Theory Of Acoustic Radiation Research Articles

Vibration and acoustic radiation of bogie area under random excitation in high-speed trains

Based on the experiments on a platform with real vehicle structure and finite element simulation, the vibration and interior acoustic radiation under random excitations of high-speed trains’ bogie area were studied. Firstly, combined with line tests, a vehicle body with a length of 7 m was used as the research object. By comparing the results of experiment and simulation, the accuracy of the finite element model was verified. Secondly, the power spectral density curves at typical measuring points in bogie area were obtained by processing and calculating the line test data, which was measured when the vehicle ran at high speeds, and the standard vibration spectrum of the bogie area was obtained by the extreme envelope method. Furthermore, the random vibration test and simulation prediction analysis of the real vehicle structure were carried out to further verify the accuracy of the noise and vibration prediction model. Finally, according to the vibration and acoustic radiation theory, the indirect boundary element method was adopted to predict the acoustic response of the real vehicle. The analysis shows that the simulated power spectral density curves of acceleration and sound pressure level are highly consistent with the experimental ones, and the error between the simulated prediction and the experimental result is within the allowable range of 3 dB.

Reception pattern influence on magnetoacoustic tomography with magnetic induction**Project supported by the National Basic Research Program of China (Grant No. 2011CB707900), the National Natural Science Foundation of China (Grant Nos 11274176 and 11474166), and the Priority Academic Program Development of Jiangsu Higher Education Institutions, China.

Based on the acoustic radiation theory of a dipole source, the influence of the transducer reception pattern is studied for magnetoacoustic tomography with magnetic induction (MAT-MI). Numerical studies are conducted to simulate acoustic pressures, waveforms, and reconstructed images with unidirectional, omnidirectional, and strong directional transducers. With the analyses of equivalent and projection sources, the influences of the model dimension and the layer effect are qualitatively analyzed to evaluate the performance of MAT-MI. Three-dimensional simulation studies show that the strong directional transducer with a large radius can reduce the influences of equivalent sources, projection sources, and the layer effect effectively, resulting in enhanced pressure and improved image contrast, which is beneficial for boundary pressure extraction in conductivity reconstruction. The reconstructed conductivity contrast images present the conductivity boundaries as stripes with different contrasts and polarities, representing the values and directions of the conductivity changes of the scanned layer. The favorable results provide solid evidence for transducer selection and suggest potential practical applications of MAT-MI in biomedical imaging.

Suspending force modeling based on nonlinear acoustics and high-speed running experiments for an ultrasonic journal bearing

As a kind of promising noncontact bearings, ultrasonic bearings actuated by smart materials such as lead zirconate titanate ceramics show a good application prospect in high-speed machines and precision-measuring devices. The suspending force is one of the most important parameters that play a dominated role on the bearing’s static and dynamic performance. A suspending force model based on acoustic radiation theory for cylindrical object near sound source is built to predict the radial carrying capacity of an ultrasonic bearing actuated by three piezoelectric transducers. To validate the model, an ultrasonic bearing prototype is developed and a testing system is established. For observing the bearing’s dynamic running performance at high speeds, the bearing’s running experiment is carried out and the rotor center’s trajectory data and frequency spectrum are acquired to analyze the bearing’s dynamic characteristics at high speeds. The suspending force model and running performance experiments will contribute to the design, detection, and test of this type of bearings.

Miguel Junger: Legacy contributions to the field of structural acoustics

The field of structural acoustics, i.e., the theory of acoustic radiation and scattering from elastic structures, developed primarily in the last half of the 20th century in response to Navy needs. Miguel Junger and colleagues at Cambridge Acoustical Associates under the sponsorship of the Office of Naval Research Sound and Structures made seminal contributions to the field. This presentation reviews some of this research, which ultimately was included in the book, “Sound, Structures and Their Interaction.”

The Optimization of the Design of a Railway Wheel in Terms of the Acoustic Radiation under the Vertical Excitation

Railway wheel acoustic radiation takes a large proportion of the wheel-rail noise . This paper mainly focuses the ways to reduce railway wheel acoustic radiation to control wheel-rail acoustic radiation, and ultimately to reduce the railway environmental noise. In this paper, Optimization mathematical model of wheel acoustic radiation is built according to the wheel vibration and acoustic radiation theory, and obtaining the section optimization and acoustic radiation power of wheel by drawing up the genetic algorithm (GA) program and analyzing the acoustic radiation of the wheel according to Finite element and boundary element model. The result shows that the optimized acoustic power is reduced to some extent, even by 2dB at the peak point within 5000Hz. Since high-speed railways are put into operation in China, it has been more convenient for people to go out. However, serious railway environmental noise occurs by the way. The noise produced when the train is running affects not only passengers and working staff on the train, but also environment and residents around the railway. For this reason, to reduce the noise with proper measures is good for environment protection, sustained and healthy development of rail transportation as well. According to wheel-rail noise theory, the main approaches to reduce noise as follows:(1) Adopt damped wheel. (2) Add rubber isolation layer between tread and web of the wheel to form resilient wheel. (3) Optimize the wheel shape. (4) Reduce acoustic radiation efficiency of the wheel. This paper discusses how to reduce acoustic radiation of the wheel and railway environmental noise according to optimize the wheel shape by mainly analyzing the wheel of high frequency radiation noise.

Booms and Busts in the Deep

AbstractDeep sea (5 km) pressure and velocity at the Hawaii-2 Observatory (H2O), midway between Hawaii and California, exhibit a number of remarkable features that are interpreted using the Longuet–Higgins theory of acoustic radiation from oppositely directed surface waves. A change in the slope of the bottom spectra near 5 Hz can be associated with a transition near 2.5 Hz (25-cm wavelength) of the surface wave spectrum from the classical κ−4 saturated (wind independent) Phillips spectrum to a distinct band of ultragravity waves. Bottom spectra are remarkably stable. Occasional 15-dB busts in the gravities and booms in the ultragravities are prominent features in the bottom records and can be associated with calms and storms at the sea surface. For strong winds, two broad lobes in the directional spectrum of the gravity waves are nearly perpendicular to the wind; as the wind drops, the lobes become narrower and more nearly aligned with the wind, leading to busts.

Miguel C. Junger, an inspirational mentor in structural acoustics

When Lord Rayleigh wrote his book, The Theory of Sound in the 19th century, he treated vibrations of structures and sound radiation in two separate volumes. In the last half of the 20th century, the field of structural acoustics, i.e., the theory of acoustic radiation and scattering from elastic structures, was developed in response to Navy needs. Miguel C. Junger is one of the seminal contributors to this field of structural acoustics, and has been the inspirational mentor to myself and others associated with him at Cambridge Acoustical Associates. This presentation discusses how this mentoring proceeded, the resulting research derived from this, and the circumstances leading to our book Sound, Structures and their Interaction originally published by MIT Press, and now published by the Acoustical Society of America.

Theory of acoustic radiation over a 3-D hyperbolic ocean ridge

An analytic solution to a 3-D problem of ocean acoustics involving horizontal refraction is presented. An expression for the acoustic field due to a harmonic point source in an isovelocity ocean overlying a hyperbolic ridge with perfectly reflecting boundaries is given as a finite modal sum of integrals. The integrals are in terms of Mathieu functions, the eigenfunctions of the reduced wave equation in the elliptical coordinate system. These eigenfunctions are approximated away from the low-frequency limit by standard WKB techniques and the resulting integrals are then estimated by first- and second-order stationary-phase asymptotics. This gives an approximation in terms of elliptical functions for which standard numerical routines are available. The approximation is very accurate in the shallow depth and gentle slope limits appropriate to the physical situation of ridges in an isovelocity ocean. The solution includes the locations of the caustics and shadow zones and predicts a complicated intramodal interference pattern resulting from the intersection of up to three rays in a given mode. The intermodal interference from the finite modal sum is also evident in the full solution. The explicit representation of the features arising from horizontal refraction makes this model useful as a 3-D benchmark solution.

Theory of acoustic radiation near a hyperbolic ridge

A solution to the acoustic field due to a harmonic point source near a hyperbolic ridge with perfectly reflecting boundaries in an isovelocity ocean is derived and developed. An exact expression for the field is given as a modal sum of integrals. The integrals are in terms of eigenfunctions of the reduced wave equation in the three-dimensional elliptical coordinate system. The eigenfunctions are approximated away from the low-frequency limit by standard WKB techniques. The resulting integrals are estimated by first and second order stationary phase asymptotics, which are matched in the vicinity of the caustics, yielding a complete representation of the field. The field is given in terms of standard elliptic functions for which fast numerical routines are available. The solution includes the locations of the caustics and shadow zones, as well as predicting a complicated intramodal interference pattern resulting from the intersection of up to three rays in a given mode. The explicit representation of these features arising from horizontal refraction makes this theoretical model useful as a new fully three-dimensional benchmark solution.

A Generalization of Squeeze Film Theory and Acoustic Radiation Theory. 2nd Report. Inertia Effects and Relationship between Squeeze Film Pressure and Langevin Radiation Pressure.

The theory of squeeze film pressure and the theory of acoustic radiation pressure have been generalized to a new theory in this study. When the two flat faces are separated by a compressible fluid film, a dynamic pressure is generated in their normal direction by the oscillation of the faces. In this paper, an analytical solution to the differential equation for the phenomenon considering both the inertia and the viscosity of the fluid is presented. The relationship between the squeeze film pressure and Langevin radiation pressure is also investigated theoretically. The results show that the inertia efects of the fluid on the pressure reveal when a Reynolds number is larger then 1. If a Reynolds number is small enough to neglect the inertia effects, the conventional lubrication theory can be applied to the phenomenon. The time average value of the pressure generated by the inertia of the fluid can be considered to be Langevin radiation pressure.

A Generalization of Squeeze Film Theory and Acoustic Radiation Theory. 1st Report. Fundamental Equation and Relationship between Squeeze Film Pressure and Rayleigh Radiation Pressure.

The theory of squeeze film pressure and the theory of acoustic radiation pressure have been generalized to a new theory in this study. When the two fiat faces are separated by a compressible fluid film, a dynamic pressure is generated in their normal direction by the oscillation of the faces. One of the authors derived a fundamental equation for the phenomenon considering both the inertia and the viscosity of the fluid. In case of neglecting the inertia effects and assuming the isothermal change, the equation is reduced to the Reynolds equation used in the conventional lubrication theory. In this paper, an analytical solution of the Reynolds equation on the adiabatic squeeze film is presented. The results show that compressibility effects of the fluid are dominant at high squeeze numbers. The relationship between the squeeze film pressure and Rayleigh radiation pressure is also investigated theoretically.

Vibration and Low Frequency Acoustic Analysis of Piecewise-Activated Adaptive Composite Panels

This paper presents an analytical modeling technique which uses the Ritz method, classical laminated plate theory, and finite panel acoustic radiation theory to pre dict the modal and structural acoustic behavior of locally activated shape memory alloy hybrid composite panels. This technique for performing a spatial integral within the Ritz approximation of the laminated plates with nonlinear material properties can also be ap plied to analysis of laminated plates with stiffeners and other spatially nonlinear character istics. The application of interest for this presentation is structural analysis of laminated plates. However, this technique may also be used for analyzing plates with ribs and stiffeners, etc. By minimizing the total energy functional, integrating piece-wise over dis crete homogeneous panel regions characterized as activated and unactivated and summing these integrals over the total panel area; stiffness matrices are found to determine natural frequencies, mode shapes and steady-state dynamic response to periodic incident plane wave acoustic excitation. This information is then used to determine the structural acoustic response as a function of frequency for a laminated plate with material nonlinearities. Analytical results are presented for balanced symmetric adaptive panels to demonstrate how various localized activation scenarios affect modal and structural acoustic behavior.

Theory of acoustic radiation in corners with homogeneous and mixed perfectly reflecting boundaries

An exact solution in the form of uncoupled normal modes is derived for the harmonic field from a point monopole source in a corner with perfectly reflecting boundaries (either homogeneous Dirichlet, homogeneous Neumann, or mixed Dirichlet–Neumann). Each mode coefficient is the sum of two integrals, representing the image and diffraction components of the field, neither of which can be expressed explicitly. The image mode integral shows a highly oscillatory spatial dependence in the ensonified region of the mode, a domain that is bounded by a hyperbolic caustic beyond which lies a shadow zone. First- and second-order asymptotic approximations are developed for the image mode integral that are matched in the vicinity of the caustic and that give an extremely accurate representation of the image mode field throughout the ensonified region, across the caustic, and into the shadow. The diffraction mode integral shows a relatively slow spatial dependence. A uniform asymptotic approximation is developed that provides an accurate representation of the diffraction mode integral throughout the domain of the corner. Both the matched and uniform asymptotic approximations are very fast to evaluate compared with numerical computations of the respective integrals. The mode sum yields an expression for the velocity potential consisting of a finite number of image terms plus an intractable integral for the diffracted component of the field, for which an accurate first-order stationary phase approximation is developed.

Application of a Neumann‐series method to two problems in acoustic radiation theory that are formulated in terms of Green’s functions

Two problems in radiation theory are analyzed. In the first problem, two acoustic sources in a fluid interact via their radiated pressure field. Each source may have an arbitrary shape and an arbitrary nonuniform surface vibration. The two sources may be placed in the fluid in an arbitrary fashion, so that there is no preferred orientation of one with respect to the other. A Neumann‐series method is used to simplify that term in the integral equation expressing the pressure field which describes the interactions taking place between the sources. By use of this method, the pressure field can be expressed in terms of the Green’s functions of the individual sources, rather than in terms of an abstract ad hoc Green’s function defined on the disjoint surface that comprises the surfaces of both sources. This field formulation is used to express the self and mutual radiation impedances of the sources. A physical description of the interactions taking place between the sources is given. This description is suggested by the form of the equation describing the pressure field that results when the Neumann‐series method is used. In the second problem, the exterior Neumann and Dirichlet Green’s functions are analytically determined for a radiating acoustic source with an arbitrary shape and with an arbitrary nonuniform surface vibration. These Green’s functions are constructed by using a Neumann‐series method to simplify that term in the integral equation expressing the pressure field which describes the interaction of the source with its own radiation. In principle, the exterior Green’s functions, which are expressed in terms of the geometry of the source and the free‐space Green’s function for the Helmholtz equation, are calculable for any source by performing a series of elementary mathematical operations.

A limiting form for the nearfield of the baffled piston

The circular piston on the planar, infinite, rigid baffle and the pulsating sphere are fundamental (if not classic) problems in acoustic radiation theory. Those who work in the area of radiation and scattering are very familiar with the solutions to these two problems. The solution to a somewhat more difficult problem—the radially vibrating polar cap on an otherwise rigid sphere—is also available and is well documented. Although mathematically difficult to prove, the polar cap problem (or more precisely its general solution) reduces to that of the pulsating sphere in one limiting form, and to that of the piston on the baffle in another. This notion—that the solution to the polar cap problem subsumes the solutions to the two classic radiation problems of linear acoustics—is instructive and useful, if not profound. Its significance is in the use of the general solution of the polar cap problem to generate a convergent infinite series solution for the nearfield of the piston on the baffle. Extension computat...

Statistical estimation of correlation for nonstationary aircraft noise

Based on the acoustic radiation theory for a moving source, the estimation of the correlation function of a nonstationary acoustic signal is considered. We obtain an estimator for the acoustic correlation, which is shown to be unbiased and consistent. The estimation procedure can be applied to an aircraft noise measurement, where the reflected wave can be eliminated.

A limiting form for the nearfield of the baffled piston

The circular piston on the planar, infinite, rigid baffle and the pulsating sphere are fundamental (if not classic) problems in acoustic radiation theory. Those who work in the area of radiation and scattering are very familiar with the solutions to these two problems. The solution to a somewhat more difficult problem—the radially vibrating polar cap on an otherwise rigid sphere—is also available and is well documented. Although mathematically difficult to prove, the polar cap problem (or more precisely its general solution) reduces to that of the pulsating sphere in one limiting form, and to that of the piston on the baffle in another. This notion—that the solution to the polar cap problem subsumes the solutions to the two classic radiation problems of linear acoustics—is instructive and useful, if not profound. Its significance is in the use of the general solution of the polar cap problem to generate a convergent infinite series solution for the nearfield of the piston on the baffle. Extension computations have been performed in limiting cases to demonstrate this convergence.

The use of linear system theory in acoustic radiation and scattering analysis

A description is given of the output of most linear systems in terms of certain properties of the system's impulse response function and of the input signal. The description is particularly simplified when the input signal has a small fractional bandwidth; furthermore, this simplified description, although based on the supposition of a small fractional bandwidth, is shown numerically to apply well even when the fractional bandwidth is as large as unity. The author's “Image Pulse” theory of acoustic echo formation and “Replica Pulse” theory of acoustic radiation are demonstrated to be particular cases of the small fractional bandwidth version of the above more general linear system theory. Examples are provided showing the very good agreement between radiated waveforms obtained by using the band limited formulae of the Replica Pulse theory and the non-band limited formulae of the linear system theory, even when employing input pulses of only a few cycles duration.

Rotary power lawn mower noise

The purpose of this study was to examine the noise of a typical rotary power lawn mower. Hearing loss and annoyance criteria were examined to determine acceptable mower noise limits. It was found that if reduced from its present level of 91 dBA at the operator to 85 dBA, mower noise would pose almost no damage risk for a typical exposure. When the spectral content of the mower noise had been determined it was found that structural radiation was responsible for most of the noise in the range 500–10 000 Hz and that both the blade and exhaust were major sources below 500 Hz. The spectral content of the noise when mowing was found to be similar to that when not mowing. The three major noise sources—exhaust, blade, and structural radiation—were studied seperately. Sources of blade noise were identified by applying the theories of propellor and fan noise generation. Of the blade parameters studied, which included fan lift, sharp trailing edge, and multiple blades, none reduced the A-weighted level of the blade noise. A 1-dBA reduction was observed when the blade was statically balanced. A vibration isolator was designed and built to reduce the vibrations of the blade enclosure and resulted in an additional 112-dBA reduction. Existing theories of exhaust system design were researched and used to design resonator-type systems. Within the assumptions of classical acoustics, no acceptable solutions were found. Applying the theory of acoustic radiation from a hole, a system was designed, built, and tested which resulted in an excess attenuation over the stock muffler of 212 dBA. With the isolator, a blade with less lift, and the improved muffler, the final mower noise level was 86 dBA at the operator. Cost of the solutions is estimated at less than $ 10.00 and none of them is expected to impair the mower's operation.

Detection of acoustic sources using long-wavelength acoustical holography

Sound sources from vibrating circular and ribbed rectangular plates are detected by holographic means using a microphone scanner and associated photographic equipment. Reconstruction of the wavefront from the acquired acoustical holograms reveals the areas on the plates which generate the far-field acoustic radiation. In all cases, the plates were driven below their coincidence frequency. The location of the sound sources on the plates supports the theory of acoustic radiation from complex vibrators except for irregularities which are due to inhomogeneities of the plate material, nonlinearities of the holographic technique, and the speckle effect.