Rama Rao V. N.
Dept. of Ocean Eng., MIT, Cambridge, MA 02139
The acoustic transmission characteristics of fluid-filled elastic pipes inside fluid-filled bores in an infinite elastic solid are examined here. This model is of interest in exploratory drilling to study the propagation of drilling-related noises within the borehole and into the surrounding rock. The axially symmetric solutions in the four media (fluid inside the pipe, pipe, fluid in the annulus and the surrounding solid) are coupled through the boundary conditions. The resulting characteristic determinant is 9x9. The dispersion behaviors of the various modes are analyzed. The limiting behaviors at low and high frequencies are investigated. The cases of the surrounding solid being acoustically ``fast'' or ``slow'' compared to the fluid in the annulus are also examined.