Towing response and drag reduction in a semi-submersible floating offshore wind turbine platform with fairings

Abstract

To reduce the wet-towing resistance of a semi-submersible floating offshore wind turbine (FOWT) platform, this study proposes the installation of fairings on the outer columns and investigates their influence on the platform motion response during towing through numerical simulation. The drag reduction performance of a single fairing on a cylindrical column is experimentally validated through scaled towing tank tests. Four fairing arrangement schemes are then designed, from which two schemes that satisfy intact stability requirements are selected. A platform-level CFD analysis is further conducted to quantify the drag reduction in the full platform, showing that Scheme 1 (all forward) and Scheme 2 (two forward, one aft) achieve drag reductions of 5.09% and 5.95%, respectively. A numerical representation of the complete towing system, comprising the platform, tugboat, and cables, is developed within the AQWA environment. The hydrodynamic model of the unmodified platform is numerically validated against free-decay data. The study proceeds with a frequency-domain assessment of the platform’s hydrodynamic behavior, followed by time-domain simulations to evaluate its motion responses under regular wave excitation. The results show that the triangular fairing provides stable drag reduction under different towing speeds and draft conditions. The fairings predominantly alter the added mass, radiation damping, and RAO in the pitch direction, while their influence on the heave and roll motions is relatively limited. For Scheme 1, the peak pitch added mass increases by 36.7%, the peak pitch radiation damping increases by 223.8%, and the peak pitch RAO increases by 20.3% relative to the bare platform. Scheme 2 induces smaller overall perturbations to the motion response compared with Scheme 1, while also offering a slightly higher drag reduction at the platform level. The study reveals that while fairings effectively reduce towing resistance, they also significantly modify the pitch motion characteristics of the platform. In engineering applications, both drag reduction benefits and motion performance changes should be comprehensively considered, and the fairing arrangement should be selected accordingly.