摘要:

Over the last two years, the author [J. Acoust. Soc. Am.65, 1190–1197 (1979)] and other researchers have reanalyzed the plate‐fluid interaction problem from different perspectives. In this paper the eigensolutions to the fluid‐loaded thick plate equation are presented as a function of modulus of elasticity fluid loading and structural damping. The thick plate equation allows for the inclusion of shear deformation and rotary inertia effects on the vibrational response of the plate. Solutions for loci of the different modes as a function of frequency are presented in the fluid wavenumber plane. It is shown that under certain conditions the roots of the system cross from one Riemann sheet to the other thus changing the basic characteristics of the plate response and also of the radiated acoustic field. Internal structural damping is also shown to have the same effect upon the behavior of the root loci. Some of the phenomena discussed are a result of the rotary inertia terms in the plate equations and, therefore, cannot be explained by the use of the simpler thin plate analysis.

ISSN:0001-4966    

DOI:10.1121/1.2017649

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A model for an imperfectly bonded interface between two elastic media has been proposed. Displacement across this surface is not required to be continuous but it is taken to be linearly related to the stress traction which is continuous across the interface. For isotropic interface behavior, there are two independent interface compliances,ηNand ηT, where the component of the displacement discontinuity normal to the interface is given by ηNtimes the normal stress and the parallel component is given by ηNtimes the shear stress. Stoneley wave velocities (possibly complex) at such interfaces between two elastic halfspaces are calculated and are found to be dispersive even when the compliances, ηNand ηT, are real and frequency independent. When the interface is purely dissipative such that the stress traction is proportional to the velocity discontinuity, the compliances are pure imaginary and proportional to the inverse of frequency yielding complex, but in this case, nondispersive, Stoneley wave velocities.

ISSN:0001-4966    

DOI:10.1121/1.2017702

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

This personal philosophy has evolved from eight years of active participation in the research and the design of Navy ships for controlled noise characteristics. The design for the control of noise begins with the establishment of requirements. Noise specifications must serve an understandable operational purpose that can be communicated to the many people that will design and build the ship. The requirements must be capable of being met within the state of the art, and at a cost that is commensurate with the value of the noise control. The cost must be acceptable to the producer as well as the customer, and the producer must understand from the beginning the amount of engineering and test that he is committed to. The techniques for controlling the noise of ships are well known, but there are choices to be made for those techniques to be used in construction, and those that can be used to come up to specification after test. An allowance should be made for the cost of test and for the cost of corrections to be made after test.

ISSN:0001-4966    

DOI:10.1121/1.2017749

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

In recent years, shipboard airborne noise criteria have been applied much more stringently than in the past. Further, noise criteria are likely to be lowered for future ship designs. In response to this, more noise sources and transmission paths need to be considered in the acoustical design process. This paper considers noise control treatments which are presently coming into accepted practice in this country and discusses the merits as well as liabilities of these treatments. Needs for future research and development efforts are also presented in light of more restrictive noise criteria.

ISSN:0001-4966    

DOI:10.1121/1.2017801

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Measurements of acoustic backscatter in the lower planetary boundary layer and optical line‐of‐sight scintillation in the surface layer are used separately to compute the sensible heat flux in the unstable surface layer. Comparisons with simultaneous low‐level point measurements by eddy correlation show good agreement both in absolute magnitude and response to rapid changes, indicating that acoustic methods may be successful over less homogeneous terrain where conventional surface layer measurement techniques are often inaccurate. Corrections to lake into account the effects of humidity fluctuations are found necessary in order to achieve accuracies within 10%. Free convection is assumed to permit interpretation of the sodar data, while either forced or free convection is assumed for the scintillation data. A systematic overestimate of surface heat fluxes is found from acoustic measurements made during the morning when the convectively mixed layer is rapidly increasing in height. [Work supported by U.S. Dept. of Energy and U.S. Environmental Protection Agency.]

ISSN:0001-4966    

DOI:10.1121/1.2017857

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

We have utilized a simplified second‐order turbulence closure scheme to predict acoustic scattering profiles as a function of time from a numerical model of the atmospheric boundary layer under statically stable conditions. Comparisons have been made with data obtained at South Pole Station, Antarctica. Two cases in particular were analyzed. The first was that of warm air advection over a cold surface. The second involved the thin boundary layer and elevated scattering layers that form when the geostrophic pressure gradient force opposes the thermally driven slope winds characteristic of the East Antarctic ice sheet.

ISSN:0001-4966    

DOI:10.1121/1.2017908

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The magnitude of temperature structure coefficient is computed by sounder echo data. The results showed that the magnitude ofCT2has an obvious fluctuation with time. It has a character of positive bias distribution, and fits the logarithmic normal distribution. The analysis of the spectraCT2showed that, the spectrumF(k) ofCT2usually fits thek−4rule in stable and unstable stratifications. There exists a peak range of energy on the frequency range 10−1− 3 × 10−4s−1. The analysis ofCT2on time‐height counter section indicates that the distribution of CrCT2has horizontal stratum structure in stable stratification and it fits the ruleCT2 ∝ z−4/3in unstable stratification. These results measured by acoustic radar agree with earlier direct observations by airplanes [L. R. Tsvang, Radio Sci.4(12) (1962)].

ISSN:0001-4966    

DOI:10.1121/1.2017966

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The just noticeable increase in bandwidth of a two‐tone complex was measured as a function of bandwidth at three center frequencies: 500, 2000, and 4000 Hz. The bandwidths of the stimuli ranged from one‐fourth to four times the critical bandwidth, the overall intensity was 60 dB SPL and the duration of each two‐tone complex was 600 ms with 25 ms rise‐fall time and 600 ms interstimulus interval. Using a same‐different paradigm, discrimination threshold was determined with a transformed up‐down procedure. The just noticeable increase in bandwidth is small at narrow bandwidths, but increases dramatically once the bandwidth exceeds some limit. At 500 and 2000 Hz, the limit corresponds to the critical bandwidth, whereas at 4000 Hz, the limit corresponds to approximately half the critical bandwidth. As the bandwidth is increased beyond two to three times the critical bandwidth, a second change in the function occurs, and the just detectable increase in bandwidth remains constant or decreases slightly. These results suggest that the interaction between two tones within a critical band can give rise to a new, discriminable cue, i.e., envelope frequency. [Work supported by NIH Grant No. 2R01NS07270‐07A1 and HEW Grant No. RR07143.]

ISSN:0001-4966    

DOI:10.1121/1.2018026

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

In general, modelling of the auditory system on the basis of long‐term spectral characteristics of signals has proved adequate for prediction of monaural performance. There is evidence, however, that for time‐varying signals, such as short duration tonal glides, detectability of signals with identical long‐term spectra may differ due to other characteristics, e.g., direction and rate of frequency changes [Collins and Cullen, J. Acoust. Soc. Am.63, 469–473 (1978)]. In the present study, difference limens were determined for signals with similar long‐term spectra which were different in the time‐frequency domain. The stimuli were signals composed of 30 ms tonal glides preceded or followed by 200 ms fixed frequency segments. Measurements were made about reference glide segments with 0‐, 17‐, or 34‐Hz/ms linear rate of frequency change. Experienced, normal‐hearing listeners served as subjects, and an adaptive procedure was used. Smaller difference limens were obtained when glide segments followed rather than preceded the fixed frequency segment. This finding cannot be easily explained by peripheral events alone. Rising glides tended to be more discriminable than falling glides when comparing signals with glide segments of equal rate and temporal position relative to the fixed frequency segment. The latter observation can be accounted for on the basis of phase differences between rising and falling, spectrally similar signals, and a model will be presented. [Work supported by NINCDS, Grant No. IF32 NS 06053.]

ISSN:0001-4966    

DOI:10.1121/1.2018032

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

In the late babbling and early word stages of development, the vowels that children produce are not as “well formed” as those of adults. Taking into consideration the higher formant frequencies of children's vowels, which follow from their shorter supralaryngeal vocal tracts, one finds, for example, thatF1of an [i] is higher than it should be relative toF2at ages of approximately 70 weeks. This is presumably a consequence of the shorter length of the child's pharynx relative to the oral cavity (King, 1952). As the child matures, the relative position ofF1andF2of [i] come closer to the adult model. In addition, there is a greater variability in the formant frequencies of all vowels at earlier ages. This may be a consequence of the child's pharynx not being equal in length to the oral cavity, making vowels like [i]less characteristically “quantal” (Stevens, 1952). This variation may also be due to a lack of motor control. In this study, the relative importance of quantalness versus motor control is assessed by comparing the variability of quantal vowels, such as [i] and [u], with other vowels as a function of age.

ISSN:0001-4966    

DOI:10.1121/1.2017562

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP