James E. Brooks

Controlled implosive downhole seismic source

A controlled implosive downhole seismic source having a substantially hollow closed vessel body adapted to be lowered in a borehole and means for selectively causing at least a portion of the vessel body to implode under pressure thereby producing seismic waves.

Sampling statistics for vibrating rectangular plates

A thin, uniform, rectangular, elastic plate is freely supported in air, and driven so that it vibrates flexurally at a resonance frequency. The modal function, which describes the vibrational displacement over the surface of the plate, is approximated as the product of two sine functions. From this modal function the probability density function (pdf), P(s), for random sampling over the plate surface of the rms acceleration, is calculated to be 4π−2 K(1−s2), where K is a complete elliptic integral. Using this expression and experimental values sampled randomly over the plate surface, estimates of known precision can be made of the mean vibrational level of the plate. Experimental results are given for a steel plate measuring 4 ft×3 ft×1/4 in., resonating at a single frequency; they agree quite well with the theoretical cumulative function derived from the pdf given above. Also considered are cases where two overlapping modes are excited at a given frequency. The corresponding pdfs are found, by Monte Carl...