摘要:

Three‐dimensional ray‐tracing equations are presented for tracing acoustic rays in an inhomogeneous anisotropic atmosphere which are based on Hamilton's equations for geometrical optics. The equations are converted to a form suitable for direct numerical integration. Simplified ray equations for the special case of horizontal stratification are obtained. Results of ray tracing in an atmosphere with both vertical and angular wind shear are outlined, and the formation of a shadow zone in the downwind direction is demonstrated.

ISSN:0001-4966    

DOI:10.1121/1.1913331

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

An approximate numerical technique is presented whereby the pressure‐radiation patterns in a liquid half‐space produced by radiation from the end face of a circular cylindrical, semiinfinite, solid rod set flush in an infinite rigid baffle at the boundary of the half‐space can be calculated as a function of the elastic properties of the solid rod. The method is restricted to the low‐frequency range such that the lowest numbered mode in the solid rod is the only propagating mode. Axisymmetric longitudinal modes are the only ones assumed to exist in the rod. The velocity distribution of the rod end face does not have to be known or assumed. The radiation impedance of the rod end is calculated and compared with that of the rigid piston, as are the pressure radiation fields. The work here presents farfield radiation only, though the method can easily be extended to study the nearfield radiation patterns in the liquid half‐space.

ISSN:0001-4966    

DOI:10.1121/1.1913332

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Equations derived earlier for multiple scattering by arbitrary three‐dimensional configurations are applied to a line of equally spaced identical obstacles. We develop several different representations and approximations for the field and derive the appropriate energy and scattering theorems. Spherically symmetric scatterers are considered as a special case. In general, the results are analogous to those obtained before for the two‐dimensional problem of scattering by a planar grating of identical cylinders but differ essentially in that now the scattered modes are conical instead of planar. A major difference is that resonance maxima (analogous to the Wood's anomalies for the planar grating) may occur not only for wavelengths that are slightly larger than the grazing (Rayleigh) wavelengths, but also for wavelengths that are slightly smaller. We also derive closed‐form approximations for small scatterers with arbitrary spacing, and then specialize the results to small spacing.

ISSN:0001-4966    

DOI:10.1121/1.1913334

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A technique is developed to find the axial mass distribution of rods and beams based upon desired properties of its first vibrational mode deflection function. This is an inverse Sturm‐Liouville problem for rods. The cases of particular interest are when a specified characteristic function does not satisfy the boundary conditions of the problem or continuity conditions. For example, a uniformly strained fixed‐free rod vibrating axially cannot exist because the strain must be zero at the free end. Using calculus of variations, a method is developed whereby the rod or beam is found whose first characteristic function can be as close as possible to the specified unattainable function. This is done for linearly elastic axially nonuniform materials vibrating axially or transversely. Examples include the application of the technique to the design of ultrasonic resonators.

ISSN:0001-4966    

DOI:10.1121/1.1913309

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A finite element beam‐type model considering transverse shear deformation is presented which utilizes Timoshenko's original kinematic variables. A direct calculation of the distribution of energies due to extension, flexure, and shear is indicated. For beam vibrations, comparison of the present results with other analyses shows that the current formulation is extremely effective for cross sections whose depth is comparable to a wavelength. Natural frequencies of frames and arches are computed using the present element and are compared with values based upon neglect of transverse shear deformation to illustrate this effect quantitatively.

ISSN:0001-4966    

DOI:10.1121/1.1913310

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

By means of integral‐transform techniques, the problem of steady motion and simultaneous harmonic oscillation of a smooth flat indenter is formulated and solved. The boundaries of the indenter are assumed to be fixed with respect to a coordinate system moving with steady velocity. A low‐frequency approximation for this case is obtained. The results of the approximation are subsequently used with a method of Crozier and Hunter to obtain the magnitude of the changing boundary when a curved or wedge indenter is considered.

ISSN:0001-4966    

DOI:10.1121/1.1913311

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A finite‐element procedure for predicting the frequency of axial‐flexural coupling vibration of frameworks is presented. In addition to the rectilinear beams, the formulation and the procedure are also shown to be highly accurate in the analysis of axial‐flexural coupling vibration of a portal frame by comparing the results with an analytical solution presented herein. Additional examples include a two‐bay portal frame and the single‐bay multi‐story frames. It is found that in the case where the horizontal beam contains floor masses or the frame is composed of multiple stories, substantial discrepancies exist between the axial‐flexural frequencies and the flexural frequencies. In those cases, the axial motion is no longer negligible in the vibrational analysis.

ISSN:0001-4966    

DOI:10.1121/1.1913312

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Geometrical acoustics problems in oceanic applications are solved using complicated computer codes. This paper presents some cases which may be used to verify these codes. The velocity profiles are depth dependent, range dependent, and depth and range dependent. The ray path solutions, as well as the velocity profiles, are all expressed in terms of analytical, closed form, or at worst, tabulated functions.

ISSN:0001-4966    

DOI:10.1121/1.1913313

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Rytov's method has been the subject of arguments as to whether or not it has a greater domain of applicability than the method of small perturbations. In order to be able to use the result of Rytov's method one must assume that the sizes of the patches of inhomogeneity are much larger than the wavelength of the sound, i.e., λ≪l. Making use of this assumption, when we use the solution for Ψ′ to compare the discarded term |▿Ψ′|2with the remaining terms, we discover that Rytov's method has thesamedomain of applicability as the method of small perturbations. Using a simple geometrical model we deduce by physical reasoning the results of Mintzer and Bergmann. This model is then used to extend the theoretical prediction for the amplitude fluctuations in the (Mintzer) range(λL)12≫L0to cover the case where the fluctuations are large.

ISSN:0001-4966    

DOI:10.1121/1.1913314

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The frequency response function of a propagation channel is formulated by the coherent (vectorial) summation of CW signals arriving via many ray paths between source and receiver. Six months of continuous measurements of water temperature from a moored thermistor string in the Florida Straits are analyzed to determine the temporal variation of the sound speed profile. The observed average profile and its temporal variations are shown to be closely modeled by fitting the data with two layers of linear sound speed gradient. In order to investigate the effects on propagation of temporal variations of the two layers, a model of Refracted Bottom‐Reflected (RBR) propagation is developed for the particular case of a bottomed source and receiver. Model computations determine the relative influence of the parameters of the two layers upon the interference of broad‐band signals. The general features of multipath interference which are observed in the Florida Straits are presented and discussed. Model simulations of multipath interference are used to interpret experimental results. Some characteristics of the propagation channel (e.g., bandwidth of an interference fade) are shown to depend on average values of the model parameters, while others (e.g., CW amplitude) depend on small fluctuations about the averages and thus cannot be estimated with idealized propagation models. For typical profiles the gradient near the bottom determines the average properties of the channel frequency response function.

ISSN:0001-4966    

DOI:10.1121/1.1913315

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP