Showing papers on "Acoustic radiation published in 1974"
TL;DR: In this paper, an approximation method for solving the equations of motion that describe the vibration of an elastic structure immersed in an infinite acoustic fluid medium is presented, which avoids the difficulties encountered at eigenvalues of the interior problem by determining exactly the one degree of freedom needed to overdetermine the surface equations.
Abstract: An approximation method is presented for solving the equations of motion that describe the vibration of an elastic structure immersed in an infinite acoustic fluid medium. The mathematical model that is developed uses the finite element method to calculate the vibrational characteristics of the elastic body and the acoustic pressure field of that portion of the fluid which closely surrounds the vibrating body. Analytical methods are used to obtain the boundary conditions for this mathematical model. This technique can be used to predict the response of an elastic structure over a wide range of frequencies and the acoustic pressure at a large number of field points in both the nearfield and farfields. It avoids the difficulties encountered at eigenvalues of the interior problem by determining exactly the one degree of freedom needed to overdetermine the surface equations. Experimental validation of theoretical predictions is given for a piezoelectric cylinder, and a computer‐generated contour plot of a predicted nearfield pressure distribution is shown.
57 citations
TL;DR: In this paper, the authors analyzed the radiated power due to a prescribed transverse beam motion by modeling the beam as a finite, long, slender strip with a thin elliptical cross section.
38 citations
TL;DR: In this paper, the wave-equation governing the radiation of sound in an environment with flow and flow gradients is derived, and the steady state flow in the axial and transverse directions appear as coefficients in the terms of the waveequation.
30 citations
TL;DR: It is shown that the commonly used predictions for edge‐mode radiation obtained by neglecting the influence of the fluid on the membrane displacement are valid except when the fluid loading is very high.
Abstract: Free wave motion on a fluid‐loaded semi‐infinite membrane whose plane is extended by a rigid baffle is discussed. We consider in particular the membrane displacement field and the associated acoustic radiation when a wave on the membrane is normally incident on the membrane boundary. Typical values for the reflection coefficient for the waves, and for the radiated acoustic power are given for a wide range of membrane in vacuo wavespeeds and fluid loading parameters. It is shown that the commonly used predictions for edge‐mode radiation obtained by neglecting the influence of the fluid on the membrane displacement are valid except when the fluid loading is very high.
22 citations
TL;DR: In this article, the amplitude and phase of low-frequency sound propagated to long range in the ocean are predicted based on measured and modeled internal wave spectra, and it is shown and experimentally verified that mean square phase fluctuations are depth dependent.
Abstract: Fluctuations in the amplitude and phase of low‐frequency sound propagated to long range in the ocean are predicted. Phase fluctuations are attributed to the passage of acoustic radiation through the internal gravity‐wave field; predictions are based on measured and modeled internal wave spectra. Ray theory is used to determine phase and amplitude variations as a function of time, space, and acoustic frequency. It is shown and experimentally verified that mean‐square phase fluctuations are depth dependent.
12 citations
TL;DR: In this paper, a time harmonic pressure is applied at the inner boundary of an acoustic fluid body, composed of two parallel, nonconcentric circular cylinders, which is itself embedded in another infinite acoustic fluid.
Abstract: A time harmonic pressure is applied at the inner boundary of an acoustic fluid body, composed of two parallel, nonconcentric circular cylinders, which is itself embedded in another infinite acoustic fluid. The resulting radiation is determined as an expansion in terms of the nonconcentricity. For an applied internal pressure in a j th spatial mode, each order of this expansion introduces a “nearest neighbor” mode, e.g., the first order requires a (j + i)th and a (j − i)th mode. The solution procedure is based on an expansion of the Helmholtz integral equation formulation.
10 citations
TL;DR: In this paper, an experimental study has been conducted to determine the strength of the acoustic radiation generated in the combustion and turbine stages of a JT8D core engine and transmitted out through the primary jet exhaust duct.
Abstract: An experimental study has been conducted to determine the strength of the acoustic radiation generated in the combustion and turbine stages of a JT8D core engine and transmitted out through the primary jet exhaust duct. The acoustic field within the tail pipe duct extension was measured by an array of microphones flush mounted on the extension wall. The interpretation of the cross‐power spectral densities of the microphone signals by means of a theoretical model of the sound propagation within the duct permitted the acoustic energy transmission out of the nozzle exit to be determined. The results show that the internally generated noise is a dominant noise component from the core engine at larger angles from the jet axis for the case of low engine power settings. Although the internally generated core engine noise component lies well below the JT8D engine jet noise and fan noise components at the higher engine power settings, it represents an additional noise parameter that must be considered in the application of fan noise and jet noise suppression techniques.An experimental study has been conducted to determine the strength of the acoustic radiation generated in the combustion and turbine stages of a JT8D core engine and transmitted out through the primary jet exhaust duct. The acoustic field within the tail pipe duct extension was measured by an array of microphones flush mounted on the extension wall. The interpretation of the cross‐power spectral densities of the microphone signals by means of a theoretical model of the sound propagation within the duct permitted the acoustic energy transmission out of the nozzle exit to be determined. The results show that the internally generated noise is a dominant noise component from the core engine at larger angles from the jet axis for the case of low engine power settings. Although the internally generated core engine noise component lies well below the JT8D engine jet noise and fan noise components at the higher engine power settings, it represents an additional noise parameter that must be considered in the appli...
8 citations
TL;DR: In this paper, the forced steady state response of an infinite cylindrical shell immersed in an acoustic fluid bounded by an elastic half-space is investigated, and the solution is obtained by using the Helmholtz integral to express the acoustic velocity potential, utilizing the Fourier transform to determine the influence coefficients for the pressure-velocity relationship at the boundary of the halfspace, and by using a modal analysis to express shell response.
Abstract: The problem of the forced steady‐state response of an infinite cylindrical shell immersed in an acoustic fluid bounded by an elastic half‐space is investigated. The solution is obtained by using the Helmholtz integral to express the acoustic velocity potential, utilizing the Fourier transform to determine the influence coefficients for the pressure‐velocity relationship at the boundary of the half‐space, and by using a modal analysis to express the shell response. By enforcing the appropriate boundary conditions at discrete points of the interfaces, a system of simultaneous equations is obtained. The solutions of these equations yield the values of the unknown source strengths which are then used to determine the pressure field.
6 citations
TL;DR: In this paper, a double exposure of a supersonic air jet using a pulse ruby laser was used to investigate optically the acoustical radiation field and the related fluctuating turbulent field from SUAVs.
Abstract: A new experimental method was used to investigate optically the acoustical radiation field and the related fluctuating turbulent field from supersonic air jets. The method utilizes double exposure of a supersonic jet using a pulse ruby laser. The jet remains on during both exposures eliminating the no‐flow exposure. The time separtion between the pulses can be varied, depending on the spectral component of the radiation and flow field to be observed. Optical records were obtained for supersonic jets with exit Mach number ranging from 1.0–3.0. It was found that high‐frequency acoustic radiation mainly originates from the regions near the nozzle exit, 1–3 nozzle diameters, whereas the low‐frequency noise is generated from regions of 8–10 diameters downstream. (The resulting three‐dimensional optical data also reveal information on the relative intensity of the observed spectral component.) These findings are consistent with the acoustic data obtained by other investigators. The other experimental details on the acoustic radiation from supersonic jets and potential applications of this technique to other aeroacoustics problems are also discussed.
2 citations
TL;DR: In this article, the vibrational response of and the associated acoustic radiation from a semi-infinite membrane in contact with a compressible fluid is considered and the effect of arbitrary fluid loading on the membrane response and on the acoustic farfield is evaluated.
Abstract: The vibrational response of and the associated acoustic radiation from a semi‐infinite membrane in contact with a compressible fluid is considered The plane of the membrane is extended by a rigid baffle A pressure field with sinusoidal time and space dependence acts on the membrane The pressure field is such that far from the edge of the membrane only acoustically slow waves are excited The acoustic radiation into the fluid thus is generated in the vicinity of the edge of the membrane A closed‐form solution is obtained by using the Wiener‐Hopf technique The effect of arbitrary fluid loading on the membrane response and on the acoustic farfield is evaluated It is shown that the usual edge‐mode approximation of neglecting fluid‐loading in determining the membrane response and subsequently estimating the radiation is a reasonable one even for quite high fluid loading
2 citations
01 Feb 1974
TL;DR: In this article, the transfer functions of a vehicle's dynamic systems, which denote the exciting force characteristics of driveline, vibration transmissibility of body structures and the characteristics of acoustic radiation from vehicle floors, are determined by forced vibration experiments.
Abstract: The transfer functions of a vehicle's dynamic systems, which denote the exciting force characteristics of driveline, vibration transmissibility of body structures and the characteristics of acoustic radiation from vehicle floors, are determined by forced vibration experiments. These three transfer functions are combined together into one, and frequency response characteristics of the vehicle's dynamic systems, composed of vibration and acoustic elements, are obtained by computer simulation techniques. By application of this approach, the relationship between the sound pressure in the passenger compartment and the parameters of vehicle components is investigated and the technical criteria for improvement of vibration/acoustic characteristics are clarified.
TL;DR: In this article, a linear control of the acoustic radiation of a single-electrode section of a surface-wave transducer is described using the field effect transistor (FET).
Abstract: The field-effect transistor is used for a linear control of the acoustic radiation of single-electrode section of the surface-wave transducer. The electrically controlled surface-wave filters and delay lines, the characteristics of which may be specified by a set of constant control voltages, are described on this basis.
TL;DR: In this article, a one-seventh scale model has been constructed to investigate the sources of acoustic radiation from a gas turbine exhaust, which geometrically scales the flow path downstream of the rotating parts including support struts and turning vanes.
Abstract: To investigate the sources of acoustic radiation from a gas turbine exhaust, a one-seventh scale model has been constructed. The model geometrically scales the flow path downstream of the rotating parts including support struts and turning vanes. A discussion and comparison of different kinds of aerodynamic and acoustic scaling techniques are given. The effect of the temperature ratio between model and prototype is found to be an important parameter in comparing acoustical data.
TL;DR: In this paper, a small metal mass attached to a rectangular vibrating plate was shown to give rise to far-field sound as shown in the hologram wavefront reconstruction, and a holographic technique has been used to experimentally verify this theory qualitatively.
TL;DR: In this paper, a description of two separate methods of calculating the far-field and near-field pressure distributions associated with an acoustic radiator is presented. But the body geometry is not constrained, but the method is best suited to relatively long, thin bodies.