The radiating near-field asymptotics of a normal time-harmonic circular ultrasonic transducer in an elastic half-space

1998 ◽  
Vol 104 (3) ◽  
pp. 1178-1187 ◽  
Author(s):  
Larissa Ju. Fradkin ◽  
Aleksei P. Kiselev ◽  
Eugenia Krylova
Keyword(s):  
Half Space ◽  
Ultrasonic Transducer ◽  
Near Field ◽  
Elastic Half Space ◽  
Time Harmonic

Asymmetric Wave Propagation in an Elastic Half-Space by a Method of Potentials

1987 ◽  
Vol 54 (1) ◽  
pp. 121-126 ◽  
Author(s):  
R. Y. S. Pak
Keyword(s):  
Wave Propagation ◽  
Dynamic Response ◽  
Half Space ◽  
Elastic Half Space ◽  
Displacement Potential ◽  
Uniform Distributions ◽  
Time Harmonic ◽  
Method Of Potentials ◽  
Transformed Stress ◽  
Asymmetric Wave

A method of potentials is presented for the derivation of the dynamic response of an elastic half-space to an arbitrary, time-harmonic, finite, buried source. The development includes a set of transformed stress-potential and displacement-potential relations which are apt to be useful in a variety of wave propagation problems. Specific results for an embedded source of uniform distributions are also included.

Dynamic response of an elastic half-space to time-dependent surface tractions over an embedded spherical cavity. III (With comments on a paper by R. D. Gregory)

1969 ◽  
Vol 309 (1498) ◽  
pp. 313-329 ◽  
Keyword(s):  
Dynamic Response ◽  
Half Space ◽  
Rayleigh Waves ◽  
Spherical Cavity ◽  
Elastic Half Space ◽  
Time Dependent ◽  
Plane Boundary ◽  
Surface Motion ◽  
Harmonic Solution ◽  
Time Harmonic

Discussion of the problem of an elastic half-space with spherical cavity is continued in respect of Rayleigh waves on the plane boundary. Displacements in the initial and first group of higher order Rayleigh waves are derived by using the time-harmonic solution developed in part I of this series with attention confined to the case of time-harmonic normal stress at the cavity. These are employed to find also the response to an exponential shock at the cavity and graphs are presented showing the surface motion due to the initial Rayleigh waves. Finally, in an appendix to the paper, some comments are given on a recent paper by R. D. Gregory on the problem of the half-space with cavity.

The Wavefield Radiated Into an Elastic Half-Space by a Transducer of Large Aperture

1988 ◽  
Vol 55 (2) ◽  
pp. 398-404 ◽  
Author(s):  
John G. Harris
Keyword(s):  
Power Series ◽  
Plane Wave ◽  
Half Space ◽  
Wave Equations ◽  
Ultrasonic Transducer ◽  
Elastic Half Space ◽  
The Other ◽  
Circular Region ◽  
Asymptotic Power ◽  
Normal Traction

The wavefield radiated into an elastic half-space by an ultrasonic transducer, as well as the radiation admittance of the transducer coupled to the half-space, are studied. Two models for the transducer are used. In one an axisymmetric, Gaussian distribution of normal traction is imposed upon the surface, while in the other a uniform distribution of normal traction is imposed upon a circular region of the surface, leaving the remainder free of traction. To calculate the wavefield, each wave emitted by the transducer is expressed as a plane wave multiplied by an asymptotic power series in inverse powers of the aperture’s (scaled) radius. This reduces the wave equations satisfied by the compressional and shear potentials to their parabolic approximations. The approximations to the radiated waves are accurate at a depth where the wavefield remains well collimated.

Elastodynamic Stress-Intensity Factors for a Crack Near a Free Surface

1981 ◽  
Vol 48 (3) ◽  
pp. 539-542 ◽  
Author(s):  
J. D. Achenbach ◽  
R. J. Brind
Keyword(s):  
Stress Intensity ◽  
Half Space ◽  
Stress Intensity Factors ◽  
Elastic Half Space ◽  
Mode I ◽  
Dimensionless Frequency ◽  
Subsurface Crack ◽  
Intensity Factors ◽  
Time Harmonic ◽  
Crack Tips

Elastodynamic Mode I and Mode II stress-intensity factors are presented for a subsurface crack in an elastic half space. The plane of the crack is normal to the surface of the half space. The half space is subjected to normal and tangential time-harmonic surface tractions. Numerical results show the variation of KI and KII at both crack tips, with the dimensionless frequency and the ratio a/b, where a and b are the distances to the surface from the near and the far crack tips, respectively. The results are compared with corresponding results for a crack in an unbounded solid.

Scattering by a surface inhomogeneity on an elastic half-space, with application to fluid-structure interaction noise

1990 ◽  
Vol 429 (1876) ◽  
pp. 203-226 ◽  
Keyword(s):  
Turbulent Flow ◽  
Half Space ◽  
Near Field ◽  
Elastic Solid ◽  
Viscous Sublayer ◽  
Elastic Half Space ◽  
Diffraction Radiation ◽  
Frequency Spectra ◽  
Low Mach Number ◽  
Surface Inhomogeneity

A harmonic point source is situated in fluid bounded by a nominally plane interface with an elastic half-space. The source is close to a small protrusion of the elastic medium into the fluid, and it is required to determine the interaction (‘diffraction’) radiation, i. e. the acoustic, elastic-body and surface (Scholte) waves produced by the scattering of the near field of the source by the protrusion. The solution of this canonical problem is applied to the prediction of acoustic and structural noise generated by low Mach number turbulent flow over an inhomogeneity on the boundary of an elastic solid. Estimates are presented of the frequency spectra of the power delivered to the various wave modes and their dependence on the elastic properties of the solid, and a comparison is made with empirical predictions of excitation of the same modes in the absence of the inhomogeneity. The scattered radiation can be significant even when the surface inhomogeneity does not penetrate beyond the viscous sublayer into the turbulent flow.

The attenuation of a Rayleigh wave in a half-space by a surface impedance

1966 ◽  
Vol 62 (4) ◽  
pp. 811-827 ◽  
Author(s):  
R. D. Gregory
Keyword(s):  
Surface Wave ◽  
Rayleigh Wave ◽  
Half Space ◽  
Logarithmic Singularity ◽  
Elastic Half Space ◽  
Body Waves ◽  
Impedance Boundary Condition ◽  
Impedance Boundary ◽  
Elastic Potentials ◽  
Time Harmonic

AbstractA time harmonic Rayleigh wave, propagating in an elastic half-space y ≥ 0, is incident on a certain impedance boundary condition on y = 0, x > 0. The resulting field consists of a reflected surface wave, scattered body waves, and a transmitted surface wave appropriate to the new boundary conditions. The elastic potentials are found exactly by Fourier transform and the Wiener-Hopf technique in the case of a slightly dissipative medium. The ψ potential is found to have a logarithmic singularity at (0,0), but the φ potential though singular is bounded there. Analytic forms are given for the amplitudes of the reflected and transmitted surface waves, and for the scattered field. The reflexion coefficient is found to have a simple form for small impedances. A uniqueness theorem, based on energy considerations, is proved.

An expansion theorem applicable to problems of wave propagation in an elastic half-space containing a cavity

1967 ◽  
Vol 63 (4) ◽  
pp. 1341-1367 ◽  
Author(s):  
R. D. Gregory
Keyword(s):  
Free Surface ◽  
Half Space ◽  
Radiation Condition ◽  
Elastic Half Space ◽  
Potential Fields ◽  
Governing Equations ◽  
Expansion Theorem ◽  
Surface Conditions ◽  
Harmonic Vibrations ◽  
Time Harmonic

AbstractThis paper is principally concerned with the two-dimensional time harmonic vibrations of an elastic half-space y ≥ 0, containing a submerged cavity in the form of an infinite circular cylinder. Two sequences of line source potentials are obtained which are singular along the axis of the cylinder, satisfy the free surface conditions on y = 0, and represent outgoing waves at infinity. (The radiation condition.) It is proved that any solution of the governing equations which satisfies the free surface conditions and consists of outgoing waves at infinity is expansible as a sum of these fundamental source potentials, with coefficients to be determined from the boundary conditions on the cylinder only.The requirement of outgoing waves is carefully discussed and it is shown that the conditions taken give rise to, and are satisfied by, potential fields which would be regarded intuitively as representing outgoing waves.

The propagation of waves in an elastic half-space containing a cylindrical cavity

1970 ◽  
Vol 67 (3) ◽  
pp. 689-710 ◽  
Author(s):  
R. D. Gregory
Keyword(s):  
Half Space ◽  
Cylindrical Cavity ◽  
Elastic Half Space ◽  
System Of Equations ◽  
Expansion Theorem ◽  
Elastic Potentials ◽  
Time Harmonic ◽  
Propagation Of Waves ◽  
Radiation Conditions ◽  
Conditions At Infinity

AbstractThe problem of the propagation of time harmonic waves in an isotropic elastic half-space containing a submerged cylindrical cavity is solved analytically. Linear plane strain conditions are assumed. Using an expansion theorem proved in a previous paper (Gregory (3)), the elastic potentials are expanded in a series form which automatically satisfies the governing equations, the conditions of zero stress on the flat surface, and the radiation conditions at infinity. The conditions of prescribed normal and tangential stresses on the cavity walls are shown to lead to an infinite system of equations for the expansion coefficients. This system of equations is shown to be a regular L2-system of the second kind and from its unique l2-solution, the solution to the problem is constructed. The fundamental questions of existence and uniqueness are fully treated and methods are described for constructing the solution.Three applications of the general theory are presented dealing respectively with the production, amplification and reflexion of Rayleigh waves.

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