Journal of Computational Acoustics

In the highly cluttered undersea environment, sonar array systems require enhanced acoustic signal processing algorithms and sophisticated architectures in order to meet dependability and real-time mission requirements. The probability of hydrophone and processing element failures is very high in such severe operating environments. Adaptive matched-field processing (MFP) algorithms localize sources accurately with moderate levels of signal-to-noise ratio (SNR) and precise knowledge about environments by employing full-wave acoustic propagation models. However, they highly distort output beam patterns with significant increase of sidelobes in the presence of environmental mismatches and element failures. These problems make the development of advanced fault-tolerant signal processing algorithms imperative to tolerate the element failures in cases where replacement of defective elements is impossible or impractical. In this paper, three fault-tolerant MFP algorithms are presented to compensate for the performance degradation generated by the inherent failure characteristics of vertical line arrays. The beamforming performance and computational complexities for these fault-tolerant algorithms are analyzed in terms of the number of faulty elements, their positions in the array, and SNRs. The simulation results demonstrate that these fault-tolerant techniques provide a feasible solution for real-time and highly reliable beamforming implementation on sonar array systems.

Sound generation by vortical disturbance in a subsonic flow around a cylinder is investigated, using different vortex formulations, by solving both linearized and nonlinear Euler equations numerically. Numerical errors associated with the finite-difference discretization and boundary conditions are kept small using the high-order-accurate spatial differentiation and time marching schemes along with accurate nonreflecting boundary conditions and the sponge layer. If the radial velocity in vortex is assumed equal to zero, the intensity and directivity of acoustic wave patterns appear to be quite similar for all vortex models. If the radial velocity is taken into consideration, for single-cell vortex, there is no noticeable change happening to the acoustic wave; for two-cell vortex, although the radial velocity is still much smaller than the tangential velocity, the former plays an important role in generation and propagation of nonsymmetrical sound waves. If only initial tangential velocity or only initial radial velocity of the two-cell vortical flow disturbance is considered, the generated sound level would increase with the Mach number of mean flow while the angular distribution of sound directivity remains the same. If the two-cell vortex with both velocity components is considered, the Mach number of the background flow would change not only the amplitude of the acoustic pressure but also the directivity of sound. As the Mach number increases, the maximum amplitude of acoustic pressure will be shifted to the upper half-plane.

We develop and analyze finite difference schemes for the two-dimensional Helmholtz equation. The schemes which are based on nine-point approximation have a sixth-order accurate local truncation order. The schemes are compared with the standard five-point pointwise representation, which has second-order accurate local truncation error and a nine-point fourth-order local truncation error scheme based on a Padé approximation. Numerical results are presented for a model problem.

The paper uses analytical modification of the classical boundary integral equations (BIEs) for the Helmholtz equation to facilitate the process of practical definition of the boundary geometry. Instead of defining the boundary by means of a boundary integral, the modification makes use of Bézier curves exclusively. As a result, a new parametric integral equation system (PIES) is obtained in which boundary geometry is taken into account in original fundamental boundary solutions. Such boundary definition makes it easy to approximate boundary functions. The proposed method to obtain numerical solution of the PIES for the Helmholtz equation is characterized by high effectiveness.

This paper describes the relationship between the eigenfrequencies of CT scanned realistic human head model and the subjective detecting pitch, which is given by providing the bone-conducted ultrasound. Our goal is to develop the optimal bone-conducted ultrasonic hearing aid for profoundly hearing-impaired persons. An ascent of a speech intelligibility is the requirement of hearing aid. To improve it, the perception mechanism of the bone-conducted ultrasound must be clarified, but the conclusive agreement of it has not been reached yet, although many hypotheses were reported.

The authors feel an interest in the detecting pitch of bone-conducted ultrasound with no frequency-dependence and predict that the cochleae are related to the perception mechanism for bone-conducted ultrasound, since it has been verified that the auditory cortex responds to bone-conducted ultrasound by MEG study.

In this paper, waves propagating from the mastoid to both cochleae are numerically analyzed and the characteristics of transfer functions are estimated as a first step to clarifying the perception mechanism for detecting pitch of bone-conducted ultrasonic stimuli.