The bassoon tonehole lattice: Links between the open and closed holes and the radiated sound spectrum

The bending wave generated by the actuator exciting a panel can be controlled to be in the traveling wave form void the structural resonances, which deteriorates the radiated sound if the panel is used as a speaker. Although such traveling-wave control method (TCM) yields a wider effective frequency range than the modal control method, the requirement of using many actuators is the practical problem yet. If a beam is employed instead of a plate as a panel speaker, the number of actuators can be reduced despite a smaller radiating surface than a plate. This study adopts three actuators for the beam control using TCM. An actuator excites the beam in the middle position, and the two actuators near the two edges are used to suppress the reflected waves from the boundaries. The control result shows that the driving-point mobility of the primary actuator is converted into that of an infinite beam, which means that the boundaries are changed into anechoic ones and the structural resonances are eliminated. Accordingly, the beam radiates a smooth sound spectrum without sharp peaks and troughs related to the resonant responses. Effects of material and dimension in determining the effective frequency range are also explored.

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Radiated Sound of a High-Speed Water-Jet-Propelled Transportation Vessel

The Effects of Noise on Aquatic Life II - Advances in Experimental Medicine and Biology ◽

10.1007/978-1-4939-2981-8_117 ◽

2016 ◽

pp. 951-956

Author(s):

Alexis B. Rudd ◽

Michael F. Richlen ◽

Alison K. Stimpert ◽

Whitlow W. L. Au

Keyword(s):

High Speed ◽

Water Jet ◽

Radiated Sound

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Effect of non-parallel mean flow on the Green’s function for predicting the low-frequency sound from turbulent air jets

Journal of Fluid Mechanics ◽

10.1017/jfm.2012.12 ◽

2012 ◽

Vol 695 ◽

pp. 199-234 ◽

Cited By ~ 16

Author(s):

M. E. Goldstein ◽

Adrian Sescu ◽

M. Z. Afsar

Keyword(s):

Green’S Function ◽

Green's Function ◽

Low Frequency ◽

Source Location ◽

Parallel Flow ◽

Numerical Calculations ◽

Mean Flow ◽

Frequency Sound ◽

The Mean ◽

Radiated Sound

AbstractIt is now well-known that there is an exact formula relating the far-field jet noise spectrum to the convolution product of a propagator (that accounts for the mean flow interactions) and a generalized Reynolds stress autocovariance tensor (that accounts for the turbulence fluctuations). The propagator depends only on the mean flow and an adjoint vector Green’s function for a particular form of the linearized Euler equations. Recent numerical calculations of Karabasov, Bogey & Hynes (AIAA Paper 2011-2929) for a Mach 0.9 jet show use of the true non-parallel flow Green’s function rather than the more conventional locally parallel flow result leads to a significant increase in the predicted low-frequency sound radiation at observation angles close to the downstream jet axis. But the non-parallel flow appears to have little effect on the sound radiated at $9{0}^{\ensuremath{\circ} } $ to the downstream axis. The present paper is concerned with the effects of non-parallel mean flows on the adjoint vector Green’s function. We obtain a low-frequency asymptotic solution for that function by solving a very simple second-order hyperbolic equation for a composite dependent variable (which is directly proportional to a pressure-like component of this Green’s function and roughly corresponds to the strength of a monopole source within the jet). Our numerical calculations show that this quantity remains fairly close to the corresponding parallel flow result at low Mach numbers and that, as expected, it converges to that result when an appropriately scaled frequency parameter is increased. But the convergence occurs at progressively higher frequencies as the Mach number increases and the supersonic solution never actually converges to the parallel flow result in the vicinity of a critical- layer singularity that occurs in that solution. The dominant contribution to the propagator comes from the radial derivative of a certain component of the adjoint vector Green’s function. The non-parallel flow has a large effect on this quantity, causing it (and, therefore, the radiated sound) to increase at subsonic speeds and decrease at supersonic speeds. The effects of acoustic source location can be visualized by plotting the magnitude of this quantity, as function of position. These ‘altitude plots’ (which represent the intensity of the radiated sound as a function of source location) show that while the parallel flow solutions exhibit a single peak at subsonic speeds (when the source point is centred on the initial shear layer), the non-parallel solutions exhibit a double peak structure, with the second peak occurring about two potential core lengths downstream of the nozzle. These results are qualitatively consistent with the numerical calculations reported in Karabasov et al. (2011).

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Acoustics of Sound Production and of Hearing in the Bladder Cicada Cystosoma Saundersii (Westwood)

Journal of Experimental Biology ◽

10.1242/jeb.72.1.43 ◽

1978 ◽

Vol 72 (1) ◽

pp. 43-55 ◽

Cited By ~ 1

Author(s):

N.H. FLETCHER ◽

K. G. HILL

Keyword(s):

Sound Production ◽

Abdominal Cavity ◽

Low Frequency ◽

Sound Intensity ◽

Electrical Network ◽

Directional Hearing ◽

Hearing Sensitivity ◽

Physical Mechanisms ◽

Radiated Sound ◽

Song Frequency

The male cicada of the species Cystosoma saundersii has a grossly enlarged, hollow abdomen and emits a loud calling song with a fundamental frequency of about 800 Hz. At the song frequency, its hearing is nondirectional. The female of C. saundersii lacks sound producing organs, has no enlargement of the abdomen, but possesses an abdominal air sac and has well developed directional hearing at the frequency of the species' song. Physical mechanisms are proposed that explain these observations in semi-quantitative detail using the standard method of electrical network analogues. The abdomen in the male, with its enclosed air, is found to act as a system resonant at the song frequency, thus contributing a large gain in radiated sound intensity. Coupling between this resonator and the auditory tympana accounts for the observed hearing sensitivity in the male, but destroys directionality. In the female, the abdominal cavity acts in association with the two auditory tympana as part of a phase shift network which results in appreciable directionality of hearing at the unusually low frequency of the male song.

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Numerical solution of acoustic scattering by finite perforated elastic plates

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2015.0767 ◽

2016 ◽

Vol 472 (2188) ◽

pp. 20150767 ◽

Cited By ~ 30

Author(s):

A. V. G. Cavalieri ◽

W. R. Wolf ◽

J. W. Jaworski

Keyword(s):

Boundary Conditions ◽

Acoustic Scattering ◽

Free Edge ◽

Solution Procedure ◽

Sound Level ◽

Vibration Modes ◽

Elastic Plates ◽

Beneficial Effects ◽

Plate Length ◽

Radiated Sound

We present a numerical method to compute the acoustic field scattered by finite perforated elastic plates. A boundary element method is developed to solve the Helmholtz equation subjected to boundary conditions related to the plate vibration. These boundary conditions are recast in terms of the vibration modes of the plate and its porosity, which enables a direct solution procedure. A parametric study is performed for a two-dimensional problem whereby a cantilevered perforated elastic plate scatters sound from a point quadrupole near the free edge. Both elasticity and porosity tend to diminish the scattered sound, in agreement with previous work considering semi-infinite plates. Finite elastic plates are shown to reduce acoustic scattering when excited at high Helmholtz numbers k 0 based on the plate length. However, at low k 0 , finite elastic plates produce only modest reductions or, in cases related to structural resonance, an increase to the scattered sound level relative to the rigid case. Porosity, on the other hand, is shown to be more effective in reducing the radiated sound for low k 0 . The combined beneficial effects of elasticity and porosity are shown to be effective in reducing the scattered sound for a broader range of k 0 for perforated elastic plates.

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The identification of the cylindrical defect position and size by measuring the radiated sound pressure on the plane

Acta Mechanica ◽

10.1007/s00707-017-2023-0 ◽

2017 ◽

Vol 230 (4) ◽

pp. 1337-1345

Author(s):

S. Iino ◽

S. Yahiro ◽

T. Nishikawa ◽

T. Tsuji

Keyword(s):

Sound Pressure ◽

Defect Position ◽

Radiated Sound

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The Effect of Attenuation from Fish on Passive Detection of Sound Sources in Ocean Waveguide Environments

Remote Sensing ◽

10.3390/rs13214369 ◽

2021 ◽

Vol 13 (21) ◽

pp. 4369

Author(s):

Daniel Duane ◽

Chenyang Zhu ◽

Felix Piavsky ◽

Olav Rune Godø ◽

Nicholas C. Makris

Keyword(s):

Remote Sensing ◽

Propagation Path ◽

Experimental Measurements ◽

Sound Sources ◽

Detection Range ◽

Acoustic Waveguide ◽

Passive Sensing ◽

Surface Vessels ◽

Theoretical Predictions ◽

Radiated Sound

Attenuation from fish can reduce the intensity of acoustic signals and significantly decrease detection range for long-range passive sensing of manmade vehicles, geophysical phenomena, and vocalizing marine life. The effect of attenuation from herring shoals on the Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS) of surface vessels is investigated here, where concurrent wide-area active Ocean Acoustic Waveguide Remote Sensing (OAWRS) is used to confirm that herring shoals occluding the propagation path are responsible for measured reductions in ship radiated sound and corresponding detection losses. Reductions in the intensity of ship-radiated sound are predicted using a formulation for acoustic attenuation through inhomogeneities in an ocean waveguide that has been previously shown to be consistent with experimental measurements of attenuation from fish in active OAWRS transmissions. The predictions of the waveguide attenuation formulation are in agreement with measured reductions from attenuation, where the position, size, and population density of the fish groups are characterized using OAWRS imagery as well as in situ echosounder measurements of the specific shoals occluding the propagation path. Experimental measurements of attenuation presented here confirm previous theoretical predictions that common heuristic formulations employing free space scattering assumptions can be in significant error. Waveguide scattering and propagation theory is found to be necessary for accurate predictions.

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The Influence of PZT Actuators Positioning in Active Structural Acoustic Control

Acta Polytechnica ◽

10.14311/968 ◽

2007 ◽

Vol 47 (4-5) ◽

Author(s):

P. Švec ◽

V. Jandák

Keyword(s):

Sound Field ◽

Structural Vibration ◽

Structural Acoustics ◽

The Finite Element Method ◽

Ansys Software ◽

Structural Vibrations ◽

Radiated Power ◽

Acoustic Control ◽

Radiated Sound ◽

The Mathematical Model

This paper deals with the effect of secondary actuator positioning in an active structural acoustics control (ASAC) experiment. The ASAC approach is based on minimizing the sound radiation from structures to the far field by controlling the structural vibrations. In this article a rectangular steel plate structure was assumed with one secondary actuator attached to it. As a secondary actuator, a specially designed piezoelectric stripe actuator was used. We studied the effect of the position of the actuator on the pattern and on the radiated sound field of the structural vibration, with and without active control. The total radiated power was also measured. The experimental data was confronted with the results obtained by a numerical solution of the mathematical model used. For the solution, the finite element method in the ANSYS software package was used.

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THEORY OF THIRD SOUND AND STABILITY OF THIN 3He–4He SUPERFLUID FILMS

International Journal of Modern Physics B ◽

10.1142/s021797920704349x ◽

2007 ◽

Vol 21 (13n14) ◽

pp. 2091-2102

Author(s):

M. D. MILLER ◽

E. KROTSCHECK

Keyword(s):

Numerical Density ◽

Boson Systems ◽

Hydrodynamic Description ◽

Third Sound ◽

Sound Speeds ◽

The Third ◽

Chemical Potentials ◽

Hypernetted Chain ◽

Superfluid Films ◽

Sound Spectrum

In this paper, we summarize the results of recent studies of third sound in thin, superfluid 3 He -4 He mixture films and the relation of the third sound spectrum to the question of the films' thermodynamic stability. We have considered films on several representative substrates: Nuclepore, glass, Li and Na . Our approach utilizes the variational, hypernetted chain/Euler-Lagrange (HNC–EL) theory as applied to inhomogeneous boson systems to calculate chemical potentials for both the 4 He superfluid film and the physisorbed 3 He . Numerical density derivatives of the chemical potentials lead to the sought-after third sound speeds. On all substrates, the third sound speeds show a series of oscillations as a function of film coverage that is driven by the layered structure of the 4 He film. We find that the effect on the third sound response of adding a small amount of 3 He to the 4 He film can depend sensitively on the particular 4 He film coverage. The third sound speed can either increase or decrease. In fact, in some regimes, the added 3 He destabilizes the film and can drive "layering transitions" leading to quite complicated geometric structures of the film in which the outermost layer consists of phase–separated regimes of 3 He and 4 He . Finally, we examine the range of applicability of the usual film–averaged hydrodynamic description. We find that at least up to film thicknesses of six liquid layers, there is no regime in which this hydrodynamic description is applicable.

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