3aSAb3. Internal--external measurement of three-dimensional velocities of a submerged shell by optical vibrometry.

Session: Wednesday Morning, May 15

Time: 11:15

Author: Joseph Vignola
Author: P. Frank
Author: L. Leka
Location: SFA, Landover, MD 20785


A unique experimental capability for measuring both the interior and exterior three-axis surface motions of a completely submerged ribbed cylindrical shell has been developed. This system is composed of two three-dimensional laser Doppler vibrometers positioned by a pair of high-precision robots. The two vibrometers work together to measure the three-components of velocity up to 50 kHz on both the interior and exterior cylinder surfaces. For the interior, a compact three-dimensional vibrometer was designed and constructed to operate in conjunction with a cylindrical-based scanner mounted to the stiff endcaps of the shell. This scanning system is capable of positioning the laser vibrometer with a precision of +/- 3 mil over 100% of the interior cylinder surface. A second three-dimensional laser vibrometer designed for exterior (in-water) operation was constructed and integrated into the NRL near-field acoustic holography system. This large workspace Cartesian-based scanner is capable of collocating the focal point of the exterior vibrometer with that of the interior to within +/- 10 mil. The design of the system will be discussed, and structural acoustic data will be presented from a series of preliminary experiments conducted to evaluate the performance of the system.

from ASA 131st Meeting, Indianapolis, May 1996