Acoustics Australia最新文献

During an experiment conducted in the deep South China Sea, a bottom-mounted horizontal linear array (HLA) collected the radiated noise from a moving cooperative ship at a distance less than 13 km. Bearing-time records of the HLA through plane-wave beamforming showed significant bearing estimation errors and two or three split bearing tracks of the ship that leads to misjudgment of target numbers. To reveal the physics underlying the experimental phenomena, the directional response of the HLA to an acoustic source at close range was developed by normal mode theory. Numerical simulations were conducted to analyze the acoustic intensity distribution characteristics and the arrival structures of the acoustic field. Comparative results of beamforming obtained with normal mode and ray theory show that the ray model provides an easy way to predict the split bearings for HLA beamforming. When sources are near the endfire of the array, significant bearing estimation errors and the beam splitting effect for a large aperture array were the main issues. For sources near the broadside of the array, the beam broadening effect was the most significant concern. The effect of the array length on the beamforming anomalies and the array gain loss was also investigated. With the present theories, the HLA beamforming anomalies during the experiment were well explained.

During daily work, bus drivers are exposed to various environmental factors, and their mental responses to these risk factors are still poorly understood. This study aimed to investigate the cognitive performance of bus drivers with respect to noise and vibration exposure. The study was conducted in 103 healthy city bus drivers. Based on their work schedule, the drivers' exposure to noise and vibration was measured using the Svantek SV 104 noise dosimeter and the SV 106 vibration meter, respectively. The simple Stroop test was used to measure drivers' selective attention capacity and skills as cognitive performance indicators. Drivers' job stress was determined using a standard questionnaire. The drivers' exposure levels to noise, whole-body vibration, and hand-arm vibration was 79.50 ± 3.51 dB, 0.620 ± 0.159 m/s², and 0.438 ± 0.064 m/s², respectively. Significant differences were observed in the interference score (IS) and interference time (IT) after driving (p < 0.05), which indicates a decrease in the number of true responses and an increase in response time. The multiple linear regression model showed that noise and vibration, as main environmental stressors in the presence of other individual's covariates such as age, work experience, and job stress, have significant effects on cognitive performance based on changes in IS and IT during driving (model accuracy; r = 0.61 and r = 0.57). The traffic load was also significantly associated with changes in IS and IT (p < 0.05). The possibility of mental function loss while driving indicates that appropriate occupational health surveillance must be implemented for bus driving occupations.

The flow field around a hydrophone generates self-noise which may contaminate the sound-field detection by a hydrophone. Hence, four hydrophone dome models are designed, and the flow field and sound field around them are compared. The RNG k–ε turbulence model is used for steady calculation. The results show that the four models have a fine diversion effect, and there is no obvious vortex and circumfluence because of them. The Curle model is used to simulate the sound source calculation of the hydrophone dome. The leading edge area of each model is found as the main noise source. The large eddy simulation/FW-H hybrid method is applied for the acoustic field calculation. The flow noise around the four models is studied. By summarizing the results of different models, the rules of flow noise around the hydrophone domes are analyzed. The suggestions for the hydrophone dome design are given based on the comprehensive evaluation of the noise generated by each hydrophone dome.

The widespread adoption of face masks is now a standard public health response to the 2020 pandemic. Although studies have shown that wearing a face mask interferes with speech and intelligibility, relating the acoustic response of the mask to design parameters such as fabric choice, number of layers and mask geometry is not well understood. Using a dummy head mounted with a loudspeaker at its mouth generating a broadband signal, we report the acoustic response associated with 10 different masks (different material/design) and the effect of material layers; a small number of masks were found to be almost acoustically transparent (minimal losses). While different mask material and design result in different frequency responses, we find that material selection has somewhat greater influence on transmission characteristics than mask design or geometry choices.

The underwater glider is a new type of unpowered, unmanned, moving observational platform with advantages of low-noise level, long operation time, far sustainable range, and high cost-effectiveness. In the paper, based on the underwater glider platform integrated with single vector acoustic sensor, an underwater acoustic glider platform is developed with the ability to detect target direction and observe the ambient noise. The acoustic measurement system and the self-noise of the glider platform under each working condition are tested to analyze the self-noise levels of the acoustic system and the primary noise sources of the platform, and conduct the vibration and noise reduction processing of the platform and optimize the working mode of the acoustic system. The test result shows that the underwater acoustic glider with the optimization has the ability to observe the ambient noise only on the pressure hydrophone channel. With the data sampled from one of the underwater gliders of the sea trial organized in a certain area of the South China Sea in August 2019, authors analyze the variation of spectrum levels of the ambient noise with the depth and the time at the center of seven frequency points (63 Hz, 100 Hz, 200 Hz, 400 Hz, 800 Hz, 1.6 kHz and 3.15 kHz) and discuss the influence of the sailing vessel close to the glider on it. The experimental result shows that the underwater acoustic glider, as an unscrewed moving platform, can be well used to monitor the ambient noise properties over a long term.

The detection and recognition of quiet, small objects in shallow water is one of the challenges in underwater acoustic signal processing, especially for buried objects. The seafloor strongly absorbs sound waves, while the object echo signals are weak, which makes the detection of the buried objects more difficult. Realizing object echo signal enhancement in a seafloor reverberation background and improving the signal-to-reverberation ratio (SRR) are critical problems. Based on the difference in energy aggregation between object echo signals and reverberation in the optimal fractional Fourier domain, a blind separation algorithm in the spatial fractional Fourier domain is presented. Expressions of the object rigid scattering components and the reverberation in the fractional Fourier domain are derived, and the energy distribution characteristics of both are analyzed. The objective function is constructed by the generalized correlation matrix of the multiple array signals in the optimal fractional Fourier domain, and the object rigid scattering components are obtained by approximate joint diagonalization. The simulation and data processing results show that the spatial fractional domain blind separation algorithm (FRFTBSS) can improve the signal-to-reverberation ratio. Compared with time–frequency domain blind separation (TFBSS), the proposed algorithm avoids the cross-item interference and performs better at lower SRR.

The aim of this research project was to investigate the scattering acoustic field by a rigid cavity in a rigid plane insonified by an arbitrary deterministic incident field. The Kobayashi potential method was used in order to derive the scattered acoustic field in a modal form. A previous model was developed using the same method for an incident plane wave (Khanfir et al. in J Sound Vib 361:251, 2016). The incident spherical source was then decomposed into plane waves. The total scattered field was determined by summing all the elementary scattered fields. In this paper, we present a new technique allowing the scattered acoustic field determination without using the decomposition into plane waves technique. This new model was compared to numerical results obtained using the previous model, the boundary element modeling method and experimental results for two rectangular cavities insonified by a spherical source. A good agreement between numerical and experimental results was obtained supporting the validity of the model.

The challenge in the acoustics design of the traditional mosque is twofold. First, the interior atmosphere of the space should create a sacred feeling on the users' holistic and phenomenological spatial perception, which is generally recognized as a direct effect of increased reverberation time (T30) and low clarity (C80). Second, speech should be adequately intelligible, which requires a low T30 and high speech clarity, contradicting the initial concern of the sacred atmosphere. We hypothesize that in Islamic architecture, wooden hypostyle mosques may comply better with the reverberation time requirements of speech intelligibility, while maintaining the sacred feeling, due to their comparatively absorptive surface finishing materials and structural elements. The Aslanhane Mosque is a unique sacred structure within its era of construction, well-known with its wooden columns and ceiling. It is an important case for room acoustics analysis of such holy spaces. This study aimed to analyze the room acoustic measurement results of the Aslanhane Mosque, evaluating the intelligibility of speech and interpreting the sacred feeling created by reverberance, envelopment, and spaciousness, which are all crucial in such holy structures. It is revealed that although the Aslanhane Mosque's subjective rating for speech intelligibility is “good,” the overall low volume of the mosque and the lack of surface reflections decrease the sacred sensation. Additionally, the intelligibility of speech is vulnerable to obstacles within the line of sight, such as load-bearing columns. Lastly, it was observed that the increase in T30 at low frequencies improved the sacred sensation, envelopment, and spaciousness, without any profound negative impact on the intelligibility of speech.

A design of the sonic crystal (SC), called the gradient-based sonic crystal (GBSC), that uses the gradient of properties of the SC array is proposed as an improvement over the traditional design of SCs. The gradient of properties is obtained by changing the resonator dimensions and the distance between them throughout the array instead of keeping them uniform. Because of this non-uniformity, the supercell approximation was used to handle the non-ideal periodic conditions it induces in the array. GBSCs in non-uniform rectangular and triangular lattices were designed and analyzed using the finite element method. The results show that the GBSCs widen existing bandgaps, create new bandgaps, induce high acoustical losses compared to the uniform SCs of Helmholtz resonators (HR) or hollow scatterers (HS) and have similar space requirements. Therefore, the GBSCs can be used for acoustic attenuation in low-mid-high frequency bands. Parameters such as increasing or decreasing order of the resonator size and distance, and the resonator orientation were found to influence the attenuation by the GBSCs. Experiments were conducted on the traditional uniform HS sonic crystals and HR sonic crystals and their finite element (FE) models were developed which were later useful for developing robust FE models of the GBSCs.