Experimental and numerical study of the hydrodynamic features of a cylindrical FPSO considering current-induced motion

Abstract

Hydrodynamic features of a cylindrical FPSO in the wave, current and coupled wave and current load conditions were experimentally and numerically studied in high sea states. In the wave condition, a large low frequency IL (inline, along the environmental load's direction) motion is observed which is mainly dominated by the 2nd order difference frequency wave loads but no CF (crossflow, perpendicular to the environmental load's direction) motion, and the heave motion is excited by the 1st order wave force. In the current condition, obvious motions are observed in the IL and CF directions, and the dominant frequency of the inline motion is about twice of that of the crossflow motion. Vortex-induced forces are supposed as the main reason. The motion amplitudes in the coupled load condition are larger than those in pure wave condition in 6 DOFs, especially for an obvious CF motion, and the mean offset is about the sum of those in the wave and current conditions. Numerical simulation is then conduced with the identified damping coefficients (from model test) and considering the current-induced motion. The wave motions can be correctly revealed in the numerical simulation by a modified panel model (including an additional damping). For the coupled-load condition, by a simplified time-domain VIM prediction method, the IL and CF motions can be revealed but the amplitude is a little overestimated. The experimental findings and numerical results reveal hydrodynamic features of a cylindrical FPSO, which also provide a reference for the design of it.