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.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:752659 |
| Date | January 2018 |
| Creators | Kurishina, Victoria |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=237154 |
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