Vortex-induced vibrations

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Starting at a low Reynolds number of about 50, and reaching the highest Reynolds numbers recorded, bluff bodies placed within an external flow form an unstable wake that results in the formation of a regular pattern of vortices, the Karman street. If the structure is flexible or flexibly mounted, these vortices may cause vibrations, leading to stresses and fatigue damage. This motion of the body influences, in turn, the vortex formation process, establishing a feedback mechanism that may lead to stable or unstable dynamic equilibria. As a result, vortex-induced vibrations are controlled by complex physical mechanisms characterized by rich dynamic properties. When elongated, flexible structures are placed in a sheared cross-flow, the fluid-structure interaction process is distributed along their length, resulting in added complexity, as parts of the structure act to transfer energy from the flow to the structure, while other parts damp the response. Vortex-induced vibrations can be a serious concern for operations and for the structural integrity of mooring cables, towing hawsers, marine risers, and moored bluff structures, such as spar buoys. We review some of the basic properties of vortex-induced responses and the effectiveness of vortex cancellation devices.

Publication Title

Springer Handbook of Ocean Engineering