摘要:

Schlieren techniques are used to show that bounded beam reflection effects occur at liquid/solid‐plate/liquid (L/SP/L) interfaces which are analogous to the bounded beam reflection effects reported previously at liquid/solid (L/S) interfaces. At L/SP/L interfaces, nongeometric effects are shown to be present in both the reflected and transmitted beams when the incident angle of an ultrasonic beam corresponds to the Lamb angle. In addition, similarities between wave phenomena at L/SP/L interfaces and L/S interfaces are presented which suggest that the description of bounded beam reflection derived by Bertoni and Tamir for a L/S interface can be qualitatively applied to the L/SP/L interface case. This theory is shown to account for the lateral extent to which a leaky Lamb surface wave, excited by mode conversion, propagates.Subject Classification: [43]35.54; [43]20.40, [43]20.30.

ISSN:0001-4966    

DOI:10.1121/1.381011

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

A mode synthesis technique is presented for determining the normal modes, natural frequencies, and responses of three‐dimensional complex structure with flexible joints. Lagrange’s equations are used to develop the equations of motion

ISSN:0001-4966    

DOI:10.1121/1.381019

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

We present an analytic and numerical study of Whispering Gallery‐type surface‐ wave modes on solid elastic cylinders imbedded in a fluid. The complex wave numbers of these waves are obtained for the case of high frequencies (ka≳15), including both their attenuation and dispersion curves for the phase velocities. It is shown that there are two different groups of Whispering Gallery modes whose wave numbers in the limit of infinite frequency or infinite cylinder radius approach the corresponding wave numbers of compressional and shear bulk waves in the cylinder material.Subject Classification: [43]40.20; [43]30.50; [43]40.55; [43]20.15; [43]35.54.

ISSN:0001-4966    

DOI:10.1121/1.381020

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The tranmissibility between the midpoint and the boundary of thin, symmetrically vibrating, circular, aluminum plates of identical dimensions has been determined experimentally in the frequency range 16–2000 Hz. The plates were clamped at their boundaries and loaded symmetrically by concentrated masses or by distributed masses (ribs) of various configurations. The loading masses were always equal to the plate mass, so that their effectiveness in reducing transmissibility could be evaluated as a function of their geometry. Consideration was given to continuous and segmented effectiveness in reducing transmissibility could be evaluated as a function ribs. The transmissibilities across plates loaded centrally by cylindircal masses of small and intentionally large contact areas, and by continuous and segmented circular ribs of small and large diameters, agreed closely with prediction, encouraging belief in the validity of the experimental results obtained for the remaining plates loaded by noncircular ribs, which had theoretically intractable geometries. The transmissibilities across an unloaded plate and a plate plus damping tile also agreed satisfactorily with prediction, even though the transmissibility across the damped plate was calculated from an expression developed for a homogeneous plate with internal damping. The greatest overall reductions in transmissibility were provided by the central loading masses, particularly by the mass having small contact area. By comparison, the reductions provided by the various rib configurations were disappointing; only the performance of the triangular rib and of the small circular rib approached that of the central masses, suggesting use of these ribs when access to the plate center is necessary.Subject Classification: [43]40.24, [43]40.20.

ISSN:0001-4966    

DOI:10.1121/1.381021

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Helmholtz‐ and Kirchhoff‐type integral formulas are presented for elastic waves in isotropic and anisotropic solids. The displacement vector field at points interior and exterior to a region bounded by a closed surface is expressed in terms of a volume integral of the body sources and a surface integral of the sources on the closed surface, namely, the traction and the displacement. The kernels of these integrals are the well‐known Green’s displacement dyadic and a third rank Green’s stress tensor. The latter is related to the former by generalized Hooke’s law. From these formulas radiation conditions for both steady‐state and transient elastic waves are established in terms of the traction, displacement, and particle velocity. In the Kirchhoff‐type formula, the retardation in time for the surface and volume sources is made with respect to the travel times for dilatational and shear waves, respectively. This clearly illustrates Huygens’ principle for the two wave fronts of the elastic wave field.Subject Classification: [43]40.20, [43]40.55; [43]20.15.

ISSN:0001-4966    

DOI:10.1121/1.381022

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

A perturbation technique described previously is applied to find the dispersion of free longitudinal waves in a long orthotropic bar of rectangular cross section as far as the fourth order of approximation. First the second‐order equations of motion and equations of compatibility are solved to find the second‐order stress distributions; then these are used to derive the exact second‐ and fourth‐order dispersion terms. The second‐ order stresses are related to a homogeneous and a nonhomogeneous potential function. The homogeneous potential function may be described by one of three analytical expressions, depending upon whether the following combination of elastic compliances is less than, greater than, or equal to unity:A= (s11s33−s132) (s22s33−s232) / [(s12s33−s13s23) +(1/2)s33s66]2.Measurements of the first two frequencies of two potassium chloride specimens, having different major orientations, are compared with theoretical predictions; the percent differences are 0.06%, 0.12%, 0.07%, and<0.01%, all of which lie well within the bounds permitted by the uncertainties in the governing parameters.Subject Classification: [43]40.22, [43]40.20; [43]20.15.

ISSN:0001-4966    

DOI:10.1121/1.381023

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

In the context of sound transmission through aircraft fuselage panels, equations for the field‐incidence transmission loss (TL) of a single‐walled panel are derived that include the effects of external air flow, panel curvature, and internal fuselage pressurization. These effects are incorporated into the classical equations for the TL of single panels, and the resulting double integral for field‐incidence TL is numerically evaluated for a specific set of parameters. Flow is shown to provide a modest increase in TL that is uniform with frequency up to the critical frequency. The increase is about 2 dB at Mach numberM= 0.5, and about 3.5 dB atM= l. Above the critical frequency where TL is damping controlled, the increase can be slightly larger at certain frequencies. Curvature is found to stiffen the panel, thereby increasing the TL at low frequencies, but also to introduce a dip (analogous to the coincidence dip at the critical frequency) at the ’’ring frequency’’ of a full cylinder having the same radius as the panel. This effect, up to now qualitatively understood, can now be quantitatively estimated. Pressurization appears to produce a slight decrease in TL throughout the frequency range, and also slightly shifts the dips at the critical frequency and at the ring frequency.Subject Classification: [43]50.50, [43]50.45; [43]55.80, [43]55.75.

ISSN:0001-4966    

DOI:10.1121/1.381024

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Numerical methods to compute double eigenvalues for circular ducts containing uniform and sheared flow are presented. A technique to verify both the maximum exponential decay and the double eigenvalue, impedance, and attenuation in ducts of different sizes are presented and discussed. For well cut‐on modes in a uniform‐flow duct, the impedance velocity by a simple relationship suggested in a previous study. However, in a sheared‐flow duct, optimum impedances are found to have much smaller values than in the uniform‐flow case.Subject Classification: [43]50.40; [43]20.45, [43]20.40.

ISSN:0001-4966    

DOI:10.1121/1.381025

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The use of an impedance tube and horn for the absolute calibration of a 180‐m3reverberant room for the measurement of sound power in tones is discussed and demonstrated. The results of the calibration procedure are found to compare quite favorably with results obtained using a one‐third‐octave‐band decay method. For a modal overlap index greater than 5, corresponding to frequencies greater than 400 Hz, the difference in the predictions of the two methods is less than 0.8 dB while at a modal overlap index as low as 1.9, corresponding to a frequency of 264 Hz, the difference is less than 1.6 dB. The results of these tests suggest that the one‐third‐octave‐band decay method is quite sufficient for the qualification of a reverberant room with a modal overlap index of 5 or greater for tone‐power measurements. The results of these tests also suggest that any room can be qualified for the measurement of sound power in a tone if it is possible to substitute the mouth of an impedance tube and horn for the source whose sound power is to be measured. The required apparatus is simple and the measurements are easily performed.Subject Classification: [43]55.65; [43]85.20, [43]85.24.

ISSN:0001-4966    

DOI:10.1121/1.381026

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

An improved method for the estimation of speech intelligibility in rooms prior to construction is described which takes into account the directional distribution of the echoes and is based on the concept of received energy being partitioned into useful and disturbing energies. Laboratory experiments are described which substantiate the applicability of the method. The possibility of computing the energy accumulated versus time by specified receivers in a room is discussed broadly; it is shown by numerical example that the image method and the ray method give closely similar results. Numerical computations based on the ray method are compared with experimentally derived energy accumulation curves for two different rooms and are found to agree substantially. Since the computational method also predicts the directional distribution as well as the time accumulation of received sound, it is conjectured that accurate predictions of speech intelligibility taking directionality of echoes into account may be made from architectural plans and from a knowledge of surface absorption coefficients.Subject Classification: [43]55.20, [43]55.40; [43]70.35.

ISSN:0001-4966    

DOI:10.1121/1.381027

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP