ABSTRACT

The paper studies damping of wind induced instabilities, using circular cylindrical nutation dampers, through a comprehensive test program having three distinct phases. To begin with, a parametric study of the damper, in conjunction with frequency response tests, is carried out using a specially designed and instrumented Scotch-Yoke type facility. It identifies important system variables contributing to significant energy dissipation. Results show that the optimum contributions of the system parameters can lead to an efficient damper, particularly if the operating conditions are conducive to wave-breaking. Next, visualization of the liquid sloshing modes, explaining the energy dissipation process at the fundamental level, is undertaken. It collaborates conclusions of the parametric study. Finally, wind tunnel tests with two- dimensional models substantiate, rather dramatically, the effectiveness of the nutation damper in arresting both vortex resonance and galloping type of instabilities. The damper continues to be effective even for the case when the structure is located in the wake of other structures, the situation frequently encountered in practice. A short video showing fluid dynamics of the damper and its effectiveness in arresting wind induced instabilites accompanies the presentation.

INTRODUCTION

The response of aerodynamically bluff bodies when exposed to a fluid stream has been a subject of considerable study for quite some time. The prevention of fluid-elastic vibrations of marine platforms, risers, towed sonars as well as ground based structures such as transmission lines, suspension bridges, tall buildings, etc. is of particular interest to engineers. Ever since the pioneering contribution by Strouhal, who correlated the periodicity of the vortex shedding with the diameter of a circular cylinder and the velocity of the fluid stream, there has been a continuous flow of important contributions resulting in a vast body of literature. This has been reviewed rather adequately by Cermak (1975) and Parkinson (1989).

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