Full text
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| Author(s): |
André Luís Condino Fujarra
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Escola Politécnica (EP/BC) |
| Defense date: | 2002-06-14 |
| Examining board members: |
Celso Pupo Pesce;
Antonio Carlos Fernandes;
Julio Romano Meneghini;
Mauro Costa de Oliveira
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| Advisor: | Celso Pupo Pesce |
| Abstract | |
The present thesis presents results from experimental and analytical investigations concerned with the Vortex-Induced Vibrations (VIV) phenomenon of circular cylinders in water. As fundamental purposes, the investigations have been carried out to enhance the understanding on the coupling mechanism between cross-flow and in-flow oscillations, as well as and to investigate the fluid-dynamics involved with the typical lower branch response of cylinders with low mass-damping coefficient. The importance of such matters on the offshore industry scenario, where bundle of risers are installed on floating production systems, has been exemplified and constitutes the former motivation of the present work. To achieve the first purpose, two different experimental set-ups were built: Experiment I, a flexible cantilever, driven in low turbulence water channels, at University of Michigan and Cornell University; Experiment II, a rigid cantilevered cylinder, elastically mounted on a two degree-of-freedom transducer, run in a towing tank, at São Paulo State Technological Research Institute - IPT. Through the experiments, coupled oscillations of large amplitude were clearly identified and its relation with structural asymmetry was suggested. Results of added mass varying with the flow velocity were also obtained, agreeing well with recent results found by other authors, obtained from numerical simulations and from distinct experimental set-ups. The second goal has been pursuedthrough Analytical-Experimental Studies, by re-addressing phenomenological approaches and by showing that a consistent interpretation of relevant hydrodynamic parameters, written as functions of reduced velocity, namely the added-mass, the fluid damping and the lift force, plays an essential role in improving analytical models of the Van der Pol oscillator type. Such a study led to a better prediction of the VIV phenomenon and allowed identifying the fluid-dynamics mechanism governing the resonant response at the lower branch. An additional merit of the present work is the effective collaboration with other national and international research institutions. The scientific exchange contributed to give greater consistency, reliability and considerable originality to the results. (AU) | |