the scenario of single, double, and triple mooring line failure. The performance indices, defined in terms of peak, root mean square, and standard deviation of the FOWT responses are evaluated for each of the cases. The designed TMD is found to be advantageous for reducing the transient response of FOWT during the mooring line failure. Therefore, the TMD can be effectively used for transient response reduction and enhancing the safety of FOWT in the event of accidental mooring line failure.