Topic
Modal testing
About: Modal testing is a research topic. Over the lifetime, 4047 publications have been published within this topic receiving 64772 citations.
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TL;DR: In this article, a two-dimensional optical coherence vibration tomography (2DOCVT) system with an ultra-precision displacement resolution of 0.1 nm is presented, which is capable of real-time absolute displacement measurement of structural line vibrations.
19 citations
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TL;DR: In this article, correlations between measured temperatures (air temperature, surface temperature, mean temperature, etc.) and modal frequencies for the slab and beam are comparatively analyzed and the quantitative models are constructed considering nonuniform temperature distribution.
Abstract: Changes of modal frequencies induced by temperature variation can be more obvious than those caused by structural damage, which will lead to the false damage identification results. Therefore, quantifying the temperature effect on modal frequencies is a critical step to eliminate its interference in damage detection. Due to the nonuniform and time-dependent characteristics of temperature distribution, it is insufficient to obtain the reliable relationships between temperatures and modal frequencies using temperatures in air or at surface. In this paper, correlations between measured temperatures (air temperature, surface temperature, mean temperature, etc.) and modal frequencies for the slab and beam are comparatively analyzed. And the quantitative models are constructed considering nonuniform temperature distribution. Firstly, the reinforced concrete slab and beam were constructed and placed outside the laboratory to be monitored. Secondly, the correlation coefficients between modal frequencies and three kinds of temperatures are calculated, respectively. Thirdly, simple linear regression models between mean temperature and modal frequencies are established for the slab and beam. Finally, five temperature variables are selected to construct the multiple linear regression models. Prediction results reveal that the proposed multiple linear regression models possess favorable accuracy to quantify the temperature effect on modal frequencies considering nonuniform temperature distribution.
19 citations
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TL;DR: In this article, amplitude fluctuation electronic speckle pattern interferometry (AF-ESPI) and modal testing were combined to investigate the patching efficiency of an edge-cracked aluminium alloy plate repaired using a composite patch.
19 citations
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TL;DR: In this article, a general form of analytical solution is developed for converting radiation damping due to energy leaking back to the half-space into equivalent modal damping, allowing the modal analysis technique to be extended to a site where radiation dampings has to be accounted for.
Abstract: For the one-dimensional analysis of soft-soil layers on an elastic half-space, a general form of analytical solution is developed for converting radiation damping due to energy leaking back to the half-space into equivalent modal damping, allowing the modal analysis technique to be extended to a site where radiation damping has to be accounted for. Closed-form solutions for equivalent modal damping ratios and effective modal participation factors are developed for a single layer with a shear wave velocity distribution varying from constant to linearly increasing with depth. Compact and recursive forms of solutions for equivalent modal damping ratios are developed for a system with an arbitrary number of homogeneous layers on an elastic half-space. Comparisons with numerical solutions show that the modal solutions are accurate. The nominal frequency of a site, i.e. the inverse of four times the total shear wave travel time through the layers, is an important parameter for estimating the high mode frequencies. A parameter study shows that for the same impedance ratio of the bottom layer to the elastic half-space, a system of soil layers with an increasing soil rigidity with depth has, in general, larger peak modal amplifications at the ground surface than does a single homogeneous layer on an elastic half-space, while a system with a decreasing soil rigidity with depth has smaller modal peak amplifications. © 1997 by John Wiley & Sons, Ltd.
19 citations
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TL;DR: In this article, a 1-kg tuned mass dampers (TMDs) were used to damp the first two FSS flexural modes, which are the main sources of jitter.
Abstract: The Gemini Planet Imager (GPi) is an instrument that will mount to either of two nominally identical Telescopes,
Gemini North in Hawaii and Gemini South in Chile, to perform direct imaging and spectroscopy of extra-solar planets.
This 2,000-kg instrument has stringent mass, center-of-gravity, flexure, and power constraints. The Flexure Sensitive
Structure (FSS) supports the main opto-mechanical sub-systems of the GPi which work in series to process and analyse
the telescope optical beam.
The opto-mechanical sub-systems within the FSS are sensitive to mechanical vibrations, and passive damping strategies
were considered to mitigate image jitter. Based on analysis with the system finite element model (FEM) of the GPi, an
array of 1-kg tuned mass dampers (TMDs) was identified as an efficient approach to damp the first two FSS flexural
modes which are the main sources of jitter. It is estimated that 5% of critical damping can be added to each of these
modes with the addition of 23 kg of TMD mass. This estimate is based on installing TMD units on the FSS structural
members. TMD mass can be reduced by nearly 50% if the units can be installed on the opto-mechanical sub-systems
within the FSS with the highest modal displacements.
This paper describes the structural design and vibration response of the FSS, modal test results, and plans for
implementation of the TMDs. Modal measurements of the FSS structure were made to validate the FEM and to assess
the viability of TMDs for reducing jitter. The test configuration differed from the operational one because some
payloads were not present and the structure was mounted to a flexible base. However, this test was valuable for
understanding the primary modes that will be addressed with the TMDs and measuring the effective mass of these
modes.
19 citations