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UBC Theses and Dissertations

Suppression of wind-induced torsional instability using partitioned nutation dampers Lim, Seng Boh


The thesis aims at the development of partitioned rectangular and toroidal dampers for suppressing wind-induced instabilities in torsion of bluff bodies like bridge-decks and bundles of transmission line conductors. To begin with, energy dissipation of the dampers as affected by the system frequency and liquid height, in the presence of partitioning, is assessed. This is followed by a qualitative flow visualization study of the surface waves to provide better appreciation of the dissipation mechanism. Finally, a set of wind tunnel tests with a square prism is undertaken to determine the effectiveness of the dampers in suppressing torsional galloping instability. Results suggest that the optimum partitioning corresponds to the compartment length to width ratio of 1.2 for the rectangular damper, while for the double toroid, it represents the diameter ratios of 1.125 and 2 for the outer and inner rings, respectively. In general, for the rectangular damper, roll motion led to a higher damping compared to the pitch degree of freedom. From flow visualization, it appeared that wave breaking as well as collision of waves promote energy dissipation. During the wind tunnel tests, both rectangular and toroidal dampers proved to be quite successful in suppressing galloping instability in torsion. The information can be used to advantage in the design of bridgedecks and high voltage transmission lines, which are often susceptible to this form of instability.

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