Tuned liquid dampers (TLD) are passive vibration absorbers of lightly damped structures such as airport towers, chimneys, skyscrapers, long-span bridges, overhead power lines, tall buildings, masts and offshore platforms. TLDs dissipate the structural vibration energy with the help of sloshing waves, hydraulic jumps, wave breaking and wave run-up in the tank walls. In shallow water condition, the frequency and damping of TLD are amplitude dependent; a "hardening- spring type" nonlinear behavior of water sloshing is documented in many literatures. The present study has accounted this hardening behavior in the numerical model. In this paper, the empirical relation, between the jump frequency ratio of TLD and the non-dimensional amplitude of external excitation, proposed by Yu et al (1999) is used.
TLD is a liquid tank and acts as a passive vibration control-system for lightly damped structures subjected to dynamic loads. The idea of TLD is to dissipate the structure's vibrational energy in terms of enhanced liquid motion. It is usually placed on the top of a structure and is preferred due to its easy installation, maintenance and low-cost. The main phenomenon inside the TLD is sloshing which is liquid motion in a partially filled container subjected to dynamic loads. The liquid's oscillation frequency (Tank frequency) is tuned to the natural frequency of the structure so that sloshing should occur in resonance. TLD dissipates the structure's vibrational energy in terms of sloshing waves, hydraulic jumps, wave breaking, wave- impact on the walls and wave run-up in the tank walls. Based on the relative water depth, TLD can be classified into the deep water TLD where baffles and screens are needed to enhance the damping effects; and the shallow water TLD which dissipates energy mainly due to wave-breaking, hydraulic jump and slamming. All modes of sloshing can be modeled by a set of mass- spring-dashpot systems based on the following principals (Ibrahim, Pilipchuk and Ikeda, 2001):
