published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Onshore and offshore structures are subject of strict safety regulations, and acceptable design implies requirements for accurate models of potentially dangerous phenomena. The phenomenon of Vortex-Induced Vibrations (VIVs) develops when a slender structure interacts with a fluid flow. Vortices grow in the disturbed boundary layer and spread behind the structure, resulting in fluctuations of the fluid forces acting on the body. Slender structures are present almost everywhere in the form of tall buildings and skyscrapers, cranes, antennas, power lines, suspension bridges, umbilicals, risers and free spans of pipelines which deliver water, oil and gas. The deeper in the water and higher in the sky these structures are, more likely they can experience VIVs and the lock-in state due to the exposure to various flow profiles. The wake oscillator method allows to model fluid variables during VIV lock-in using self-excited and self-limited oscillators of Van der Pol or Rayleigh type. In this research, the capabilities of alternative nonlinear oscillators as fluid equations are considered for modelling elastically supported rigid structures with one and two degrees-of-freedom in uniform flow. For modelling two-dimensional flexible structures in uniform and sheared flows, new wake oscillator models are developed in this work and applied with alternative damping terms. The dynamics of the uniform flow model of flexible structure is investigated in detail with the focus on coexisting solutions of the displacement amplitudes. Empirical coefficients for wake oscillator models are calibrated in this study using constrained nonlinear minimization and experimental data available in the literature. The validation performed confirms the most successful results for the suite of models of 2DOF rigid structure for low mass ratio, where agreement with both in-line and cross-flow displacement records was obtained.

No description available.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 223-230). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--Worcester Polytechnic Institute. / Keywords: fluid-structure interaction; low dimensional models; coupled map lattices; vortex shedding; cylinder wake patterns; flow control; multi-variable least squares algorithm; neural networks; adaptive estimation. Includes bibliographical references (p. 147-149).

No description available.

Thesis (Ph. D.)--University of Adelaide, Dept. of Applied Mathematics, 1987. / Includes bibliographical references (leaves 70-72).

Thesis (Ph. D.)--University of New South Wales, 2000. / Also available online.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 70-86). Also available via the Internet.