Showing papers in "The Open Acoustics Journal in 2008"

Enhanced Acoustic Separation of Oil-Water Emulsion in Resonant Cavities

Abstract: This paper explores the use of acoustics for the recovery of oil in oil-water emulsions. A series of experimental studies were conducted using acoustic standing waves in resonant cavities as means of trapping oil droplets and enhancing oil separation. Several cavity configurations were explored and the frequency range used was between 1 MHz-2 MHz. Oil-water emulsions studied were made using mineral oil and motor oil.

Vibrations of Fluid-Conveying Pipes Resting on Two-parameter Foundation

Abstract: The problem of vibrations of fluid-conveying pipes resting on a two-parameter foundation model such as the Pasternak-Winkler model is studied in this paper. Fluid-conveying pipes with ends that are pinned-pinned, clamped- pinned and clamped-clamped are considered for study. The frequency expression is derived using Fourier series for the pinned-pinned case. Galerkin's technique is used in obtaining the frequency expressions for the clamped-pinned and clamped-clamped boundary conditions. The effects of the transverse and shear parameters related to the Pasternak- Winkler model and the fluid flow velocity parameter on the frequencies of vibration are studied based on the numerical results obtained for various pipe end conditions. From the results obtained, it is observed that the instability caused by the fluid flow velocity is effectively countered by the foundation and the fluid conveying pipe is stabilized by an appropriate choice of the stiffness parameters of the Pasternak-Winkler foundation. A detailed study is made on the influence of Pasternak-Winkler foundation on the frequencies of vibration of fluid conveying pipes and interesting conclusions are drawn from the numerical results presented for pipes with different boundary conditions.

Subspecific Divergence in the Black Lemur's Low-Pitched Vocalizations

Abstract: Previous studies offered very preliminary information on the vocal repertoire of Eulemur macaco macaco and Eulemur macaco flavifrons. They agreed on the fact that both subspecies emit low-pitched vocalizations, called grunts, of different duration. Through all-occurrence and focal animal observations, we recorded the vocal activity of 31 black le- murs (12 E. m. macaco and 19 E. m. flavifrons) housed in 7 institutions, both in Europe and in Madagascar. We measured both temporal and spectral properties to describe long grunts quantitatively. We extracted acoustic parameters in the per- spective of the source-filter theory of sound production. From spectrograms, we measured call duration and 6 larynx- related features and, using Linear Predictive Coding spectra, we measured four vocal tract related acoustic properties. Our quantitative analysis has statistical support for the classification of long grunts. Using individual mean values and multi- variate Discriminant Function Analysis we have been able to successfully classify 96.8 % of the vocal signals to the sub- species of the emitter. Acoustic cues of both larynx-related and vocal tract-related acoustic parameters offered support for sub-specific recognition potential. However, univariate analyses showed that formants should be providing listeners with subspecies-specific information.

A Wave Near the Edge of a Circular Disk

Abstract: It is shown that in the Love-Kirchhoff plate theory, an edge wave can travel in a circular thin disk made of an isotropic elastic material. This disk edge wave turns out to be faster than the classic flexural acoustic wave in a straight- edged, semi-infinite, thin plate, a wave which it mimics when the curvature radius becomes very large compared to the wavelength.

Hopf Bifurcation Analysis and Approximation of Limit Cycle in Coupled Van Der Pol and Duffing Oscillators

Abstract: Using Routh-Hurwitz criterion and Hopf bifurcation theorem, stability of the equilibrium points and Hopf bi- furcation of coupled van der Pol and Duffing oscillators are investigated. The parametric curve corresponding to Hopf bi- furcation and the existence region for the limit cycle in the parameter space are derived. The method of multiple time scales is used to deduce the analytical approximation of the limit cycle, and the accuracy of the analytical approximation is verified by direct numerical integration.

Bridge Condition Evaluation by In Situ Dynamic Data

Abstract: The performance of vibration-based damage identification techniques for current condition evaluation of exist- ing bridges is studied through their application to dynamic response of an existing concrete bridge. First, in situ dynamic tests were performed and modal parameters (mode shapes and frequencies) were identified. As previous sets of in situ dy- namic parameters were not available, the reference dynamic parameters were obtained from a finite element model of the bridge. Comparing modal parameters of the finite element bridge model and the in situ experimental results through dam- age identification techniques, the bridge current condition was examined. That evaluation results showed that techniques like strain energy and flexibility curvature present promising results for current condition evaluation of existing bridges.

Finite-Element Electroacoustic Analysis and Taguchi Design of Piezoelectric Buzzers Based on the Vibration Absorber Model

Abstract: Lumped parameter models of piezoelectric buzzers are established with finite element-based electroacoustic parameter identification procedures. The analysis starts with modeling the diaphragm structure by using finite element method (FEM). The FEM model is then converted into electro-mechanical two-ports to fit into the electro-mechano- acoustical (EMA) analogous circuit. Electrical impedance of the piezoelectric diaphragm is simulated using the model. An 'added-mass' method is developed to identify the lumped parameters. Electrical impedance and on-axis sound pressure level (SPL) of a piezoelectric buzzer (containing the diaphragm and case) can be simulated by solving the loop equations of the analogous circuits. On the basis of the model, optimal structural parameters and configurations for the buzzer can be found to maximize the sound pressure output, using the Taguchi method and constrained optimization. Simulation and experimental results showed that the performance has been significantly improved using the optimal design. Design guidelines for the piezoelectric buzzers are summarized.

Noise Diagnostics of Scooter Faults by Using MPEG-7 Audio Features and Intelligent Classification Techniques

Abstract: A scooter fault diagnostic system that makes use of feature extraction and intelligent classification algorithms is presented in this paper. Sound features based on MPEG (Moving Picture Experts Group)-7 coding standard and several other features in the time and frequency domains are extracted from noise data and preprocessed prior to classification. Classification algorithms including the Nearest Neighbor Rule (NNR), the Artificial Neural Networks (ANN), the Fuzzy Neural Networks (FNN), and the Hidden Markov Models (HMM) are employed to identify and classify scooter noise. A training phase is required to establish a feature space template, followed by a test phase in which the audio features of the test data are calculated and matched to the feature space template. The proposed techniques were applied to classify noise data due to various kinds of scooter fault, such as belt damage, pulley damage, etc. The results reveal that the performance of methods is satisfactory, while varying slightly in performance with the algorithm and the type of noise used in the tests.