Abstract
Barge-type floating wind turbines with moonpools have been shown to have reasonably good seakeeping performance in the literature. Following our previous studies, the main purpose of this work is to develop a time-domain numerical analysis tool implemented with the open-source hydrodynamic code NEMOH for conducting pre-hydrodynamic analysis in frequency domain. Special attention of this study is paid to quadratic transfer function (QTF), which is calculated by NEMOH and is included in time-domain simulations. To investigate the effect of second-order wave drift force on motion responses, we considered a barge-type floating foundation prototype under the available typhoon-induced wave condition and calculated the responses in frequency and time domains. It was found that the moonpool resonances may lead to considerable difference-frequency QTFs. The numerical results including difference-frequency QTF influence showed that the barge with moonpools had large-amplitude horizontal resonant motions at low frequencies, which dominated the total responses. This result indicates that the second-order wave drift loads play an important role in surge and sway responses. Regarding heave and roll (and pitch) motions, the wave drift loading can also cause the responses at low frequencies, but these low-frequency response amplitudes are generally small and non-dominant.
