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

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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
11:30 5aSA10. Vibration control of optomechanical components. Vyacheslav M. Ryaboy Newport Corp., 1791 Deere Ave., Irvine, CA, 92606, vyacheslav.ryaboy@newport.com The purpose of optomechanical components is to anchor optical elements such as light sources, lenses, mirrors, etc. in space so that the optical paths would be unperturbed by environmental impacts, first of all by vibration. Dynamic alignment of components is a main design optimization criterion for the optomechanical systems. An optical table or breadboard is often used as a common base for the whole optomechanical assembly. It can be sufficiently isolated from the floor vibration, but its own flexural resonance vibrations may still cause misalignments. The paper estimates various ways of vibration damping of optical tables, including new methods of passive damping combined with motion transformation, as well as active damping. Optical rods and posts offset optical elements from the table. These components have their own resonance properties. The paper presents analytical estimates and optimization methods for introducing damping materials in the optical posts. Experimental results comparing dynamic properties of damped and non-damped structures will be presented. 11:45 5aSA11. Whole body vibration measurements on forklift trucks. Alberto Behar Noise Control, 45 Meadowcliffe Dr, Scarborough, ON, Canada, M1M 2X8 behar@sympatico.ca and Steven Libich WESA Data on acceleration values on forklift trucks related to Whole Body Vibration are notably missing in the literature. Although there are several standards that provide guidance on how measurements have to be performed, they are somehow conflicting and difficult to implement since they require simultaneous measurement and processing of data in the three axes, x, y and z. Standards also provide limit values for safety of the personnel exposed to the vibrations. The development of new instruments has made these kind of measurements much easier to perform and to interpret the results, since they include filters following the standards and allow for the use of tri-axial accelerometers. This paper describes measurements done on 11 forklift trucks in a real-life situation, while performing tasks normal for their use. The trucks are of the standing-operator type. The accelerometers were mounted on the body of the truck, so that vibrations were representative for what the operators were exposed to. The three-axes orientation of the accelerometer were taken into account. The paper will present results of the measurements and their assessment following the existing ISO and BS Standards. FRIDAY MORNING, 20 MAY 2005 REGENCY D, 8:00 A.M. TO 12:00 NOON Session 5aSC Speech Communication: Intelligibility and Studies of Populations with Speech and Hearing Disorders „Poster Session… Sigfrid D. Soli, Chair House Ear Inst., 2100 W. Third St., Los Angeles, CA 90057 Contributed Papers All posters will be on display from 8:00 a.m. to 12:00 noon. To allow contributors an opportunity to see other posters, contributors of odd-numbered papers will be at their posters from 8:00 a.m. to 10:00 a.m. and contributors of even-numbered papers will be at their posters from 10:00 a.m. to 12:00 noon. 5aSC1. Evaluation of effect of presbycusis on speech intelligibility by several kinds of speech test in rooms. Hiroshi Sato Inst. for Human Sci. & Biomed. Eng., Natl. Inst. of Adv. Industrial Sci. and Technol., 1-1-1 Higashi, Tsukuba, Japan and Hayato Sato Kobe Univ., Rokko, Nad, Kobe 657-8501, Japan Word recognition tests with logatom and word familiarity controlled word lists and sentence intelligibility test in simulated sound fields with noise and/or reverberation were carried out to assess the effect of hearing loss due to aging on speech communication in rooms. The result demonstrates that 1 speech recognition scores of elderly listeners are 25% lower than those of young adults for any kinds of speech test. This difference is equal to the 5 dB increase of ambient noise for elderly listeners. 2 Detailed speech recognition process in noise and/or reverberation is described with scores of various kinds of speech test. 3 Peripheral auditory functions are mainly affected by aging. On the other hand, central auditory processing functions of the aged examined with word familiarity and meanings of words shows same performance as the young. These results were expected to lead the discussion for speech communication in aged society and the standardization for sound environment. 5aSC2. Effect of training using lexically easy and hard words on speech understanding in noise. Matthew H. Burk and Larry E. Humes Dept. of Speech and Hearing Sci., Indiana Univ., Bloomington, IN 47405, maburk@indiana.edu Older hearing-impaired adults often have difficulty understanding speech in noise, even with proper amplification. One reason for this difficulty may be a lack of practice or inability to make use of new auditory information, which has been absent due to a progressive, peripheral hearing loss over many years. An often overlooked aspect of the rehabilitation process, which could help to improve this deficit, is listener training. The goal of this study was to create a word-based training protocol which could improve speech understanding in noise when listeners are presented with new, novel stimuli outside the clinic. Previous work with word-based training using one talker showed a large training effect that generalized to novel talkers; however, sufficient generalization to novel words and sentences was lacking. The current study attempts to increase generalization by training listeners with multiple talkers and lexically hard words. Generalization to novel words, both lexically easy and lexically hard, novel talkers, and sentences, with the latter also constructed from lexically easy 5a FRI. AM 2603 J. Acoust. Soc. Am., Vol. 117, No. 4, Pt. 2, April 2005 149th Meeting: Acoustical Society of America 2603
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