Sound Radiation From Point Acoustic Sources With Shield of Large Prolate Spheroidal Baffles

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Xiongtao Cao ◽  
Mingsheng Wang ◽  
Lei Shi
Keyword(s):  
Coordinate System ◽  
High Frequency ◽  
Sound Pressure ◽  
Sound Radiation ◽  
Acoustic Power ◽  
Far Field ◽  
Frequency Range ◽  
Prolate Spheroidal ◽  
Sound Sources ◽  
Field Sound

Sound radiation from stationary and rotating point acoustic sources with shield of rigid prolate spheroidal baffles is explored in the prolate spheroidal coordinate system. The formulae of far-field sound pressure and acoustic power are derived and acoustic power spectral density (PSD) in terms of circumferential and azimuthal wavenumber is manifested from the low frequency range to high frequency range. Acoustic wave propagation features in the spherical coordinate system as a particular case of the prolate spheroidal coordinate system are presented. Rotating sound sources cause the frequency veering phenomenon and change the patterns of PSD. Some spheroidal harmonic waves with lower and higher wavenumber for the large prolate spheroids cannot contribute to far-field sound radiation in the high frequency range when sound sources are close to the axes of the spheroids. Sound pressure directivity and acoustic power of stationary point sound sources are also analyzed with the variation of source location.

Sound Radiation From Shear Deformable Stiffened Laminated Plates With Multiple Compliant Layers

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Xiongtao Cao ◽  
Hongxing Hua
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Plate Theory ◽  
Sound Radiation ◽  
Laminated Plates ◽  
Far Field ◽  
Frequency Range ◽  
First Order ◽  
Shear Deformable ◽  
Field Sound

Sound radiation from shear deformable stiffened laminated plates with multiple compliant layers is theoretically studied. Equations of motion for the composite laminated plates are on the basis of the first-order shear deformation plate theory, and the transfer matrix method is used to describe sound transmission through compliant layers. The first and second sets of stiffeners interact with the plate through normal line forces. By using the Fourier transform and stationary phase method, the far-field sound pressure is obtained in terms of analytical expressions. Comparisons are made between the first-order shear deformation plate theory and the classical thin plate theory. Three principal conclusions are drawn in the study. (1) The transverse point force acting on the stiffeners yields lower far-field sound pressure in the middle and high frequency range. Specifically, the transverse point force exerting on the large stiffeners produces the lowest far-field sound pressure among three different reactive points at the plate, small stiffener and large stiffener. (2) The far-field sound pressure spectra are confined by an acoustic circle and remain unchanged. Lots of flexural waves in the structure cannot radiate sound into the far field. (3) The sound attenuation of stiffened plates with compliant layers is mainly caused by the sound isolation of compliant layers rather than vibrational reduction. Compliant layers can effectively reduce the radiated sound pressure in the medium and high frequency range.

scholarly journals Construction of an Omnidirectional Parametric Loudspeaker Consisting in a Spherical Distribution of Ultrasound Transducers

Sensors ◽  
2018 ◽  
Vol 18 (12) ◽  
pp. 4317 ◽  
Author(s):  
Marc Arnela ◽  
Oriol Guasch ◽  
Patricia Sánchez-Martín ◽  
Joan Camps ◽  
Rosa Alsina-Pagès ◽  
...  
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Nonlinear Propagation ◽  
Ultrasound Transducers ◽  
Frequency Range ◽  
Carrier Wave ◽  
Sound Sources ◽  
Low Frequencies ◽  
Structural Assembly ◽  
Chamber Measurements

Omnidirectional sound sources are needed to perform a large variety of tests in acoustics. Typically, they consist of conventional speaker drivers arranged in a dodecahedron. However, the directivity of the speaker drivers sharpens with frequency, which induces an intense decrease of the sound pressure levels at the edges of the dodechaedron. In this work, the problem is mitigated by building an Omnidirectional Parametric Loudspeaker (OPL), which contains hundreds of small ultrasound transducers set on a sphere. Each transducer emits an ultrasonic carrier wave modulated by an audible signal. Thanks to nonlinear propagation, the air itself demodulates the signal bringing it back to the audible range. The construction of an OPL prototype is challenging. The structure has been built by 3D-printing a set of pieces that conform to the sphere. Each piece contains the exact location of the transducers, which are aligned in parallels to facilitate the structural assembly and the wiring. The performance of the OPL has been tested in an anechoic chamber. Measurements show that the OPL has a good omnidirectional behavior for most frequencies. It clearly improves the directivity of dodechaedral sources in the high frequency range, but performs worse at low frequencies.

scholarly journals An Analytical Solution for the Vibration and Far-Field Sound Radiation Analysis of Finite, Semisubmerged Cylindrical Shells

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Wenjie Guo ◽  
Zhou Yang ◽  
Yueyang Han
Keyword(s):  
Cylindrical Shell ◽  
Free Surface ◽  
Present Method ◽  
Sound Pressure ◽  
Low Frequency ◽  
Sound Radiation ◽  
Far Field ◽  
Vibration Responses ◽  
Frequency Excitation ◽  
Field Sound

The vibration response and far-field sound radiation of a semisubmerged, finite cylindrical shell with low-frequency excitation are studied. The solution to this problem can be divided into two steps. The first step is to apply the wave propagation approach to determine the vibration response of the cylindrical shell. In the cylindrical coordinate system, the Flügge shell equations and Laplace equation are used to describe the cylindrical shell and surrounding fluid so that the vibration responses of the shell can be addressed analytically. The fluid free surface effect is taken into account by applying the sine series to force the velocity potential on the free surface to be zero. Furthermore, compared with the FEM (the finite element method), the present method is not only reliable but also effective. In the second step, the far-field sound radiation is solved by the Fourier transform technique and the stationary phase method in accordance with the vibration responses of the shell from the previous step. The boundary element method is applied to validate the reliability of the acoustical radiation calculation. The circumferential directivity of far-field sound pressure is discussed, and it is found that the maximum value of the sound pressure always appears directly under the structure when the driving frequencies are relatively low. Besides, in consideration of simplicity and less computation effort, the present method can be used for the rapid prediction of the vibration and far-field sound pressure of a semisubmerged cylindrical shell with low-frequency excitation.

Hydro-Acoustics of a Cavitating Screw Propeller; Far-Field Approximations

1981 ◽  
Vol 25 (02) ◽  
pp. 90-94
Author(s):  
L. Noordzij ◽  
J. van der Kooij
Keyword(s):  
Sound Pressure ◽  
Field Approximation ◽  
Far Field ◽  
Frequency Range ◽  
Radiated Noise ◽  
Model Scale ◽  
Screw Propeller ◽  
Field Sound

To predict the far-field radiated noise of a cavitating screw propeller, acoustic tests have to be performed on model scale. In this paper the far-field approximation of the sound pressure of the cavitating screw propeller is derived. The conditions for which the sound pressure, as obtained on model scale, can be considered to be the far-field sound pressure, and the resulting frequency range, are discussed.

The Study of Method for Calculating Geometric Average Sound Intensity in Scattering Field

2010 ◽  
Vol 458 ◽  
pp. 185-191
Author(s):  
Feng Li Luo ◽  
Guang Yu Li
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Computing Time ◽  
Sound Intensity ◽  
Frequency Range ◽  
Average Value ◽  
Geometric Average ◽  
Scattering Field ◽  
Measurement Efficiency ◽  
Frequency Area

When calculating sound intensity by indirectly measuring way, the sound pressures obtained from two microphones should be mathematically averaged as the sound pressure of measured point. The research showed that the method exists lower of allowable value in the high frequency area. Using the geometric average value of two measured points to replace the sound pressure of measured point, studying the measurement of sound intensity in scattering field, the errors from which were compared. The result showed that the error of geometric average sound intensity was more flat than that of mathematic average. So the sound intensity obtained from geometric average sound pressure is more suitable for the measurement of a wider frequency range. And the computing time is short, which can raise the measurement efficiency and the real-time of measurement.

On-axis and far-field sound radiation from resilient flat and dome-shaped radiators

2009 ◽  
Vol 125 (3) ◽  
pp. 1444-1455 ◽  
Author(s):  
Ronald M. Aarts ◽  
Augustus J. E. M. Janssen
Keyword(s):  
Sound Radiation ◽  
Far Field ◽  
Field Sound

Reconstruction of the unsteady rotating forces of fan’s blade from far-field sound pressure

2014 ◽  
Vol 86 ◽  
pp. 126-137 ◽  
Author(s):  
Hassen Trabelsi ◽  
Majdi Abid ◽  
Mohamed Taktak ◽  
Tahar Fakhfakh ◽  
Mohamed Haddar
Keyword(s):  
Sound Pressure ◽  
Far Field ◽  
Field Sound

Active Control of Low-Frequency Sound Radiation From Vibrating Panel Using Planar Sound Sources

2001 ◽  
Vol 124 (1) ◽  
pp. 2-9 ◽  
Author(s):  
Kean Chen ◽  
Gary H. Koopmann
Keyword(s):  
Active Control ◽  
Near Field ◽  
Low Frequency ◽  
Sound Radiation ◽  
Sound Field ◽  
Sound Power ◽  
Frequency Range ◽  
Sound Sources ◽  
Frequency Sound ◽  
Secondary Sources

Active control of low frequency sound radiation using planar secondary sources is theoretically investigated in this paper. The primary sound field originates from a vibrating panel and the planar sources are modeled as simply supported rectangular panels in an infinite baffle. The sound power of the primary and secondary panels are calculated using a near field approach, and then a series of formulas are derived to obtain the optimum reduction in sound power based on minimization of the total radiate sound power. Finally, active reduction for a number of secondary panel arrangements is examined and it is concluded that when the modal distribution of the secondary panel does not coincide with that of the primary panel, one secondary panel is sufficient. Otherwise four secondary panels can guarantee considerable reduction in sound power over entire frequency range of interest.

Prediction of Far-Field Sound Pressure of a Semisubmerged Cylindrical Shell With Low-Frequency Excitation

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
T. Y. Li ◽  
P. Wang ◽  
X. Zhu ◽  
J. Yang ◽  
W. B. Ye
Keyword(s):  
Cylindrical Shell ◽  
Free Surface ◽  
Sound Pressure ◽  
Acoustic Radiation ◽  
Phase Method ◽  
Far Field ◽  
Radiation Model ◽  
New Approaches ◽  
Modal Coupling ◽  
Field Sound

A sound–structure interaction model is established to study the vibroacoustic characteristics of a semisubmerged cylindrical shell using the wave propagation approach (WPA). The fluid free surface effect is taken into account by satisfying the sound pressure release condition. Then, the far-field sound pressure is predicted with shell's vibration response using the stationary phase method. Modal coupling effect arises due to the presence of the fluid free surface. New approaches are proposed to handle this problem, i.e., diagonal coupling acoustic radiation model (DCARM) and column coupling acoustic radiation model (CCARM). New approaches are proved to be able to deal with the modal coupling problem efficiently with a good accuracy at a significantly reduced computational cost. Numerical results also indicate that the sound radiation characteristics of a semisubmerged cylindrical shell are quite different from those from the shell fully submerged in fluid. But the far-field sound pressure of a semisubmerged shell fluctuates around that from the shell ideally submerged in fluid. These new approaches can also be used to study the vibroacoustic problems of cylindrical shells partially coupled with fluid.

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