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We developed a computer-aided defect inspection system based on computed tomography (CT). The system consists of a homemade small cone-beam CT (CBCT) system and a graphical toolbox, which is used to extract a computer-aided design (CAD) model from the CT data. In the small CBCT system, the x-ray imaging detector is based on a complementary metal-oxide-semiconductor photodiode array in conjunction with a scintillator. Imaging performance of the detector was evaluated in terms of modulation-transfer function, noise-power spectrum, and detective quantum efficiency. The tomographic imaging performance of the small CBCT system was evaluated in terms of signal-to-noise ratio and contrast-to-noise ratio. The graphical toolbox to support defect inspection incorporates various functional tools such as volume rendering, segmentation, triangular-mesh data generation, and data reduction. All the tools have been integrated in a graphical-user interface form. The developed system can provide rapid visual inspection as well as quantitative evaluation of defects by comparing the extracted CAD file with the original file, if available, of an object. The performance of the developed system is demonstrated with experimental CT volume data. [ABSTRACT FROM AUTHOR]

A significant vortex-induced vibration (VIV) was observed in a suspension bridge under a wind velocity of approximately 6 and 7 m/s, and with a maximum amplitude that exceeded the serviceability limitations. Since the observation of VIV in an operating bridge was an infrequent event, this study investigated the cause of unexpected VIV. A series of wind tunnel tests revealed the main cause of the VIV was temporary screens applied over the guardrails to shield the curing surface during replacement of epoxy-coated pavement. The characteristics of the measured VIV were consistent with those from experimental results in terms of amplitude and lock-in wind speed range. The effect of Scruton numbers on VIV amplitude was examined for several dominant modes with different modal mass and damping ratios. Since the VIV amplitude is sensitive to the inherent damping ratio, the modal damping ratios of the bridge were identified from output-only modal analysis by using the frequency domain decomposition. This approach was efficient in identifying the damping ratios of high modes that were challenging due to weakly excited signals. The damping ratio of the triggered mode for VIV was the lowest among the investigated modes and estimated to be the level of the design-damping ratio. [ABSTRACT FROM AUTHOR]

A cost-effective digital radiographic system with a large field-of-view (FOV) of 17' x 17' has been developed. The cascaded imaging system mainly consists of three parts: 1) a phosphor screen to convert incident X-rays into visible photons; 2) a matrix of 8 x 8 array of lens assembly to efficiently collect visible photons emitted by the phosphor screen; and 3) 8 x 8 complementary metal-oxide-semiconductor (CMOS) image sensors, aligned to the corresponding lens assembly. Although low in cost due to economical CMOS image sensors, the overall performance features are comparable with other commercial digital radiographic systems. From the analysis of signal and noise propagation, the system is not an 'X-ray quantum-limited' system, rather the system has secondary quantum sink at the light collecting stage. The system resolution is about 2 line pairs per millimeter from both of measured from X-ray images of a line-pair test pattern and the calculation of the modulation-transfer function. Detailed experimental and theoretical analysis of performance will be discussed. Index Terms--Complementary metal-oxide-semiconductor (CMOS), digital radiography (DR), parallel-hardware architecture, X-ray imaging.