摘要:

The experimental investigations that first showed excess of sound absorption in gases above the classical value are described, and the theoretical ideas that lead to their explanation by relaxation processes are discussed. A survey is then given of later progress, which is closely connected with the rapid development of electronics, and of the parallel refinement of the theory. The work in liquids started somewhat later. The theoretical situation is more complex, but, for that very reason, ultrasonic measurements in liquids give information about problems absent in gases. The consideration of viscous liquids led to a connection with the behavior in glasses, in accordance with Simon's theory. In metals, the starting point, the methods, and the important frequency range for loss measurements were originally different; but here, too, the investigations and theoretical viewpoints have been multiplied and diversified.

ISSN:0001-4966    

DOI:10.1121/1.1909958

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The exact series solution for the scattering of a plane wave by a soft spheroid is used to obtain explicit long‐wavelength approximations. The farfield scattering amplitude is given to the sixth power of the frequency and the near field is given to the second power. The results are valid for prolate and oblate spheroids and arbitrary angles of incidence and observation.

ISSN:0001-4966    

DOI:10.1121/1.1909959

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

A dispersion relation for low‐frequency disturbances in an isothermal atmosphere with constant horizontal winds is derived. It relates the three components of the wave‐propagation vectorkto the angular frequency ω and depends on the sound speed, the wind velocityv, and the acceleration of gravityg. The relation is obtainable from that for propagation in an isothermal atmosphere without winds if ω is replaced by ω−k⋅v. The dispersion relation is studied with reference to the problem of the propagation of waves from a stationary source of limited spatial extent viewed by a stationary observer. The topology of the propagation surface inkspace is examined. Propagation modes are defined as corresponding to disjoint portions of the surface inkspace for fixed ω. The criteria for a given mode existing for given wind speed and frequency are derived and the group velocity of each type of mode is studied. The theory predicts the existence of two wind modes that, at sufficiently high frequencies, have group velocities nearly identical to the wind velocity. Phase velocities of the wind modes also tend to equal the wind velocity. In the latter portion of the paper, the trajectories of fluid particles are studied for each type of wave‐propagation mode. It is shown that, in terms of particle motions, the wind modes are physically indistinguishable from the gravity mode predicted for an isothermal atmosphere at rest when viewed by an observer moving with the wind.

ISSN:0001-4966    

DOI:10.1121/1.1909960

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The exact solution for the impedance of a manifold of differing but uniform transmission lines is derived. The number of uniform structures contained in the manifold is arbitrary and can be increased without bound. The exact solution to the manifold is used to obtain the impedance of a continuously tapered structure having a characteristic impedance and a velocity of propagation that varies along the length of the structure. This solution to the continuously tapered structure can be made as accurate as desired. An approximation to the continuous solution is derived that is valid provided the maximum value of the product of the internal reflection coefficient and the wavelength is much less than unity. The application at this approximate solution to the synthesis of tapered structures is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1909961

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

This paper describes the derivation of frequency equations for the propagation of small sinusoidal waves in an infinitely long isotropic elastic cylinder that has been initially stressed.

ISSN:0001-4966    

DOI:10.1121/1.1909962

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The transverse motion of a tensioned string driven parametrically by a moving end support is examined both analytically and experimentally. The conditions required to linearize the equations of motion for vibrations over a large‐amplitude range at constant frequency are developed and shown to be physically realizable.

ISSN:0001-4966    

DOI:10.1121/1.1909963

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Starting with the idea that wave mechanics should be useful in dealing with mechanical properties of solids, a connection between particle waves and deformation in crystals is developed. The connection is one in which Planck's constanthplays a prominent part. According to the view described, nonelastic deformation in crystals arises through the propagation of internally generated particle momentum waves with the de Broglie wavelength λ =h/mvi. Here,mandviare the mass and velocity, respectively, of certain, initially field‐free atoms that exist because of lattice defects in the crystal. The particle waves in question are not the probability waves of contemporary, orthodox quantum theory which satisfy the Schrödinger equation. Instead, real‐property waves governed by a new differential equation are proposed. Solutions to this equation for both finite and infinite lattices lead to frequency‐wave vector conditions from which a number of interesting results follow. These include the occurrence of characteristic frequencies or modes associated with nonelastic deformation, and, in particular, the existence of discrete audiofrequency modes whose frequencies depend on Planck's constant, atomic mass, and lattice segment length. The particle‐wave view thus leads directly to predictions of nonelastic audiofrequency resonances in vibration experiments and to expectations of acoustic emission during unidirectional plastic deformation. Applications of these same ideas to other aspects of mechanical behavior are also described briefly.

ISSN:0001-4966    

DOI:10.1121/1.1909964

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Additional experimental evidence and analysis are presented that tend to confirm the fundamental nature of previously reported nonelastic audiofrequency modes or resonances in solids. The evidence cited includes some results recently advanced by others to demonstrate that the resonances arise from contact and/or apparatus effects, but these results really confirm the resonances as material properties. The particle‐wave view of deformation is also strongly supported by these same, supposedly adverse, experimental results.

ISSN:0001-4966    

DOI:10.1121/1.1909965

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The simultaneous application of two dynamic absorbers to an undamped cantilever beam is discussed theoretically. The dynamic absorbers possess viscous damping. They are tuned and damped in the so‐called optimum manner for which it is possible to suppress the resonances of the beam in a uniform and symmetrical fashion. The beam is exalted by a sinusoidally varying force situated either at its free end or at its midpoint. It is to these locations that the dynamic absorbers are attached. The absorbers are tuned to suppress the first and second beam resonances, the optimum values of absorber tuning and damping depending upon the location of the absorbers and upon the beam resonance that is of concern. In addition to the rôle of the absorbers in suppressing the first and second beam resonances, excitation of the third resonance is essentially avoided when the driving force is situated at the midpoint of the beam because a nodal point of the third mode occurs very near to the beam center.

ISSN:0001-4966    

DOI:10.1121/1.1909966

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Expressions are derived that describe the steady‐state behavior of infinitely long beams with uniformly spaced attached impedances and that permit damping and fluid loading to be taken into account readily. The case where the attached impedances produce only lateral forces is treated on the basis of classical beam‐flexure theory. Relations governing the segment‐to‐segment propagation constant and the impedance the system presents to a force acting at an impedance attachment point are derived; the response to forces acting at all impedance attachment points, with a constant phase difference between adjacent forces, is also deduced. Additional results, applicable only in the region outside the near fields of the impedance attachment points, in cases where the interval between attached impedances encompasses many flexural wavelengths, are formulated in terms of the reflection and transmission coefficients that are effective at the impedance attachment points, and thus apply for impedances of any degree of complexity. A corresponding expression for the propagation constant is obtained, and a method (which is suitable also for numerical analysis of a wide variety of complex one‐dimensional systems) is developed for determining the steady‐state oscillations resulting from a given wave or waves injected at a given location.

ISSN:0001-4966    

DOI:10.1121/1.1909967

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP