VORTEX-INDUCED VIBRATIONS OF STRUCTURES

Vortex-induced oscillations, often of concern when a bluff structure is exposed to fluid cross-flow, are considered herein using a semi-empirical modeling approach. Based on the fluid momentum theorem, the model involves a highly simplified abstraction of the complex flow field, and major assumptions concerning the nature of the coupling between the fluid and the oscillating structure.;The model produces a set of nonlinear, ordinary differential equations describing the coupled fluid/structure oscillations. Steady-state oscillatory solutions to these equations are found analytically and are examined for stability. Using various regression techniques, the steady-state solutions are then fit to experimental data for forced and spring-mounted cylinders. Finally, the model's predictions for elastic cables are used to postulate a qualitative picture of modal interaction, certain features of which have been observed experimentally.;Three prototype problems are studied, including harmonically forced cylinders, spring-mounted cylinders, and taut elastic cables; in each case the structure is assumed to be of circular cross-section and situated in a uniform cross-flow. Only oscillations transverse to the flow are considered. The problem of modal interaction for elastic cables, typically of interest when the fluid flow excites high-mode-number resonances, is given particular attention.