The next generation of tall structures are being designed to be lighter and more flexible making them susceptible to wind, ocean waves and earthquake type of excitations. One approach to vibration control of such systems is through energy dissipation using a liquid sloshing damper. Such dampers are already in use for vibration control of tall structures in Japan and Australia. The present parametric study focuses on enhancing the energy dissipation efficiency of a rectangular liquid damper through introduction of a two-dimensional obstacle. A parametric free vibration study, aimed at optimum size and location of the obstacle, is described first. Results suggest a significant increase in the energy dissipation, up to 60%, in presence of the obstacle. An extensive wind tunnel test-program was undertaken which substantiated effectiveness of the improved damper in suppressing both vortex resonance and galloping types of instabilities. Ability of the damper to control structural oscillations with less amount liquid is quite attractive for real-life applications.
A flexible structure could experience dynamic motion due to a variety of causes. In case of ground and ocean based structures the excitation is in the form of a single or combination of physical causes such as wind, ocean waves/currents and earthquakes. The resulting structural motion could be due to fluid-structure interaction instabilities (e.g. vortex-induced vibrations, galloping motion, flutter and turbulence-induced buffeting) or wave-induced motions (e.g. heave, surge, pitch etc.) of the structure. It should be noted that such excitations could be narrow band periodic or random in nature. In case of earthquake, the structure experiences irregular base-excitation. There are also significant differences in the spectral content of the excitation signals among these sources. For example, at frequencies below 1 Hz, the wind-induced loading dominates, whereas in the range 1 to 10 Hz, the earthquake type of loading is stronger (Kwok, 1991). The response is primarily in the first mode where most of the vibrational energy is stored.