摘要:

The Napier (relaxation) frequency of oxygen has been determined as a function of methane and deuterated methane impurity at room temperature and at 100°C, using the pressurized Kundt's tube developed in this laboratory. Methane is three times as effective as hydrogen itself, and is comparable with water vapor in causing shift to higher frequencies. Deuterated methane is about14as effective. The shifts are in all cases linear with the (small) concentration, up to 2%.

ISSN:0001-4966    

DOI:10.1121/1.1909304

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

We consider configurations of arbitrary scatterers (s= 1, … ,N) in two dimensions, such that the circles circumscribing the scatterers do not intersect. As shown previously [V. Twersky, inElectromagnetic Waves, R. E. Langer, Ed. (University of Wisconsin Press, Madison, 1962), pp. 361–389], the solution can be written in terms of the multiple‐scattered scattering amplitudesGs, and theGsare specified by the presumably known farfield isolated scattering amplitudesgsby a set of integral equationsG(g) (which can be converted to algebraic equations involving Hankel functions of the separationsbst, etc.). Among other applications, the previous paper gave the complete asymptotic series forG(g) in inverse powers of theb's; this was based essentially on Hankel's asymptotic expansion for the Hankel functionsHn. The present paper derives the analogous convergent representation ofG(g) based on the exact representation ofHnin terms of Lommel polynomials. ForNscatterers, we give the multiple‐scattering solution as a series inH0,H1,b−n, and the derivatives ofgwith respect to angles. For two scatterers, we give a closed form in terms of a differential operator.

ISSN:0001-4966    

DOI:10.1121/1.1909310

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

This paper considers the response of a semiinfinite viscoelastic rod subject to an enforced sinusoidal displacement of its end. The rod has external elastic constraint along its length. Above a certain critical frequency, the steady‐state solution consists of damped traveling waves moving away from the forced end. For lower frequencies, however, the wave travels out of the rod toward the forced end. A brief explanation of this interesting phenomenon is given by studying the work done on the rod. The transient analysis is performed, for the rod initially at rest, by applying a Fourier sine transform to the space variable. The resulting integral solution is integrated numerically for a purely viscous rod being forced at a frequency below the critical frequency. This solution shows how the disturbance is initially propagated away from the forced end and subsequently settles down to the steady‐state solution of the wave traveling toward the forced end.

ISSN:0001-4966    

DOI:10.1121/1.1909293

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

A theory is presented that permits the extension of the method of normal modes to guided‐wave propagation in a medium with properties varying slowly with horizontal coordinates in addition to varying with the vertical coordinate. The principal assumption is the neglect of coupling between normal modes. It is predicted that different frequencies in different modes follow different horizontal paths. A ray‐tracing method is described for computing these paths. The theory is then applied to the study of the dispersion of waves from an explosive source in shallow water with slowly varying depth.

ISSN:0001-4966    

DOI:10.1121/1.1909303

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The attenuation of plane compressive waves in a semiinfinite composite bar is studied. The bar is composed of a main strip and two serrated septa symmetrically bonded to the main strip by viscoelastic material. The one‐dimensional solution gives two complex wavenumbers whose values depend on the complex shear modulus of the viscoelastic material, the frequency, and the relative dimensions. It is shown that maximum attenuation occurs for an optimum value of the loss tangent of the shear modulus. For a typical practical example, this attenuation is about 20 dB in the first three wavelengths for a loss tangent of 0.32.

ISSN:0001-4966    

DOI:10.1121/1.1909305

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The Reissner linearized equations of motion, including hysteretic‐ and viscous‐damping terms, are adopted in the study of the dynamics of a finite, thin, elastic cylindrical shell of circular cross section. The integral representation of the radial displacement solution is obtained for an arbitrary, time‐dependent pressure field over the shell surface and the associated Green's‐function solution is calculated. In particular, the shell response to a moving shock wave (step‐function discontinuity), impinging upon the shell at an arbitrary angle of incidence, is calculated. In the special case of axial symmetry, two additional waveforms are considered, that of a moving exponentially decaying shock wave and of a ramp/step‐function wave. Typical numerical results are given in the form of displacement‐time curves and the effects of the pressure‐wave parameters (decay and rise time) are examined. The dynamic behavior of a prepressurized shell is also considered. It is shown that the Green's‐function solution remains form‐invariant under the introduction of an internal static pressureP0; this, in turn, leads to a simple rule for deducing the response to a given external pressure field whenP0≠0 from known solutions corresponding to the case ofP0= 0.

ISSN:0001-4966    

DOI:10.1121/1.1909306

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The highlights of a successful vibration‐data measurement program—from sensor selection and evaluation to data processing—are reviewed. Time‐sampled data from missile flights are analyzed and various errors attendant to spectral analysis are considered. Unique methods of data presentation are discussed also. Finally, the respective accuracies of the data analyses are compared, and the impact of these data on design specifications is noted.

ISSN:0001-4966    

DOI:10.1121/1.1909307

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Following previous investigations on forced‐vibration methods of determining dynamic mechanical properties of viscoelastic materials, this article is proposing a similar technique for determining the complex Poisson's ratio and the complex dilatation constants. Through the study of forced vibration of a free viscoelastic sphere with internal harmonic oscillating source, it is found that the above mentioned properties of the test material are related to the ratio of the vibration amplitude of two measurable points. Thus, when using the criterion of this ratio approaching its maximum, the maximum amplitude ratio, these properties can be expressed in simple relationship with the laboratory‐measurable quantities: namely, the maximum amplitude ratios and their corresponding vibration frequencies. Investigations have been carried out for three sphere sets.

ISSN:0001-4966    

DOI:10.1121/1.1909308

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

An approximate one‐dimensional theory is derived for the extensional motion of elastic bars or plates of thin rectangular cross section. The resonant frequencies of extensional vibrations of a thin rectangular plate are obtained for a, range of plate dimensions, and a comparison made with some recent experiments. The theory predicts the frequency plateaus characteristic of the incidence of edge modes, as well as displacements at the edge‐mode frequency that are localized to the corner edges.

ISSN:0001-4966    

DOI:10.1121/1.1909309

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

A technique for determining the frequency response of linear mechanical systems is presented that lends itself to solution by graphical means or by digital computer. It provides a means for analyzing multimass systems and the various types of damping associated with these systems and, in addition, provides a means for tracing the contributions of the various elements. The technique involves determining the displacement and force transmissibilities of each element of a multimass system as an individual single‐degree‐of‐freedom system. The equations of motion are then written in terms of these individual transmissibilities and the desired response calculated by either graphical or computer methods. Because the response equations are written in terms of transmissibilities and not spring and damping constants, various types of damping can be utilized and even interchanged within a given problem without affecting complexity. In this paper, three types of damping are discussed: viscous, structural, and elastically supported viscous damping. Additional forms can be added by the user as necessary.

ISSN:0001-4966    

DOI:10.1121/1.1909311

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP