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Tag: vibration
  • Geotechnical Effects on Fiber Optic Distributed Acoustic Sensing Performance

    Abstract: Distributed Acoustic Sensing (DAS) is a fiber optic sensing system that is used for vibration monitoring. At a minimum, DAS is composed of a fiber optic cable and an optic analyzer called an interrogator. The oil and gas industry has used DAS for over a decade to monitor infrastructure such as pipelines for leaks, and in recent years changes in DAS performance over time have been observed for DAS arrays that are buried in the ground. This dissertation investigates the effect that soil type, soil temperature, soil moisture, time in-situ, and vehicle loading have on DAS performance for fiber optic cables buried in soil. This was accomplished through a field testing program. Signal to Noise Ratio (SNR) of the DAS response was used for all the tests to evaluate the system performance. The results of the impact testing program indicated that the portions of the array in gravel performed more consistently over time. The results also indicated that time DAS performance does change somewhat over time. Performance variance increased in new portions of array in all material types through time. Overall, this dissertation provides guidance that can help inform the civil engineering community with respect to installation design recommendations related to DAS used for infrastructure monitoring.
  • Vibration Survey of Room 47 with a Laser Doppler Vibrometer: Main Laboratory Basement, U.S. Army ERDC-CRREL

    ABSTRACT:  Plans are underway to create an acousto-optic laboratory on the campus of the Cold Regions Research and Engineering Laboratory. For this purpose, existing space in the basement of the Main Laboratory will be renovated. Demanding measurement techniques, such as interferometry, require a sufficiently quiet vibration environment (i.e., low vibration levels). As such, characterization of existing vibration conditions is necessary to determine vibration isolation requirements so that highly sensitive measurement activities are feasible. To this end, existing vibro-acoustic conditions were briefly surveyed in Room 47, a part of the future laboratory. The survey measured ambient noise and ambient vertical floor vibrations. The ambient vibration environment was characterized according to generic velocity criteria (VC), which are one-third octave band vibration limits. At the time of the survey, the ambient vibration environment fell under a VC-A designation, where the tolerance limit is 2000 µin/s across all one-third octave bands. Under this condition, highly sensitive measurement activities are feasible on a vibration-isolated working surface. The conclusion of this report provides isolation efficiency requirements that satisfy VC-E limits (125 µin/s), which are necessary for interferometric measurements.