摘要:

A rigid prolate spheroidal obstacle that is part of a mass‐spring‐dashpot system in an acoustical medium is struck by a plane pressure wave and also by a spherical pressure wave.ZP* (k) andZS* (k) are the Fourier transforms of the motion of the spheroid in the plane‐wave case and spherical‐wave case, respectively, andf* (k) andg* (k) are the respective transforms of the incident pressures in these cases. The equation relatingZP* (k) andf* (k) and the equation relatingZS* (k) andg* (k) are derived. The asymptotic forms for the acoustical admittancesZP* (k)/f* (k) andZS* (k)/g* (k) are computed forksmall and from these results the condition thatfandgmust satisfy in order thatZP(t)∼ZS(t) fortlarge is derived. Finally the distancecbetween the foci of the spheroid is allowed to approach 0, yielding the preceding results in the case of a spherical obstacle.

ISSN:0001-4966    

DOI:10.1121/1.1913193

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The problem of the reflection of elastic stress pulses at the interface between a rod and a half‐space is treated theoretically and experimentally. The axis of the rod is taken to be perpendicular to the free surface of the half‐space and its flat end to be in frictionless contact with this surface. It is shown that for the reflection of an infinite train of sinusoidal waves at such a boundary the conditions are analogous to those that apply for the reflection of such a train at the boundary between an elastic and a linear viscoelastic rod, and that a “cross‐over effect” may be observed. This effect is that a critical frequency ωcmay exist such that if the frequency of the incident wave is ω the phase of the reflected wave shows a sudden jump of π as ω passes through ωc. Thus if a dc pulse is reflected at the interface and if its relevant Fourier spectrum extends over this critical frequency, an s shaped pulse is found to be reflected. It is also shown in this paper that the accuracy with which the dynamic properties of the material of the haft‐space can be determined is limited by the precision with which the values of the Fourier components of the incident and reflected pulses are known.

ISSN:0001-4966    

DOI:10.1121/1.1913194

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The stability of plane steady oscillations of a slender elastic rod subjected to lateral harmonic excitation is investigated. For certain values of excitation amplitudes and frequencies the planar response is unstable, and nonplanar motions are parametrically excited. Steady nonplanar motions are characterized by each point on the rod centerline tracing an elliptical path perpendicular to the rod axis. The investigation is restricted to cantilevered rods with nearly equal principal moments of inertia of the cross‐section, and excitation is always in the direction of one of the principal axes of inertia. The effects of damping and of slight variations of the natural frequencies associated with motions in the two principal planes are investigated. Supporting experimental evidence is presented. Finally, the principal features of the transversely driven rod response are compared with the response for the same type rod excited axially.

ISSN:0001-4966    

DOI:10.1121/1.1913195

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The transient vibration problem of beams with hysteresis damping is studied. The hysteresis damping is characterized by being strain dependent, frequency independent, and having a stress‐strain loop with sharp corners. The mathematical solution employing the asymptotic method is given first, followed by the equivalent linear solution. Finally, the usefulness of the equivalent linear solution is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1913196

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

In the present paper, the free flexural vibrations of an elliptical plate with simply supported edge are considered by the use of Mathieu functions and modified Mathieu functions which are solutions of the differential equation of motion. The boundary conditions of simple support of an elliptical plate are obtained and the frequency equation of symmetrical vibrations about both axes is lead from those boundary conditions. The nondimensional frequencies calculated numerically for the first five normal modes of vibrations are shown in graphs for various eccentricities.

ISSN:0001-4966    

DOI:10.1121/1.1913197

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

A rigid moveable sphere which is part of a mass‐spring‐dashpot system is constrained to move with one degree of freedom in an acoustical medium. The motion which ensues when the sphere is struck by a transient incident plane wave and, second, by a transient incident spherical wave, is studied. The motion of the sphere is computed and analysis is given for the inverse problem which seeks to determine the properties of the incident wave from the known motion of the sphere.

ISSN:0001-4966    

DOI:10.1121/1.1913198

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The heat generation in a viscoelastic cylinder which results from thermomechanical coupling behaviors is investigated. Material behaviors and the dissipation function are temperature dependent. The inner surface of the hollow cylinder is subjected to cyclic shear loadings at high frequencies. This assumption leads to a nonlinear differential equation for stress distributions and the dissipation. A closed‐form approximate solution is obtained by using the familiar WKB technique. The temperature distributions resulting from dissipation are solved by means of a finite‐difference method. Numerical examples for a solid propellant are given. It is found that a large temperature rise will occur at the inner surface.

ISSN:0001-4966    

DOI:10.1121/1.1913199

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

A method is developed for determining the modes of propagation for progressive harmonic waves in infinite rectangular elastic bars. The faces of the bar are covered with a distributed mass of negligible stiffness, as found with a layer of insulation or a damping treatment. An approximate solution is obtained by expanding the displacements as a power series in the thickness coordinates and retaining only terms through first order. The D'Alembert force due to the acceleration of the mass produces surface tractions which influence the motion and introduce coupling between the longitudinal, torsional, and flexural motions. If equal mass distributions are applied over opposite faces, the motions are qualitatively similar to the motions of a free bar. If unequal masses are added to opposite faces, the motions are more coupled than those of a free bar. The addition of mass to two adjacent faces leads to a yet higher degree of coupling.

ISSN:0001-4966    

DOI:10.1121/1.1913200

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The bistatic scattering strengthS(φi,φs) = 10 logs (φi,φs) of the ocean surface has been measured in12‐octbands over the frequency range 62.5–4000 Hz for a wide range of grazing angles of incidence and scattering, φiand φs. Explosive charges at the bottom of a vertical string of hydrophones were used to ensonify the surface. Concurrent measurements of surface roughness were taken with an accelerometer float.Swas obtained for rms waveheightsĤbetween 1.9 and 2.8 ft and rms omnidirectional slopes tanΘ̂ between 0.10 and 0.13. For frequencies between 62.5 and 1440 Hz, the bistatic scattering coefficientsmay be represented in the forms=CeD[sinφi+sinφ2]2, whereCandDare functions of the surface roughness parameterskĤand tanΘ̂. The functions have one form when surface shadowing of the scattered radiation is weak (φi>Θ̂, φs>Θ̂), and another form when surface shadowing is strong (φi>Θ̂, φs⪅ Θ̂).

ISSN:0001-4966    

DOI:10.1121/1.1913201

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Sound‐speed equations having standard deviations between 0.013 to 0.101 m/sec are fit to 627 replicate observations on standard sea water modified to salinities between 30 to 41‰S. Measurements were made for realistic conditions over a total range of 0°–40°C and 0–1000+kg/cm2(15 000 psi) gauge.

ISSN:0001-4966    

DOI:10.1121/1.1913202

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP