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Bulk-wave ultrasonic propagation imagers
No full textLaser-based ultrasound systems are described that utilize the ultrasonic bulk-wave sensing to detect the damages and flaws in the aerospace structures. These systems apply pulse-echo or through transmission methods to detect longitudinal through-the-thickness bulk-waves. These thermoelastic waves are generated using Q-switched laser and non-contact sensing is performed using a laser Doppler vibrometer (LDV). Laser-based raster scanning is performed by either two-axis translation stage for linear-scanning or galvanometer-based laser mirror scanner for angular-scanning. In all ultrasonic propagation imagers, the ultrasonic data is captured and processed in real-time and the ultrasonic propagation can be visualized during scanning. The scanning speed can go up to 1.8 kHz for two-axis linear translation stage based B-UPIs and 10 kHz for galvanometer-based laser mirror scanners. In contrast with the other available ultrasound systems, these systems have the advantage of high-speed, non-contact, real-time, and non-destructive inspection. In this paper, the description of all bulk-wave ultrasonic imagers (B-UPIs) are presented and their advantages are discussed. Experiments are performed with these system on various structures to proof the integrity of their results. The C-scan results produced from non-dispersive, through-the-thickness, bulk-wave detection show good agreement in detection of structural variances and damage location in all inspected structures. These results show that bulk-wave UPIs can be used for in-situ NDE of engineering structures
Comparative Study in Pyroshock Measurement using Noncontact Remote Laser and Bolted Accelerometers
No full textFPGA-based Implementation of Ultrasonic Energy Mapping for Non-destructive Evaluation Applications
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
회전체 진동 및 회전스캔 펄스-에코 초음파 센싱을 위한 레이저 도플러 진동계의 고속 스캐닝 연구
No full text학위논문(박사) - 한국과학기술원 : 항공우주공학과, 2019.2,[vii, 77 p. :]Laser Doppler vibrometer (LDV) is widely used as a tool for non-contact velocity measurement in aerospace as well as automotive industry because it offers remote operation, high frequency measurement, and high spatial resolution. Due to these benefits, laser Doppler vibrometer (LDV) is also an effective optical sensing tool that can be used for non-destructive evaluation (NDE) applications. Applying point-by-point scanning using LDV can be very effective for vibration analysis of a moving object and for the ultrasonic testing of various structures. This dissertation presents the development of high-speed scanning laser Doppler vibrometer (SLDV) that is optimized and tested for the two real-world applications. Firstly, it meets the demand for a tracking system to apply for the vibration measurement of a rotating object underwater and secondly, it offers high-speed scanning of up to 10 kHz for pulse-echo ultrasonic testing in a novel system called angular scan pulse-echo ultrasonic wave propagation imager (A-PE-UPI). The scanning laser Doppler vibrometer consists of a scanning head, controller unit, and data acquisition (DAQ) system. In vibration measurement system of a rotating object, the scanning head is comprised of Galvanomotor-based mirror scanner and 633 nm helium-neon laser Doppler Vibrometer. Whereas, in angular scan pulse-echo ultrasonic wave propagation imager, scanning head also includes a 1064 nm Q-switched diode-pumped solid state (DPSS) laser for the generation of ultrasonic wave, and optical mirrors to combine the sensing and generation laser beam. The data acquisition was integrated and graphical user interface (GUI) application was developed to perform real-time measurement and result generation.
In addition, the scanning LDV was first tested on an aluminum propeller inside a water tank. Circular scanning function was implemented synchronized with the propeller rotation to track a single point in each revolution. During the implementation phase, the major challenges that were investigated and solved are misalignment between rotational axis and scanning LDV and synchronization between propeller, DAQ, and sensing beam. The bolt impact test was performed on propeller blade at 60 RPM while changing the conditions such as in air and underwater. The results were acquired and processed to observe in both time domain and frequency domain. In all conditions, a good agreement in results was observed in the frequency components for each case.
In addition, this PhD study also presents the integration of scanning laser Doppler vibrometer in angular scan pulse-echo ultrasonic wave propagation imager (A-PE-UPI) development. A-PE-UPI employs pulse-echo method using a sensing and a generation laser beam to obtain the thickness measurement and damage detection of a structure. In this system, raster scan method was implemented in scanning LDV for the scanning of specimen under test using combined sensing and generation laser beams. Multiple damage detection algorithms namely pulse-echo wave propagation imaging (PE-UWPI) and variable time window amplitude map (VTWAM) were implemented in the system to identify damages at a very high scan speed. The main objective in the development of this system was to achieve 10 kHz scan speed and on-the-fly signal processing to produce real-time result visualization. A-PE-UPI was applied on various real-world structures to demonstrate high-speed inspection. A-PE-UPI results produced for the inspection of 160,000 points at 10 kHz scan speed takes only 16 seconds which saves up to 96.3% inspection time as compared to mechanical scanning based linear pulse-echo ultrasonic propagation imaging (L-PE-UPI) system. Moreover, the secondary objective was to enhance the flexibility and portability of the scan head for the localized inspection which was achieved by employing a rotational stage to rotate the mirror scanner for the inspection of angled surfaces. Also, thermal elements were installed in the scan head and the controller to operate A-PE-UPI at challenging low temperature conditions. As for the future works, to enhance the accessibility of A-PE-UPI to perform inspection of in-situ large scale complex structures, a robotic arm will be considered and integrated in to A-PE-UPI.한국과학기술원 :항공우주공학과
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