As one of the efforts to harness energies from ocean, the hybrid offshore-wind and tidal-current turbines (HOTTs) have been studied for several years. In the HOTTs, the supporting structural parts including tower and foundation play an important role to secure the power generation facilities such as blades, hub and nacelle and to resist environmental loadings from wind, wave, and tidal current. The purpose of this study is to develop the structural integrity monitoring system and the damage detection method for the HOTT supporting structures through laboratory experiments. The laboratory experiments for the HOTT supporting structure have been performed using the scaled HOTT model in water flume. The dynamic characteristics
of the HOTT model are estimated by least-squared frequency domain decomposition (LS-FDD) using the measured responses, and compared with those calculated by the commercial FEA
software. The natural frequencies estimated by LS-FDD are very close to those of the FEA. To detect structural damages in the HOTT supporting structure, two different approaches are
considered, (1) coherence-based method and (2) improved autoregressive (AR) model based method. It is found that the improved AR model based method is superior to the coherencebased method and structural damage can be alarmed by the proposed improved AR model method.