Journal of Computational Acoustics

In this paper, it is proved the existence of a transmutation operator between two schrödinger equations with perturbed exactly solvable potential. An explicit formula for the solution of nucleus function by using Varsha and Jafari's method is also provided.

A three-dimensional (3D) ocean environment is assimilated with measured ocean data in the ASIAEX SCS (Asian Seas International Acoustics EXperiment, South China Sea) experiment. The experiment site is characterized as an active internal wave propagation region along the Northwestern shelf break of the South China Sea. Three-dimensional acoustics effects in the area are studied using FOR3DW, a wide-angle version of the parabolic equation code FOR3D (a Finite difference solution, an Ordinary differential equation, and Rational function approximations for solving 3D problems), and MOS3DPEF (MOdal Spectrum analysis based on 3D PE Field). The TL comparison between Nx2D and 3D calculations are shown to demonstrate the 3D effects. Variations in topography of the shelf break and in the water column due to the internal waves cause the 3D effects in the acoustic field. The intercomparison of the importance of bottom steering 3D effects and nonlinear internal wave refraction 3D effects is therefore proposed to realize which possesses the major part of the 3D effects. Also, 3D modal analysis results show that the nonlinear internal wave front causes severe horizontal refraction for higher modes.

In shallow water environments where the uppermost sediment layer is a fine-grained fabric (e.g. clay or silty-clay), the observed reverberation may be dominated by scattering from the sub-bottom. Here, reverberation predictions from normal mode and energy flux models are compared for the case where the scattering arises from a sub-bottom half-space under a fine-grained sediment layer. It is shown that in such an environment, the position of the angle of intromission, in addition to the angular dependence of the scattering kernel, is a factor controlling the reverberation and its vertical angle distribution. It is also shown that the reverberation from a sub-bottom horizon is typically governed by higher grazing angles than the case where the scattering occurs at the water–sediment interface. There was generally very close agreement between the models as a function of frequency (200–1600 Hz), layer thickness (0–8 m), and range (1–15 km). The model comparisons, showing some differences, illuminate the result of different approximations in the two approaches.

A so-called FuzzBEM methodology for analyzing the influence of uncertain acoustic and structural parameters on the radiated sound field of vibrating structures combining fuzzy arithmetic and fast multipole boundary element method is introduced. Uncertainties in acoustic properties may result from uncertain parameters of the vibrating mechanical structures, e.g. material density or geometry, as well as from uncertainties in the acoustic domain, e.g. sound velocity. The use of the transformation method in the proposed approach allows to employ simulation tools based on the crisp number arithmetic by appropriate preprocessing of the fuzzy numbers modeling the uncertain input parameters and postprocessing of the simulation results to determine the fuzzy numbers for the considered output quantities.

In this contribution, the proposed FuzzBEM procedure is applied to a sound radiating, vibrating stiffened cylindrical shell where the investigated uncertainties include the shell wall thickness and the driving frequency of a monofrequency point load and the air density and sound velocity. As exemplary output quantities of acoustic performance, the acoustic pressure at multiple field points and the radiated sound power are evaluated.

The proposed coupling of fuzzy arithmetic and acoustic boundary elements yields run times two orders of magnitudes or more longer than a single BEM calculation. Nevertheless, the systematic parameterization obtained by the proposed fuzzy analysis has the potential to reveal input–output relationships difficult to identify with individual conventional BEM simulation runs.

This study examines the sound generated by the interaction between turbulent vortices and solid bodies, and its propagation in a nonuniform flow. Single vortex encounters with a flat plate and a nonrotating cylinder are considered. The solutions show that as the turbulence intensity increases, the sound radiated by the vortex–body interaction is strengthened while the effect of the mean flow speed on the sound waves weakens. The sound profile and sound directivity do not change with the Reynolds number. Neglecting turbulence in vortices will not affect the prediction of the fundamental properties of the radiated sound waves; however, it will underestimate the magnitude of the produced sound.

This paper is concerned with the active control of sound fields in enclosures. Specifically, the numerical problem of determining the optimum locations of control sensors and actuators is addressed. A new method for determining the optimum secondary sources strength is proposed, based on the explicit prediction of the sound field, which makes the simulation of realistic acoustical applications feasible, in terms of the enclosure's boundary conditions. The irregular geometry of a car cabin with complex boundary conditions is used in order to demonstrate the application of the new method to a test case where the existing methods cannot theoretically apply without resolving to significant numerical error. The new method of determining the secondary sources strength is combined with a modified genetic and a gradient optimization algorithm so as to locate the optimum positions of active noise control transducers for global sound field control. The overall algorithm, constituting of the method for calculating the secondary sources' strength and the optimization algorithms, is adjusted with computational improvements for better performance.