FRIDAY MORNING, 20 MAY 2005 REGENCY E, 8:30 A.M. TO 12:00 ...

ducer placement scoring process, involving Hankel singular values
HSVs, is combined with a genetic optimization routine to find spatial
locations robust to boundary condition variation. Predicted frequency response
characteristics are examined, and optimized results are discussed in
relation to boundary condition variations. Results indicate it is possible to
minimize the impact of uncertain boundary conditions in active structural
acoustic control by optimizing the placement of transducers with respect
to uncertainties. Both analytical and experimental results will be discussed.
10:00–10:15 Break
energy sinks do not require presence of damping in the classical sense. A
set of undamped oscillators that make up an energy sink collectively absorb
the vibratory energy and retain it in their phase space. Earlier optimization
studies by the authors have shown the feasibility of vibration
absorption and retention by energy sinks if the set of oscillators have a
particular frequency distribution. Experimental results support the concept
of energy sinks. Different physical realizations of energy sinks demonstrate
the significance of frequency distributions and the ability of energy
sinks to reduce vibration amplitude of a primary structure to which they
are attached.
10:15
5aSA5. Optimal energy dissipation in a semi-active friction device.
Paulin Buaka, Philippe Micheau, and Patrice Masson GAUS, Mech.
Eng. Dept., Université de Sherbrooke, Sherbrooke, QC, Canada J1K 2R1,
Patrice.Masson@USherbrooke.ca
A semi-active device is presented for vibration control using energy
dissipation by dry friction at contact surfaces. Semi-active behavior is
provided by two piezoelectric stack actuators driven in real time to apply
a normal force on a mobile component through two friction pads. Theoretical
and experimental results show that there is an optimal constant
normal force to maximize the energy dissipated for the case of a harmonic
disturbance. In order to improve the energy dissipation by real time control
of the normal force, two nonlinear controllers are proposed: 1 the
Lyapunov method leading to a nonlinear bang-bang controller law and 2
the feedback linearization approach leading to equivalent viscous friction.
The implementation of both strategies is presented and both are experimentally
assessed using a clamped-free beam with the semi-active device
attached to the beam. It is shown that a proper choice for the parameters of
the controllers leads to an increased energy dissipation with respect to the
case where the normal force is constant. This dissipation is further increased
by adjusting a phase shift in the nonlinear feedback loop in order
to avoid a stick-slip motion of the mobile component.
10:30
5aSA6. Energy sinks: Vibration absorption by an optimal set of
undamped oscillators. Ilker Koç Mech. Eng. Dept., Carnegie Mellon
Univ., Pittsburgh, PA 15213, Antonio Carcaterra Universita Degli Studi
di Roma ‘‘La Sapienza,’’ 00184 Roma, Italy, Zhaoshun Xu, and Adnan
Akay Carnegie Mellon Univ., Pittsburgh, PA 15213
This presentation offers the concept of energy sinks as an alternative to
conventional methods of vibration absorption and damping. A prototypical
energy sink envisioned here consists of a set of oscillators attached to, or
an integral part of, a vibrating structure. The oscillators that make up an
energy sink absorb vibratory energy from a structure and retain it in their
phase-space. In principle, energy sinks do not dissipate vibratory energy as
heat in the classical sense. The absorbed energy remains in an energy sink
permanently so that the flow of energy from the primary structure appears
to it as damping. This paper demonstrates that a set of linear oscillators
can collectively absorb and retain vibratory energy with near irreversibility
when they have a particular distribution of natural frequencies. The approach
to obtain such a frequency response is based on an optimization
that minimizes the energy retained by the structure as a function of frequency
distribution of the oscillators in the set.
10:45
5aSA7. Experiments on vibration absorption using energy sinks.
Adnan Akay, Zhaoshun Xu Mech. Eng. Dept., Carnegie Mellon Univ.,
Pittsburgh, PA 15213, Antonio Carcaterra Universita Degli Studi di
Roma ‘‘La Sapienza,’’ 00184 Roma, Italy, and Ilker Koç Carnegie
Mellon Univ., Pittsburgh, PA 15213
This presentation describes experiments that demonstrate the concept
of energy sinks where a set of multiple undamped linear oscillators attached
to a vibrating structure can absorb most of its energy. In principle,
11:00
5aSA8. Experimental study on passiveÕactive hybrid isolation. Zi Jun
Zhang, Woo Suk Chang, Koon Meng Nyang, and Yew Wing Chan DSO
Natl. Labs., Singapore. No 20, Sci. Park Dr., Singapore 118230
This paper discusses the control of a high stroke low stiffness nonlinear
actuator which formed the key element of a smart engine mount
system that provides strong support for the engine while at the same time
absorbing the engine vibration energy. The actuator is made of a stacked
PZT embedded in an elliptical shaped metal frame, in the horizontal direction.
Due to the geometry of the frame, the displacement generated by
the PZT stacks is amplified up to about 5 times in the vertical direction.
However, due to the geometry of the actuator, the vertical and horizontal
motions are non-linear and excite motions at multiples of the driving frequency.
Feedback controllers cannot be used since the high frequency
motion causes spillover problem and control becomes unstable. The
filtered-X adaptive controller with sufficient high sampling rate is tested
and found to be a useful and reliable controller for the actuator for suppressing
the vibration to almost ambient noise level. This actuator requires
relatively lower driving voltage level and delivers larger stroke range. This
would be more suitable for vibration isolation application where the actuator
is serially connected with passive dampers.
11:15
5aSA9. Comparison between control strategies for active constrained
layer damping treatment to control the sound radiation from a
vibrating structure. Hui Zheng, Chun Lu, and Heow Pueh Lee Inst. of
High Performance Computing, 1 Sci. Park Rd., #01-01 The Capricorn, Sci.
Park II, Singapore 117528
A comparative study is presented of three control strategies for active
constrained layer damping ACLD treatments to control the sound radiation
from a vibrating planar structure. The first control strategy is one
commonly used in most existing studies of ACLD for structural vibration
control; i.e., the error signal to be minimized for the controller is the
vibration response sensed by point transducers, and a proportional derivative
controller is employed where the sensor signal and the voltage output
is related by real-valued feedback gains. The second control strategy is
similar to the first, except that the real-valued control gains are substituted
by complex-valued ones. In the third control strategy, the discrete structural
acoustic sensing approach is introduced for observing the sound radiation
from the structure, and the estimated sound power constitutes the
controller input. The control gains aiming to reduce the sound radiation
from a simply-supported beam are optimized respectively for the three
control strategies, and the control performances are compared. Numerical
results show that using the complex-valued control gain in the controller
design is always better than using real-valued gain. Furthermore, the
ACLD treatments adopting the third control strategy require lowest control
efforts.
2602 J. Acoust. Soc. Am., Vol. 117, No. 4, Pt. 2, April 2005 149th Meeting: Acoustical Society of America 2602