Investigation for the effect of the column step on the flow-induced motion of a TLP

Abstract

Significant flow-induced motion (FIM) can severely threaten the security of large marine floaters, which has brought paid more and more attention in academia and engineering. It is necessary to study the effective control methods to mitigate the FIM, commonly divided into active control and passive control methods. In this study, seven different column step variations including three parameters (cross section shapes, circumferential coverage and radial thickness), are presented as passive control methods to break the coherence of the vortex structures along the columns, and FIM responses are expected to be mitigated. To investigate the suppression effect of these various column steps on the FIM behaviors of a Tension Leg Platform (TLP), experimental tests were conducted in a towing tank. Three typical incident angles, i.e., 0∘, 45∘, and 90∘-incidences were tested. The results showed that the mitigation effect of each column step on the transverse motion response varied with the type of the column step and the incident angle. The column steps produced the most significant reduction in the transverse motions at 0∘-incidence, while the reduction was the most negative at 90∘. However, the drag coefficient did not show a big difference at 0∘ and 90∘, rather than the transverse motion. In addition, only the FSAS (with the column steps of 90∘ circumferential coverage, 1/4 column diameter for radial thickness, and arc shape) exhibited positive mitigation effect at all tested current incidences for the transverse FIM response.