Experimental studies of the unsteady hydrodynamic loads on a tension-leg platform at high Reynolds numbers

Abstract

This paper presents experimental studies on the unsteady hydrodynamic loads (forces and moments) on a Tension-Leg Platform (TLP) due to the action of a steady current at high Reynolds numbers (Re) in a high-speed cavitation water tunnel. Five current incidence angles (θ) ranging from 0° to 45° are selected for the present tests. The achieved Reynolds numbers of 9.5×104≤Re≤5.7×105 span from the subcritical to supercritical flow regimes. The experimental results show that at Re<2.2×105, the mean streamwise force coefficient C¯x increases as Re grows for 0° current incidence, while it reduces slightly for 15°, 22.5∘, 30° and 45° current incidences. At Re≥2.2×105, C¯x remains roughly unvaried with Re for each current incidence angle. The fluctuating streamwise force coefficient Cx′ drops gradually as Re increases from 9.5×104 to 2.2×105, and then they rise slightly for all the current incidences. The fluctuating transverse force coefficients (Cy′) in the supercritical regime (2.2×105<Re<5.7×105) are less than those in the subcritical regime (9×104<Re<1.5×105), which is independent of θ. The fluctuating yaw moment coefficients (CMz′) show a declining trend with the increase of Re for 0°, 15°, 22.5∘ and 30° current incidences. In the supercritical regime, the measured Cy′ and CMz′ for 22.5∘ current incidence are larger, comparing with those for the other current incidence angles. In addition, the correlations between forces and yaw moment indicate that the fluctuating transverse force is the main contribution to the fluctuating yaw moment. Furthermore, the effect of the immersed column height (H) on the forces and yaw moment is examined. It is found that, in the supercritical regime, generally Cy′ and CMz′ grow as H∕D (where D is the column diameter) increases from 1.0 to 1.57.