摘要:

This paper summarizes the results of rather extensive tests on the attenuation of shear waves in Teflon ®. The method used is described and the results of the measurements are presented. This technique is an extremely simple one requiring a minimum apparatus, and, in addition to yielding some fundamental data, makes a very nice student experiment in a teaching laboratory. The method and apparatus is not limited to Teflon, but can be used with lead or other materials that have a reasonable amount of damping. The method is not suitable for very highQmaterials like aluminum or quartz.

ISSN:0001-4966    

DOI:10.1121/1.1910032

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The mathematical theory of geometric diffraction with a circular elastic‐wave source and receiver in a fluid half‐space shows that the phase at maximum received amplitude does not correspond to the plane‐wave value, i.e., ωl−kz. The excess phase 〈φ〉 plays the rôle of phase shift in an electrical network. Therefore, the value of −d〈φ〉/dω can be used to estimate the delay, due to geometrical diffraction in arrival of the bulk of a pulse. Under usual pulse echo measurement conditions, the velocity measured will seldom be 0.01% smaller thanv0, the true plane‐wave phase velocity. It is assumed here that measurements are made to parts of the pulse where steady‐state geometrical diffraction is occurring. It is further assumed that transient diffraction effects exist for only a small fraction of the pulse. The possibility of diffraction contributing to changes in velocity caused by an external parameter (strain, magnetic field, etc.) is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1910033

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The omnidirectional characteristics of the scattering of acoustic waves from statistically rough surfaces were experimentally investigated. The average differential scattering cross section was measured bistatically as a function of the angles of incidence and observation. Measurements for two surfaces of different roughnesses indicate the increase in the width of the scattering pattern's major lobe in the specular direction with increasing roughness. Scatter in directions other than near the specular (including the backscatter direction) is essentially independent of direction.

ISSN:0001-4966    

DOI:10.1121/1.1910034

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

This paper deals with the dynamic treatment of a transient thermoelastic problem for an elastic half‐space that is exposed to step temperature and velocity on its entire plane boundary and is constrained against transverse displacements. The stress distribution pertaining to this problem, whose plane boundary is subjected to step‐ and/or ramp‐type temperature only, was previously treated by V. I. Danilovskaya [Prikl. Mat. i Mekhan.14, 316–318 (1950)], T. Mura [Proc. Japan Natl. Congr. Appl. Mech., 2nd, pp. 9–13 (1952)], and E. Sternberg and J. G. Chakravorty [J. Appl. Mech.26, 503–509 (1959)]. In physical reality, when the boundary experiences temperature variations, it often also experiences velocity variations. A comparison of present results with previous results reveals that the stress distributions are changed considerably once the velocity variation on the boundary is considered.

ISSN:0001-4966    

DOI:10.1121/1.1910035

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Nontorsional extensional axisymmetric modes and frequencies of elastic prolate spheroidal shells as a function of eccentricity are obtained by a numerical technique. The mode spectra have two distinct branches, analogous to those of spherical and cylindrical shells. Extensive results are presented for the lower branches.

ISSN:0001-4966    

DOI:10.1121/1.1910036

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Theoretical damping values have been determined for three‐ and five‐layer beams having representative cross sections. Trends are obtained that show damping effects produced by changes in cross‐sectional geometry of the beam and properties of the damping material. The results are a series of characteristic curves displaying an increase in damping with increased frequency for the low frequency range, a peaking of the curves in the midfrequency range and a decrease in damping for the high frequencies. In addition, they show that increased viscoelastic material thickness and increased shear storage modulus shift the damping curve toward the low frequencies, while an increased thickness of the elastic layers, considered herein, appear to have no appreciable effect on composite damping behavior. For equal over‐all beam thickness and equal viscoelastic‐material thicknesses, the three‐layer beam provided higher damping at the low frequencies whereas the five‐layer beam yielded better damping at the peak, and at higher frequencies. Approximate analytical expressions are derived that verify the low‐ and high‐frequency characteristics and predict the peak damping frequency and composite loss factor.

ISSN:0001-4966    

DOI:10.1121/1.1910037

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Matrix equations of rigid‐body motion for a general isolation system are presented and conditions for decoupling translational and rotational motions are discussed. The effective rotational and translational stiffnesses of a set of isolators arbitrarily oriented with respect to the center of mass of an isolated rigid body are developed by matrix techniques. Influence coefficients for determining loadings on the isolator's elastic axes owing to arbitrary g loads at the system center of mass are also presented in matrix form. The application of the matrix techniques presented to the design of vibration isolation systems is illustrated through an example.

ISSN:0001-4966    

DOI:10.1121/1.1910038

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Space‐time correlations of ambient sea noise were measured with vertical pairs of hydrophones in the frequency range of 125–1131 cps and with horizontal pairs in the range of 22–63 cps at various sea states (SS) in the deep ocean. The experimental results are compared with those obtained from theoretical models of a uniform distribution of surface‐noise sources, radiating with an intensity pattern of cos2nα, where α is the angle from the vertical. At SS5 and frequencies above 400 cps, a good fit to the experimental spatial correlations as well as to the principal peak of the space‐time correlation is obtained forn= 1. At the same sea state, the 250‐cps data correspond ton = 12. In the low‐frequency range, omnidirectional noise sources explain the experimental data up to and including SS5. The model does not give a sufficient explanation for the space‐time correlations at SS3 in the range 400–1131 cps.

ISSN:0001-4966    

DOI:10.1121/1.1910040

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Further studies of the threshold‐of‐cavitation noise in liquid helium have been made with an ultrasonic plane‐wave system. The behavior of this threshold was found to have a similarity to that of the specific heat in the λ region. Both above and below the λ temperature, the threshold was very insensitive to variations of static pressure and unchanged by addition of solid air or the imposition of electric fields. These results are difficult to explain on the basis of conventional theories of nucleation, but possibly indicate that nucleation involves the aggregation of submicroscopic structures.

ISSN:0001-4966    

DOI:10.1121/1.1910042

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Experiments are described in which heat flow from a metal into a bathing liquid is measured in the absence and in the presence of acoustic streaming. The streaming is produced by a resonant vibrating air bubble resting on a solid plane, of which the heated metal forms a part. The temperature difference between the heated metal and the main body of surrounding fluid is kept constant. In these experiments, the heat flow rate is found to increase approximately linearly with the first‐order sonic amplitude when the liquid is water. Increases up to 10‐fold over the nonstreaming values of heat flow are obtained. When more‐viscous liquids (glycerin‐water mixtures) are used, the relationship between heat flow and sonic amplitude is non‐linear. In the latter situation, a region appears in which the flow rate decreases with increasing sonic amplitude. It is found that the decrease is associated with a reversal in direction of the streaming above the vibrating bubble. An order‐of‐magnitude theory is presented that gives rough numerical agreement with experiment and that predicts a linear relationship between heat flow and sonic amplitude.

ISSN:0001-4966    

DOI:10.1121/1.1910043

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP