ISSN:0001-4966    

DOI:10.1121/1.1912899

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1912900

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Within the past two decades, the combined contributions of scientists and engineers in this country and abroad have resulted in development of systematic and reliable methods for the prediction of sonic‐boom phenomena. The prediction techniques reviewed in the present paper permit the calculation of sonic booms produced by rather complex conventional supersonic aircraft designs performing level nonaccelerated flight in a quiet atmosphere. It has been found that the calculated characteristics for a quiet atmosphere are representative of nominal conditions in a statistical sense for a real atmosphere. Basic concepts of supersonic flow analysis, for representation of an airplane as a linear distribution of disturbances and for determination of the resultant pressure field complete with shocks, are outlined. Numerical techniques for implementation of the theory are discussed briefly, and examples of the correlation of theory with experimental data from wind tunnel and flight tests are presented. Special attention is given to presentation of a simplified method for rapid “first‐cut” estimation of farfield bow‐shock overpressure. Finally, some problems encountered in attempts at applying the prediction techniques for the nearfield at high supersonic Mach numbers are recognized, and the need for further refinement of present techniques or the development of new systems is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1912901

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

There have been many attempts to reduce or eliminate the sonic boom. Such attempts fall into two categories: (1) aerodynamic minimization and (2) exotic configurations. In the first category changes in the entropy and the Bernoulli constant are neglected and equivalent body shapes required to minimize the overpressure, the shock pressure rise and the impulse are deduced. These results include the beneficial effects of atmospheric stratification. In the second category, the effective length of the aircraft is increased or its base area decreased by modifying the Bernoulli constant a significant fraction of the flow past the aircraft. A figure of merit is introduced which makes it possible to judge the effectiveness of the latter schemes.

ISSN:0001-4966    

DOI:10.1121/1.1912902

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The evolution of the sonic‐boom signature from a supersonic aircraft is discussed and treated. This treatment is the basis for a general algorithm and computer program for sonic‐boom prediction in a stratified atmosphere with steady winds. The treatment is based upon geometric acoustics with calculation of nonlinear distortion, and takes arbitrary maneuvers of the aircraft into account.

ISSN:0001-4966    

DOI:10.1121/1.1912903

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

A review is given of information obtained in recent years concerning the effects on sonic‐boom signatures of departures of the atmosphere from a perfectly stratified time invariant model. These effects include the observed random variations in boom overpressures from those expected for a stratified atmosphere, the anomalously large and variable rise times, and the occurence of spiked or rounded waveforms rather than the characteristicNwaves. The extent of the variability in data recorded during actual flight tests is summarized in the form of histograms, representing experimentally obtained probability density functions. The physical mechanisms believed to be responsible for the variations and the anomalous features in the signatures are described. These include refraction and subsequent wavefront rippling by turbulence, the possible focusing or defocusing of rays, the formation of caustics, and the phenomenon of wavefront folding, diffraction, and scattering. Recent statistical theories of shock propagation through a turbulent atmosphere proposed by Crow, George and Plotkin, Pierce, Horning, and others are reviewed.

ISSN:0001-4966    

DOI:10.1121/1.1912904

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Research on aircraft‐generated sonic booms has led to the development of special techniques to generate controlled sonic‐boom‐type disturbances without the complications and expense of supersonic flight operations. This paper contains brief descriptions of several of these techniques along with the significant hardware items involved and indicates the advantages and disadvantages of each in research applications. Included are wind tunnels, ballistic ranges, spark discharges, piston phones, shock tubes, high‐speed valve systems, and shaped explosive charges. Specialized applications include sonic‐boom generation and propagation studies and the responses of structures, terrain, people, and animals. Situations for which simulators are applicable are shown to include both small‐scale and large‐scale laboratory tests and full‐scale field tests. Although no one approach to simulation is ideal, the various techniques available generally complement each other to provide desired capability for a broad range of sonic‐boom studies.

ISSN:0001-4966    

DOI:10.1121/1.1912905

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Sonic booms produced by aircraft moving at supersonic speeds apply moving loads to the earth's surface. In deep water, a moving underwater pressure field is observed to accompany the hyperbolic boom trace sweeping over the surface. The pressure waveform underwater near the surface is almost identical to that of theNwave in air, but it is rapidly smoothed and attenuated with depth, typically becoming one‐tenth as large at a depth less than 0.6 of theNwavelength. Overpressures may exceed background noise pressures by factors of up to 100 at moderate depths for frequencies between 2 Hz and 100 Hz, but are less than 0.16% of pressures known to harm marine life in single exposures. Adequate quantitative theories for the underwater effect have been developed, and have been verified by scale‐model experiments. On land, which is generally stratified, there are two major effects: the “static” deformation field traveling with the surface load, and air‐coupled Rayleigh wavetrains following eachN‐wave transient. The latter have frequencies and amplitudes determined by the geology and the aircraft speed. The former has always been the largest effect in over 1003 seismograms recorded in field tests. Its amplitude is proportional to the sonic‐boom overpressure. The maximum ground motion recorded was about 100 times the largest natural, steady seismic noise background, but was still less than 1% of the accepted seismic damage threshold for residential structures. Movement is greater in soft ground than on hard rock, and decreases rapidly with depth. Present quantitative theories for the major seismic effects agree reasonably well with the experiments. Seismic forerunner waves, which begin at least 7 sec before arrival of the sonic boom, might be exploited for automatic warnings to lessen the startle effect. Sonic booms probably cannot trigger earthquakes, but might possibly precipitate incipient avalanches or landslides in exceptional areas which are already stressed to within a few percent of instability.

ISSN:0001-4966    

DOI:10.1121/1.1912906

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Concepts of sonic‐boom pressure loading of building structures and the associated responses are reviewed, and results of pertinent theoretical and experimental research programs are summarized. The significance of sonic‐boom load time histories, including waveshape effects, are illustrated with the aid of simple structural elements such as beams and plates. Also included are discussions of the significance of such other phenomena as three‐dimensional loading effects, air cavity coupling, multimodal responses, and structural nonlinearities. Measured deflection, acceleration, and strain data from laboratory models and full‐scale building tests are summarized, and these data are compared, where possible, with predicted values. Damage complaint and claim experience due both to controlled and uncontrolled supersonic flights over communities are summarized with particular reference to residential, commercial, and historic buildings. Sonic‐boom induced building responses are compared with those from other impulsive loadings due to natural and cultural events and from laboratory simulation tests.

ISSN:0001-4966    

DOI:10.1121/1.1912907

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

This paper reviews reports and studies of animal response to sonic booms. Individual domestic or pet animals may react to a boom, a simple startle response being the most common reaction. However, specific reactions differ according to the species involved, whether the animal is alone, and perhaps whether there has been previous exposure. Occasional trampling, moving, raising head, stampeding, jumping, and running are among the reactions reported. Avian species occasionally run, fly, or crowd. Reactions vary from boom to boom and are not predictable. Animal reactions to booms are similar to their reactions to low‐level subsonic airplane flights, helicopters, barking dogs, blown paper, and sudden noises. Conclusive data on effects of booms on production are not available, but no change in milk production by one dairy herd was noted. The reactions of mink to sonic booms have been studied in considerable detail. Female mink with kits may be alerted, pause in activity, and look for source of sound. Sleeping females may awaken and mating pairs may show momentary alertness, but the mating ritual is not disturbed. No wounding, killing, carrying, or burying of kits in nest by females have been observed in the studies. In one series of observations the reactions of the mink to barking dogs, truck noises, and mine blasting were similar to their reactions to booms. The effect of booms on eggs being hatched under commercial conditions was examined in detail, and no effects on hatchability were found. However, a mass hatching failure of the Dry Tortugas Sooty Tern occurred in 1969, and the circumstantial evidence suggests that physical damage to the eggs by severe sonic booms caused by low‐level supersonic flights was responsible. Observations on wild and zoo animals are quite limited, but those made on deer, reindeer, and some zoo animals revealed no reaction or only minimal and momentary reaction, such as raising the head, pricking the ears, and scenting the air.

ISSN:0001-4966    

DOI:10.1121/1.1912908

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP