This paper presents lift coefficients of an oscillating cylinder based on experiments with a very dense, elastically mounted cylinder, Since the cylinder is dense, it takes many cycles to build up the response to its maximum level. The lift coefficient in phase with the cross-flow velocity of the cylinder is found by requiring that the increase in potential energy is equal to the input energy from the fluid forces minus that dissipated by the structural damping. Estimates of lift coefficients are presented and compared to other empirical data available in the literature.
The response of risers and cables due to vortex shedding contributes to fatigue damage accumulation and increases the drag forces which may lead to operational limitations. Prediction of vortex-induced vibration (V1V) may be classified in three categories: a) Amplitude response found directly as a function of the mode-shape and a non-dimensional damping parameter (reduced damping). The method may be usable when the current is constant over the whole length, and single low-mode response is likely, (e.g. free-spanning pipelines). Examples of this kind of response model are found in Griffin et. al.(1975), Iwan (1975), Blevins (1977), Sarpkaya (1978), Det Norske Veritas (DNV) (1991), and the Brown & Root lbrmula option in SHEAR7 (1996). b) Solution of the dynamic equation of motion for the system based on empirically determined fluid forces. The force coefficients are functions of different parameters: displacement amplitude and response frequencies at the given cross-section, flow velocity, Reynolds number, roughness, etc. Due to the non-linearity of the interaction between the fluid and the structure an iterative solution of some kind is required. Examples of these semi-empirical prediction programs are SHEAR7 (Vandiver, MIT), VIVA (Triantafyllou, MIT), and VIVANA (Larsen, MAR1NTEK/NTNU).
