摘要:

A rough surface is assumed to be composed of a slowly varying large‐scale roughness and a rapidly varying small‐scale roughness, and it is assumed that these are correlated. The exponential forms of both the autocorrelations of these surfaces and their crosscorrelation were used. This paper shows that the return from such a composite surface for a plane‐wave incidence can have either one of the following terms contribute a major portion of the total return power: namely, the large‐scale roughness term, small‐scale roughness term, and the crosscorrelation term. It is therefore concluded that contribution due to each term must be evaluated before neglecting its effect on the total return power. These results are equally applicable to acoustic and radar cases.

ISSN:0001-4966    

DOI:10.1121/1.1909754

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

A simple analysis shows that, when a transient plane wave in an elastic medium is reflected at a plane boundary with a lossy medium, the transient waveform of the reflection is affected by the loss parameters of the second medium. If the attenuation in the second medium is small, and if the ρcproducts of the two media are matched, then the reflected waveform is the convolution of the incident waveform, with the integral of the Fourier transform of attenuation as a function of frequency. Thus, attenuation for a lossy solid or liquid can be obtained by this external‐pulse technique. Where attenuation is some simple function of frequency, its Fourier transform is some recognized generalized function. Sample waveforms have been observed using airborne sound in specially prepared tubes; good qualitative agreement with predicted waveform was obtained.

ISSN:0001-4966    

DOI:10.1121/1.1909756

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

A thin, truncated conical shell is analyzed for the initial transient response due to the passage of a pressure front of constant velocity and amplitude. The principle of virtual work is applied to a segment of the shell, between two adjacent generatrices, treated as a beam on an elastic foundation. The ends of the shell are considered to be simply supported. The natural or free modes of vibration are approximated using an 8‐term series of functions each satisfying the boundary conditions, and the resulting modes are used in conjunction with time‐dependent coefficients to formulate the forced response.

ISSN:0001-4966    

DOI:10.1121/1.1909758

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The equivalent network for the transversely vibrating uniform bars under various end conditions are given, the value of each element of the networks is determined, and graphs showing the frequency characteristics of each element in the matrices for the bars are given. Some considerations such as the effect of the neglect of the distributed mass are given. The analysis by the method of normalized functions is briefly explained by citing a few examples.

ISSN:0001-4966    

DOI:10.1121/1.1909760

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The use of active feedback elements to produce damping of multiresonant structures has been extended to include the case in which the damping‐force generator is supported by the structure being damped. A theoretical damping equation is developed and experimental verification is obtained for the particular case of a uniform aluminum beam damped at its midpoint. In this structure‐borne configuration, the active damper is potentially applicable to a wider variety of vibration problems because external support for the damping‐force generator is no longer necessary. When applied to the uniform beam, an experimental structure‐borne damper demonstrated damping bandwidth in excess of 10 kc/sec and equivalent loss factors of up to 0.22 for resonant frequencies below 2 kc/sec.

ISSN:0001-4966    

DOI:10.1121/1.1909762

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

An experiment to determine some characteristics of long‐range underwater sound propagation was undertaken by the U.S. Naval Ordnance Laboratory in April 1964. In this experiment, Project Neptune, sound signals were dropped at various ranges from a listening station in Bermuda. To supplement this and other stations, one was established, by the New Zealand Naval Research Laboratory, off southern New Zealand to record the sound signals dropped on the final phase between Cape Town, South Africa, and Perth, Australia. The recorded energy was analyzed in13‐oct bands to determine the transmission‐path characteristics for low frequencies. The signal envelopes were found to differ in shape from the usual solar case, and the attenuations were much larger than previously obtained for either RSR (refracted‐surface reflected) or sofar propagation. These differences may be explained in terms of the different velocity structure of the Southern Ocean from that sound in the Atlantic or Pacific Oceans. In particular, the thermocline is not as pronounced as in temperate or tropical regions and is absent south of the Antarctic convergence. Thus, the energy was transmitted by a mixture of RSR and sofar modes, little sofar energy arriving from those shots whose tracks crossed the Antarctic convergence.

ISSN:0001-4966    

DOI:10.1121/1.1909764

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The problems arising from the generation of harmonic distortion by underwater sound devices are discussed. Expressions are derived for the harmonic distortion of spherically propagating finite‐amplitude sound waves, and distortion is calculated for a typical high‐intensity sound source. The calculation illustrates that finite‐amplitude effects can produce a significant amount of second‐harmonic distortion in a practical situation.

ISSN:0001-4966    

DOI:10.1121/1.1909766

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

An experiment was conducted to provide an empirical evaluation of attenuation in sea water in the frequency range of 354–3540 cps. Recordings were made of solar shots detonated every 5 miles along a 500‐mile track. The receiving elements were located near the axis of the sofar channel. An analysis is outlined both in terms of received energy spectrum and transmission loss as a function of range. The experimental data have been statistically fitted by least‐squares methods to a mathematical model of the formNW = H0+10 log R+aR, whereH0represents the transmission loss in excess of inverse first‐power spreading. These results have been combined with those from a subsequent experiment, conducted in the same geographical area, that extended the frequency coverage to 112 cps. The regression line fitting the joint set of coefficients to an upper limit of 1780 cps is given bya = 5.42×10−5 fkcps1.50 dB/yd. The present evaluation is compared with other results, and an apparent systematic anomaly is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1909768

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

A theoretical and experimental study of the influence of shear flow on the attenuation of sound in a lined duct is presented. Both upstream and downstream propagation are considered. Solutions of the linearized equations for acoustic‐wave propagation in flow, based upon both uniform and power‐law models of the mean‐flow profile, are compared with attenuation measurements in a duct having two opposite side walls lined with a porous fiberglas® blanket for a frequency‐geometry rangekδ⩽1 and midstream Mach numbersMl<0.2. Here,kis the plane wavenumber and δ is the aerodynamic boundary‐layer thickness. Both profile models yield results in close agreement with experiments at low frequencies,kδ<0.1. For intermediate and high frequencies, 0.1

ISSN:0001-4966    

DOI:10.1121/1.1909770

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The use of rating‐scale isosensitivity data for testing discrete, two‐state detection models is admitted to be inappropriate, unless additional assumptions are made. It is suggested that simple assumptions may, in fact, be made by which this model may maintain its basic description of sensory processes and yet make predictions about rating results. The predictions are shown to produce the same isosensitivity curves (ROC curves) as did the original, two‐choice version of the model. These functions do not describe the results of rating experiments.

ISSN:0001-4966    

DOI:10.1121/1.1909772

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP