摘要:

The results of an experimental study of a relatively unfamiliar mode of propagation are presented: the zero‐order mode in a tube with massive wall reactance. The observed and theoretical disperison curves, which show good agreement, display a high‐pass cut‐off frequency. There is a dead zone between this frequency and the ring resonant frequency of the tube.The phase velocitiesc2are measured indirectly from the directivity patterns of a receiver in the form of a long rubber hose coupled to a microphone; these patterns are characterized by two symmetrical lobes whose angular separation is 2 cos−1c/c2,cbeing the sound velocity.

ISSN:0001-4966    

DOI:10.1121/1.1908237

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

A theory is developed for the propagation of stress waves in a porous elastic solid containing compressible viscous fluid. The emphasis of the present treatment is on materials where fluid and solid are of comparable densities as for instance in the case of water‐saturated rock. The paper denoted here as Part I is restricted to the lower frequency range where the assumption of Poiseuille flow is valid. The extension to the higher frequencies will be treated in Part II. It is found that the material may be described by four nondimensional parameters and a characteristic frequency. There are two dilatational waves and one rotational wave. The physical interpretation of the result is clarified by treating first the case where the fluid is frictionless. The case of a material containing viscous fluid is then developed and discussed numerically. Phase velocity dispersion curves and attenuation coefficients for the three types of waves are plotted as a function of the frequency for various combinations of the characteristic parameters.

ISSN:0001-4966    

DOI:10.1121/1.1908239

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The theory of propagation of stress waves in a porous elastic solid developed in Part I for the low‐frequency range is extended to higher frequencies. The breakdown of Poiseuille flow beyond the critical frequency is discussed for pores of flat and circular shapes. As in Part I the emphasis of the treatment is on cases where fluid and solids are of comparable densities. Dispersion curves for phase and group velocities along with attenuation factors are plottedversusfrequency for the rotational and the two dilational waves and for six numerical combinations of the characteristic parameters of the porous systems. Asymptotic behavior at high frequency is also discussed.

ISSN:0001-4966    

DOI:10.1121/1.1908241

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Applications of ultrasonics in neurosurgery involve the production of lesions of a specified size at a specified location, and in a reproducible fashion. Control of the dosage required for a given lesion depends on the geometry of the focal region, the exact determination of focal intensity and the relation between irradiation parameters and biological effect. From an analysis of these factors an optimum frequency for each focal depth is determined and an empirical dosage relationship based on ultrasonically produced paralysis in mice is stated. The mechanism of cell destruction by ultrasound is shown to be a temperature‐dependent mechanical effect originating at weak points in the tissue. The difficulties in extrapolating results obtained with experimental animals to applications in human neurosurgery are pointed out.

ISSN:0001-4966    

DOI:10.1121/1.1908244

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

It is shown that the detailed group‐theoretical analysis of molecular vibrations can be extended to continuous bodies of various shapes by regarding them as the limits of discrete systems with the number of particles becoming indefinitely large. In this paper an elementary review of the method is given and its application is illustrated with 2‐dimensional systems and thin systems having pyramidal symmetry (i.e., tents and shells). Both stationary and rotating systems containing any number of particles arranged with the symmetry of a regular polygon or polygonal pyramid are considered. For macroscopic systems, unlike molecules, different possible constraints must be taken into account in enumerating the genuine vibrations of various types. Otherwise, one proceeds as in the molecular case. By going to the limit of large numbers of particles, one obtains the fractional occurrence numbers of vibrations of various symmetry types for stationary or spinning membranes, plates, tents, or shells of all regular polygonal shapes.

ISSN:0001-4966    

DOI:10.1121/1.1908246

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

An integral solution to the differential equations of elastodynamics is given. The solution for the displacement at any point in an isotropic homogeneous, elastic medium is obtained in terms of the initial distribution of body forces within a given volume and the initial distribution of displacements and stresses over the bounding surface of the volume. These quantities appear in the solutions as retarded displacements, stresses, and body forces, with two types of retardation depending upon the velocities of longitudinal and transverse waves.From the integral solution the diffraction of elastic waves through large apertures bounded by opaque walls in solid materials is formulated. The incident wave motions may be either of longitudinal or transverse polarizations. The expected shear‐compression interaction is obtained in the course of the computation. By analogy with optical procedure, Fraunhofer diffraction of elastic waves may be investigated as a special case.In the example of diffraction by a slit, an incident compression wave is diffracted into (1) a compression wave with the “ordinary” spatial distribution similar to that obtained in the corresponding optical problem and (2) a weaker shear wave with an “extraordinary” distribution. In the case of incident shear waves, there is obtained a diffracted shear wave with an ordinary distribution, and a possible weak compression wave with the extraordinary distribution. The presence of the diffracted compression wave depends upon the polarization of the incident shear wave.Opacity in the Kirchhoff sense is a property of materials which are perfectly rigid.

ISSN:0001-4966    

DOI:10.1121/1.1908247

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

A study is made of the ultrasonic field produced by a circular quartz crystal transducer and the integrated response of a quartz crystal receiver with the same dimensions as the transducer. The transducer and receiver are taken to be coaxial, and it is assumed that the transducer behaves as a piston source while the integrated response is proportional to the average pressure over the receiver area. Computations are made for cases of interest in the megacycle frequency range (ka=50 to 1000;a=piston radius; λ=wavelength;k=2π/λ). The results contain features of use in identifying and correcting for diffraction errors. These features which apparently have been missed in previous investigations are compared with available experimental data. Finally correction formulas to account for diffraction effects in the accurate measurement of attenuation are discussed. It is shown that the order of magnitude of the diffraction attenuation is given by one decibel pera2/λ.

ISSN:0001-4966    

DOI:10.1121/1.1908249

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The interaction between an acoustic field and a thermal field is worked out for the case of a sound wave propagating down a channel in which the convection of heat occurs in a potential flow. The analysis restricted to inviscid fluids shows that the magnitude of the sound wave is reinforced as it propagates through the thermal field. The extent of this reinforcement is given in the form of an amplification factor which depends on the parameter of the flow and on the frequency of the sound wave.

ISSN:0001-4966    

DOI:10.1121/1.1908252

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Fifty‐three references from the open literature dealing with organ‐pipe combustion oscillations are reviewed; these oscillations were generated in various types of combustion systems by the flame, or the combustion process. The many systems discussed range from simple singing‐flame burners to industrial furnaces and high‐duty rockets. The combustion systems are classified, for purposes of discussion, according to the basic arrangement of the components of the unit. These classes are burners with singing diffusion flames, flash tubes, gauze‐tone burners, rocket‐shaped burners, burners utilizing secondary air, and ram‐jet type burners. The acoustical behavior of each system is described, and possible driving mechanisms for producing the observed oscillations are indicated. Some general remarks are made, based on the survey, concerning the mathematical formulation of mechanisms to explain the oscillations in particular cases.

ISSN:0001-4966    

DOI:10.1121/1.1908253

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Data are presented on acoustic oscillations produced by a burner using a hexagonal bank of hypodermic tubes as deep ports. Most of the tests were made with ethane as the fuel, but some tests were run with methane and propane, for comparison. Both the diameter and length of the combustion chamber were varied.It was found that the combustion chamber could be considered as a driver which forced the slugs of gas in the ports to oscillate. Burning of the incremental pulses of combustible mixture periodically issuing from the ports furnished energy to drive the oscillations when the pulses burned in phase with the oscillating component of the pressure in the chamber. The phasing depended on a time‐lag factor which was a function of the velocity of the gases through a space, similar to dark space, between the burner ports and the mean burning points, and the width of the space itself.The oscillations not only ceased when there was a failure to satisfy the timing criterion, but also ceased upon approach to either rich or lean blowoff limits of the conventional type. This premature cessation apparently results from the flame burning from fewer ports as the limits are approached, less driving energy being available.

ISSN:0001-4966    

DOI:10.1121/1.1908255

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP