The Equivalent Force System Of A Monopole Source In A Fluid-Filled Open Borehole

The elastodynamic body-wave field outside a fluid-filled open borehole due to a monopole source in the fluid, is reduced to the radiation-field due to a suitable equivalent force system (EFS) in the absence of the borehole, consisting of a monopole plus a vertical dipole. Theoretical seismograms of the EFS displacements in the solid are shown to be in excellent agreement with those obtained from the exact solution to the fluid-filled open borehole problem.United States. Defense Advanced Research Projects Agency (Contract F1962889-K-0020

Linear and nonlinear elastic wave propagation in a fluid-filled borehole

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1993.Includes bibliographical references (leaves 180-187).by Sergio Kostek.Ph.D

Tube Waves, Seismic Waves And Effective Sources

A simple asymptotic analysis, based on the smallness of the ratio of the borehole radius to the wavelength, reveals the interaction between tube waves and seismic waves. The pressure field in a tube wave acts as a secondary source of seismic waves and conversely an incoming seismic wave excites a tube wave. The asymptotic analysis leads to a characterization of these sources in terms of the solution to two-dimensional elastostatic problems. These may be solved exactly when the borehole has an elliptical cross-section even in an anisotropic formation. Also the borehole need not be straight provided that its radius of curvature is large compared with a wavelength

Modeling of elastic wave propagation in a fluid-filled borehole excited by a piezoelectric transducer.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1991.Includes bibliographical references (leaves 71-74).M.S

Gaussian-beam modeling of ultrasonic transducers using near-field experimental data

We wish to develop a model for the pitch-catch response of real transducers which is both accurate and efficient. Wen and Breazeale [1, 2] have shown that the fields of a uniformly active, planar disk transducer can be modelled by a small number of coaxial Gaussian beams (eg, 10 or 15). Margetan, Thompson and Gray [3] have similarly modelled the fields of a uniformly active, planar disk transducer in terms of Hermite Gaussian beams, and further picked the radius of the ideal transducer to match the main lobe of experimental data collected with a very small receiver,to approximate a point probe. Here we use the expansion of Wen and Breazeale and reciprocity to model the pitch-catch response of two transducers facing each other and having parallel axes, as a function of the displacement vector between the two transducers. Further, we fit this pitch-catch model directly to experimental pitch-catch data by choosing the parameters of the Gaussian beams, without assuming that the transducers are uniformly active, planar disks. Finally we show that the model developed by fitting over one set of displacements accurately describes the experiments over a disjoint set.</p