Application of Improved Sliding DFT Algorithm for Non-Integer k

An algorithm and network is described in this paper that implements a sliding Discrete Fourier Transform, such that it outputs an estimate of the DFT value for every input sample. Regular DFT algorithms calculate a complex value that is proportional to the amplitude and phase of an equivalent sine wave at the selected analysis frequency. The analysis frequency that can be selected is typically an integer multiple of the frequency increment of the DFT algorithm, and this might not necessarily correspond to the desired analysis frequency. The sliding DFT algorithm proposed here overcomes this limitation, and permits the analysis frequency to be any value up to half the sampling frequency. The proposed sliding DFT algorithm is demonstrated by analysing a synthetic sine wave, and the exhaust noise from a V8 diesel engine.Carl Q. Howar

Molecular dynamics simulation of classical sound absorption in a monatomic gas

Sound wave propagation in argon gas is simulated usingmolecular dynamics (MD) in order to determine the attenuation of acoustic energy due to classical (viscous and thermal) losses at high frequencies. In addition, amethod is described to estimate attenuation of acoustic energy using the thermodynamic concept of exergy. The results are compared against standing wave theory and the predictions of the theory of continuum mechanics. Acoustic energy losses are studied by evaluating various attenuation parameters and by comparing the changes in behavior at three different frequencies. This study demonstrates acoustic absorption effects in a gas simulated in a thermostatted molecular simulation and quantifies the classical losses in terms of the sound attenuation constant. The approach can be extended to further understanding of acoustic loss mechanisms in the presence of nanoscale porous materials in the simulation domain.M. Ayub, A.C. Zander, D.M. Huang, B.S. Cazzolato, C.Q. Howar

Molecular dynamics simulations of acoustic absorption by a carbon nanotube

Acoustic absorption by a carbon nanotube (CNT) was studied using molecular dynamics (MD) simulations in a molecular domain containing a monatomic gas driven by a time-varying periodic force to simulate acoustic wave propagation. Attenuation of the sound wave and the characteristics of the sound field due to interactions with the CNT were studied by evaluating the behavior of various acoustic parameters and comparing the behavior with that of the domain without the CNT present. A standing-wave model was developed for the CNT-containing system to predict sound attenuation by the CNT and the results were verifi ed against estimates of attenuation using the thermodynamic concept of exergy. This study demonstrates acoustic absorption effects of a CNT in a thermostatted MD simulation, quanti es the acoustic losses induced by the CNT and illustrates their effects on the CNT. Overall, a platform was developed for MD simulations that can model acoustic damping induced by nanostructured materials such as CNTs, which can be used to further understanding of nanoscale acoustic loss mechanisms associated with molecular interactions between acoustic waves and nanomaterials.M. Ayub, A. C. Zander, D. M. Huang, C. Q. Howard and B. S. Cazzolat

Erratum: “Power transmission from a vibrating body to a circular cylindrical shell through passive and active isolators” [J. Acoust. Soc. Am. 101, 1479–1491 (1997)]

Carl Q. Howard and Colin H. Hanse

Acoustic analyses using Matlab (R) and Ansys (R)

Software for the book can be downloaded for free from: http://www.mecheng.adelaide.edu.au/avc/softwareDownload all the Matlab source code, ANSYS APDL code, and ANSYS Workbench archive project files that accompany the book in one zip file.Carl Q. Howard and Benjamin S. Cazzolat

Variation in acoustic performance of an adaptive quarter wave tube with orifice geometries of side-branches in a duct with flowing gas

It is well known that the acoustic performance of silencing elements decreases with an increase in exhaust gas flow. Tests were conducted on three orifice geometries of side-branches on an adaptive quarter-wave tube to determine which was the least compromised by the high-speed exhaust gas passing over the side-branch. The geometries that were tested included a sharp edge, a backward inclined branch, and a bell mouth. The experimental results show that the side-branch with a bell-mouth resulted in the greatest noise reduction by an adaptive quarter-wave tube.Carl Q. Howard, Richard A. Crai

The importance of bearing stiffness and load when estimating the size of a defect in a rolling element bearing

The change in the static stiffness of a bearing assembly is an important discriminator when determining the size of a defect in a rolling element bearing. In this article, the force–displacement relationships for defective bearings under various static radial loadings at various cage angular positions are analytically estimated and experimentally measured and analyzed. The study shows that the applied load has a significant effect on the static stiffness variations in defective rolling element bearings. The experimental measurements of the effect of the defect size on the varying stiffness of the bearing assembly, which has not been shown previously, provides valuable knowledge for developing methods to distinguish between defective bearings with defects that are smaller or larger than one angular ball spacing. The methods and results presented here contribute to the wider experimental investigation of the effects of loadings on the varying static stiffness of defective bearings and its effects on the measured vibration signatures. A large data set was obtained and has been made publicly available.Francesco Larizza, Alireza Moazen-Ahmadi, Carl Q Howard and Steven Grainge

Sound Improves Player Performance in a Multiplayer Online Battle Arena Game

Sound in video games is often used by developers to enhance the visual experience on screen. Despite its importance in creating presence and improving visual screen elements, sound also plays an important role in providing additional information to a player when completing various game tasks. This preliminary study focuses on the use of informative sound in the popular multiplayer online battle arena game, Dota 2. Our initial results indicate that team performance improves with the use of sound. However, mixed results with individual performances were measured, with some individual performances better with sound and some better without sound

Calculation of vibratory power transmission for use in active vibration control

Typical active vibration isolation experiments use point measurements of acceleration or force at the junction between the vibratory source and the receiving structure. This does not necessarily lead to the minimization of the transmitted vibrational energy. A simple method is described to generate a signal which is proportional to the harmonic vibratory power transmission at the driving frequency, which is suitable for use as an error signal with an existing filtered-x feedforward active vibration controller