Numerical Study on Vortex Induced Motion of Circular Cylinder With Low Aspect Ratio in Currents

Abstract

This paper presents the investigation results of the VIM phenomenon, discloses the characteristics of the relative motions of a floating cylinder. Floating circular platforms present a large characteristic diameter associated with a large natural period of motions in the horizontal plane. In this paper, the VIM around floating circular cylinders, m* = 1.0, with very low aspect ratio, L/D = 2, as a motivation for better understanding the VIM of Spar platforms. In order to study vortex induced motions (VIM) response of a circular cylinder, numerical computations are carried out by our in-house VIM solver vim-FOAM-SJTU. In the CFD simulations the cylinder is moored with linear springs to provide a range of reduced velocities. The fluid domain is gridded by an unstructured grid. The boundary layer is modeled with a first boundary layer y+≈2. The focus is on the effect of reduced velocity on the VIM response. Free decay tests and vortex-induced motion (VIM) tests have been built numerically. The Fourier analysis of the motions have been performed in order to explain in figure-eight-type motion trajectory.