Current Issue : April - June Volume : 2013 Issue Number : 2 Articles : 6 Articles
It is not uncommon for modern aquaria to be built with special entertainment areas. There are no known measurements of sound\r\nspillover from such entertainment areas into underwater animal exhibits. Entertainment organizations typically prefer to play\r\nmusic for events at 95 and 100 dBA in a ballroom at Georgia Aquarium. Concern over the potential effects of the music and\r\nnoise on animals in adjacent exhibits inspired an initial project to monitor and compare sound levels in the adjacent underwater\r\nexhibits against the typical in-air sound levels of the ballroom.Measured underwater noise levels were compared to modeled levels\r\nbased on finite element analysis and plane wave transmission loss calculations through the acrylic viewing window. Results were\r\ncompared with the model to determine how, if at all, the ambient noise level in the Cold Water Quest exhibit changed as a result\r\nof music played in the ballroom....
In this work a machine cam with five different profiles was used to investigate the linear and nonlinear dynamical behavior of\r\nasymmetric Stockbridge damper with excitation frequencies in the range of 5 = f = 17 Hz. The experimental vibration signals\r\nwere acquired through accelerometers placed along the sample. The loss factor and the Young�s modulus were estimated through\r\napproximation of the experimental and numerical results using Genetic Algorithms (GAs). Linear and nonlinear mathematical\r\nmodels were used to adjust the data. The two parameters are dependent on the excitation frequency and the amplitude of the\r\nbase displacement. The results are validated comparing typical impedance curves obtained in conventional testing using an\r\nelectromechanical shaker....
A fractional fourier transform(FrFT) based chirplet signal decomposition (FrFT-CSD) algorithm is proposed to analyze ultrasonic\r\nsignals for NDE applications. Particularly, this method is utilized to isolate dominant chirplet echoes for successive steps in\r\nsignal decomposition and parameter estimation. FrFT rotates the signal with an optimal transform order. The search of optimal\r\ntransform order is conducted by determining the highest kurtosis value of the signal in the transformed domain. A simulation\r\nstudy reveals the relationship among the kurtosis, the transform order of FrFT, and the chirp rate parameter in the simulated\r\nultrasonic echoes. Benchmark and ultrasonic experimental data are used to evaluate the FrFT-CSD algorithm. Signal processing\r\nresults show that FrFT-CSD not only reconstructs signal successfully, but also characterizes echoes and estimates echo parameters\r\naccurately. This study has a broad range of applications of importance in signal detection, estimation, and pattern recognition....
Noise control devices such as panels and barriers, when of high efficiency, generally are of difficult acquisition due to high costs\r\nturning in many cases their use impracticable, mainly for limited budget small-sized companies. There is a huge requirement for\r\nnew acoustic materials that have satisfactory performance, not only under acoustic aspect but also other relevant ones and are of\r\nlow cost. Vegetable fibers are an alternative solution when used as panels since they promise satisfactory acoustic absorption,\r\naccording to previous researches, exist in abundance, and derive from renewable sources. This paper, therefore, reports on\r\nthe development of panels made from vegetable fibers (coconut, palm, sisal, and ac�¸a�´i), assesses their applicability by various\r\nexperimental (flammability, odor, fungal growth, and ageing) tests, and characterize them acoustically in terms of their sound\r\nabsorption coefficients on a scale model reverberant chamber. Acoustic results point out that the aforementioned fiber panels play\r\npretty well the role of a noise control device since they have compatible, and in some cases, higher performance when compared\r\nto commercially available conventional materials....
Sound wave scattering by a flexible plate embedded on water surface is considered. Linear acoustics and plate elasticity are assumed.\r\nThe aim is to assess the effect of the plate�s flexibility on sound scattering and the potential in using that flexibility for this purpose.\r\nA combined sound-structure solution is used, which is based on a Fourier transform of the sound field and a finite-difference\r\nnumerical-solution of the plate�s dynamics. The solution is implemented for a circular plate subject to a perpendicular incoming\r\nmonochromatic sound wave. A very good agreement is achieved with a finite-difference solution of the sound field. It is shown\r\nthat the flexibility of the plate dampens its scattered sound wave regardless of the type of the plate�s edge support. A hole in the\r\nplate is shown to further scatter the sound wave to form maxima in the near sound field. It is suggested that applying an external\r\noscillatory pressure on the plate can reduce significantly and even eliminate its scattered wave, thus making the plate close to\r\nacoustically invisible. A uniformly distributed external pressure is found capable of achieving that aim as long as the plate is free\r\nedged or is not highly acoustically noncompact....
Vibration transmission characteristics of a cylindrical shell with a rectangular plate are discussed in this paper by the substructure\r\nreceptance method. The system is divided into two substructures: the plate and the shell. After finding the theoretical receptance\r\nfunction of each substructure, the coupling equation of the combined system is solved by considering the continuity conditions at\r\nthe joint between the plate and the shell. The numerical results are compared with the experimental ones to show the validity of\r\nthe formulation. After that, effects of the plate�s parameters on vibration transmission characteristics are discussed. The parameter\r\nstudy shows that it is important to avoid impedance matching for the plate and the shell in the design of suitable structures with\r\nlow vibration and noise radiation characteristics....
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