Vortex-Induced Vibrations (VIV) are cyclic motions in flexible slender structures that are induced by the shedding of vortices mostly transverse to the length of the structural member. The authors contend that the complete three-dimensional (3D) geometric changes that evolve in the structure are too often overlooked when investigating the basic physical nature of VIV. In this paper, we use a physics-based numerical model of a cable (a specific type of slender structure) to demonstrate the following mechanics principles:

• Fluid drag (or other field loading) results in 3D geometric changes in a suspended cable.

• Those changes necessarily include a lack of structural stiffness in the cable transverse to fluid flow.

• In those instances, the structure will inevitably deflect to any kind of transverse action, particularly fluid vortices.

• The nonlinear nature of this mechanism allows VIV to occur over a range of time periods, often called “lock-in.”

Although the vortex shedding in the fluid provides the necessary repetitive inducement action, the evolving geometry of flexible slender structure appears to be the dominant factor concerning the actual nature (amplitude, pattern, etc.) of the resulting VIV behavior.

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