摘要:

The Biot theory for the acoustics of porous media contains drag and virtual mass coefficients that depend on the physical properties of the fluid and solid constituents, the frequency, and the microstructure of the porous medium. Biot derived an equation for the drag coefficient as a function of frequency by assuming cylindrical pores. In this paper, the finite element method is used to obtain values of the drag and virtual mass coefficients for face‐centered cubic granular materials with three different porosities and compare our numerical results to Biot’s analytical solutions. By making appropriate choices of three parameters in Biot’s analytical solution for cylindrical pores—the pore size parameter, the Kozeny parameter, and the tortuosity—the analytical solution matches these numerical results very well. This suggests that with appropriate choices of these parameters the analytical approach can predict the dependence of the drag and virtual mass coefficients on frequency for an arbitrary pore geometry. These results support a relation suggested by Hovem and Ingram for approximating the pore‐size parameter for spherical grains, and they also agree with a relation suggested by Berryman for the dependence of the tortuosity on the porosity.

ISSN:0001-4966    

DOI:10.1121/1.401912

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

In this paper, results of investigations of underwater ambient noise are presented based on statistical analysis of the acoustic pressure and three orthogonal components of particle velocity of a mediumP(t),Vx(t),Vy(t),Vz(t). The mathematical analysis used includes cross‐spectral characteristics, simple coherence functions, phase spectra, and an algorithm to split the noise field into anisotropic and isotropic fields. The above approach is applied to study the anisotropic and isotropic fields of ambient noise in the deep open ocean and in a coastal area. A fundamental feature of the anisotropic field that has been revealed is that the direction of the horizontal component of dynamic noise energy flux is similar to the surface roughness propagation direction.

ISSN:0001-4966    

DOI:10.1121/1.401913

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

This paper describes the phenomenon of cancellation of opposing acoustic energy flows observed in an oceanic waveguide. One of the flows is a vertical (or horizontal) energy flow of dynamic underwater ambient noise, and the other (opposing) one is a vertical (or horizontal) energy flow from a local source. Results of a field experiment in the deep ocean are presented which show that the above‐mentioned phenomenon leads to the destruction of coherence between the vertical and horizontal components of the particle velocity and pressure.

ISSN:0001-4966    

DOI:10.1121/1.402286

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A recently developed theory by Tolstoy [IEEE J. Ocean Eng.14, 4–16 (1989); J. Acoust. Soc. Am.85, 661–669 (1989)], which exactly calculates the attenuation produced by a truncated wedge barrier, has been adapted to assume a line source parallel to the barrier. The theoretical results are compared with experimental measurements obtained using acoustic impulses and rectangular barriers up to 0.45 m wide. The results are also compared with other wide‐barrier prediction techniques. It is shown that the refinement to include multiple scattering between the vertices is generally unimportant and can lead to erroneous results if the necessary series are not summed over hundreds of terms. The phase information provided by the theory is evaluated by comparing predicted and measured impulse waveforms obtained behind the barrier.

ISSN:0001-4966    

DOI:10.1121/1.402287

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Acoustic impulses with a duration of about 2 ms have been used to measure the attenuation of full‐sized barriers, including thin edges, wedges, and wide barriers. A technique involving two microphones was used which permits the direct comparison of the diffracted and undiffracted pulse waveforms. This allows the attenuation to be determined with an accuracy of better than 1 dB over the range 700 Hz–12 kHz from a single measurement set. The experimental results are compared with predictions from a variety of approximate and exact diffraction theories. As impulses involve both phase and magnitude information, they form a rigorous test of the theories. One advantage of the experimental technique is that it permits effects due to nonideal features, such as supporting struts, to be rapidly observed.

ISSN:0001-4966    

DOI:10.1121/1.402288

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The motivation for organizing the session and a brief introduction to each speaker are presented.

ISSN:0001-4966    

DOI:10.1121/1.402289

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The sources of sound production in a low Mach number turbulent boundary layer are examined. The sources are shown to be quadrupole in nature and to result from supersonically convecting wave‐number components of the fluctuating Reynolds’ normal stresses. The primary Tollmien–Schlichting instability of the boundary layer is found to radiate no sound. Analysis of various vortical phenomena suggests that the primary source is the process of formation of horseshoe vortices, with viscous sublayer bursts a possible secondary source.

ISSN:0001-4966    

DOI:10.1121/1.402290

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Properties of the wave‐vector‐frequency spectrum of fluctuating pressure on a smooth planar wall in turbulent boundary‐layer flow at low Mach number are reviewed. In the low but incompressive wave‐number range, where ω/c≲K≲max(δ−1,U∞/ω), consistent with the Kraichnan–Phillips hypothesis for inviscid flow, the dependence would be expected to be asK2, but no experimental substantiation exists. In a higher subconvective range where δ−1≲K≲ω/U∞, most pertinent experiments suggest that the spectrum is instead wave‐number‐white. In the acoustic domain a peak is predicted atK=ω/c. A mean‐shear contribution proportional to the square of streamwise wave number appears predominant in the convective domain. An explicit model spectrum is specified that conforms in an appropriate domain to the principle of wall similarity and corresponds to boundary‐layer velocity spectra that are planar isotropic in a convected frame. The model potentially encompasses the entire inviscid domain, including the acoustic range. An alternative model exhibits a factorable dependence on the wave‐number components. In the acoustic range, the model forms are totally unvalidated by experiment. In the convective domain, the state of determination suffices for many applications, but a preference between model forms and assured choice of parameter values awaits further analysis and perhaps certain further measurements. An addendum based on recent work suggests that the wall pressure at low but incompressive wave numbers may be dominated by a wave‐vector‐white contribution originating in the viscous wall condition.

ISSN:0001-4966    

DOI:10.1121/1.402291

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

This paper is a summary account of empirical models of the turbulent boundary layer wall‐pressure spectrum and radiated sound. Terminology, definitions, and formulas are reviewed to enable the reader to gain access to the current literature. Empirical representations are given for the wall‐pressure wave number‐frequency spectrum and the acoustic pressure frequency spectrum for both smooth and rough walls at low mean flow Mach numbers, and for the wall point‐pressure spectrum at arbitrary Mach number.

ISSN:0001-4966    

DOI:10.1121/1.402292

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The propagation of finite amplitude sound in a lossless and homogeneous liquid layer that is bounded below by a rigid surface and above by a free surface is investigated theoretically. A solution is derived for the second harmonic pressure that is generated by a tone in a single mode. Dispersion causes the second harmonic mode shapes to vary with range. A nonlinear Schrödinger equation [Zabolotskaya and Shvartsburg, Sov. Phys. Acoust.33, 221–222 (1987)] is used to investigate the propagation of a narrow‐band pulse in a single mode. Pulse propagation in the waveguide is found to be stable.

ISSN:0001-4966    

DOI:10.1121/1.402293

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP