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Apr 2008

Volume 123, Issue 4, pp. 1809-EL110

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slightEffect of damping on the propensity of squeal instability: An experimental investigation

Francesco Massi and Oliviero Giannini

J. Acoust. Soc. Am. Volume 123, Issue 4, pp. 2017-2023 (2008); (7 pages) | Cited 1 time

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Friction induced vibrations in automotive brakes is recognized as a major problem in industry. Squeal is a difficult subject because of its unpredictability caused by a not completely understood sensitivity to variation of the system parameters. In the literature several analytical and numerical studies deal with the relationship between damping and system propensity to have instability. These studies highlight the existence of a nonintuitive effect of damping distribution on modal coupling that gives rise to the unstable vibrations. The complexity of commercial brakes and the difficulties to identify the values of modal damping in brake assemblies lead to the necessity to rely on experimental analysis using simplified test rigs. This paper presents an experimental investigation of the relationship between the distribution of modal damping and the propensity to develop squeal in a beam-on-disk setup, which reliably reproduces squeal events with easy control and measurement of the damping of the disk and the beam, respectively. The experiments highlight the key role played by the modal damping distribution on squeal: A nonuniform repartition of the modal damping causes an increase of the squeal propensity.
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43.40.At Experimental and theoretical studies of vibrating systems
43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles
43.20.Ks Standing waves, resonance, normal modes

A model for sonar interrogation of complex bottom and surface targets in shallow-water waveguides

Thomas E. Giddings and Joseph J. Shirron

J. Acoust. Soc. Am. Volume 123, Issue 4, pp. 2024-2034 (2008); (11 pages) | Cited 1 time

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Many problems of current interest in underwater acoustics involve low-frequency broadband sonar interrogation of objects near the sea surface or sea floor of a shallow-water environment. When the target is situated near the upper or lower boundary of the water column the acoustic interactions with the target objects are complicated by interactions with the nearby free surface or fluid-sediment interface, respectively. A practical numerical method to address such situations is presented. The model provides high levels of accuracy with the flexibility to handle complex, three-dimensional targets in range-independent environments. The model is demonstrated using several bottom target scenarios, with and without locally undulating seabeds. The impact of interface and boundary interactions is considered with an eye toward using the sonar return signal as the basis for acoustic imaging or spectral classification.
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43.40.Fz Acoustic scattering by elastic structures
43.20.Tb Interaction of vibrating structures with surrounding medium
43.30.Bp Normal mode propagation of sound in water
43.20.Fn Scattering of acoustic waves
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