Mechanical Engineering Department, National Research Centre Mechanical Engineering Department, National Research Centre
Thesis Title
| A Study of the Response of an Elastic Pivoted Cylinder Subjected to a Uniform Flow and the Response of the Flow Field to its Motion |
Awarding University and Year
| Illinios Institute of Technology, Chicago, USA, 1999 |
Abstract
| Vortex-induced vibrations of pivoted cylinder structures of different response parameter (Sg) subjected to uniform flow, in addition to, the response of the flow to the cylinder oscillations have been studied experimentally. The response parameter (Sg) of the structure was varied by changing its mass and natural frequency. The results of the study are of a practical importance for engineers in the design of elastic structures subjected to a flow. Also, the results could be extended to cables undergoing oscillations in a flow. The study involves measurements of the width of the lock-in range, response amplitude and displacement time series. The study shows that the width of lock-in region, as well as the amplitude of oscillation at resonance conditions depends on the Sg. In addition, regions of intermittent lock-in were identified. The current results show good agreement with the theoretical model developed by Belvins [1974] and experimental results obtained by Vickery [1964]. The pivoted cylinder oscillates with amplitudes that vary linearly along its span, so the 2-D and 3-D flow field behind the cylinder and along its span might change, which affects the hydrodynamic loading on the cylinder. The change of the vortex shedding mode behind a pivoted cylinder and at different locations along its span was investigated. Finally, the three-dimensional flow field was observed. The results of the study did not find vortex shedding cells along the span of a pivoted cylinder undergoing free oscillation with different amplitudes. The 2S and P+S modes of vortex shedding were observed in the first branch and second the branch of the synchronization curve of a pivoted cylinder with Sg=0.6. The P+S mode was observed at 10 cylinder-diameters form the free end of the pivoted cylinder when the amplitude of oscillation is 0.46 cylinder-diameter at the free end. Along the span of the cylinder, the 2S and P+S modes of vortex shedding were observed at two different locations in the second branch of the synchronization curve. The oscillation of the cylinder did not change the spanwise wavelength of the 3-D structures (streamwsie vortices); however, it organized the 3-D structure along the span. |