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Jan 2000

Volume 107, Issue 1, pp. 1-L6

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Plane harmonic waves in orthorhombic thermoelastic materials

J. N. Sharma, Vinod Kumar, and S. P. Sud

J. Acoust. Soc. Am. Volume 107, Issue 1, pp. 293-305 (2000); (13 pages) | Cited 1 time

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Keeping in view the increased usage of orthorhombic materials in the development of advanced engineering materials such as fibers and composites and other multilayered media, the aim of the present paper is to give a detailed account of the plane harmonic generalized thermoelastic waves in orthorhombic materials. According to the frequency equation, the four waves, a quasi-longitudinal, two quasi-transverse, and a quasi-thermal wave, can propagate in an orthorhombic crystal. When plane waves propagate along the axis of an orthorhombic solid, then only the longitudinal and thermal waves are coupled, whereas the transverse waves get decoupled from the rest of the motion. For plane waves propagating in one plane of the solid, only the SH wave in that plane remains purely transverse and gets decoupled from the rest of the motion and vice versa. The other three waves are coupled and get modified due to thermal variations and relaxation time. The particle paths and stability of the waves have been discussed and the results verified numerically. These have been represented graphically for single crystals of solid helium and cobalt material. © 2000 Acoustical Society of America.
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43.40.At Experimental and theoretical studies of vibrating systems

The influence of backward wave transmission on quantitative ultrasonic evaluation using Lamb wave propagation

T. Liu, W. Karunasena, S. Kitipornchai, and M. Veidt

J. Acoust. Soc. Am. Volume 107, Issue 1, pp. 306-314 (2000); (9 pages) | Cited 3 times

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In view of the various novel quantitative ultrasonic evaluation techniques developed using Lamb wave propagation, the influence of an important related phenomenon, backward transmission, is investigated in this paper. Using the discrete layer theory and a multiple integral transform method, the surface displacement and velocity responses of isotropic plates and cross-ply laminated composite plates due to the Lamb waves excited by parabolic- and piston-type transmitting transducers are evaluated. Analytical expressions for the surface displacement and velocity frequency response functions are developed. Based on this a large volume of calculations is carried out. Through examining the characteristics of the surface displacement and velocity frequency response functions and, especially, the different propagation modes’ contributions to them, the influence of the backward wave transmission related to quantitative ultrasonic nondestructive evaluation applications is discussed and some important conclusions are drawn. © 2000 Acoustical Society of America.
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43.40.Dx Vibrations of membranes and plates
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants

Development of an on-line diagnosis system for rotor vibration via model-based intelligent inference

Mingsian R. Bai, Ilong Hsiao, Hsuming Tsai, and Chinteng Lin

J. Acoust. Soc. Am. Volume 107, Issue 1, pp. 315-323 (2000); (9 pages) | Cited 1 time

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An on-line fault detection and isolation technique is proposed for the diagnosis of rotating machinery. The architecture of the system consists of a feature generation module and a fault inference module. Lateral vibration data are used for calculating the system features. Both continuous-time and discrete-time parameter estimation algorithms are employed for generating the features. A neural fuzzy network is exploited for intelligent inference of faults based on the extracted features. The proposed method is implemented on a digital signal processor. Experiments carried out for a rotor kit and a centrifugal fan indicate the potential of the proposed techniques in predictive maintenance. © 2000 Acoustical Society of America.
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43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission
43.40.At Experimental and theoretical studies of vibrating systems

Active control of the plate energy transmission in a semi-infinite ribbed plate

Nicole J. Kessissoglou

J. Acoust. Soc. Am. Volume 107, Issue 1, pp. 324-331 (2000); (8 pages)

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Active control of the plate flexural wave transmission through the beam in a semi-infinite beam-reinforced plate is analytically investigated. The ribbed plate is modeled as a continuous system, using equations of motion to describe the plate in flexure and the beam in both flexure and torsion. The maximum transmission of the plate flexural waves through the reinforcing beam is found to occur at resonance frequencies corresponding to the optimal coupling between the plate flexural waves and the flexural and torsional waves in the beam. A single control force is applied to the beam, and a cost function is developed to attenuate the far-field flexural energy transmission. It can be observed that the transmission peaks corresponding to the flexural resonances in the beam are reduced. Similarly, the transmission peaks corresponding to the torsional resonance conditions in the beam can be attenuated using a single control moment applied to the beam. Significant attenuation of all the resonance peaks in the flexural wave transmission can also be achieved with the application of a single force and a single moment collocated on the beam. In this paper, the feasibility of attenuating the flexural wave transmission due to both the flexural and torsional resonance conditions by using a single point force and point moment collocated on the beam is demonstrated. © 2000 Acoustical Society of America.
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43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance

Radiation modal expansion: Application to active structural acoustic control

Gary P. Gibbs, Robert L. Clark, David E. Cox, and Jeffrey S. Vipperman

J. Acoust. Soc. Am. Volume 107, Issue 1, pp. 332-339 (2000); (8 pages) | Cited 12 times

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This paper demonstrates active structural acoustic control using multiple input/output adaptive sensoriactuators combined with radiation filters and a feedback control paradigm. A new method of reduced order modeling/design of radiation filters termed radiation modal expansion (RME) is presented. For the experiments detailed in this paper, the RME technique reduced the modeling of the radiation matrix from 400 transfer functions to 6 transfer functions (multiplied by a constant transformation matrix). Experimental results demonstrate reductions of radiated sound power on the order of 5 dB over the bandwidth of 0–800 Hz. © 2000 Acoustical Society of America.
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43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance
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