Date of Award

Spring 5-2007

Degree Type

Thesis

Degree Name

Master of Applied Science (MASc)

Department

Civil Engineering

Supervisor

Michael J. Tait

Abstract

ABSTRACT

The first application of the tuned liquid damper (TLD) to mitigate the

dynamic vibrations of structures was only around 20 years ago and has just been

recently applied in North America. TLDs are partially fluid filled tanks (usually

water) with a fundamental sloshing frequency tuned close to the frequency of the

dynamic mode of structural vibration to be suppressed. Water alone is

insufficient to achieve the level of damping typically required for design.

Damping devices are often submerged in the water to greatly increase the inherent

TLD damping. The damping device investigated in this study is a thin sharpedged

horizontal-slat screen. TLDs with such screens of a particular solidity are

designed for one target amplitude of structural response and have limited

efficiency over a range of structural response. To increase the efficiency, the

concept of smart screens is introduced in this study.

Smart screens is the name given to a damping screen that alters its fluid

pressure-loss characteristics at differing levels of excitation, (ideally) in a passive

state of control. Symmetric fixed-angle screens and oscillating (rotating) parallellinked

screens are experimentally investigated inside a rectangular TLD on a

shake-table under sinusoidal motion in this study.

TLDs have similar principles to common tuned mass dampers (TMD) and

are analyzed accordingly. The TLD equipped with fixed-angle screens is

modelled with linear numerical fluid models to simulate the TLD performance for preliminary design purposes. An inclined screen alters the pressure-loss

characteristics from its typical vertical position, which in turn changes the

inherent TLD damping, allowing damping to be controlled by simple screen

rotation. The analytical models, including the utilization of a pressure-loss

coefficient for an inclined horizontal-slat screen in oscillatory flow developed in

this study, are compared with experimental results to verify their accuracy and

ascertain limitations.

Oscillating smart screens are investigated mainly for their practical

consideration in a preferred passive mode of control. The screens rotate

automatically with changes in fluid velocity (or excitation amplitude). Their

ability to maintain a near-constant amount of TLD damping (or resonant energy

dissipation) is examined. Other implementations of (passive) smart screens are

possible and suggestions for future study are recommended.

A TLD equipped with the mathematically modelled symmetric fixed-angle

screens is theoretically investigated in a hypothetical structure-TLD system. This

system demonstrates the ability of a smart screen to change its damping

characteristics-altering the angle of inclination in this study-over a range of

structural response thereby maintaining an optimal level of efficiency over a

range of structural response accelerations.


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