Investigation of Vortex Induced Excitation Employing Nonlinear Dynamics and Chaos Theory

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This project involved an in depth investigation of the dynamics of vortex-structure interaction. The lift oscillator model concept was reviewed and expanded. In the new approach proposed in this work the parameter space in the neighborhood of the Hartlen＆Currie (HC) model was searched. Continuation analysis, equivalent to numerical unfolding, showed that the neighborhood of the HC models, contains models revealing unexpected physically meaningful dynamics. A connection between vortex excitation of rigid structures and their flexible counterparts was found. Bifurcation and continuation analysis was found to be an effective tool in the search for feasible dynamical models. Peturbation analysis of the lift oscillator in the second part of this work showed that lock-in behavior was prevalent. The 2/1 lock-in was dominant. Furthermore, an analysis of a truncated form of the Navier-Stokes equations confirmed that a planar 2D inviscid flow can exhibit 3D secondary instabilities dominated by the 2/1 component, in qualitative agreement with the perturbation analysis. Finally, the foregoing findings were tested experimentally. Flow visualization coupled with hot-film anemometry showed convincing evidence that the dominant instabilities are actually physically manifested by the fluid-structure system.