Vibration mitigation of floating offshore wind turbine using tuned liquid column damper under typical limit states

To alleviate the structural responses of floating offshore wind turbines (OWTs) under stochastic marine environments, and resolve the difficulties in the design of passive vibration control devices for floating OWTs, proposing a generic and efficient optimization method for tuned liquid column damper (TLCD) mounted in floating OWT is highlighted as the key issue of the study. Thus, the simplified model with the preserved master degrees of freedom (DOFs) for a barge-type OWT with TLCD installed in the nacelle is derived using Lagrange's equations. Sequentially, the comparisons with the fully coupled numerical model in OpenFAST are carried out to identify the unknown parameters and validate the simulation accuracy of the simplified model. The exhaustive method is applied to search the feasible TLCD parameters under the designated constraints, which can minimize the free decayed motions of the tower and platform for the simplified model. Further, according to the mitigated coupled responses of the barge-type OWT in OpenFAST, the effectiveness of the optimized TLCD is evaluated. Moreover, referring to the comparisons between the optimized TLCD and TMD, the superiority of TLCD in mitigating the responses of floating OWT is proved.