Abstract
The total structural intensity in beams can be considered as composed of three types of waves: bending, longitudinal, and torsional. In passive and active control applications, it is useful to separate each of these components in order to evaluate their contribution to the total structural power flowing through the beam. In this paper, a twisted z-shaped beam is used in order to allow the three types of waves to propagate. The contributions of the structural intensity, due to these waves, are computed from measurements taken over the surface of the beam with a simple homodyne interferometric laser vibrometer. The optical sensor incorporates some polarizing optics, additional to a Michelson type interferometer, to generate two optical signals in quadrature, which are processed to display velocities and/or displacements. This optical processing scheme is used to remove the directional ambiguity from the velocity measurement and allows nearly all back-scattered light collected from the object to be detect. This paper investigates the performance of the laser vibrometer in the estimation of the different wave components. The results are validated by comparing the total structural intensity computed from the laser measurements, with the measured input power. Results computed from measurements using PVDF sensors are also shown, and compared with the non-intrusive laser measurements.
Highlights
Predicting and measuring elastic waves, propagating through a structure, can be of foremost importance in vibroacoustic problems
The contributions of the structural intensity, due to these kinds of waves, are computed from measurements taken over the surface of the beam, with a simple homodyne interferometric laser vibrometer and with piezoelectric film sensor patches (PVDF)
Due to the fact that the Laser Doppler Vibrometer (LDV) signal processing was done off-line, with digitized data, there was a compromise between the high sampling rate necessary to resolve the high frequency Doppler signal, and a sufficient signal length for the resolution of the low frequency velocity signal. 10 blocks of 15000 samples each were acquired at a rate of 50 kHz
Summary
Predicting and measuring elastic waves, propagating through a structure, can be of foremost importance in vibroacoustic problems. The energy flow to localized dampers or to neighboring structures and supports can be cardinal mechanisms through which structural vibration is damped out, which partly explains the practical difficulty in estimating internal damping coefficients in structures using ground vibration tests. It can be a key for solving structure-borne noise problems, by channeling vibrations to where they do not radiate noise, instead of trying to suppress them. Depending on the geometry of the continuum, these two basic types of waves combine into different types of waves, such as bending, torsional, and longitudinal waves, which must all be measured Both acoustic intensity and vibration intensity measurements are associated with cross measurements between closely-spaced transducers: microphones in the. Freschi et al / Analyzing the total structural intensity in beams using a homodyne laser doppler vibrometer
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