Acoustics Australia最新文献

This paper investigates the reduction of sound radiation by beams with attached acoustic black hole (ABH) pillars in resonant cavities filled with heavy fluids (e.g., water) and light fluids (e.g., air). Fluid–structure interaction systems, particularly those involving heavy fluids, present significant challenges for vibration control and noise reduction. While traditional passive control methods often fail to provide effective suppression across a broad frequency range, ABHs have shown considerable potential in mitigating both vibration and acoustic radiation. The paper analyzes the underlying mechanisms driving the behavior of the coupled system, focusing on the effects of local resonances and the acoustic impedance mismatch between the structure and surrounding fluid. The problem is examined using a displacement/acoustic displacement formulation, which is validated through comparison with finite element method simulations. The results suggest that ABH pillars offer a promising solution for noise control in submerged structures.

An analytical method for predicting the forced vibroacoustic response of a fluid-filled baffled cylindrical shell submerged in a shallow-water waveguide is presented. The structural equations are governed by a thin shell theory that is decomposed into circumferential modes with a Fourier series and axial modes using a beam function. Heavy fluid fills the exterior and interior domains of the shell. The exterior fluid domain is further constrained by acoustic boundaries of an upper free surface and lower rigid bottom, which together form an ideal shallow-water waveguide. The acoustic boundaries are enforced by employing the image source method and Graf’s addition theorem which reconciles the differing coordinate systems of the many image sources that appear in the analytical expressions for the fluid–structure coupling. Vibroacoustic characteristics due to a mechanical point excitation on the surface of the shell or acoustic excitation from an internal monopole source and influence of different waveguide depths are investigated.

This study investigates the acoustic scattering characteristics and classification of four freshwater species (Channa argus, Oreochromis niloticus, Homarus americanus, and Pelodiscus sinensis) using neural networks. Standard underwater acoustic measurements yield full-aspect horizontal scattering data from controlled tank experiments. Time-domain analysis extracts key echo features including highlight count, amplitude, time-delay differences, and pulse-width broadening, while Radon transform imaging reveals structure-scattering correlations. Frequency domain reveals interspecies differences in acoustic target strength by analyzing frequency-dependent scattering characteristics across different frequencies and incident angles. Statistical analysis demonstrates that the target strength distributions of the four freshwater species generally follow (chi^{2}) patterns. Finally, we propose a classification method based on time–frequency-domain acoustic scattering characteristics of biological targets. A backpropagation neural network (BPNN) model incorporating these time–frequency-domain scattering characteristics achieves 95% classification accuracy. This study conducts neural network classification research based on multidimensional acoustic scattering characteristics of aquatic biological targets, extending the applications of acoustic technology in fisheries exploration and aquaculture industries. The work will provide new methodological insights for deep integration of neural networks with aquaculture practices.

This paper presents a framework comprising a hybrid computational flow-induced noise solver and finite-element-based phase-conjugation (PC) technique to analyze noise sources generated by bodies immersed in hydrodynamic flow fields at low Reynolds number (Re). The test-cases considered include a bluff and streamlined body, represented by a two-dimensional circular cylinder at Re = 150 and a NACA0012 airfoil at Re = 5000 oriented at (text {5}^circ ) angle of attack, respectively. The hybrid computational flow-induced noise algorithm first resolves the hydrodynamic field using the unsteady pressure implicit splitting of operators (PISO) solver for incompressible Navier–Stokes (NS) equations, which delivers the near-field surface pressure fluctuations (SPF) that are used in the frequency-domain implementation of Curle’s analogy to predict the far-field noise. The vortex shedding plots, lift, and drag spectrum predicted by the PISO solver were in excellent agreement with the computationally expensive direct numerical simulations (DNS). The far-field sound directivity obtained using the SPF in Curle’s analogy and DNS-based prediction were in excellent agreement for the Aeolian tone, while for low-frequency tonal noise emitted from airfoil trailing edge (TE), Curle’s analogy prediction was only approximate. Next, using the boundary data obtained from the hybrid approach, PC was implemented to localize the flow-induced acoustic sources, whereby a pair of focal spots above and below the cylinder and TE revealed the dipole nature at the vortex shedding frequency. However, when the airfoil was modeled, cardioid-shaped focal spots were obtained between the mid-chord and TE due to diffraction of back-propagated waves delivering the reconstructed scattered source location.

A composite structure composed of a helix and an array of resonators is created to achieve large-amplitude and wide-band sound insulation in a pipe. Two helical structures with lengths of 5–7.5 cm are designed to block sound within two frequency bands of 1100–1700 Hz and 700–1100 Hz, respectively. An array of eight resonators is adopted to produce sound attenuation in the frequency range from 900 to 2500 Hz. Then, by assembling both structures, we can achieve large sound attenuation over 40 dB in a frequency band between 1100 and 1700 Hz or obtain an extremely wide frequency sound attenuation band of 700–2500 Hz with transmission losses from 10 to 48 dB. Thus, owing to the composite structure of the sound insulator, the performance can be optimized according to practical requirements by adjusting the parameters of both parts. Moreover, because the helix and resonator array are both hollow structures, the composite sound insulator does not block airflow and is available in applications requiring natural ventilation.

Modeling the vibroacoustic behavior of structures excited by random pressure fields, such as turbulent boundary layers (TBL), is of interest for naval applications. Most works in the literature address the problem by considering periodically stiffened plates or shells. These studies have highlighted the role of Bloch–Floquet waves in increasing radiated pressure in certain frequency bands. However, in industrial applications, the stiffened structure excited by the TBL is generally coupled with internal structures such as bulkheads, floor partitions and engine foundations. To understand how these internal structures can modify the propagation of Bloch–Floquet waves and, consequently, the pressure radiated in the far field, it is necessary to have an efficient simulation tool. We propose developing a dedicated numerical process to estimate the radiated pressure from a cylindrical shell stiffened by axisymmetric/non-axisymmetric internal frames and excited by a homogeneous TBL. The process is based on the wavenumber-point reciprocity principle, which states that the sensitivity functions at a given point M correspond to the spectral responses of the system when excited by a monopole located at M. The condensed transfer functions approach is employed to derive these responses, thereby partitioning the problem: The immersed cylindrical shell is represented by an analytical model, whereas the internal frames are described using finite element models. Numerical results highlight a significant influence of the internal structure on the acoustic radiation of the stiffened shell in far field, induced by the coupling of the circumferential modes.

In this study, the nonlinear vibro-acoustic dynamics and stability of double-walled axially moving cylindrical shell are investigated. The external surface of the outer shell is in contact with fluid and subjected to oblique incident plane sound wave. Donnell’s nonlinear shallow shell theory is used to derive the nonlinear partial differential equation of the shells for the radial motion. The Galerkin method is employed to discretize the equations of motion into the set of coupled nonlinear non-homogeneous ordinary second-order differential equations. Considering both driven and companion modes, multiple scales method is used to obtain the response of the system. The effects of the ratio of the external to internal shell radius, sound level, incident angle and axial velocity on the frequency response of the system are studied. The results show that, depending on the selection of the system parameters, the effect of driven and companion modes on the frequency response and transmission loss of the system changes.

It has been emphasised in previous studies that the definition of quiet areas, which are specified as areas to be identified and protected in the Environmental Noise Directive (END) in force for European Member States, cannot be reduced to ‘the area below certain limit values for certain noise indicator values’ and the positive effects of the presence of natural elements such as natural sounds, plants and aquatic environment on the perception of quiet areas. Therefore, this soundscape study examines not only the levels of sound, but also how sound sources, the acoustic environment, auditory perception, and personal interpretation interact in shaping our experience of a sound environment. This study investigates the potential of quiet areas to be included within the scope of nature-based solutions (NBS) through the example of Istanbul Historic Peninsula. In this study, data were collected from selected urban open and green spaces within the Istanbul Historic Peninsula through noise mapping, in situ sound recordings, and questionnaire-based surveys, all conducted in accordance with established soundscape standards. The collected data were analysed to explore the relationships between the sound environment and various physical environmental factors that influence the perception of quietness in urban settings. These relationships were further evaluated within the framework of nature-based solutions (NBS) strategies, with a particular focus on how such quiet areas can contribute to urban greening practices. Finally, the study discusses how insights gained from the soundscape analysis can inform space planning and design in urban contexts, emphasising the integration of acoustic quality in green infrastructure planning.