摘要:

Guidelines are presented for the preparation of illustrated talks which are audience oriented and which are aimed at the efficient transfer of technical information. Early decisions concerning the required number of slides are helpful in initial planning for a good‐quality talk. Detailed considerations are the establishment of limited objectives, selection of appropriate slide material, development of a text which is well coordinated with the slides, and accurate timing.Subject Classification: [43]10.60.

ISSN:0001-4966    

DOI:10.1121/1.381192

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The solution using Cagniard’s method for the reflection of a spherical wave from a locally reacting plane boundary is compared to that using the steepest descents method. The contribution from the presence of a pole is less arbitrary using this method and the transition from the pole to the no pole case is shown to be gradual. A further solution in the time domain for an incident time impluse function is also derived.Subject Classification: [43]20.15, [43]20.30; [43]28.40.

ISSN:0001-4966    

DOI:10.1121/1.381193

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

A finite‐element approach is developed to simulate acoustic transmission systems of arbitrary profile with circular cross section. Sound‐transmission characteristics are considered in which axisymmetric radial modes are taken into account. Some simple examples of acoustic filters with various profiles are calculated for which the numerical values are compared with the measured ones, as well as those of the one‐dimensional models based on an electrical transmission line analogy. The procedure is a valid and powerful means to cope with filters of any profile and may pave the way to solutions of problems of this kind.Subject Classification: [43]20.40; [43]85.32..

ISSN:0001-4966    

DOI:10.1121/1.381199

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Analysis of reflection of plane waves from a flat boundary in a micropolar half space poses tedious calculations. In this paper, utilizing the concept of slowness surfaces, a simple and efficient method is proposed as an alternative to the previous analytical methods. Critical angles of incidence, the nature of the reflected body, and boundary waves corresponding to the incident longitudinal displacement and coupled transverse displacement microtational waves are studied.Subject Classification: [43]20.15, [43]20.30.

ISSN:0001-4966    

DOI:10.1121/1.381200

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The value of a diagram in which the angle of an acoustic ray is plotted versus its depth is explored. The concept of source line in angle‐depth space is developed. Characteristics of different sound channels, reflection, multipath, caustics, and the analysis of obstacles such as seamounts are described within the context of the diagram. The application of Liouville’s theorem is discussed.Subject Classification: [43]30.20; [43]20.20.

ISSN:0001-4966    

DOI:10.1121/1.381201

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Explosive data from a carefully controlled transmission‐loss measurement in the Northeast Atlantic Ocean are used to evaluate, in detail, the capability of the AESD parabolic equation model. The analysis is performed on a path‐by‐path basis by comparison of computed (using a ray‐tracing program) and measured travel‐time differences. Sensitivtiy studies show that residual discrepancies could be attributed to uncertainties in source detonation depth and the assumption of piecewise‐linear bathymetry. The data show an arrival with no ray‐tracing counterpart; evidence, based upon its mean speed of propagation and the frequency dependence of its energy content, is presented to argue that it is an arrival ducted in the main sound channel. The behavior of this arrival with range is determined by the range dependence of the sound‐speed environment.Subject Classification: [43]30.20; [43]20.20.

ISSN:0001-4966    

DOI:10.1121/1.381202

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Estimates of sound (and infrasound) spectral levels are given using a theoretical model of acoustic production based on quadratic interactions of oppositely traveling ocean waves, and incorporating present day surface wave spectral models. It is shown that reasonable agreement with measurements exists for frequenices less than 10 Hz but predictions are 10–15 dB low and have the wrong spectral shape at higher frequencies.Subject Classification: [43]30.40; [43]20.15; [43]30.70; [43]28.65.

ISSN:0001-4966    

DOI:10.1121/1.381203

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

In a recent experiment employing a number of hydrophone systems deployed at various positions in the Northeast Pacific Ocean, several operational periods were dedicated to an ambient sea‐noise study. Signals received at hydrophones distributed at various depths throughout the water column were analyzed to characterize the noise field at each site. The results obtained revealed a noise‐level dependence on frequency, hydrophone depth, and sound velocity profile. The general features of the noise field could be interpreted in terms of distant shipping and local wind effects, the two major directional noise sources believed to be dominant in the deep ocean. This paper discusses some specific features of the noise field and examines the implication of these to the anomalously high attenuations reported so often at frequencies below 100 Hz.Subject Classification: [43]30.20, [43]30.70.

ISSN:0001-4966    

DOI:10.1121/1.381204

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

An experimental investigation to determine the acoustic transmission from a source in air to a hydrophone in a wind roughened ocean at shallow depression angles is described and the results presented. This experiment was conducted at the NUC Oceanographic Tower in 18‐m‐deep water. Data were obtained for acoustic frequencies of 500–4000 Hz and wind speeds of 3–15 knots. Short pulses of sound were used in order to distinguish the direct path from the bounce paths. The mean energy at the hydrophone was obtained by averaging the direct path energy over many independent pulses. The data show that more energy reaches the hydrophone in the rough ocean than predicted by the smooth surface theory, with the excess increasing for the shallower depression angles. The data also show that the transmission increases with increasing source frequency and ocean roughness and is independent of source altitude for the conditions considered. The experimental results are compared with a geometric rough surface model and show good agreement.Subject Classification: [43]30.20, [43]30.25; [43]20.20.

ISSN:0001-4966    

DOI:10.1121/1.381205

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Low‐frequency propagation measurements in sound channels often show a frequency‐independent excess loss that is evidently caused by internal scatter from large‐scale inhomogeneities. Using the Garrett–Munk internal wave spectrum (GM 75) as the scattering model, we have obtained an approximate solution of the ray‐diffusion equation on the deep sound‐channel axis. The estimated attenuation coefficient, ∠5×10−4dB/km, is consistent with the smaller experimental values reported.Subject Classification: [43]30.20; [43]20.20; [43]30.40.

ISSN:0001-4966    

DOI:10.1121/1.381195

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP