An Analytical Model for Turbulence-Induced Flexural Noise in Large Conformal Sonar Arrays

Large-area, hull-mounted conformal sonar arrays typically employ extended sensors that are configured to detect acoustic signals by means of thickness strains that are induced by the incident pressure field. In most cases, extended sensors also have an appreciable sensitivity to strains in the lateral dimensions. Thus, flexure of such a sensor would induce a signal that would not be differentiated from that of a target. This report presents an analytical approach and a general mathematical model for the noise arising from flexure of the array support plate coupled into the array via the lateral sensitivity of the sensor. The excitation that drives the flexure is assumed to be the turbulent boundary layer created by motion of the platform through the external fluid medium. An analytical expression is derived for the equivalent plane wave spectral density for this noise source. The result is expressed in terms of the frequency response function of the plate, the wave number-frequency spectral density of the excitation, and the spatial filtering characteristics of the array. An application is discussed to show that predictions can be obtained in closed form.... Flow noise, Planar arrays, Sonar, Extended sensors, Flexural noise, Wavenumber filtering.