摘要:

Wall‐pressure fluctuations are estimated from the flow properties in the shear layer of a separated region, using a modified form of Kraichnan's mean‐shear‐turbulence interaction equation. Experimental and calculated values of the rms wall pressure are presented as well as pressure‐correlation measurements and flow properties in a separated flow behind a thin fence mounted normal to the flow boundary.

ISSN:0001-4966    

DOI:10.1121/1.1912724

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The investigation by Pridmore‐Brown of the effects of shear on the downstream propagation of sound in rigid‐walled rectangular ducts has been extended to include upstream sound propagation as well as the effects of boundary‐layer thickness. Solutions are given in terms of a combined Galerkin‐Runge‐Kutta numerical technique as well as in terms of a technique based upon a perturbation of the well‐known zero Mach number solution. The effect of shear on upstream sound propagation is to refract the sound into the center of the duct. The effect of refraction is found to be important for boundary‐layer flows when the ratio of boundary‐layer height to acoustic wavelength is equal to or greater than unity.

ISSN:0001-4966    

DOI:10.1121/1.1912725

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

An investigation of sound transmission into small enclosures considers the effects of acoustically induced coupling between shell modes. The level of cavity reactance is examined. The noise reductions for a closed cylinder and a rectangular parallelopiped enclosure (with a single flexible panel) placed in reverberant acoustic fields are computed and experimentally checked. The transmission by resonant and nonresonant shell modes is examined, especially in relation to the statistical‐energy‐analysis approach. The nature of the predominance of one type of transmission over the other is considered in relation to shell and cavity configurations and structural damping levels.

ISSN:0001-4966    

DOI:10.1121/1.1912694

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

A statistical approach to response prediction is a method for estimating the gross features of the response of complex structures to random excitation. A method of this type is presented and illustrated by means of two simple examples. In the first example, the mean‐square velocity at a specific point of a single homogeneous beam excited by a stochastic point force is considered; in the second, the mean power flow between two homogeneous beams weakly coupled by a spring is considered when one of the two beams is excited by a stochastic point force.

ISSN:0001-4966    

DOI:10.1121/1.1912695

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The measured values for the radiation resistance of a small sonar transducer at an air‐water surface near an oblique plane brass boundary are presented and compared with the theoretical values calculated from a dipole‐image model.

ISSN:0001-4966    

DOI:10.1121/1.1912696

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Peak pressure and time measurements and impulse and energy calculations are reported of the shock wave resulting from 5‐ and 10‐mil12‐in.‐longNichrome wires. The time, impulse, energy, and gauge distance are scaled to obtain the resulting similarity curves of peak pressure, reduced time constant, reduced impulse, and reduced energy, which are plotted against the scaled reciprocal distance.

ISSN:0001-4966    

DOI:10.1121/1.1912697

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The radial mechanical driving point impedance for a submerged aluminum shell structure has been studied in two anechoic tanks. One of these tanks is lined with concrete and wood chip (Insulkrete) wedges, while the other is lined with a perforated sound‐absorbent coating (SAPER‐T). It has been found that the mechanical impedance values obtained in the wedge‐lined tank vary with time following immersion, whereas the values obtained in the other tank have a high degree of repeatability. It is postulated that the time dependence is a consequence of a chemical reaction between the aluminum shell and the highly alkaline solution contained within the wedge‐lined tank, because of the generation of minute gas bubbles.

ISSN:0001-4966    

DOI:10.1121/1.1912698

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Comments are made on the subject paper. The use of level crossing rate as a means of signal detection in white Gaussian noise is proposed. Some preliminary results are given which indicate that acceptable performance may be realized at low signal‐to‐noise ratios.

ISSN:0001-4966    

DOI:10.1121/1.1912699

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The background of our assumption, that (for practical purposes) the zero‐crossing rate can be taken as normally distributed, is explained in more detail. It is also stated that no proof of this proposition has been given in the paper.

ISSN:0001-4966    

DOI:10.1121/1.1912700

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The BIFI range is a shallow‐water acoustic range in Long Island Sound, about 19 miles long and 110 ft deep. Results of time‐smear and frequency‐smear studies made on this range are presented. It is shown how these results may be used to predict signal fluctuation. In time‐smear studies, the received signal is divided into a front, a main arrival, and a tail. The relative energies of the three sections of the signal are computed, and these results are used to predict the range of signal fluctuations. The above analysis and computation are easily carried out on a digital computer using, as input, data automatically punched on cards. Frequency smear is the Doppler shift undergone by a signal as a result of being reflected from a moving surface. Many frequency‐smear spectra were obtained for varying sea states, and, from these, dispersion as a function of sea state was calculated. The dispersion increased with sea state, in agreement with theory.

ISSN:0001-4966    

DOI:10.1121/1.1912701

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP