Finite element modeling and array interaction modeling of the ARE low-frequency flextensional transducer

Abstract

A requirement for underwater acoustic sources with higher source level and wider bandwidth at lower frequencies has, in the past 5 years, lead to interest in flextensional transducers. A low-frequency prototype has been developed, manufactured, and tested at ARE(Portland); the technology is the subject of a license agreement with industry. In this paper, finite element (FE) analyses performed in support of the prototype development using PAFEC software are described. PAFEC is a commercially available FE package with the facility to model piezoelectric materials, and exterior fluid loading by the doubly asymptotic approximation. In-air and in-water resonant frequencies are well predicted, as is the effect of hydrostatic pressure on stack prestress. The transducer is subjected to large stresses during assembly, and predictions for these have also been obtained. Problems remaining in the FE modeling, and improvements in the capabilities of PAFEC under development to overcome them, are discussed. An equivalent circuit model for an array of these flextensional transducers is described, and a comparison of admittances and farfield predictions with measurements presented.

Performance Prediction of a Volumetric Array of Free Flooded Ring Projectors

“…Helmer demonstrates that using these two arrays it is possible to obtain a front toback ratio of greater than 10dB over the whole frequency range of interest. DRA has also PERFORMANCE PREDICTION OF A VOLUMETRIC ARRAY demonstrated a similar technique using a close packed volumetric array of class IV extensional transducers [4].…”

“…Compact arrays are readily achievable with extensional transducers [4][7] as they behave very much like ideal point sources. That is, they are very much smaller than a wavelength of the sound they transmit.…”

“…DRA has previously demonstrated a method of producing such a directional source using a volumetric array of extensional transducers [4]. However, very little work has been published on how to achieve a compact directional array using freeooding ring transducers.…”

Numerical/Analytical Methods for Fluid-Structure Interaction Problems 1996

“…Helmer demonstrates that using these two arrays it is possible to obtain a front toback ratio of greater than 10dB over the whole frequency range of interest. DRA has also PERFORMANCE PREDICTION OF A VOLUMETRIC ARRAY demonstrated a similar technique using a close packed volumetric array of class IV extensional transducers [4].…”

“…DRA has previously demonstrated a method of producing such a directional source using a volumetric array of extensional transducers [4]. However, very little work has been published on how to achieve a compact directional array using freeooding ring transducers.…”