Thesis (M.S.)--University of Toledo, 2009. / Typescript. "Submitted as partial fulfillment of the requirements for the Master of Science Degree in Mechanical Engineering." "A thesis entitled"--at head of title. Bibliography: leaves 51-54.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xxiii, 187 p.; also includes graphics Includes bibliographical references (p. 179-187). Available online via OhioLINK's ETD Center

Thesis (Ph. D.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 112-121).

Thesis (Ph. D.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 211-243).

Thesis supervisors: Frederick Stern, Joseph Longo. Includes bibliographic references (p. 157-159).

Flat plate turbulent boundary layers disturbed by periodic moving wakes have been observed in an experimental rig mounted in a low speed wind tunnel. The wakes are produced periodically by cylinders traversing in front of the leading edge of a flat plate on which the boundary layers are measured. This is to simulate the unsteady flow pattern generated by upstream blades on the downstream blade boundary layer in an axial flow turbomachine. Both the time-averaged and ensemble-averaged data are taken from the free stream and boundary layer at different flow conditions. Free stream steady and unsteady wakes are compared and found to be similar to each other. The wake disturbance in the free stream is a function of time and distance from the cylinder. The periodic disturbance in the inner half of the boundary layer lags behind that in the free stream. This phase lag is due to the lower convection velocity near the solid surface. Similar to a steady wake, the velocity defect of an unsteady wake is higher in boundary layer than in free stream. This results in the maximum velocity defect amplitude in the inner half of the boundary layer. Phase lag and amplitude ratio profiles of the boundary layers are plotted and found to be similar to data obtained from axial flow turbomachines. Phase-averaged velocity and turbulence intensity profiles at different phase angles between two successive wakes are shown in a series of transparencies. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

With many decades of research devoted to the intriguing nature of vortex-induced vibrations, the offshore industry is constantly looking for new effective solutions in predicting VIV of slender marine structures such as riser pipes. These structures are very sensitive to excitations induced by vortex shedding, which results in vibrations that in certain combinations of waves and current develop into a structural resonance phenomenon known as lock-in. This kind of vibrations can be destructive to some structures and lead to collapse. Many of VIV aspects are far from being understood and advanced modelling is required to investigate the impact of the phenomenon, which significantly affects the service life of marine structures. The main objective of this research is to contribute to the family of semi-empirical models used for prediction of vortex-induced vibrations, with emphasis on low mass ratio elastically supported cylinders capable of moving in cross-flow and in-line directions. In this work a new two degree-of-freedom wake oscillator model has been developed, where vortex-induced lift and drag forces were modelled with two nonlinear self-excited oscillators of van der Pol type. Phenomena exclusive for two degreeof- freedom motion at low mass ratios were examined in detail. Computational fuid dynamics was applied to the problem in order to tune the model parameters. Twodimensional flow past an elastically supported cylinder was considered, and CFD simulation results were used to calibrate the wake oscillator model predictions of the complex fluid-structure interaction.

Abstract not available

Abstract not available