The performance of a tuned liquid damper equipped with inclined and oscillating damping screens

Abstract

<p>ABSTRACT</p> <p>The first application of the tuned liquid damper (TLD) to mitigate the</p> <p>dynamic vibrations of structures was only around 20 years ago and has just been</p> <p>recently applied in North America. TLDs are partially fluid filled tanks (usually</p> <p>water) with a fundamental sloshing frequency tuned close to the frequency of the</p> <p>dynamic mode of structural vibration to be suppressed. Water alone is</p> <p>insufficient to achieve the level of damping typically required for design.</p> <p>Damping devices are often submerged in the water to greatly increase the inherent</p> <p>TLD damping. The damping device investigated in this study is a thin sharpedged</p> <p>horizontal-slat screen. TLDs with such screens of a particular solidity are</p> <p>designed for one target amplitude of structural response and have limited</p> <p>efficiency over a range of structural response. To increase the efficiency, the</p> <p>concept of smart screens is introduced in this study.</p> <p>Smart screens is the name given to a damping screen that alters its fluid</p> <p>pressure-loss characteristics at differing levels of excitation, (ideally) in a passive</p> <p>state of control. Symmetric fixed-angle screens and oscillating (rotating) parallellinked</p> <p>screens are experimentally investigated inside a rectangular TLD on a</p> <p>shake-table under sinusoidal motion in this study.</p> <p>TLDs have similar principles to common tuned mass dampers (TMD) and</p> <p>are analyzed accordingly. The TLD equipped with fixed-angle screens is</p> <p>modelled with linear numerical fluid models to simulate the TLD performance for preliminary design purposes. An inclined screen alters the pressure-loss</p> <p>characteristics from its typical vertical position, which in turn changes the</p> <p>inherent TLD damping, allowing damping to be controlled by simple screen</p> <p>rotation. The analytical models, including the utilization of a pressure-loss</p> <p>coefficient for an inclined horizontal-slat screen in oscillatory flow developed in</p> <p>this study, are compared with experimental results to verify their accuracy and</p> <p>ascertain limitations.</p> <p>Oscillating smart screens are investigated mainly for their practical</p> <p>consideration in a preferred passive mode of control. The screens rotate</p> <p>automatically with changes in fluid velocity (or excitation amplitude). Their</p> <p>ability to maintain a near-constant amount of TLD damping (or resonant energy</p> <p>dissipation) is examined. Other implementations of (passive) smart screens are</p> <p>possible and suggestions for future study are recommended.</p> <p>A TLD equipped with the mathematically modelled symmetric fixed-angle</p> <p>screens is theoretically investigated in a hypothetical structure-TLD system. This</p> <p>system demonstrates the ability of a smart screen to change its damping</p> <p>characteristics-altering the angle of inclination in this study-over a range of</p> <p>structural response thereby maintaining an optimal level of efficiency over a</p> <p>range of structural response accelerations.</p>