摘要:

This report describes some of the highlights of underwater sound and other naval acoustical technology in the United States during the period of World War I to World War II. A number of accomplishments in subaqueous acoustics of the Naval Research Laboratory are given, emphasizing sonar equipment research and development. Acoustic studies in air and ocean environments carried out at NRL are also described; and a general glimpse of the research climate in the early decades of NRL is portrayed.

ISSN:0001-4966    

DOI:10.1121/1.1910963

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

This paper is concerned with the transient problem of waves in an infinite one‐dimensional medium owing to a monochromatic source whose positionX(t) is a stochastic function of time. Asymptotic results for the farfield are given for the general class of stationary source motions and for the case in whichX(t) is a Wiener process, corresponding to Brownian motion.

ISSN:0001-4966    

DOI:10.1121/1.1910964

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

An approximate solution is obtained for the problem of steady‐state longitudinal‐wave propagation in anisotropic bars of infinite length and rectangular cross section by employing the variational method of Ritz. The first three dispersion curves are presented for orthotropic, tetragonal, hexagonal, cubic, and isotropic systems.

ISSN:0001-4966    

DOI:10.1121/1.1910965

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

A shock wave with an N‐shaped pressure profile is propagated in the equatorial plane of a weak spark in air. In the present work, the directional dependence of the acoustic waveform is examined for 0.5‐ and 1.0‐cm sparks having discharge energies between 0.01 and 0.1 J. The transient signals are detected with a wide‐band capacitor microphone that has a rise time of less than 1 μsec. As the spark axis is approached, an interval with no acoustic disturbance appears near the center of the waveform. The angular dependence of both the shock amplitude and the length of this central interval is found to be in qualitative agreement with the results of a linear analysis in which it is assumed that each point along the spark acts as a source of N waves.

ISSN:0001-4966    

DOI:10.1121/1.1910966

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

This paper presents an analysis of an elastically coupled piezoelectric resonator system consisting of a linear array of two or more counter electrode pairs placed on the major surfaces of a quartz crystal plate. Each pair of counter electrodes establishes resonator having a transverse thickness mode of motion. The equations describing this system are derived and applied to an array ofncoupled resonators and specific numerical computations are made for the cases wherenis equal to 2, 3, and 6. These results are plotted and show the dependence of the effective interresonator coupling on the dimensions of the electrode configuration.

ISSN:0001-4966    

DOI:10.1121/1.1910967

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The growth of acceleration waves propagating in an isotropic elastic material is examined. The underlying assumption made is that the material is at rest in its reference configuration. First, we establish that only longitudinal or transverse acceleration waves may propagate, and the wave speeds are determined. Then, we derive the differential equation governing the growth of the amplitude of longitudinal acceleration waves and obtain explicit solutions for plane, cylindrically or spherically expanding waves. These results indicate that the amplitude of acceleration waves may either decay to zero in infinite time or become infinite (shock formation) in finite time; the radius effect on the amplitudes of cylindrical or spherical acceleration waves are not of the form1/r12or 1/r, as predicted by lineary theory. On the other hand, the behavior of transverse waves is similar to that obtained by linear theory.

ISSN:0001-4966    

DOI:10.1121/1.1910968

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

This paper is concerned with the resonant properties of free, piezoelectric ceramic rectangular parallelepipeds, such as cubes. By means of the calculus of variations, the electroelastic differential equations are transformed into an approximate matrix characteristic value problem. Solution of this problem yields the resonant frequencies, the particle displacement patterns at resonance, and the equivalent circuit parameters such as the motional capacitances. Structures of the present type possess eight distinct symmetry families of modes; however, only one of these is excitable piezoelectrically with two opposite faces completely electroded. The resonant frequencies of the first 50 modes of this family are presented graphically versus Poisson's ratio for the special case of an isotropic cube. The frequency and dynamic capacitance of the first 30 modes of the same family are given for a piezoelectric ceramic square cylinder as the thickness‐to‐width ratio is varied from zero (thin square plate case) to unity (cube case). This result demonstrates the fact that the so‐called thickness mode of a thin plate is actually a composite of many high contour‐extensional overtones. Numerous modal displacement patterns are sketched for the square cylinder and cube special cases. Lastly, experimental results are reported that correspond reasonably well with the theory: Agreement is on the order of 3% for resonant frequency values and 20% for other quantities.

ISSN:0001-4966    

DOI:10.1121/1.1910969

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The propagation of small‐amplitude free harmonic waves in an elastic sandwich ring is studied by using a Timoshenko‐type theory, which takes into account the effects of radial shear deformation, rotatory inertia, and extension of the neutral axis. The form of the equations of motion is the same for both homogeneous and sandwich rings, but the range of values for the parameters involved in the latter case can lead to qualitative changes in the wave propagation characteristics of the system. It is shown that the ratio of the ring's extensional stiffness to its shear stiffness has an important influence on the frequencies and group velocities of sandwich rings. When this ratio becomes large, two of the three modes of wave propagation become less dispersive. Numerical examples are presented and discussed.

ISSN:0001-4966    

DOI:10.1121/1.1910970

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

An analytic method is presented for the determination of the vibrational characteristics of ring‐stiffened cylindrical shells. The stiffening rings, which are assumed to be uniform and evenly spaced, are treated as discrete members, and the inter‐ring shell motions are fully and exactly accounted for within the linear shell theory used in the analysis. The flexural, extensional, and torsional rigidities of the rings are retained in the analysis as well as all in‐plane inertia terms. Numerical comparison made with the results from existing energy methods and orthotropic model approach. It is found that for high circumferential wavenumbers, the inter‐ring displacements may become very pronounced.

ISSN:0001-4966    

DOI:10.1121/1.1910933

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

A physical model is proposed for the deep‐sea ambient noise. Ambient noise is hypothesized to be caused by the high‐frequency caipllary patches that are randomly distributed over the ocean surface. The random surface‐roughness spectrum implied by the ambient‐noise measurements and that implied by the hypothesis are discussed. The results are found self‐consistent and comparable to those of other investigators. They also agree with the idea of convolution radiation (proposed by) Longuet‐Higgins, Marsh, and Kuo. The analysis strongly indicates simple relationship among the physical parameters controlling ambient noise, noise frequencyf, noise direction θ, and the sea state (implied by λw). The relationship is given by 2π/λw= 2πfsinθ/cw, where λwis energy containing gravity wavelength,cwis acoustic velocity in the water, and θ is radiation direction with respect to the normal of the mean sea level. When one physical parameter was arbitrarily held constant, the other two physical parameters varied consistently with actual measurements.

ISSN:0001-4966    

DOI:10.1121/1.1910934

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP