ASA 125th Meeting Ottawa 1993 May

2aEA6. Determination of electrical drives for a cylindrical wave-number calibration array.

L. D. Luker

Naval Res. Lab., Underwater Sound Reference Detachment, P.O. Box 568337, Orlando, FL 32856-8337

The ``flow noise'' produced by a turbulent boundary layer is generally characterized by pressure distributions that are transported along the surface at speeds much less than the sound speed in water and therefore have spatial wave numbers that are larger than the acoustic wave number. This paper describes several methods for computing the electrical drives for a prototype cylindrical wave-number calibrator (CWC) designed to generate a pressure field consisting of essentially a single nonacoustic wave number inside the free-flooded calibrator. This geometry is suitable for the evaluation of line acoustic sensors such as in towed sonar arrays. The prototype CWC consists of a cylindrical tube of PVDF with an electrode pattern along the tube length that allows the PVDF to be operated as 40 independent bands each of which can be driven at a specified amplitude and phase. The required drive voltages are calculated using the electroacoustic transfer matrix of the CWC at the desired drive frequency. This transfer matrix can be determined by actual measurements or by using a computer model of the CWC. Drives were computed using transfer matrices that were determined with several modeling methods including the acoustic-radiation program CHIEF and the finite-element program ATILA. Measured pressure fields inside the CWC are compared with desired and predicted fields at selected spatial wave numbers for drive frequencies of 800 and 1600 Hz. These results are also compared with previous results produced using measured transfer matrices. [Work jointly supported by ONR and ONT.]