Earthquake Engineering Research - HKU Libraries - The University ...

234
The purpose of the robust compensator (psat(ar)) is to reduce the undesirable so-called chattering
phenomenon. Continuity of the control force between the upper bound and the lower bound of sliding
surface reduces chattering.
3 EXPERIMENTAL RESULTS OF ACTIVE VIBRATION SUPPRESSION
3.1 Experimental Setup
The control objective is to show the effectiveness of various vibration suppression strategies for a 3-floor
model building by using smart sensors and actuators. The setup is shown in Figure 1. Two pairs of larger
PZT patches are surface-bonded both support beams near their base ends. These PZT patches are used as
actuators to excite the building and to enable active control of the model building vibration. There are also
four smaller PZT patches surface-bonded on one the support beam of
the model building. These four PZT patches act as sensors for the
feedback of the signal in the active control algorithms. The sensor
signal from the bottom floor (near the actuator pair) of the model
building is used for feedback control. The sampling frequency for real
time control was set to Ik Hz.
Fig. 1 Experimental setup
In the research, various vibration control algorithm are used to control
vibration of the model building. The modal parameters of the first two
modes have been determined by experiment before control design and
implementation. The fundamental frequency and the corresponding
damping ratio were found experimentally to be 7.81Hz and 0.0081
respectively. The second natural frequency is 24.0Hz. In each test, the
system is excited by a combination of a sinusoidal signal at the first
modal frequency and a white noise for the initial 5 seconds. Various
control methods are then applied to control the induced vibration. The
uncontrolled response of model building is shown Figure 2.
3.2 PPF Experimental Results
The positive position feedback control was implemented using the experimental set up described in the
previous section. The first mode vibration control is investigated first. Different values of gains were
tested. The PPF controller-damping ratio q c was set to 0.4 and controller frequency co c was set at 49
rad/sec (7.8Hz). The controller-damping ratio q c was chosen as a compromise between damping
effectiveness and robustness.
Figure 3 shows the corresponding PPF controlled vibrations of the model building. The PPF
controlled vibrations of the model building damp out within 5 seconds after excitation. The PSD plot
for 5-15 seconds is shown in Figure 4(a). A drop of 51dB as compared to the uncontrolled energy level is
observed during this period of active control. The corresponding damping ratio was calculated and found
to be 0.0499, as compared with the free vibration damping ratio of 0.0081. This represents an increase of
516%. A number of tests were conducted with variation in the PPF gain while keeping c, c at 0.4 and co c at
49 rad/sec. The results are shown in table 1, which shows that maximum damping is achieved at the gain
of 15.
PPF control is then extended to control several modes simultaneously. If the first two modes are under
control, the modal selectivity is also achieved by tuning the compensator frequency co c on the targeted