Current Issue : July - September Volume : 2012 Issue Number : 3 Articles : 5 Articles
Industrial spaces are known to be very noisy working environment. This noise exposure can be uncomfortable, tiring, or even\r\nharmful, at worst. Industrial spaces have several characteristics: they are often huge flat volumes fitted with many obstacles and\r\nsound sources. Moreover, they are usually surrounded by rooms where low noise levels are required. The existing prediction tools\r\ncan seldom model all these phenomena accurately. In this paper, a prediction model based on a diffusion equation is presented.\r\nThe successive developments carried out to deal with the various propagating phenomena met in industrial spaces are shown. For\r\neach phenomenon, numerical or experimental examples are given to highlight the validity of this model. It is also shown that its\r\ncomputation load is very little in comparison to ray-tracing-based methods. In addition, this model can be used as a reliable and\r\nflexible tool to study the physics of the coupling between rooms. Finally, an application to a virtual factory is presented....
New-coded signals, transmitted by high-sensitivity broadband transducers in the 40ââ?¬â??200 kHz range, allow subwavelength material\r\ndiscrimination and thickness determination of polypropylene, polyvinylchloride, and brass samples. Frequency domain spectra\r\nenable simultaneous measurement of material properties including longitudinal sound velocity and the attenuation constant as\r\nwell as thickness measurements. Laboratory test measurements agree well with model results, with sound velocity prediction\r\nerrors of less than 1%, and thickness discrimination of at least wavelength/15. The resolution of these measurements has only\r\nbeen matched in the past through methods that utilise higher frequencies. The ability to obtain the same resolution using low\r\nfrequencies has many advantages, particularly when dealing with highly attenuating materials. This approach differs significantly\r\nfrom past biomimetic approaches where actual or simulated animal signals have been used and consequently has the potential for\r\napplication in a range of fields where both improved penetration and high resolution are required, such as nondestructive testing\r\nand evaluation, geophysics, and medical physics....
This paper proposes different design strategies of robust controllers for high-order plants. The design is tailored on the structure\r\nof the equations resulting from modeling flexible structures by using modal coordinates. Moreover, the control laws have some\r\ncharacteristics which make them specially suited for active vibration reduction, such as strong stabilization property and bandpass\r\nfrequency shape. The approach is also targeted the case of more sensors than actuators, which is very frequent in practical\r\napplications. Indeed, actuators are often rather heavy and bulky, while small and light sensors may be placed more freely. In\r\nsuch cases, sensors can be usefully placed in the locations where the primary force fields act on the structure, so as to provide the\r\ncontroller with a direct information on the disturbance effects in terms of structural vibrations. Eventually, this approach may\r\nlead to uncolocated control strategies. The design problem is here solved by resorting to a Linear Matrix Inequality technique,\r\nwhich allows also to select the performance weights based on different design requirements, for example, a suitable bandpass\r\nfrequency shape. Experimental results are presented for a vibration reduction problem of a stiffened aeronautical panel controlled\r\nby piezoelectric actuators....
This paper presents a variational formulation for the free vibration analysis of unsymmetrically laminated composite plates with\r\nelastically restrained edges. The study includes a micromechanics approach that allows starting the study considering each layer\r\nas constituted by long unidirectional fibers in a continuous matrix. The Mori-Tanaka method is used to predict the mechanical\r\nproperties of each lamina as a function of the elastic properties of the components and of the fiber volume fraction. The resulting\r\nmechanical properties for each lamina are included in a general Ritz formulation developed to analyze the free vibration response\r\nof thick laminated anisotropic plates resting on elastic supports. Comprehensive numerical examples are computed to validate the\r\npresent method, and the effects of the different mechanical and geometrical parameters on the dynamical behavior of different\r\nlaminated plates are shown. New results for general unsymmetrical laminates with elastically restrained edges are also presented.\r\nThe analytical approximate solution obtained in this paper can also be useful as a basis to deal with optimization problems under,\r\nfor instance, frequency constraints....
A semi-analytical method for finding the elastic modes propagating along the edge of an anisotropic semi-infinite plate is\r\npresented. Solutions are constructed as linear combinations of a finite number of the corresponding infinite plate modes with\r\nthe constraint that they decay in the direction perpendicular to the edge and collectively satisfy the free boundary condition over\r\nthe edge surface. Such modes that are confined to the edge can be used to approximate solutions of acoustic ridge waveguides\r\nwhose supporting structures are sufficiently far away from the free edge. The semi-infinite plate or ridge is allowed to be oriented\r\narbitrarily in the anisotropic crystal.Modifications to the theory to find symmetric and antisymmetric solutions for special crystal\r\norientations are also presented. Accuracy of the solutions can be improved by including more plate modes in the series. Numerical\r\ntechniques to find modal dispersion relations and orientation dependent modal behavior, are discussed. Results for ridges etched\r\nin single crystal Silicon are found to be in good agreement with Finite Element simulations. It is found that variations in modal\r\nphase velocity with respect to crystal orientation are not significant, suggesting that anisotropy may not be a critical issue while\r\ndesigning ridge waveguides in Silicon....
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