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UBC Theses and Dissertations

Hydroelastic oscillations of square cylinders Bouclin, Denis N.


A program of research has been undertaken to examine the interaction between vortex shedding and the galloping type oscillation which square cylinders are subject to when immersed in a water stream. It is possible that the fluctuating force from the vortex shedding could quench the galloping oscillation if it acts as a forced oscillation (independent of cylinder motion). An experiment was designed where a square cylinder with one degree of freedom could oscillate transversely to the water flow. The amplitude and frequency of the cylinder oscillation were measured. By using a hot film anemometer spectra of the fluctuating velocity in the wake were taken to determine what frequencies vortex shedding occurred at. The results show that for velocities greater than the resonant velocity the galloping oscillation is dominant and the cylinder motion controls the frequencies of the wake. For velocities less than the resonant velocity no galloping occurs and the vortex shedding seems to control any cylinder motion which occurs. To explain this type of response a mathematical model has been constructed. The model is a set of two coupled self excited oscillators} one with the characteristics of the galloping oscillation and the other with the characteristics of the fluctuating lift force from the vortex shedding. Using the model some aspects of the observed interaction are explained.

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