摘要:

The propagation paths from shallow explosive sources to a SOFAR axial receiver located near Midway Island were determined by examination of the arrival pattern making up each received shot signature. The sources were detonated at shallow depths (200 m) along a 1650 km track NE of the hydrophone. Shot signatures were aligned by computer on the basis of travel time and range. The identification of arrivals was based upon a comparison of this signature alignment with one produced by computed signatures using TRIMAIN, a mathematical ray trace model. The principal ray paths are RR, deep cycling rays which can be classified by the number of times they have turned under below the SOFAR axis. Large scale oceanographic features determine the arrival structure and serve to identify the ray paths producing it.

ISSN:0001-4966    

DOI:10.1121/1.382269

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A super‐resolution imaging method in connection with spectral synthesis is presented. The basic idea is to apply the sampling theorem to the heterodyned signal in the frequency domain and to estimate the data obtainable within a wide frequency range through matrix calculation, using the data obtained within a narrow bandwidth. The principle and some practical problems in the use of this method, such as the required number of the raw data and the effect of additive noise in the received signal, are described theoretically, and the effectiveness of super‐resolution in range is demonstrated by using the results of computer simulation and laboratory experiment.

ISSN:0001-4966    

DOI:10.1121/1.382270

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

An optical method is described for studying acoustical pulses as short as two or three cycles in duration in the low‐megahertz frequency range. A collimated light beam having a width of one ultrasound wavelength is observed in the optical farfield of the ultrasonic grating midway between the maxima of the central and first diffraction orders. A close approximation to both the amplitude and phase of the acoustical pressure along the light path is obtained. This method is proposed as a simple calibration procedure for recording the transmit pulse characteristics of medical ultrasound systems.

ISSN:0001-4966    

DOI:10.1121/1.382271

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Ultrasonic and hypersonic property of liquid pyridine has been studied at 20° and 30°C with three techniques: pulse‐echo‐overlap, high‐resolution Bragg reflection, and Brillouin scattering. The sound velocity observed over the frequency range from 3 MHz to 7 GHz suggests two relaxation regions, one centered at 762 MHz and the other at 3.9 GHz at 20°C. The velocity‐dispersions in the UHF and in the hypersonic ranges are 94 m/s and 65 m/s, respectively. The same type of vibrational double relaxation as observed in liquid benzene is hypothesized. Quantitative analysis of the relaxation strength indicates that the vibrational specific heat associated with both the lowest and the second lowest modes relaxes in the hypersonic range and all the rest, in the UHF range.

ISSN:0001-4966    

DOI:10.1121/1.382272

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Poroelastic materials are two phase material systems consisting of a porous linear elastic solid phase filled with a Newtonian viscous fluid. Analytical investigations have demonstrated that poroelastic structures can, depending on loading and geometry, exhibit elastic response or the creep and relaxation response associated with various models of linear viscoelastic materials. This paper examines the dynamic response to harmonic loading of a disk or slab of poroelastic material. Biot’s dynamic theory for deformable poroelastic media is applied to derive expressions for a complex modulus of the material in terms of poroelastic material coefficients. Both a quasistatic analysis, accounting for dissipation but neglecting inertia, and a dynamic analysis, which neglects dissipation, are presented. For a choice of poroelastic coefficients roughly appropriate to water filled sandstone or compact bone, the poroelastic layer is shown to exhibit rubber‐to‐glass transition in a low‐frequency range. Resonance effects arising due to inertia are shown to take place at much higher frequencies than those at which changes due to dissipation take place.

ISSN:0001-4966    

DOI:10.1121/1.382273

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

To study the mechanism of the source of acoustic emission, we analyze the transient waves which are generated by four kinds of point sources, a single force, double force, and center of dilatation, all inside an infinite plate, and a single force on the surface of the plate. Some of these forces or a combination of them could be used to model the dynamic process of material defects. The analysis is based on the generalized ray theory and Cagniard’s method. Transient solutions are obtained by evaluating the ray integrals with a complex algorithm. Numerical results are shown for receivers that are located at a distance up to six plate thickness, and for a duration less than ten transit time for aP‐wave to cross the thickness of a plate.

ISSN:0001-4966    

DOI:10.1121/1.382274

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

In order to discuss the sound radiation from a direct‐radiator loudspeaker in the high‐frequency region, an elastically supported circular plate in an infinite baffle is used. The normal modes of this plate is consistently treated from the free boundary to the simply supported boundary, which are the limiting cases of the elastically supported boundary, by defining a dimensionless parameter representing the ratio of the edge stiffness to the bending stiffness of the plate. It is found that the frequency response curve is determined by the resonance between the plate and the acoustic fluid for heavy loading, and between the plate and the mechanical impedance of the voicecoil for light loading, both with different shapes of response curves around the resonance frequencies.

ISSN:0001-4966    

DOI:10.1121/1.382252

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Two experiments examined the acoustical correlates of traffic sound aversiveness. In experiment I all pairs of 13 45‐s traffic sound recordings were presented; subjects chose the sound of each pair to which they would rather be exposed and judged the relative similarity of the sounds. The energy equivalent sound level, Leq, accounted for choice and similarity judgments better than any other noise index, and there was no substantial improvement in ability to account for subjective judgments when other indices were used in conjunction with Leq. In experiment II subjects judged the same sounds which had been made equal in Leqlevel. Responses were nonrandom, showing that Leqis not the only subjectively important information in traffic sounds, but no acoustical measure employed in the study captured that information. Instead, two subjective measures of information content accounted best for the data of experiment II. Response data for the equal Leq sounds were less structured than for the sounds differing in Leq. The data of the two experiments were statistically related; it is argued that the data sets were related via the measure of information content. Experiment I replicated a previously reported study, while experiment II failed to replicate the results of a second study.

ISSN:0001-4966    

DOI:10.1121/1.382253

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A laboratory investigation was directed at the development of criteria for the prediction of ride quality in a noise‐vibration environment. The stimuli for the study consisted of octave bands of noise centered at 500 and 2000 Hz and vertical floor vibrations composed of either 5 Hz sinusoidal vibration, or random vibrations centered at 5 Hz and with a 5 Hz bandwidth. The noise stimuli were presented atA‐weighted sound pressure levels ranging from ambient to 95 dB and the vibration at acceleration levels ranging from 0.02–0.13 grms. Results indicated that the total subjective discomfort response could be divided into two subjective components. One component consisted of subjective discomfort to vibration and was found to be a linear function of vibration acceleration level. The other component consisted of discomfort due to noise which varied logarithmically with noise level (power relationship). However, the magnitude of the noise discomfort component was dependent upon the level of vibration present in the combined environment. Based on the experimental results, a model of subjective discomfort that accounted for the interdependence of noise and vibration was developed. The model was then used to develop a set of criteria (constant discomfort) curves that illustrate the basic design tradeoffs available between noise and vibration.

ISSN:0001-4966    

DOI:10.1121/1.382254

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The peak in sound transmission through a single isotropic panel at the critical frequency causes a drop in transmission loss (TL) of that panel and of composite walls constructed with such a panel as a face sheet. In investigations on a composite wall with plywood face sheets and Styrofoam core, such a coincidence dip was not observed. The aim of this study is to investigate the disappearance of coincidence notch and the probable causes for such a phenomena. The bending stiffness of a single ply of plywood changes gradually from the softest direction to the stiffest direction. Therefore, the bending wave phase velocity and sound transmissibility change with direction. It is hypothesized that for a group of sound waves randomly incident on the panel, this change in transmissibility eliminates or lowers the peak and, therefore, the coincidence notch smoothens. A plywood panel consists of plies laminated with their grains in different directions. These laminations of the plys may reduce orthotropy in thick plywood panels. A comparison of theoretically redeicted and experimentally observed TL of plywood sheets supports the hypothesis that antisotropy is the reason for a lack of coincidence transmission for some plywood sheets.

ISSN:0001-4966    

DOI:10.1121/1.382255

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP