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Related papers
Finite Element Model Updating From Full-Field Vibration Measurement Using Digital Image Correlation
Journal of Sound and …, 2010
The comparison of structural responses, e.g. natural frequencies and mode shapes, between predictions and measurements is an important step in finite element (FE) model updating. Full-field measurement techniques such as high speed cameras with digital image correlation (DIC) algorithms provide detailed, global displacement data. It is necessary to compress huge amounts of full-field data before implementing the comparison procedures. Image processing and pattern recognition techniques offer effective ways of doing this. Image decomposition using integral transformation is one of the most common procedures. It is found that appropriate selection or construction of the transformation kernels usually generates succinct and effective shape feature terms. Thus, the discrepancies between the geometric mode shapes may be assessed by using distance measures between the shape feature vectors. In the present study, vibration mode shapes of a composite panel are measured by a DIC system and predicted by a FE model. Succinct and effective shape features of the full-field mode shapes were obtained by employing the Tchebichef moment descriptor. Mode shape discrepancies are clearly indicated by the resultant Tchebichef features. The FE model was then modified and updated. Results show that including only the shape features results in a better updated model than when natural frequencies only are used. The most improved model was obtained when both natural frequencies and shape features are included in the updating routine. © 2010 Elsevier Ltd. All rights reserved.
Performance of Optical Structural Vibration Monitoring Systems in Experimental Modal Analysis
Sensors (Basel, Switzerland), 2021
Image-based optical vibration measurement is an attractive alternative to the conventional measurement of structural dynamics predominantly relying on accelerometry. Although various optical vibration monitoring systems are now readily available, their performance is currently not well defined, especially in the context of experimental modal analysis. To this end, this study provides some of the first evidence of the capability of optical vibration monitoring systems in modal identification using input–output measurements. A comparative study is conducted on a scaled model of a 3D building frame set in a laboratory environment. The dynamic response of the model to an impulse excitation from an instrumented hammer, and an initial displacement, is measured by means of five optical motion capture systems. These include commercial and open-source systems based on laser Doppler velocimetry, fiducial markers and marker-less pattern recognition. The performance of these systems is analysed...
Full field optical measurements for advanced structural dynamics: first outcomes
A growing activity of the first author on full-field vibration measurements and promising analyses on dynamic characterisation of components, on dynamic strain & stresses and on cumulative damage maps has drawn the attention of a foreign institution such as Vienna University of Technology up to offer full access to its Schwingungs-und Strukturanalyse / Optical Vibration Measurement Laboratory, equipped with state-of-the-art instruments implementing different & complementary approaches, in order to give the researcher the unique opportunity to extend the stream of researches in the strategic field of image-based measurement technologies. The early activity carried on in the frame of the settled Full-Field Optical Measurements for Advanced Structural Dynamics project is discussed in detail, showing the first achievements.
Modal Analysis Using Digital Image Correlation Technique
Materials
The present paper discusses a new approach for the experimental determination of modal parameters (resonant frequencies, modal shapes and damping coefficients) based on measured displacement values, using the non-contact optical method of digital image correlation (DIC). The output is a newly developed application module that, based on a three-dimensional displacement matrix from the experimental measurement results, can construct a frequency response function (FRF) for the purpose of experimental and operational modal analysis. From this frequency response function, the modal parameters of interest are able to be determined. The application module has been designed for practical use in Scilab 6.1.0, and its code interfaces directly with the ISTRA4D high-speed camera software. The module was built on measurements of a steel plate excited by an impact hammer to simulate experimental modal analysis. Verification of the correctness of the computational algorithm or the obtained modal p...
Displacement Based Approach for a Robust Operational Modal Analysis
Conference Proceedings of the Society for Experimental Mechanics Series, 2011
Robust estimation of the dynamic modal parameters of structures during shaking table experiments is done by means of efficient time domain data-driven Crystal Clear Stochastic Subspace Identification (CC-SSI) of vibration data recorded by a new, innovative, high resolution 3-D optical movement detection and analysis tool tracking the dynamic displacement of several selected points of the structures during the dynamic tests of natural (earthquake) and artificial (mechanical) induced vibrations. The measure of the displacements is a crucial task for the numerical and experimental studies in structural dynamics, especially within the displacement based approach in seismic design and calculations. The innovative monitoring technique measures 3 axial absolute displacements with easy and fast test setup, high accuracy and the possibility to link the 3D-motion time histories of the tracked markers with CAD drawings of the structure and validate the FE models in real time experimental data assimilation.
Optics and Lasers in Engineering, 1996
Digital Speckle Pattern Interferometry (DSPI) is a non destructive testing optical method allowing the vizualAĂation of the defects or the deformations of an object submitted to static deformation or to vibration. This method can be applied to a lot of cases within a range of displacements between tens of nanometers and tens of micrometers. DSPI can be applied to detect the natural frequencies and to vizualize the mode shapes of a vibrating object. It is very convenient to study small and weak objects because no contact is required comparing to classical modal analysis using accelerometers. DSPI was successAßlly applied to study a cantilever aluminium plate (5 cm x IO cm x Imm). The experimental iso-displacement fringe maps are compared to comAŁtational results using a finite element method.