摘要:

The assumptions underlying the exact equations of motion for a thermoviscous fluid are reviewed and the complete equations are given, for reference convenience, in both tensor and vector form. The first‐ and second‐order acoustic equations are then exhibited and used to obtain the source terms that account for the generation of vorticity and streaming. In order to preserve a broad base from which to make the approximations appropriate under various circumstances, all terms are retained explicitly including those arising from any functional dependence of the viscosity and thermal coefficients on the state variables.The distinction between spatial and material coordinate systems is carefully drawn and conversion transforms are derived rigorously and their use illustrated. The general properties of finite‐amplitude waves are demonstrated by including the second‐order terms in a plane‐wave solution of the exact wave equation in material coordinates, with special concern for the effects of large amplitude on speed of propagation and on wave‐form distortion.Sound absorption and dispersion measures for a viscous conducting fluid are analyzed in terms of Truesdell's recent exact solution of the first‐order secular equation. These differ characteristically from the corresponding measures predicted for pure relaxation in a two‐fluid mixture. It is concluded that a complete and adequate theory of sound absorption and dispersion will need to take into accountbothrelaxation and viscothermal phenomena as well as their interaction, and that until such a general theory is available, theexacttheory of viscothermal effects—rather than the crude linear approximation commonly, but inappropriately, called “classical”—should be used in computing the “excess” absorption and dispersion to be accounted for by relaxation processes.The exact solutions of the secular equation permit a new evaluation, in series form, of the characteristic acoustic impedance for a thermoviscous medium. The notes conclude with a revised account of the spectral character of thermal noise in the acoustic medium based on the quantum hypothesis and a merger of the concepts of architectural acoustics and specific‐heat theory.

ISSN:0001-4966    

DOI:10.1121/1.1908106

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

The attenuation resulting from heat conduction of the quasi‐plane mode in a cylindrical conduit is discussed in the high‐frequency (narrow boundary layer) limit. The heat conduction part of the Kirchhoff losses is derived by means of a volume integral whose physical interpretation can be given.Preliminary to considering the Kirchhoff case, the heat conduction attenuation of a plane wave is computed to illustrate the use of the integral form.Finite thermal conductivity of the walls, as it gives rise to attenuation in guided propagation, is also discussed.

ISSN:0001-4966    

DOI:10.1121/1.1908108

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

The reflection and transmission of sound by a moving medium are investigated theoretically and the reflection and transmission coefficients are determined. These coefficients are found to depend only upon that component of the velocity of the medium which lies in the plane of incidence. The reflection coefficient increases with the velocity of the moving medium until a velocity is reached at which total reflection occurs. Total reflection persists until a still higher velocity is reached above which the reflection coefficient decreases as the velocity increases.

ISSN:0001-4966    

DOI:10.1121/1.1908110

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

Visualization of the vortex flow pattern in typicalprimary Pfeifentonjets was made by means of shadow‐graph techniques to show the transition in form of the vortex pattern as it moves downstream in the jet, as well as, the dependence of the downstream translational vortex velocity and the geometry of the vortex pattern on the Reynolds number of the jet.Results of experiment are compared with available theory. These studies were carried out with carbon dioxide jets discharging into the atmosphere. The flow channel geometry consisted of a pipe78 in.in diameter, 12.013 in. long effectively, open at one end which was inserted into a large stilling tank and terminated at the other end by an orifice plate containing a sharp‐edged circular orifice, 0.250 in. in diameter and 0.093 in. thick.

ISSN:0001-4966    

DOI:10.1121/1.1908112

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

The front of a shock wave in an ideal fluid is characterized by a discontinuous transition from the undisturbed state to a highly compressed state in which the entropy of the fluid has increased. The relations between pressure, density, propagation velocity, and particle velocity behind the shock front are represented by the equations for conservation of mass, momentum, and energy and by the equation of state of the fluid. The entropy change produced by the transition is third order in the compression for weak shocks. The propagation of shock waves through metals can be described by a hydrodynamic theory which assumes that the metal is an ideal fluid behind the shock front, and that the hydrostatic equation of state is applicable there. Three hydrostatic equations of state for Al, Cu, Fe, and Pb are compared with experimental data at low pressures and quantum mechanical calculations pressures up to several hundred megabars. With these equations of state the hydrodynamic theory is used to calculate explicitly the entropy increase across the shock front, the amount by which the pressure exceeds the adiabatic pressure for a given compression, and the temperature rise after the shock pressure has been relieved for the metals mentioned above.

ISSN:0001-4966    

DOI:10.1121/1.1908114

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

Solutions are given for the lowest natural frequency of flexural vibration of isosceles trapezoidal flat plates which have simply supported edges. The results of the calculations are presented graphically so that one may determine rapidly a desired fundamental frequency. The range of the values of the geometric parameters defining the plate is large enough to cover most practical cases.

ISSN:0001-4966    

DOI:10.1121/1.1908116

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

A wave theoretical analysis of symmetric mode propagation in a medium confined by a cylindrical elastic shell is carried out. An expression is obtained for the axial propagation constant, specialized to that case of a thin steel shell surrounding a column of air. This is further restricted to the description of the lowest symmetric mode.The dispersion predicted by the analysis is in order of magnitude agreement with that obtained on a transmission line picture.

ISSN:0001-4966    

DOI:10.1121/1.1908118

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

Results are presented giving values of the phase velocities and the relative magnitudes of the components of displacement for all possible free waves in the wall of a thin, elastic, cylindrical shell. Three classes of waves are identified and their natures are discussed as frequency is varied continuously. The vibrations are interpreted not only as standing waves and waves progressing the axial direction, but also as fully free waves traveling in a helical direction in the wall of the cylinder.

ISSN:0001-4966    

DOI:10.1121/1.1908120

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

Reverberation chambers used for acoustical measurements should have completely random sound fields. We denote byRthe cross‐correlation coefficient for the sound pressures at two points a distancerapart.R = 〈p1p2〉Av/(〈p12〉Av〈p22〉Av)12, wherep1is the sound pressure at one point,p2that at the other, and the angular brackets denote long time averages. In a random sound field,R= (sinkr)/kr, wherek= 2π/(the wavelength of the sound). An instrument for measuring and recordingRas a function of time is described. A feature of this instrument is the use of a recorder's servomechanism to measure the ratio of two dc voltages. The results of correlation measurements in reverberant sound fields are given.

ISSN:0001-4966    

DOI:10.1121/1.1908122

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

The acoustical properties of carpet are of interest in the design of auditoriums and studios, since the absorption which it contributes may be quite significant. However, little data exist on the acoustical properties of carpet and the scanty data available make no distinction among the various types of carpet. This paper describes measurements of the normal absorption coefficient and flow resistance for a wide variety of carpet samples. The normal absorption data were used to investigate which of many variables in carpet construction are important from the standpoint of acoustical absorption. On the basis of these data, certain key samples were selected for chamber test at the National Bureau of Standards for comparison with the tube measurements.

ISSN:0001-4966    

DOI:10.1121/1.1908124

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP