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Aeroelastic galloping of tall structures in simulated winds Sullivan, Peter P.


This thesis studies the effects of model aspect ratio on the static forces and galloping vibrations of bluff shapes when exposed to a turbulent boundary layer similar to the atmosphere. Previous investigations have analyzed the galloping oscillations of finite prismatic bodies exposed to a turbulent shear flow on the basis of the quasi-steady theory and the assumption of an average lateral force. Herein consideration is given to the variation of lateral forces with height and the galloping oscillations of two finite square towers are predicted. The turbulent boundary layer was grown over a long fetch of roughness and at the location of the static and dynamic tests was 28" deep and had properties similar to a suburban or forested full scale exposure. The geometric scale of the models found from an analysis of velocity spectra was about 1/500. For the height to width ratios examined, aspect ratio had little effect on the average static forces for small angles of attack. The local static forces, measured from the pressure distribution, had a wide variation over the height of the model. For the finite sections examined the response predicted from the local forces gave higher amplitudes for the same reduced velocity as compared, to the response found from the average forces. The results of the dynamic tests agreed with the galloping response predicted from the local sectional forces indicating that the three-dimensional effects are important in the consideration of the galloping phenomenon. The measurements of velocity spectra in the wake of the rigid 28" model indicate that the Strouhal shedding frequency varies along the span of the model. Similar velocity spectra behind the galloping 28" model did not exhibit a discernible peak at the stationary value of the Strouhal number.

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