Cylindrical floating production storage offloading (CFPSO) is an alternative for oil filed development drawn many attentions recently due to its low construction and transportation cost, especially for the mid-water-depth. However, for its circular water plane, the hydrodynamic features of a CFPSO are quite different from the conventional offshore ship-type floating structures, especially in the coupled wave and current load condition. A scaling model test has been conducted with regular, bichromatic waves and current to study this phenomenon. It is observed that the out-plane motions (including heave and roll/pitch) amplitude in the coupled load condition is a little larger than those observed from the pure wave cases. A quasi-lock-in phenomenon and nonnegligible mean displacement in heave is observed in the coupled load case, and vortex-induced force is supposed as the reason for the phenomenon. Moreover, large frequency components, far away from the eigenfrequency cannot be neglected in the coupled load case (bichromatic) compared with that in the pure wave case. Findings in this paper provide a basic reference for the initial strength and fatigue design of the CFPSO considering coupled wave and current effects.
For the high-cost efficiency requirement of the oil field exploitation, the cylindrical floating production storage and offloading (CFPSO) unit had drawn more attentions in recent years for its low construction cost. Similar as the conventional ship-type FPSO, this new concept is normally moored in the open sea, as shown in Fig. 1. It sometimes works in a strong coupled load condition (combined wave and current), especially in South China sea. Previous scholars normally focused on the mooring system of the CFPSO, and the difference frequency wave loads, since the natural frequency of the surge or sway are well within the content in the spectra of the slowing vary wave loads (Afriana, 2011; Vidic-Perunovic et al., 2017; Wang et al., 2016). They studied in-plane motions (such as surge and sway) of the structure in different sea state and loading conditions.
