1,721,095 research outputs found
Non-invasive measurements of structural damage by laser scanning vibrometer: an experimental comparison among different exciters
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A “mechanical” vision of image-based identification methods in structural dynamics
No full textImage-based measurements are nowadays well-established techniques, and their further development seems endless considering the fast evolution of cameras, computer hardware and software. New algorithms for structural dynamics are continuously developed and, frequently, made available in the computer community. On the other hand, experimental set-up is still an issue. This tutorial aims to focus the attention to this aspect, and will cover:The basic of the experiment design;The selection of the hardware set-up (object preparation, lighting, cameras, acquisition parameters);Limits of the acquisition and uncertainty of the measure;New acquisition technologies The proposed discussion gives basic and advanced considerations to improve the quality of the processing results and images obtained can be elaborated with different processing algorithms
Flow pressure fluctuation measurement by means of interferometric technique combined with tomographic reconstruction
No full textSubsonic jet pressure fluctuation characterization by tomographic laser interferometry
No full textThis paper describes the application of a nonconventional experimental technique based on optical interferometry for the characterization of aeroacoustic sources. The specific test case studied is a turbulent subsonic jet. Traditional experimental methods exploited for the measurement of aerodynamic velocity fields are laser Doppler anemometer and particle image velocimetry which have an important drawback due to the fact that they can measure only if the flow is seeded with tracer particles. The technique proposed, by exploiting a laser Doppler interferometer and a tomographic algorithm for 3D field reconstruction, overcomes the problem of the flow seeding since it allows directly measuring the flow pressure fluctuation due to the flow turbulence. A laser Doppler interferometer indeed is sensitive to the density oscillation within the medium traversed by the laser beam even though it integrates the density oscillation along the entire path traveled by the laser. Consequently, the 3D distribution of the flow density fluctuation can be recovered only by exploiting a tomographic reconstruction algorithm applied to several projections. Finally, the flow pressure fluctuation can be inferred from the flow density measured, which comprehends both the aerodynamic pressure related to the turbulence and the sound pressure due to the propagation of the acoustic waves into the far field. In relation to the test case studied in this paper, e.g., the turbulent subsonic jet, the method allows a complete aeroacoustic characterization of the flow field since it measures both the aerodynamic "cause" of the noise, such as the vortex shedding, and the acoustic "effect" of it, i.e., the sound propagation in the 3D space. The performances and the uncertainty have been evaluated and discussed, and the technique has been experimentally validated
Non-contact modal analysis by laser excitation: Estimation of the "equivalent" input force
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