摘要:

In this study, a three‐mode approximate theory governing axisymmetric motions in transversely isotropic rods is developed. The development of this approximate theory follows closely the method adopted by Mindlin and McNiven when they developed a three‐mode theory for isotropic rods. There is, however, one significant departure. After the generalized displacements and generalized strains are defined, the equilibrium and constitutive equations and the kinematic relations are derived using a variational theorem due to Hu and Washizu. The approximate theory is analyzed numerically for two transversely isotropic materials, and spectral lines derived from the theory are compared with those from the exact three‐dimensional theory.

ISSN:0001-4966    

DOI:10.1121/1.1912624

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The response of a semiinfinite transversely isotropic rod to a time‐dependent input on the end of the rod is found using the method of characteristics. The rod is of circular section and the material of the rod is arranged so that the axes of isotropy are parallel to the axis of the rod. To reduce the problem to one where motions depend on only one space variable and time, use is made of an approximate theory developed by the authors in a previous study. Numerical results are found for an input which has a step distribution in time and for two different materials, magnesium and a fiber‐reinforced material. For each material the response is found in terms of four quantities: radial strain, axial strain both on the lateral surface and along the axis of the rod, and the generalized axial stress.

ISSN:0001-4966    

DOI:10.1121/1.1912625

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

An analytical study of the natural frequencies and mode shapes of anisotropic thin plates is presented. The plates are considered to be constructed from an orthotropic material such that the principal elastic axes of the materials are not parallel to the plate edges. By use of Galerkin's method, the change in natural frequencies and mode shapes are investigated as the material elastic axes are rotated with respect to the natural geometric coordinates. Three sets of edge conditions are considered: (1) all edges simply supported; (2) one pair of opposite edges fixed with the other pair free; and (3) one edge fixed with remaining edges free. The results of this investigation show that the plate mode shapes are strongly affected by the orientation of the elastic axes and that they cannot be predicted on the basis of conventional isotropic‐ or orthotropic‐plate analysis.

ISSN:0001-4966    

DOI:10.1121/1.1912626

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The first five branches of the dispersion curves for straight‐crested waves propagating in an infinite isotropic elastic plate, in a state of plane strain, that is covered by a layer of an incompressible inviscid liquid are determined numerically from the exact dispersion relation. Using the classical theory of flexure, the Mindlin theory of flexure, and the Kane‐Mindlin theory of extensional motion in elastic plates, approximate dispersion relations are derived, and the effect of coupling between the flexural, extensional, and fluid modes is studied. Upon comparison of the exact and approximate results, it is found that the coupling of flexural and extensional motions arising through the velocity continuity condition at the liquid‐plate interface is rather weak, so that good approximations to the fluid, flexural, and thickness‐shear branches of the dispersion curves can be obtained by neglecting the coupling with the extensional and thickness‐stretch branches. Furthermore, the extensional branch is not appreciably influenced by the coupling condition, and the thickness‐stretch approximation is a good one in the low‐frequency range only if the mass density of the plate is much greater than that of the liquid.

ISSN:0001-4966    

DOI:10.1121/1.1912627

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

An experimental investigation of the effect of hydrostatic pressure on cavitation erosion is described. A focusing acoustic system enclosed in a pressure chamber permitted the sound pressure and the hydrostatic pressure to be varied independently over the range of 1–20 atm. The intensity of cavitation, as measured by the erosion rate of aluminum, was found to grow at an increasing rate with hydrostatic pressure. Experimental results obtained in this pressure range correlate with published Russian data taken at pressures up to 75 atm. A correspondence between cavitation erosion and electromagnetic radiation is postulated. The agreement between experimental results and those predicted by this correspondence is quite good.

ISSN:0001-4966    

DOI:10.1121/1.1912628

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

This article treats an underwater isovelocity surface duct overlying a negative velocity gradient layer that requires two distinct families of normal modes to represent the acoustic field in the image‐interference region. Each family contains an infinite number of modes. The significance of the two families of modes at short ranges is demonstrated by comparing numerical results obtained from ray theory with results from normal‐mode theory. The contribution to the total normal‐mode solution by the second family of modes is a complicated function of the gradient below the surface channel, the range, and the receiver depth. Within the image‐interference region, the second family of modes becomes increasingly important as the range and gradient decrease and the receiver depth increases. However, beyond the image‐interference region, the second family of modes may be neglected without appreciable error. The properties of the various modal elements are investigated and some generalizations concerning the second family are derived.

ISSN:0001-4966    

DOI:10.1121/1.1912629

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Underwater gas bubble expansion as a function of the ambient‐pressure to bubble‐pressure ratiop′, in the interval 0⩽p′⩽1, is investigated. At the endpoints, a simple analytic solution to the nonlinear equations of motion in closed form may be found; but, for intermediate values ofp′, an approximation is required. In the noncompressive case, representations suitable for large bubble radii, nearp′=0, and small‐amplitude motion, nearp′=1, are derived. A result of this analysis is that the Willis bubble pulse formula, correct in the limitp′ → 0, in agreement with experiment, appears to be valid over much of the interval, but it starts to break down asp′ → 1. The power law governing finite‐ and small‐amplitude periods is different; the actual period has no simple power law dependence, but may be deduced for allp′ by fitting a curve to the asymptotically correct values atp′=0 andp′=1, respectively. Owing to radiation and other loss mechanisms, bubble starting out as finite‐amplitude pulsation, with a cusplike shape at the minimum, is gradually transformed into a small‐amplitude damped sine wave; concurrentlyT1→T̄. (Analysis in this paper refers to caseγ = 43.)

ISSN:0001-4966    

DOI:10.1121/1.1912630

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

An experimental study of sound attenuation in lead‐wool‐polyurethane composites and nickel‐Cerrobend composites was conducted for different compositions, frequencies, and pressures. At specific compositions, the attenuation reached a maximum considerably higher than the attenuation of the components. The maximum attenuation occurred where the compressional modulus is changing most rapidly with composition; at this composition, the attenuation is most unstable with pressure.

ISSN:0001-4966    

DOI:10.1121/1.1912631

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

It is shown that, if the sensitivities and resonant frequencies of elements in a hydrophone array can be accurately determined before they are placed in an array, it is possible to select their positions in the array so as to reduce minor lobes significantly. An expression for the sensitivity of an individual element that depends on easily and accurately measured quantities has been derived. The variation in phase depends primarily on the resonant frequencies of the elements, if element positions can be held to sufficiently close tolerances. Comparisons of calculated results are made with experimental measurements and with computed results of random placement of the transducer elements.

ISSN:0001-4966    

DOI:10.1121/1.1912632

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

An experimental apparatus has been developed as part of a continuing program of deep‐sea acoustic‐scattering research. It consists of a computer‐based shipboard console and a cable‐suspended package which contains the acoustic sources and receivers. The computer provides for preprocessing, recording, and display of the data, and for control of the experimental sequence. The sensor package operates at depths to 1600 m, acquiring scattering data for eight frequencies from 4 to 25 kHz.

ISSN:0001-4966    

DOI:10.1121/1.1912633

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP