摘要:

Similarity solutions are determined for nonhomogeneous elastic semi‐infinite thin rods subjected to suddenly initiated and uniformly sustained stress at the origin. The system of governing nonhomogeneous partial differential equations along with its initial and boundary conditions is transformed to an ordinary differential equation and the corresponding auxiliary conditions by means of the similarity transformations. The representation so obtained is integrated. From the general solution of the problem, two special cases, one for the homogeneous rod and the other for the nonhomogeneous rod, are solved in closed form. The difference of behavior in two cases is graphically discussed.

ISSN:0001-4966    

DOI:10.1121/1.381831

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Using the scattering‐matrix approach to elastic wave scattering, numerical results are presented for the scattering ofP,SV, andSHwaves from a cylinder of elliptic cross section for ratios of minor to major axis ranging from 0.25 to 1.0 and for nondimensional wave numbers in the range 0.1–3.2. Calculations were made for a tungsten cylinder embedded in aluminum and also for a cylindrical cavity in aluminum. The incident waves are taken to be plane waves incident obliquely with respect to the major axis of the ellipse.

ISSN:0001-4966    

DOI:10.1121/1.381832

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The acoustic radiation pressure has found practical application in recent years in instruments measuring sound intensity and in experiments on acoustic levitation. The concept of radiation pressure has, however, long fascinated both optical and acoustical physicists. The history of light radiation pressure goes back more than 200 years to Leonhard Euler, while the concept of acoustic radiation pressure dates from the time and work of Rayleigh. It was pointed out by Brillouin that what we call radiation pressure is not a pressure at all, but a diagonal tensor, all the diagonal terms of which are not identical. The size of the effect is small, and the values obtained for the radiation pressure are very sensitive to boundary conditions and to the approximations that must necessarily be employed. In addition, although the phenomenon is primarily one of nonlinear acoustics, it can be observed down to the lowest sound intensities under certain conditions. Thus, the Rayleigh radiation pressure vanishes for the linear case, but the usually measured Langevin pressure does not. It might be said that radiation pressure is a phenomenon that the observer thinks he understands—for short intervals, and only every now and then.

ISSN:0001-4966    

DOI:10.1121/1.381833

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

We have set up and are using an apparatus for the measurement of total sound power output of a piezoelectric transducer radiating into water. This apparatus combines the better features of previously used methods which depend on radiation pressure. The input is modulated at a low frequency and the output power is intercepted by a target which experiences a force at the modulation frequency. The target is mounted on the armature of an electromagnetic receiver provided with an independent coil through which a current at the modulation frequency is adjusted in amplitude and phase, either manually or automatically by feedback, to arrest the motion of the armature. When the armature is stationary the force depends only on the current, and the apparatus can be calibrated using direct current and dead weights. It is thus absolute. In practice, the carrier frequency is swept over any part of the range 0.1–15 MHz while a recording of power output versus frequency is made. The results of comparisons made with those of other mehtods are encouraging. Examples of curves from normal and defective transducers are shown.

ISSN:0001-4966    

DOI:10.1121/1.381834

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The changes in the thickness‐shear resonance frequencies of circular crystal plates subjected to steady in‐plane acceleration of arbitrary direction are studied. A closed‐form solution for a circular plate under acceleration with three or more points of mounting is obtained. From this solution, initial stress and strain fields are computed at each and every point of the plate as a function of plate orientation, direction of acceleration, and positions of supports. These fields are then taken into account in the coupled equations of the incremental thickness‐shear and flexural vibrations through the second‐ and third‐order elastic stiffness coefficients of the crystal. Due to the space dependence or nonuniformity of the initial fields and the smallness of the frequency changes, (Δf/foin order of 10−9) a perturbation method is used to calculate the changes in the thickness‐shear resonances. The frequency changes as function of the acceleration direction for several configurations of the supports forATcut of quartz are computed. These are then compared with experimental values of A. W. Werner [Interim Reps. 10−11, Bell Telephone Labs. (1959)] and W. L. Smith [Interim Reps. 12−13, Bell Telephone Labs. (1960)].

ISSN:0001-4966    

DOI:10.1121/1.381835

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Intense low‐frequency sound can severely attenuate sound of higher frequencies via spectral redistribution. On the other hand, intense high‐frequency sound does not appreciably alter a lower‐frequency sound field. An experiment is described wherein a 68‐kHz underwater sound beam was made to propagate collinearly with a 244‐kHz beam, demonstrating the absorption of sound by sound. The results are in good agreement with the theory of F. H. Fenlon [J. Acoust. Soc. Am. 51, 284–289 (1972)].

ISSN:0001-4966    

DOI:10.1121/1.381836

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The Trott planar nearfield calibration array (NFCA) is a two‐dimensional array of small, reciprocal hydrophones whose responses are shaded to produce a nearly uniform plane wave throughout a volume in the nearfield of the array. When a transducer to be calibrated is placed in the plane‐wave volume, the signal received by the NFCA is proportional to the farfield pressure radiatied by the transducer in the direction opposite to the plane wave. Previous NFCA’s were shaded so that the plane‐wave direction was normal to the array. It was necessary to rotate the transducer in order to obtain the farfield pressure distribution. In the present study we obtain shading coefficients that allow the nearfield plane wave to be steered to angles up to 70° from the normal to the array. These coefficients allow the determination of a 140° sector of the azimuthal farfield pattern without rotating the transducer. We experimentally verified the shading coefficients by successfully calibrating a large piston transducer. Here we synthesized the steered planar NFCA by combining responses of a single line of shaded hydrophones to form a virtual NFCA. The synthetic aperture technique allows the calibration of large sound sources without having to build the entire NFCA.

ISSN:0001-4966    

DOI:10.1121/1.381837

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Experiments on four different types of subsonic jet‐noise suppressors are reported. The suppressors were compared to a clean circular jet on an equal‐thrust per unit‐exit‐area basis. On this basis the noise production of the different jets varied only slightly, in contrast to some results reported previously.

ISSN:0001-4966    

DOI:10.1121/1.381838

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A widely used experimental version of the acoustic monopole consists of an acoustic driver of restricted opening forced by a discrete frequency oscillator. To investigate the effects of forward motion on this source, it was mounted above an automobile and driven over an asphalt surface at constant speed past a microphone array. The shapes of the received signal were compared to results computed from an analysis of a fluctuating‐mass‐type point source moving above a finite impedance reflecting plane. Good agreement was found between experiment and theory when a complex normal impedance representative of a fairly hard acoustic surface was used in the analysis.

ISSN:0001-4966    

DOI:10.1121/1.381839

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Particles are assumed to have oblate and prolate spheroidal, spherical, disklike, and needlelike shapes, with symmetry axes for oblate and prolate spheroids assumed to be either parallel or perpendicular to the acoustic field. The disk‐shaped and needle‐shaped particles are assumed to be either broadside or edgewise (or end on) to the acoustic field. A wave equation is developed for dilute suspensions of the particles which yields a formula for sound velocity and viscous absorption coefficient. For large differences in densities between suspension components, computations indicate substantial effects of particle shape, orientation, and ultrasound frequency on the velocity of sound through the suspension. A particle moving edgewise or end‐on to the acoustic field causes a greater loss of sound energy than a particle moving broadside to the acoustic field.

ISSN:0001-4966    

DOI:10.1121/1.381814

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP