摘要:

Exact general solutions of the three‐dimensional elasticity equations of motion in polar cylindrical coordinates are written for axisymmetric and antisymmetric axial shear vibrations. The frequency equation follows immediately from the boundary conditions for the problem of the infinitely long, composite cylinder with two concentric circular‐cylindrical layers which are perfectly bonded at their interface. The branches of the frequency equation are plotted and analyzed. The conditions are pointed out under which it is possible to obtain reasonably accurate estimates of the natural frequencies by assuming that the motions of the casing and core are uncoupled.

ISSN:0001-4966    

DOI:10.1121/1.1908468

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

An analysis is presented of the effect of weak damping on the natural frequencies of linear dynamic systems. It is shown that the highest natural frequency is always decreased by damping, but the lower natural frequencies may either increase or decrease, depending on the form of the damping matrix.

ISSN:0001-4966    

DOI:10.1121/1.1908470

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Axial resonances of long rods and tubes were used to generate motion for accurate calibration of vibration pickups over the frequency range from below 1 to above 20 kc at acceleration levels up to 12 000g. The resonators were driven by an electromagnetic shaker at low frequencies and by a piezoelectric ceramic stack shaker at high frequencies. Vibration amplitude was measured optically by means of a microscope using stroboscopic light and by means of the interference fringe disappearance technique. Adequate overlap between the two methods was achieved by going up to the 60th disappearance of the fringes. A simple, direct measurement of the phase angle between the pickup signal and the motion is described. Construction details of a small, light pickup which is unaffected by the high acceleration levels are given.

ISSN:0001-4966    

DOI:10.1121/1.1908472

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Expressions have been derived from which the isolation provided by a simple mounting system when supported by any nonrigid foundation may be determined, if the mechanical impedance of the foundation is known. As an example, the mechanical impedance of a damped beam at its midpoint has been employed to simulate the behavior of such a foundation. Knowledge of the dynamic mechanical properties of natural rubber and a high‐damping synthetic rubber has enabled the behavior of antivibration mountings to be described realistically.If the ratio of the mass of the mounted item to the mass of the foundation is large, the isolation afforded by a mounting is found to be much less than that predicted by its transmissibility curve, which relates to an ideally rigid foundation. It is shown, however, that the isolation provided by a mounting can be increased significantly at high frequencies if an additional mass is employed to load the foundation, the greatest isolation then being provided by a low‐damping rubber such as natural rubber. Damping of the foundation is found to have little influence upon the over all level of the isolation afforded by the mounting system.

ISSN:0001-4966    

DOI:10.1121/1.1908474

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Measurements are reported of some characteristics of the response of a simple panel to a steady periodic sound pressure intense enough to cause nonlinearity in the response. The panel is a 2‐in. wide, thin aluminum strip, clamped at its ends with the clamp faces 12 in. apart, and left free on its edges. Attention is focused principally on the fundamental resonance point, which occurred at frequencies as large as twice the low‐level resonance frequency.Measurements of the frequency and strain at resonance, under various levels of excitation, are compared with predictions from a simple one‐mode nonlinear dynamic equation. For good agreement it is found necessary to include not only a nonlinear stiffness but also a nonlinear damping term. Theoretical predictions of the nonlinear stiffness from the physical characteristics of the panel are in error by a factor of 4.7 when based on an assumed mode shape for transverse deflection which is identical with the linear characteristic function of a clamped‐clamped beam.

ISSN:0001-4966    

DOI:10.1121/1.1908476

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The dynamic tensile strength of a piezoelectric lead titanate zirconate ceramic used for power transducers was tested by driving small bars of ceramic electrically at their longitudinal resonance until they fractured. The measured dynamic tensile strength of small specimens of ceramic of good quality was found to be about 13 000 psi. This value was very drastically reduced for ceramic which was not of optimum quality.

ISSN:0001-4966    

DOI:10.1121/1.1908478

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A simplified theory is presented for obtaining the frequencies, deflections, and stresses in cross stiffened and sandwich plates under dynamic loading. Formulas are derived giving the effect of the water on the natural frequency and the approximateQof the plate. The application of resonant plates as underwater sound radiators is discussed, and procedures for designing such radiators are given.

ISSN:0001-4966    

DOI:10.1121/1.1908480

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Bottom reverberation measurements were made during September, 1954, with 530‐ and 1030‐cps sound in 2100 fathom water near San Diego for ping durations of 0.1, 0.25, 0.5, 1.0, and 2.0 sec with omnidirectional sources and receivers. The data were analyzed by assuming that the returned sound consisted of both specularly and nonspecularly reflected sound, analogous to the regular and diffuse reflected light from Bristol board. At normal incidence the losses on reflection for the 530‐ and 1030‐cps sound were 19.5±2.5 db and 15.4±1.7 db, respectively. The other sound returning from the bottom as reverberation was assumed to be due to nonspecular reflections obeying Lambert's law of diffuse reflection. The reverberation level due to the nonspecular reflections was then analyzed to obtain the scattering constant μ of the bottom. A value of 10 logμ=−27 db was obtained for both the 530‐ and 1030‐cps sound. The curves computed for a sine squared dependence fit the data for grazing angles from 90° to 30°. A comparison with published values of other investigators indicates that for clays, muds, or fine grained sands there appears to be no significant frequency dependence over a range of seven octaves.

ISSN:0001-4966    

DOI:10.1121/1.1908482

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Computation of propagation losses are presented for 200‐ to 2000‐cps sound in 25‐fathom water to ranges of 250 miles over different bottoms for a zero gradient (isospeed), and out to 50 miles for a both weak negative gradient and a strong negative gradient. The ray method is used, together with the assumption of random phase after the first bottom reflection, to formulate the theory. The resulting computed transmission loss anomalies exhibit a marked dependence on: (1) the ratio of source depth to wavelength, (2) the sound‐speed gradients, and (3) bottom reflection losses at small grazing angles. The bottom reflection losses are strongly dependent on the attenuation in the bottom. Some long‐range experimental data are presented which show a quantitative agreement with the computed curves out to ranges of 40 miles.

ISSN:0001-4966    

DOI:10.1121/1.1908484

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

While extensive information is available on flat pistons and on spherical radiators, no data have been given in the literature for the intermediate case of convex circular pistons of elliptical profile. In order to fill this gap, this paper presents information on the radiation loading and on the near and far field of such pistons. For the case of a free piston it is found that at smallka(where 2ais the diameter or major axis) the reactance decreases with increasing thickness (minor axis), while the resistance increases at smallkaand decreases at largekawith increasing thickness. In the intermediateka‐region, that is, when the wavelength in the fluid is of the order of magnitude of the dimensions of the piston, the dependence of the impedance on the thickness is more complicated. For the case of a piston in an infinite baffle the behavior of the reactance is similar to that for the free pistons. The resistance however is independent of the thickness in the limit of smallkaand decreases with increasing thickness at largerka. The effect of flexure on the impedance is briefly considered for the case of the free piston.

ISSN:0001-4966    

DOI:10.1121/1.1908486

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP