Rapid, Wide-Field Measurements of Complex Transient Shell Vibrations

[+] Author and Article Information
Roman W. Motriuk

TransCanada Pipelines Ltd., Calgary, Alberta T2P 5H1, Canadae-mail: roman_motriuk@transcanada.com

Timothy Schmidt

Holographics Inc., Richmond Hill, NY 11418e-mail: TimothySchmidt@compuserve.com

J. Pressure Vessel Technol 123(4), 537-543 (May 23, 2001) (7 pages) doi:10.1115/1.1388286 History: Received October 31, 2000; Revised May 23, 2001
Copyright © 2001 by ASME
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Recording a hologram. The laser output is expanded and split; the reference beam directly illuminates a film while the second beam reflects off an object onto the film.
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Recording process for a double-pulsed holographic interferogram. Two 30-ns laser pulses are emitted while the object is deforming. The superposition of two holograms on one film results in optical contouring of the out-of-plane deformation in addition to a visual record of the object.
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Holographic interferogram of a bending cantilever fixed at the bottom illustrates the principle of fringe formation and decoding. Total displacement at the tip is 48×0.35=∼17 microns.
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For a harmonic vibration, the laser pulses, represented by the dotted lines, would be fired at the peak and antipeak of the vibration to ensure recording maximum displacement. For high amplitudes, the time delay could be reduced to record a known fraction of the total displacement.
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A more complex waveform with three dominant frequencies and varying amplitudes and phase relationships. To capture worst-case displacements, the laser would be fired at the time interval shown. To study local higher-frequency events, additional recordings would be made with a shorter time delay.
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Resonant and nonresonant vibration images captured from spool pipe during field vibration survey—(a) Strong spiral pattern is progressing from lower right to upper left at 4200 rpm. Gas flow is from right to left. (b) Spiral pattern has reversed direction and is now progressing from lower left to upper right, as indicated by the linked antinodes. This was taken at 3800 rpm compressor speed; spirals in both directions were observed at every compressor speed studied. (c) Mixed vibrations at 4200 rpm. (d) A localized vibration minimum occurred at 4200 rpm. (e) Undistorted vibration pattern typical of a barrel at resonance, with antinode centers annotated with white boxes. This antinode pattern was largely repeatable as it occurred from time to time at 3800 rpm.
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“Shock” wave vibration captured at 4200 rpm compressor speed, a singular occurrence out of 110 total recordings. There is a sudden, significant decrease in fringe density (displacement) in the center of the spool.
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Laboratory test rig comprised an ASME compliant vessel with mounted shaker, strain gage rosettes, and accelerometers
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Sample location of strain gage rosette and accelerometer for lab study
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PulsESPI and holographic results at 1065 Hz showing an example of mixed vibrations for “stiff” vessel at 100 psi
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PulsESPI and holographic results at 821 Hz indicating a spiral vibration that only occurred for “stiff” vessel filled with water




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