摘要:

The sound powers of small uncased centrifugal‐fan rotors were measured at low‐tip Mach numbers. Correlation of the data by use of a similarity relationship derived from theory has shown that the broad‐band rotor sound is a result of randomly oriented dipole sources caused by fluctuations in fluid momentum. Deviations of the dependence of sound power on speed from that theoretically predicted were found. Speed dependences less than that predicted can be explained as a nearfield effect; the lack of agreement between theory and the fan law for sound can be explained on the same basis. Observed speed dependences greater than that predicted appear to result from having fixed frequency limits on the measurement system. A sharp wedge placed near the rotor periphery was found to generate discrete‐frequency dipole sound. Quadrupole sound appeared to be negligible.

ISSN:0001-4966    

DOI:10.1121/1.1909566

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Recent interest in (1) the directional control of highly collimated light beams and (2) internal modulation of laser action has stimulated a variety of experiments. This paper reports on experiments utilizing a barium titanate ceramic transducer formed into an arc of a short section of right circular cylinder and radiating into a tetrachloroethylene‐filled cell at 400 kc/sec. A helium‐neon laser beam was used to examine the index of refraction gradients produced in the liquid and to illustrate the possible deflection patterns. When the beam traversed the cell near the focal line, circular scanning was observed, with maximum deflection angles of approximately ±1.0°. Linear scanning reached ±1.3°. Data describing the experimentally observed beam motion showed good agreement with a theoretical analysis of the complex acoustic field in this region. Deflections produced by pulse excitation of the transducer exceeded ±1.5°. Ruby laser spiking was modulated to follow the 400‐kc/sec field, and in pulsed operation giant spikes were obtained, using the cell to control theQof the optical resonator cavity. High‐speed photographs of both the partial standing acoustic wave, the traveling shock waves, and the circular beam‐deflection pattern were taken.

ISSN:0001-4966    

DOI:10.1121/1.1909568

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The Napier frequency (frequency of maximum absorption per wavelength) in oxygen and in air is shifted to higher values by water vapor according to a quadratic law that has different coefficients in the two cases. It is shown that proper treatment of the relevant equations leads to the correct experimental relationship between them. From this relationship, all the various velocity constants in the equilibrium equations may be determined numerically. It turns out that nitrogen has a somewhat stronger effect than oxygen on the relaxation of water vapor, and that the rate of resonant interchange of energy between oxygen and water vapor is, in fact, smaller than the rate of relaxation of water vapor by itself. It is also shown that the postulate of dimer formation in water vapor as an explanation of the quadratic relationship leads to a contradiction with experiment.

ISSN:0001-4966    

DOI:10.1121/1.1909570

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The reflection and refraction of a plane sound wave by a nonequilibrium relaxing medium are examined. Since the medium is dissipative, Snell's law of refraction is modified depending not only on the properties of the media, but also on the angle of incidence. The amplitudes of the reflected and refracted waves are complex. Variations of both the angle and amplitude are analyzed and supplemented with calculations for different reaction rates and relative Mach numbers.

ISSN:0001-4966    

DOI:10.1121/1.1909572

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Stationary, wide‐band vibrations of complex dynamic systems are treated in terms of energy quantities, neglecting details of structure and excitation. Approximate relations between the average energies in loosely and conservatively coupled systems are obtained in terms of modal densities, internal losses, and coupling losses. It is shown that the products of modal density and coupling‐loss factor are equal within each pair of subsystems. The general theory is applied to study the noise reduction of a rectangular box, and experimental results are compared with theoretical predictions with generally good agreement. The transmission behavior of a box at a given frequency is shown to depend on the relation of this frequency to the lowest mechanical‐ and acoustic‐resonance frequencies and the critical frequency of the walls. Theory and experiment show that near the lowest mechanical resonances the pressure in the box may considerably exceed that in the incident sound field.

ISSN:0001-4966    

DOI:10.1121/1.1909574

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

In many cases of interest to experimentalists and geophysicists, the situation exists where a light, thin layer of material, such as glue or adhesive, is bonded to a heavier structure. If the layer is thin enough and if its acoustic impedance is small as compared to the underlying structure, then the layer can be thought of as having little effect upon the motion of the substructure. Thus, the effect of the substructure is to force motion of the thin layer. This paper considers the dynamic problem of a thin layer forced by displacements on the lower face and tractions upon the upper face. The exact solution is derived for the two‐dimensional case, while the three‐dimensional case is first considered using Bernoulli‐Euler‐Kirchhoff plate theory and, after this, including the effects of shear deformation and rotatory inertia. It is found that, if shear deformation and rotatory inertia are included, the theory is fairly accurate for problems in which the quarter‐wavelength of the disturbance is greater than or equal to the plate thickness.

ISSN:0001-4966    

DOI:10.1121/1.1909506

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

A two‐part study concerning the wave propagation of free harmonic waves in hollow and solid circular cylinders of transversely isotropic material is discussed on the basis of the linear theory of elasticity. The three‐dimensional equations of elastodynamics are solved in terms of three displacement potentials, and the resulting frequency equation is discussed for several special cases.

ISSN:0001-4966    

DOI:10.1121/1.1909508

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Numerical results to the exact frequency equations obtained in Part I [J. Acoust. Soc. Am.37, 1016–1021 (1965)] are presented here for hollow circular cylinders, and comparisons are made with an approximate shell theory developed previously.

ISSN:0001-4966    

DOI:10.1121/1.1909510

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

An approximate theory of rod vibration given Love has been extended to describe the occurrence of wave effects, or wave resonances, in rubber antivibration mountings. Thus, the longitudinal vibration of a mass‐loaded rubber mount of significant lateral dimensions and uniform cross section has been determined with the assumption that the elastic modulus and damping factor of the rubber are frequency‐ dependent quantities. Knowledge of the manner in which the elastic modulus and damping factor of natural rubber, natural rubber filled with carbon black, and a high‐damping synthetic rubber depend upon frequency has enabled realistic computations of transmissibility to be made. These computations have been contrasted with results obtained, for the same rubbers, from the simple one‐degree‐of‐freedom theory in which the occurrence of wave effects is disregarded. The effectiveness of the natural‐rubber mountings, which have relatively small clamping, is overestimated by the simple theory at high frequencies, although transmissibility will normally remain a small quantity. In the case of the high‐damping rubber considered, the results of the simple and Love theories are in relatively close agreement.

ISSN:0001-4966    

DOI:10.1121/1.1909512

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

A strong interference pattern has been observed in the reflection of monochromatic, acoustic pings from the ocean bottom. In our experiment, performed in the Gulf of Mexico at 24°16′N, 85°15′W, the pings had a frequency of 120.5 cps, a length of 0.12 sec, and were repeated every 5 sec. The transmitter was at a depth of 75 ft and the receiver at 3000 ft. The energy in successive bottom reflections varied by as much as 6 to 1, with a mean fluctuation of 30%. This rapid change in level was largely owing to the fact that the source was shallow and the air‐water interface was rough. Averaging the bottom reflections in groups of ten produces a moderately smooth relation between signal level and range. This relation exhibits a pronounced interference structure. The pattern observed can be interpreted in terms of a 130‐ft bottom layer having a velocity of 6650 ft/sec.

ISSN:0001-4966    

DOI:10.1121/1.1909514

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP