Acoustics Australia 

About: Acoustics Australia is an academic journal published by Springer Science+Business Media. The journal publishes majorly in the area(s): Noise control & Noise. It has an ISSN identifier of 0814-6039. Over the lifetime, 349 publications have been published receiving 2764 citations.

The fundamentals of power ultrasound - a review

Abstract: INTRODUCTION Power ultrasound refers to the section of the sound spectrum from 20 kHz through to around 1MHz. The basis of many applications of ultrasound in this frequency range is acoustic cavitation, which is the formation, growth and collapse of microbubbles within an aqueous solution [1] resultant from pressure fl uctuations that occur in the applied sound fi eld. The event of a collapsing bubble is a microscopic implosion that generates high local turbulence and the release of heat energy. The consequence is a signifi cant increase of temperature and pressure of up to several thousand degrees Kelvin and several hundred Bar. These physical phenomena are the same as those reported in hydrodynamic cavitation which results in damage of mechanical items such as pumps and propellers [2]. These effects can be exploited in a vast array of benefi cial applications [3]. Elevated temperatures [4] in the vicinity of collapsing bubble “hot spots” can be utilised to enhance the chemical reaction rates of some processes, due to the increased heat and the formation of free radicals. Strong disturbances of pressure resultant from shockwave emissions lead to mechanical effects such as mixing and shearing which, for a chemical reaction, can serve to increase encounters between reactants, accelerate dissolution or aid the renewal at the surface of a solid reactant. These conditions, generated by the collapse of bubbles, are the basis for most aspects of sonoprocessing and sonochemistry. Examples of signifi cant applications of acoustic cavitation developed for commercial use include wastewater treatment [5], food and beverages processing [6], and the formation of protein microbubbles which can be used for image contrast agents [7] or drug delivery vehicles [8]. The current review briefl y covers the main concepts which are vital to the understanding of the cavitation phenomena followed by an overview of some of the current applications of ultrasound induced cavitation and some thoughts on what will be in store for the future. On the subject of acoustic cavitation, Neppiras [9] has written an excellent review that covers the important physics of cavitation in sound fi elds. Other invaluable sources of information can be found in the books by Young [1], Brennen [10] and Leighton [11] which detail the mathematical derivations of the basic theories of cavitation and bubble dynamics along with experimental data for these theories. A more recent review by Lauterborn [12] is another excellent reference for those wishing to gain an insight to the fundamental behaviour of bubbles in an acoustic fi eld.

The Microflown, an acoustic particle velocity sensor

Abstract: The Microflown is an acoustic sensor directly measuring particle velocity instead of sound pressure, which is usually measured by conventional microphones. Since its invention in 1994 it is mostly used for measurement purposes (broadband1D and 3D-sound intensity measurement and acoustic impedance). Possible applications are near and far field sound source localization, in situ acoustic impedance determination and a non contact method to measure structural vibrations (an alternative for a laser vibrometer). Although the Microflown was invented only some years ago, the device is worldwide commercially available, see further www.microflown.com.

Health Effects Related to Wind Turbine Sound, Including Low-Frequency Sound and Infrasound

Abstract: A narrative review of observational and experimental studies was conducted to assess the association between exposure to wind turbine sound and its components and health effects in the general population. Literature databases Scopus, Medline and Embase and additional bibliographic sources such as reference sections of key publications and journal databases were systematically searched for peer-reviewed studies published from 2009 to 2017. For the period until early 2015 only reviews were included, while for the period between January 2015 and January 2017 all relevant publications were screened. Ten reviews and 22 studies met the inclusion criteria. Most studies examined subjective annoyance as the primary outcome, indicating an association between exposure levels and the percentage highly annoyed. Sound from wind turbines leads to a higher percentage of highly annoyed when compared to other sound sources. Annoyance due to aspects, like shadow flicker, the visual (in) appropriateness in the landscape and blinking lights, can add to the noise annoyance. There is no evidence of a specific effect of the low-frequency component nor of infrasound. There are indications that the rhythmic pressure pulses on a building can lead to additional annoyance indoors. Personal characteristics such as noise sensitivity, privacy issues and social acceptance, benefits and attitudes, the local situation and the conditions of planning a wind farm also play a role in reported annoyance. Less data are available to evaluate the effects of wind turbines on sleep and long-term health effects. Sleep disturbance as well as other health effects in the vicinity of wind turbines was found to be related to annoyance, rather than directly to exposure.

Acoustic Absorption Characterization and Prediction of Natural Coir Fibers

Abstract: The remarkable properties of natural lignocellulosic fibers such as biodegradability, light weight, low density, low cost and non-toxicity as well as being an alternative to sound absorbers made of synthetic fibers have attracted many researchers in the field of acoustics. The purpose of the present study was to compare the estimated sound absorption coefficient of composite samples made of natural coconut fibers by using empirical models and comparing them with the results of experimental data. The normal sound absorption coefficients of the samples were measured with an impedance tube. The samples were fabricated in three different thicknesses (25, 35 and 45 mm) with air gaps behind them and had a constant density of 200 kg/m3. Next, calculations were made to estimate the absorption coefficients of the samples by coding in MATLAB and using the differential equation algorithm along with Delany–Bazley, Miki and Johnson–Champoux–Allard models. Based on the results, the sound absorption coefficients of the samples increased significantly with increasing frequency. Additionally, increasing the thickness of materials at constant densities increases the absorption of sound, especially at lower frequencies (< 1000 Hz). Comparison of the experimental data and estimations of the models showed that by increasing thickness, the predicted acoustic absorption coefficients for the samples become closer to the data from the experimental tests. At frequencies < 1000 Hz, increasing the air gap at the back of the sample to 3 cm would elevate the values of sound absorption coefficient. The samples made of coir fibers would effectively dissipate the energy of sound waves. It is noted that increasing the absorption of the sound in such materials is related to the longer depreciation process of thermal and viscous transfer between the air and the absorbing materials in the composite.

Influence of the Position of Artificial Boundary on Computation Accuracy of Conjugated Infinite Element for a Finite Length Cylindrical Shell

Abstract: Structural finite element coupled with the conjugated infinite element method is an efficient numerical technique for solving the acoustic radiation problem due to the vibration of underwater objects. However, for large complex structures, the total acoustic mesh would become very large if the artificial boundary is too far away from the structural wetted surface. Thus, the calculation time can become too long to confine the application of the conjugated infinite element method. On the other hand, if the artificial boundary is close to the structural wetted surface, it will lead to computation accuracy losing due to the near-field effects. Consequently, it is essential to present some guidelines based on the physical mechanism of structural acoustics to choose a suitable artificial boundary that optimizes calculation accuracy and efficiency. In present work, the evanescent wave theory of an infinite length cylindrical shell is adopted to theoretically analyze the decay characteristic of evanescent waves in near field. Then, the effect of the position of artificial boundary on computation accuracy of conjugated infinite element for a finite length ring-stiffened cylindrical shell is numerically investigated. Results suggested that for the cylindrical shell mentioned in this study, the artificial boundary can be placed at least 0.4 times the acoustic wavelength away from the structural wetted surface. What’s more, for high frequencies or large-scale structures, the required non-dimensional distance between the artificial boundary and the structural wetted surface increases.