An experimental investigation on flow-induced motion and fluid force of a tension leg platform in complex flows

Abstract

Investigating the dynamic response of tension leg platform (TLP) in complex flows could better reduce or avoid its influence on the fatigue of mooring system and riser system. In this study, full-water-depth tendons and top-tension risers (TTRs) model were adopted, while linear springs arranged horizontally were adopted to instead of mooring system in traditional models, and different types of shear flow with uneven distribution along the water depth were set up to conduct an in-depth study of TLP response at 45° heading. Significant FIM and lock-in phenomena were found in the research, with the maximum amplitude occurring at Vr = 7. The law of response of TLP when local flow accelerates around the column or pontoon was discussed, the reasons for the increase of response outside the lock-in region was clarified and the non-linear effect of the mooring system demonstrated experimentally. To deeply understand the forces during the motion of TLP, this analysis puts forward a method to reconstruct the fluid force, which is divided into two parts: the disturbing force and the radiation force. The proposed method may provide reference for further studies of the deep mechanical rules of flow-induced motion (FIM).