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May 1990

Volume 87, Issue S1, pp. S1-S164

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back to top Session HHH. Engineering Acoustics VIII and Structural Acoustics and Vibration VII: Underwater Damping and Vibration
Invited Papers
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New panel measurement methodologies relevant to damping material characterization (A)

Jean C. Piquette

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S146-S146 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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New techniques for evaluating measurements acquired in panel calibration tests are described. A summary of the ONION panel‐measurement method is provided. This method is based on least‐squares fitting of panel calibration data to a multiple‐layer panel model. The technique produces not only the reflection and transmission coefficients for the sample panel, but also sound speeds and losses for each individual panel layer as a function of test temperature, test pressure, and test frequency. Applications of the technique to data acquired using a normal‐incidence interrogating wave, as well as to data acquired using an offnormal incidence interrogating wave, are discussed.
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Efficient anechoic tank linings (A)

Wayne T. Reader and Robert W. Megill

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S146-S146 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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Viscoelastic polymers containing gas‐filled voids are frequently used to fabricate anechoic linings for water‐filled tanks. Shaped sheets or wedges of the polymer can be employed to provide efficient linings—efficiency being measured in terms of the degree and frequency bandwidth of the acoustical reflectivity; and in terms of cost of the installed treatment. Acoustical efficiency results by virtue of the gradual transition from the impedance of water to a highly dissipative region. Pecuniary efficiency results from minimization of the volume of polymer required to fabricate the treatment. However, neither acoustical nor pecuniary efficiency can be realized without the use of a viscoelastic polymer whose moduli and loss factor are appropriate for the frequency and temperature regions over which the tank is to operate. A geometric transition concept and a family of polymers is described that provide the versatility to design anechoic tank linings capable of providing 10 dB or more reflection loss over several decades of frequency and water temperatures ranging between freezing and boiling.
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Active underwater acoustic damping coating (A)

Vijay K. Varadan, Thomas R. Howarth, Xiaoqi Bao, and Vasundara V. Varadan

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S146-S146 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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An active control coating for the absorption of normally reflected acoustic pressure waves is presented. This polymer matrix coating encapsulates large area polyvinylidene fluoride (PVDF) plates for characterization of the impressed acoustic field and a piezocomposite actuator for the absorption of the reflected acoustic pressure. The sensing and actuating devices are connected via an external electronic network. Background analysis will describe the adopted system and component methodologies. Experimental data of the individual components and the complete system, as measured in a underwater acoustic pulse tube, will be presented.
Contributed Papers
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Measurements of the complex dynamic shear compliance and loss tangent of pilot whale blubber and the role of blubber in flow‐noise reduction (A)

James W. Fitzgerald and Edwin R. Fitzgerald

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S147-S147 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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The complex dynamic shear compliances and loss tangents of pilot whale blubber (BLB), pork‐belly fat (PBF), and beef‐belly fat (BBF) have been measured over a frequency range of ≃ 45 to 4500 Hz, using the Fitzgerald apparatus [E. R. Fitzgerald and J. D. Ferry, J. Colloid Sci. 8, 1–34 (1953)]. Representative values at 100 Hz for J∗ and tan ζ PBF, J∗  =  3 × 10−9 cm2/dyn, tan ζ = 0.5; BLB, J∗  =  2 × 10−6 cm2/dyn, tan ζ = 0.7; BBF, J∗  =  2 × 10−8 cm2/dyn, tan ζ = 0.1. Thus beef‐belly fat is ≃ 100 times stiffer (less compliant) and pork‐belly fat is ≃ 15 times less stiff (more compliant) than whale blubber. The general shape of the compliance curves are similar except for a frequency shift in the peak values. The broad peak in J∗ and tan ζ implies a relaxation mechanism in all three fats. The high loss tangent in blubber and its intermediate value of compliance suggests that it plays a role in reducing flow noise by acting as a “matched load” to the boundary layer “turbulence generator.” A polyvinyl gel, with dynamic shear properties closely matched to those of blubber, is proposed as a “synthetic blubber: for studies of turbulent flow over compliant surfaces.” [Work had fragmentary support from NUSC/NLON.]
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The damping of panels by thick layers of elastic porous media (A)

N.‐M. Shiau, T. J. Wahl, and J. S. Bolton

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S147-S147 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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In this paper a technique is presented for calculating the response of a panel to a line force input when loaded by both a finite‐depth layer of elastic porous material and a heavy fluid. Damping theories normally require that an attached damping layer be thin compared to the flexural wavelength in the base panel. Here this requirement is avoided by allowing explicitly for wave propagation within the damping layer. Specifically, the porous damping layer is modeled using a theory derived by Biot that allows for the existence of two dilatational waves and a transverse wave. Conditions required to couple the porous medium to the panel and an adjacent fluid will be discussed. A formal solution for the plate response may be obtained easily in the wavenumber domain. Although it is not possible to obtain the spatial response analytically in this instance, it will be shown that under practical circumstances the required inversion integral may be evaluated efficiently and “exactly” by using the fast fourier transform algorithm. Results will be given illustrating the damping potential of thick layers of porous materials.
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Interpenetrating network polymers as underwater damping materials (A)

Robert Y. Ting

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S147-S147 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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In recent years, new blends of crosslinking polymers have been developed to form interpenetrating network (IPN) structures that contain no covalent bonds or grafts between the networks. These IPNs can be prepared so that component polymers with good miscibility would lead to domains as small as 0.1 μm or less. Such a finely dispersed two‐phase morphology suggests that the IPNs are potentially useful for underwater damping applications. In addition to the damping characteristics of component polymers, one could also take advantage of the internal friction between the two networks as a new loss mechanism in the material. A series of IPN samples containing urethane‐epoxy networks have been designed in order to demonstrate their potential as a new class of damping materials. The samples were prepared via a simultaneous polymerization technique, and their dynamic mechanical properties were determined to show a broadband damping behavior. The effects of urethane/epoxy ratio, fillers, cure conditions, and water soaking on these properties were also studied.
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Comparison of dielectric and Young's modulus in four types of elastomers (A)

J. Burns, R. N. Capps, and P. S. Dubbelday

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S147-S147 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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Underwater Sound Reference Detachment, Naval Res. Lab., P.O. Box, 568337, Orlando, FL 32856‐8337. The complex Young's modulus is compared with the complex dielectric modulus in four different types of elastomer in the rubbery regime above the glass transition temperature. The elastomers measured included 5109G unfilled neoprene, PR1526 polyurethane, 334‐270 natural rubber, and B252 butyl rubber. Results of the comparison support the view that there is a correspondence between the two effects as predicted from thermodynamic considerations. Possible models for the coupling are discussed.
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Static and dynamic moduli measurement and temperature dependence for elastomers and composites (A)

J. Serocki, B. L. Beaton, K. Wetterskog, D. A. Brown, and S. L. Garrett

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S147-S148 (1990); (2 pages)

Online Publication Date: 13 Aug 2005

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Castable elastomers are currently being evaluated for use in fiber‐optic interferometric acoustic sensors. The sensitivity and depth tolerance of elastomer‐based hydrophones are functions of the Young's modulus (E), the shear modulus (G), and the yield strength of the material. The moduli are a function of temperature. This presentation will describe the methods used, materials tested, and results obtained to date. The dynamic moduli measurement method employs a resonant technique with electrodynamic transducers attached to a rod of circular cross section placed in a magnetic field. This method allows continuous measurement of the moduli over temperature. Here, E determined from the dynamic technique was one‐fourth to one‐half of that determined from static test methods (ASTM638). Of the 17 material samples tested to date, the most promising is a glass‐filled epoxy that has 0.35%/°C moduli changes [(1/E)(∂E/∂T) = (1/G)(∂G/∂T)] at 1500 Hz. The worst temperature‐dependent material is an unfilled polyurethane (URALITE™ 3130) with a 3.1%/°C change in shear modulus at 250 Hz and a 2.1%/°C change in Young's modulus at 30 Hz. [Work sponsored by Naval Sea Systems Command and the Naval Postgraduate School Direct Funded Research Program.]
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Shear and pressure wave transmission into and through elastomeric layers on infinite plates (A)

John C. Alberghini and Courtney B. Burroughs

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S148-S148 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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An analytic model for the transmission of shear and pressure waves into and through an elastomeric layer on an elastic infinite plate is developed. The effects of fluid viscosity on the transmission of incident pressure waves into and through the layers are assessed. The dependencies of the transmission of pressure waves through the layer into the transverse vibration response of the plate on wavenumber and frequency, and coating and plate geometric and physical properties are explored by example.
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The wavenumber‐frequency filtering characteristics of compliant layers (A)

James E. Phillips, Courtney B. Burroughs, and W. Jack Hughes

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S148-S148 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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Techniques for the measurements of the wavenumber‐frequency filtering characteristics of compliant layers mounted on an elastic structure and subject to unsteady pressures were developed. In order to measure the performance of the layer at arbitrary wavenumbers and frequencies, an array of shakers was fabricated and used to generate a standing wave pattern of the input forces where the maximum spectrum levels of the input forces could be concentrated at selected wavenumbers independent of the selected frequency. The wavenumber‐frequency admittances of a coated and uncoated beam were measured and used to determine the effectiveness of compliant layers in reducing the vibration response of the beam as a function of wavenumber and frequency. Arrays of thin‐film transducers were designed, fabricated, and used to measure the wavenumber‐frequency pressure spectra above and below compliant layers. The measured wavenumber‐frequency pressure spectra were then used to determine the wavenumber‐frequency transmission loss of compliant layers as a function of wavenumber and frequency.
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The reflective properties of compliantly coated uniform panels (A)

G. Maidanik and J. Dickey

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S148-S148 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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Cladding a panel with various layers designed to achieve radiative, reflective, and transmissive properties that are substantially different from those of the bare panel is a common noise control procedure. The achieved changes in these properties are often assessed on the basis of changes that occur in uniform panels on components that are normal to the surface of the panels. In this paper the practice of this kind of assessment is examined. In particular, a specific anomaly in the reflective property of a compliantly coated panel is presented and discussed. The relevance of the anomaly in the assessment of the reflective property at angles of incidence other than normal is also discussed.
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Comparison of a rigid and a dynamic structure absorber model (A)

Thomas L. Hoffman and Beat Marty

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S148-S148 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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Rayleigh's model for porous material is based on a rigid frame consisting of parallel tubes. In order to extend the model to consider the structure‐borne sound transmitted through the skeleton of an absorbent, a model derived by Zwikker and Kosten was used. This model introduces a dynamic structure matrix while leaving the basic concept of Rayleigh's model untouched. The theoretical results show that in the case of heavy absorbers (density > 100 kg/m3) or thick absorbers (thickness > 0.5 m) the structure takes over the main contribution of the transmission. Resonance phenomena are obtained for the case of absorbers of finite thickness. The use of absorbing material in double partition walls in theory and practice shows only a minor influence of the transmission loss caused by structure borne sound. Only if very heavy or thick layers of absorbents are used the structure‐borne sound transmitted through the frame may exceed the sound conducted by the enclosed air. For all other cases Rayleigh's model is sufficient to determine the transmission loss.
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Reduction of plate vibrations by fluid‐layer attenuators (A)

Taner Önsay and Adnan Akay

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S148-S148 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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Experimental results on the attenuation of bending vibrations of a plate by a thin layer of fluid applied at different locations of the plate surface are presented. Small stiff blocks were positioned parallel to a thin plate where a layer of air is squeezed by the transverse vibrations of the plate. Effects of layer thickness and the location of the blocks on the attenuation of plate vibrations are discussed. For fluid gaps of the order of the viscous boundary layer thickness, up to 37‐dB reduction of modal amplitudes were obtained. Highest attenuations were achieved by positioning the blocks near the antinodes of the free‐plate modes. It is shown that selective modal attenuation can be obtained by adjusting the location of the attenuators. [Work supported by NSF.]
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