2.3.4.6 TUNED LIQUID DAMPER
The basic principles involved in applying a tuned liquid damper (TLD) to
reduce the dynamic response of structures is quite similar to that
discussed above for the TMD. In effect, a secondary mass in the form of
a body of liquid is introduced into the structural system and tuned to
act as a dynamic vibration absorber. However, in the case of TLDs, the
damper response is highly nonlinear due either to liquid sloshing or the
presence of orifices. TLDs have also been used for suppressing
wind-induced vibrations of tall structures. In comparison with TMDs, the
advantages associated with TLDs include low initial cost, virtually free
of maintenance and ease of frequency tuning. The TLD applications have
taken place primarily in Japan for controlling wind-induced vibration.
Examples of TLD-controlled structures include airport towers and tall
buildings [17].
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ACTIVE PROTECTION SYSTEM
The active protection system applies counteracting control forces
externally or by creating reactive internal forces in the structure to
reduce structural response[21]. The counteracting control forces are
applied externally by actuators driven by an adequate power source. The
regulation of the control force is done according to an appropriate
algorithm. In comparison with passive control, active control of
structural response is characterized essentially in terms of the
following two features: (i) a certain amount of external power or energy
is required; and (ii) a decision-making process based on
real-time-measured data is involved. In this regard, active control
includes a wide range of technologies.
An active control system is one in which an external source powers
control actuator(s) that apply forces to the structure in a prescribed
manner. These forces can be used to both add and dissipate energy in the
structure. In an active feedback control system, the signals sent to the
control actuators are a function of the response of the system measured
with physical sensors (optical, mechanical, electrical, chemical, and so
on)