1,721,214 research outputs found
INSITU ESTIMATION OF AN ACOUSTIC SOURCE IN AN ENCLOSURE AND PREDICTION OF INTERIOR NOISE BY USING THE PRINCIPLE OF VIBROACOUSTIC RECIPROCITY
No full textThe volume velocity of an acoustic source can be widely used in determining the vibroacoustic transfer functions, in measuring the acoustic transfer impedances, and in finding the generated power of an acoustic source. Several techniques utilizing special experimental devices have been proposed for this purpose, including the laser velocimetry, the internal pressure measurement, and the face-to-face electroacoustic measurement. However, for a source in an enclosure with flexible walls, the vibroacoustic coupling should be considered, especially in the case of a loudspeaker source that has low internal mechanical impedance. The present method, which uses the principle of vibroacoustic reciprocity, can give a reasonable estimation of the transfer functions and can be used in determining the volume velocity of a source in situ. Because the present method does not require a special facility or the information on the source surface vibration, the method can be applied to any irregularly shaped source in a flexible enclosure. With the obtained vibroacoustic transfer functions, the interior noise field in an enclosure can be predicted by vectorial summation when the boundary points are excited by uncorrelated dynamic forces. The predicted internal pressure in an enclosure is in good agreement with the measured internal pressure even in the presence of sound absorbers inside the enclosure
On the reconstruction of the vibro-acoustic field over the surface enclosing an interior space using the boundary element method
No full textThe vibrational velocity, sound pressure, and acoustic power on the vibrating boundary comprising an enclosed space are reconstructed by the boundary element method based on the measured field pressures. The singular value decomposition is used to obtain the inverse solution in the least-square sense and to express the acoustic modal expansion between the measurement and source fields. In general, such an inverse operation has been considered an ill-posed problem having a divergence phenomenon involved with extremely small measurement errors. The ill-conditioned nature of the acoustic inverse problem is caused by the singularity of the transfer matrix which produces nonradiating wave components. In order to minimize the singularity and to also reduce the number of measurement points, optimal measurement positions are determined by the effective independence method. Regularization methods are used to stabilize the reconstructed field by suppressing nonradiating components resulting in the singular transfer matrix. In order to enhance the resolution of the reconstructed field, the optimal regularization order for yielding the minimum mean-square error is estimated from the known measurement noise variance by virtue of the statistical analysis. A half-scaled automotive cabin is considered an example for validating and demonstrating the proposed reconstruction process. It is noted that the present method can improve the resolution of the reconstructed field; thus vibro-acoustic parameters of the vibrating boundary can be estimated in reasonably good precision. (C) 1996 Acoustical Society of America
A viscoelastic constitutive model of rubber under small oscillatory load superimposed on large static deformation
No full textA viscoelastic constitutive equation of rubber that is under small oscillatory load superimposed on large static deformation is proposed. The model is derived through linearization of Simo's nonlinear viscoelastic constitutive model and reference configuration transformation. Most importantly, in this model, static deformation correction factor is introduced to consider the influence of pre-strain on the relaxation function. Natural statically predeformed state is served as reference configuration. The proposed constitutive equation is extended to a generalized viscoelastic constitutive equation that includes widely used Morman's model as a special case using objective stress increment. The proposed constitutive model is tested for dynamic behavior of rubber specimens with different carbon black content. It is concluded from the test that the assumption that the effects of static deformation can be separated from time effects, which is the basis of Morman's model, is only applicable to unfilled rubber. The viscoelastic constitutive equation for filled rubber must include, therefore, the influence of the static deformation on the time effects. The suggested constitutive equation with static deformation correction factor shows good agreement with test values
Wave Vector Filtering for the Regularization in Using the Near-Field Acoustic Holography
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Reconstruction of Vibration Field Using the Acoustic BEM and measured Interior Pressures
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