Numerical simulations of vortex-induced vibration on flexible cylinders

The main purpose of the research described in this paper is to investigate the hydroelastic interactions that take place between oscillating flexible cylinders and fluid forces. The cylinders are subject to currents and shear flow, and the hydrodynamic forces are estimated by a discrete vortex method. The calculations are compared with results obtained using the quasi-steady theory, as proposed by Bearman et al. (Appl. Ocean Res. 6(3) (1984) 166) and employed by Ferrari (Ph.D. Thesis, University of London, UK, 1998). In addition, the calculations are compared with experiments carried out by Fujarra (M.Sc. Thesis, Universidade de Sao Paulo, 1997) involving a cantilever flexible cylinder immersed in a current. The normalized amplitude curve obtained in the calculations is compared with the experimental results. Visualizations of the wake indicate a hybrid mode of vortex shedding along the span. Employing the terminology suggested by Williamson and Roshko (J. Fluids Struct. 2 (1988) 355), a 2S mode is found in regions of low amplitudes, changing to a 2P mode in regions of larger amplitudes. The position where transition of modes occurs varies with the reduced velocity. A practical case of a vertical marine riser is shown, and the numerical results for various current profiles are discussed. (C) 2004 Elsevier Ltd. All rights reserved.